Boron-based fuels,recognized for their high energy density and potential in energetic applications,encounter challenges such as long ignition delays and incomplete combustion,which result in reduced combustion efficie...Boron-based fuels,recognized for their high energy density and potential in energetic applications,encounter challenges such as long ignition delays and incomplete combustion,which result in reduced combustion efficiency and limited performance in aerospace propulsion.In this study,boron carbide(B4C)is investigated as an alternative fuel to pristine boron due to its favorable gas-phase combustion.Both metal oxide(nickel oxide(NiO))and metal fluoride(nickel fluoride(NiF_(2)))are selected as oxidizing modifiers to enhance the reactivity of B4C.A method combining laser ignition with optical diagnostics is employed to investigate the enhancing effects of different oxidizers on the ignition and combustion characteristics of B4C.Both NiO and NiF_(2)can significantly increase the combustion radiation intensity and reduce the time to maximum intensity of B4C.Differential scanning calorimetry,in-situ X-ray diffraction,and Fourier transform infrared spectroscopy were used for simultaneous thermal analysis of the B4C composite powders.Combined thermal analysis showed that the effects of NiO and NiF_(2)on promoting B4C combustion is mainly achieved via the formation of NimBn and the release of a large number of gas products.It is reasonable to speculate that the phase separation at the B2O3/NimBn interface forms new pathways for oxygen diffusion and reaction with the B core.The difference in the combustion mechanism of B4C with NiO and NiF_(2)lies in the gas phase products,i.e.,CO_(2)and BF3,respectively,thus leading to significant differences in their reaction processes.展开更多
The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 ℃to 1080 ℃ with strain rate of 1-20 s-1...The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 ℃to 1080 ℃ with strain rate of 1-20 s-1. The activation energy（Q） for the tested steel is calculated to be around 682.99 k J/mol at a deformation strain of 0.6. Microstructural analysis by SEM shows that the dynamic recrystallization（DRX） behavior is dependent sensitively on the deformation strain, temperature and strain rate, while an exponential relationship between DRX grain size and Z parameter is obtained from the computational formula. Moreover, the M6C-type carbides（〈1 μm） act as the main prohibitor of grain coarsening, and the polynomial regression relationship between them is worked out. With electron backscatter diffraction（EBSD） observation, DRX is the main nucleation mechanism responsible for the formation of new grains during hot compression. In conclusion, the interaction between DRX affected by hot deformation parameters and carbides precipitation determines the ultimate grain size refinement.展开更多
A method, doping WC with La(NO 3) 3, of producing cemented carbide with rare earth was introduced. The effects of lanthanum on the mechanical properties and microstructure of WC 9(Co 75%Ni) cemented carbide were studi...A method, doping WC with La(NO 3) 3, of producing cemented carbide with rare earth was introduced. The effects of lanthanum on the mechanical properties and microstructure of WC 9(Co 75%Ni) cemented carbide were studied and a rock drilling experiment was carried out.The experimental results show that both transverse rupture strength (TRS) and hardness of WC 9(Co 75%Ni) rare earth cemented carbides can match that of WC 9Co cemented carbide, when La 2O 3 / (Co+Ni) ratio is 0.3%, the abnormal growth of WC grain in the cemented carbide can be restrained effectively, the homogeneity of grain size in microstructure and the wear resistance are improved, which can be matchable to that of WC 9Co cemented carbide for mining.展开更多
The electrodeposition of nickel-silicon carbide coatings on a copper electrode was done by mixing SiC particles in the nickel electrodeposition solution.The influence of surfactants and silicon carbide particle size o...The electrodeposition of nickel-silicon carbide coatings on a copper electrode was done by mixing SiC particles in the nickel electrodeposition solution.The influence of surfactants and silicon carbide particle size on uniformity and quantity of silicon carbide particles in nickel-silicon carbide composite coatings was investigated.It was found that particle size affects the nucleation overpotential,with 40 nm silicon carbide nanoparticles more effective in promoting nickel nucleation than 500 nm particles due to an increase in active nucleation sites.In terms of surfactants,anionic surfactant sodium dodecyl sulfate(SDS)produced better dispersion of 40 nm silicon carbide particles than cationic surfactant cetyltrimethyl ammonium bromide(CTAB),but little difference was found between the two when 500 nm silicon carbide particles were used.Thus,although the suspension of silicon carbide particles can be improved and their co-deposition can be promoted with a cationic surfactant CTAB,it is less effective than an anionic surfactant SDS in terms of surface finish.展开更多
For developing new binder phase with high performance, Co-Ni-Fe alloy was used as binder in cemented carbides. The mechanical properties of WC-CoNiFe and WC-Co cemented carbides with different grain sizes were studied...For developing new binder phase with high performance, Co-Ni-Fe alloy was used as binder in cemented carbides. The mechanical properties of WC-CoNiFe and WC-Co cemented carbides with different grain sizes were studied. The results show that the reprecipitation of WC-CoNiFe is inhibited compared with that of WC-Co during sintering process, and the grains in WC-CoNiFe cemented carbides are more of smooth shape, resulting in a slightly lower hardness and higher transverse rupture strength. With the increase of the grain size, the hardness of the two cemented carbides decreases, and the transverse rupture strength increases. However, the slope values of K in Hall-Petch relationship are higher in WC-CoNiFe than those in WC-Co, indicating the high toughness of medium entropy alloy Co-Ni-Fe.展开更多
Three observation methods were used to investigate the existing form and the behavior of rare earth during the sintering process of high activity mischmetal （RE, with lanthanum and cerium） doped WC-8%Co-0.048%RE（ma...Three observation methods were used to investigate the existing form and the behavior of rare earth during the sintering process of high activity mischmetal （RE, with lanthanum and cerium） doped WC-8%Co-0.048%RE（mass fraction） alloy with low carbon-containing level by scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDXS）, considering the fact that the addition amount of rare earth in the alloy is very minute. The directional migration process and mechanism of cerium were discussed. First, the sinter skin （surface） is observed. oxide on the sinter skin, and lanthanum in these cerium observed, and lanthanum containing phase/micro-zone in It is shown that there exists a dispersedly distributed cerium containing enrichment positions is very minute. Secondly, the polished section is the alloy is identified. Finally, based on the fact that the fracture of cemented carbide is resulted from the heterogeneous phase or other defects within the microstructure, the fracture surface is observed and cerium containing phase/micro-zone in the fracture source approximately 260 μm from the surface is identified. These combined observations reveal adequately the fact that lanthanum and cerium get separated and cerium predominantly migrates towards the surface during the sintering process.展开更多
The behaviors of the precipitation and decomposition of carbides in AISI M2 high-speed steel modified by nitrogen and mischmetal were investigated using DSC, XRD, SEM and TEM. The as-cast microstructure of the experim...The behaviors of the precipitation and decomposition of carbides in AISI M2 high-speed steel modified by nitrogen and mischmetal were investigated using DSC, XRD, SEM and TEM. The as-cast microstructure of the experimental steel consists of dendrites of iron matrix, networks of eutectic carbides and secondary carbides. The average distance between networks is about 34 μm. The carbides mainly include M_2C, M(C,N) and M_6C, and their relative contents are 58.5%, 30.3% and 11.2%, respectively. The average spacing between the M_2C fibers is 1.5 μm. The decomposition of M_2C occurs from 897.2 to 1221.5 ℃(heating rate of 200 ℃/h). Some precipitated carbide particles occur in the M_2C matrix after holding for 15 min at 1100 ℃. With increasing holding time, the carbide fibers neck down more and more obviously until they are broken down. The spectral peaks of M_2C almost disappear after holding for 60 min. The spectral peaks of M_6C gradually strengthen with the holding time, and the relative content of M_6C increases to 79.8% after holding for 60 min. After holding for 180 min, the carbide fibers disappear, and the decomposition products consist of fine carbide particles(about 300 nm) and short rod-like carbides(about 3.5 μm).展开更多
Aluminium composites are inevitable in ship building,commercial and defence aircrafts construction due to their light weight,high strength to weight ratio,admirable properties and cost affordability.In this study,the ...Aluminium composites are inevitable in ship building,commercial and defence aircrafts construction due to their light weight,high strength to weight ratio,admirable properties and cost affordability.In this study,the microstructural characteristics of explosive cladded dissimilar grade aluminium(Al 1100-Al 5052) clad composites reinforced with silicon carbide(SiC) particles is presented.Microstructure taken at the interface by optical and scanning electron microscopes(SEM) revealed the formation of a silicon carbide layer between the dissimilar grade aluminium sheets.Though reaction layers were witnessed at few locations along the interface,the diffusion of atoms between the participant metals is not visible as confirmed by energy dispersive spectroscopy,elemental mapping,line analysis and X-ray diffraction(XRD).The variation in microhardness at various regions of the silicon carbide reinforced dissimilar aluminium explosive clad is reported.The increase in tensile strength of the SiC laced clad is also presented.展开更多
At the present, the cutters used in button bits and rock bits are mainly cobalt tungsten carbide in our country. Because of its low abrasive resistance, the bit service life and drilling efficiency was very low when t...At the present, the cutters used in button bits and rock bits are mainly cobalt tungsten carbide in our country. Because of its low abrasive resistance, the bit service life and drilling efficiency was very low when the hard and extremely hard formations were being drilled. Owing to its high abrasive resistance, the diamond composite material is widely used in drilling operations. However, its toughness against impact is too low to be used in percussion drilling, only can it be used in rotary drilling. In order to solve the problems encountered by DTH hammer in hard rock drilling, make bit life longer, increase rate of penetration and decrease drilling cost, a new type diamond enhanced tungsten carbide composite button with high abrasive resistance and high toughness against impact, which may be used in percussion drilling, has been developed. The key problems to make the button are to improve the thermal stability of diamond, to increase the welding strength between diamond and cemented tungsten carbide, and to lower the sintering temperature of tungsten carbide. All these problems have been solved effectively by pretreatment of diamond, low temperature activation hot-press sintering and high sintering pressure. (1) To plate tungsten on the surface of diamond. Diamond suffers easily from erosion in the environment of high temperature containing oxygen and iron family elements. There is very high energy between the interface of diamond and bonding metal and so the metallurgical bond can’t form at the interface between diamond and bond metal. This will lower greatly the bending strength and the toughness against impact of diamond enhanced tungsten carbide composite button. In order to improve thermal stability of diamond and increase the bonding strength of the interface between diamond and bond metal, to plate tungsten on the surface of diamond by vacuum vapor deposit is adopted. (2) To lower the sintering temperature by adding nickel, phosphorus and boron etc into conventional mixed powder. In general, the sintering temperature of cemented tungsten carbide is more than 1 350 ℃ in which diamond will suffer from serious heat erosion, so the sintering temperature must be lowered. To add nickel, phosphorus and boron etc into cobalt-base bond whose melting point is more than 1 350 ℃ will lower the sintering temperature to about 1 050 ℃. To add phosphorus can lower the temperature of liquid phase occurring and promote the densification of matrix alloy in advance because the co-crystallization temperature of Ni-P and Co-P is 880 ℃ and 1 020 ℃ respectively. The proper adding amount of nickel, phosphorus and boron etc is a key problem. To substitute nickel for partial cobalt can improve the toughness against impact of diamond enhanced tungsten carbide composite button and lower the sintering temperature. To add boron is helpful for sintering and improving the toughness against impact of diamond enhanced tungsten carbide composite button. (3) To increase the sintering press. Under the same sintering temperature, to improve the sintering press can improve the density and strength of sintering products. In this study to increase the sintering press 35 MPa in the usual conditions to 50～60 MPa in sintering diamond enhanced tungsten carbide button by adopting ceramic material as pressing rod has improved the sintering quality effectively. The properties of the button have been measured under lab conditions. The testing results show that its hardness is more than HRA86 and that its abrasiveness resistance is 100 times more than conventional cemented tungsten carbide, and its toughness against impact is more than 100J. All these data theoretically show that the button has very good mechanical properties that can meet the need of percussion drilling, and can solve the problems encountered with button bit of conventional cemented tungsten carbide.展开更多
High velocity ballistic impact deformation behaviour of Titanium/GFRP Fiber Metal Laminates(FML)has been explored.Both single and multiple projectiles impact conditions were considered.Ti/GFRP FML targets were fabrica...High velocity ballistic impact deformation behaviour of Titanium/GFRP Fiber Metal Laminates(FML)has been explored.Both single and multiple projectiles impact conditions were considered.Ti/GFRP FML targets were fabricated with addition of 5%and 10%weight percentage of boron carbide(B_(4)C)particles.Mechanical properties of Ti/GFRP FML targets were determined as per ASTM standards.High velocity ballistic experiments were conducted using Armour Piercing Projectile(APP)of diameter 7.62 mm and velocity ranging between 350 and 450 m/s.Depth of penetration of the projectile into the target was measured.The deformation behaviour of Ti/GFRP targets with and without the presence of ceramic powder(B_(4)C)was investigated.“Ductile hole growth”failure mode was observed for pure GFRP target when subjected to single projectile impact whereas“plugging”failure mode was noted for Ti/GFRP targets.The presence of B_(4)C(5%by weight)particles has significantly improved the ballistic resistance of the Ti/GFRP FML target by offering frictional resistance to the projectile penetration.Further addition(10%by weight)of B_(4)C has reduced the ballistic performance due to agglomeration.None of the targets showed‘brittle cracking’or‘fragmentation’failures.When compared to the published results of Aluminium(Al 1100/GFRP and Al 6061/GFRP)FMLs,Ti/GFRP FML showed lesser DoP which increases its potential application to aerospace industry.展开更多
The phase composition, phase transition and phase structure transformation of the wire-cut section of functionally graded WC-Co cemented carbide with dual phase structure were investigated by XRD phase analysis. It is...The phase composition, phase transition and phase structure transformation of the wire-cut section of functionally graded WC-Co cemented carbide with dual phase structure were investigated by XRD phase analysis. It is shown that the composition of η phase in the core zone is Co_3W_3C (M_6 C type). The structure of cobalt based solid solution binder phase is fcc type. At the cooling stage of the sintering process, the phase transition of η phase, i.e. M_6C→M_12C and the martensitic phase transition of the cobalt based solid solution binder phase, i.e. fcc→hcp are suppressed, which facilitates the strengthening of the alloy. Because the instantaneous temperature of the discharge channel is as high as 10 000 ℃ during the wire cutting process, the processed surface is oxidized. Nevertheless, the oxide layer thickness is in micro grade. In the oxide film, η phase is decomposed into W_2C and CoO, and cobalt based solid solution binder is selectively oxidized, while WC remains stable due to the existence of carbon containing liquid organic cutting medium.展开更多
Ultrafine tungsten carbide and fine cobalt as well as nano yttrium oxide powders were used as the raw materials. The effects of hot-press below the eutectic temperature and conventional liquid phase sintering on the s...Ultrafine tungsten carbide and fine cobalt as well as nano yttrium oxide powders were used as the raw materials. The effects of hot-press below the eutectic temperature and conventional liquid phase sintering on the structures and properties of WC-20Co-1Y2O3 cemented carbide were studied. It is shown that hot-pressed alloy has the character of isotropic properties and microstructure with homogeneous and ultrafine WC grains. However, the ultrafine and fully-densified structure is developed at the cost of the presence of large amount of cobalt-lake （unevenly distributed binder phase）, and thus lower strength. Yttrium oxide in the alloy cannot play the role of grain growth inhibitor fully when cemented carbide with high content of cobalt and ultrafine raw materials is sintered at high liquid phase sintering temperature. Peculiar platelet-enhanced bi-model structure is formed in WC-20Co-1Y2O3 cemented carbide by conventional liquid phase sintering, which points out that yttrium oxide in the alloy facilitates the formation of plate-like WC grain.展开更多
Aluminium composites are inevitable in the manufacture of aircraft structural elements owing to less weight,superior corrosion resistance and higher specific properties.These composites reduce the weight of the aircra...Aluminium composites are inevitable in the manufacture of aircraft structural elements owing to less weight,superior corrosion resistance and higher specific properties.These composites reduce the weight of the aircraft,improve the fuel efficiency and enhance the maintenance duration.This study proposes the development of dissimilar grade aluminium(aluminium 1100-aluminium 5052)composites with different reinforcement’s viz.,stainless steel wire-mesh,silicon carbide(SiC)powders and SiC powder interspersed wire-mesh,by explosive cladding technique.Wire-mesh enhances the friction and restricts the movement of flyer plate to craft a defect free clad,while SiC particles form a band on the interface.Highest strength is obtained when SiC powder interspersed wire mesh is employed as reinforcement.The dissimilar aluminium explosive clad with SiC particle reinforcement results in lower strength,which is higher than that of the weaker parent alloy and that of the conventional dissimilar aluminium explosive clads without any reinforcement.展开更多
In order to investigate the effects of brazing temperature, heating rate and cooling methods on shear strength, hardness, magnetic saturation and coercivity of the ultrafine cemented carbide, the ultrafine cemented ca...In order to investigate the effects of brazing temperature, heating rate and cooling methods on shear strength, hardness, magnetic saturation and coercivity of the ultrafine cemented carbide, the ultrafine cemented carbide was fabricated according to conventional powder metallurgical procedures, and then brazed to the stainless steel with silver-based filler alloy by supersonic frequency induction brazing. The microstructure was observed using scanning electron microscope （SEM）, energy dispersive spectroscopy （EDS） and the magnetic properties were tested utilizing coercimeter and cobalt magnetism instrument. The results show that no micro-crack is found in the cemented carbide after brazing because of silver-based sandwich compound used as filler alloy. In the melted silver layer, there is more carbon in the region adjacent to the cemented carbide. Varied shear strengths, hardnesses, magnetic saturations and coercivities are present under different brazing temperatures, heating rates and coolings. This phenomenon is correlated with some factors such as wettability and fluidity of filler alloy, brazing stress, oxidation of cemented carbide, and allotrope transition of cobalt. Shear strength reaches the maximum of 340 MPa and hardness of ultrafine cemented carbide remains 1879 HV at the brazing temperature of 730℃. The carbon increases with the of increase of the heating rate. What＇s more, and there is no r/phase found under this condition. content decreases with the increase of brazing temperature, and it the lowest magnetic saturation reaches 81.8% of the theoretic value,展开更多
High speed machining (HSM) technology is one of important aspects of advanced manufacturing technology. Nickel-based superalloys have been widely used in the aircraft and nuclear industry due to their exceptional ther...High speed machining (HSM) technology is one of important aspects of advanced manufacturing technology. Nickel-based superalloys have been widely used in the aircraft and nuclear industry due to their exceptional thermal resistance and the ability to retain mechanical properties at elevated temperatures of service environment over 700 ℃. However, they are classified as difficult-to-cut materials due to their high shear strength, work hardening tendency, highly abrasive carbide particles in the microstructure, strong tendency to weld and form built-up edge and low thermal conductivity. They have a tendency to maintain their strength at high temperature that is generated during machining. The Inconel 718 workpiece material used in the experiment was in the hot forged and annealed condition. The commercially available inserts (all inserts were made by Kennametal Inc.) were selected for the tests, a PVD TiAlN coated carbide, a CVD/PVD TiN/TiCN/TiN coated carbide and a CVD Al 2O 3/TiC/TiCN coated carbide were used at the cutting speed range about 50～100 m/min. Three kinds Sialon grade inserts with various geometry and cutting angles were used at the cutting speed range from 100 m/min to 300 m/min. For evaluating the inserts machinability when high speed cutting Inconel 718, Taylor Formula within certain cutting speeds, an high speed cutting experiment of tool life was carried out to establish the models of tool life by means of rapid facing turning test. The conclusions drawn from the turning of Inconel 718 with silicon nitride based ceramic; PVD and CVD coated carbide inserts are as follows: Studies on tool wear in high speed machining. The thorough investigations and studies were made on the tool wear form, wear process and wear mechanism in high speed cutting of difficult-to-machine materials with ceramic tools and with coated carbides. The major wear mechanisms of nickel-based alloys are interactions of abrasive wear, adhesion wear, micro-breakout and chipping. Optimization analysis on the application of high speed machining. Based on the experimental results, the optimal cutting parameters were determined for machining of Inconel 718 at high speed. The recommendation of tool inserts for high speed cutting inconel 718 were ceramic inserts of KY2000 with negative rake angle and KY2100 with round type, the PVD coated carbide insert KC7310 was recommended for its lower price.展开更多
The oxidation behavior at 973 1 273 K and the effect of oxidation on the room temperature tribological properties of hot pressed boron carbide ceramic were investigated. Oxidized samples were studied by X ray diffract...The oxidation behavior at 973 1 273 K and the effect of oxidation on the room temperature tribological properties of hot pressed boron carbide ceramic were investigated. Oxidized samples were studied by X ray diffractometer and scanning electron microscopy. It is demonstrated that the oxidation results in the formation of a thin transparent B 2O 3 film, and the oxide film is severely cracked during cooling due to the thermal expansion mismatch between the oxide film and B 4C substrate. B 2O 3 reacts with moisture in air to form boric acid, which is a kind of solid lubricant. The sliding friction factors of oxidized B 4C pair are about 0.05 0.08, compared to 0.25 0.35 of the as received B 4C pair. When the oxidation temperature is up to 1 273 K, severe unstability and increase of friction factor are observed. Visual inspection of the wear track reveals that the lubricant film is broken and some debris particles occur on and around the rubbing surfaces, because the friction interface is rough by the severe etching of grain boundaries.展开更多
High strength-to-weight ratio of non-ferrous alloys, such as aluminium, magnesium and titanium alloys, are considered to be possible replacement of widely accepted steels in transportation and automobile sectors. Amon...High strength-to-weight ratio of non-ferrous alloys, such as aluminium, magnesium and titanium alloys, are considered to be possible replacement of widely accepted steels in transportation and automobile sectors. Among these alloys, magnesium is self explosive and titanium is costlier, and aluminium is most likely to replace steels. Application of aluminium or its alloys is also thought of as an appropriate replacement in defence field, especially to enhance the easiness in mobility of combat vehicles while maintaining the same standard as that of conventional armour grade steels. Hence most of the investigations have been confined to aluminium or its alloys as base material and open an era of developing the newer composite materials to address the major limitation, i.e. tribological properties. The surface composites can be fabricated by incorporating the ceramic carbides like silicon carbide, carbides of transition metals and oxides of aluminium using surface modification techniques, such as high energy laser melt treatment, high energy electron beam irradiation and thermal spray process which are based on fusion route. These techniques yield the fusion related problems, such as interfacial reaction, pin holes, shrinkage cavities or voids and other casting related defects, and pave the way to need of an efficient technique which must be based on solid state. Recently developed friction stir processing technique was used in the present investigation for surface modification of AA7075 aluminum alloy, which is an alternative to steels. In the present investigation, 160 μm sized boron carbide powder was procured and was reduced to 60 μm and 30 μm using high energy ball mill. Subsequently these powders were used to fabricate the surface composites using friction stir processing.Ballistic performance testing as per the military standard(JIS.0108.01) was carried out. In the present work, an analytical method of predicting the ballistic behavior of surface composites was developed. This method was based on energy balance, i.e., the initial energy of impact is same as that of energy absorbed by multi layers. An attempt also has been made to validate the analytical results with the experimental findings. Variation between the analytical and experimental results may be accounted due to the assumptions considering such as isotropic behavior of target and shearing area of contact as cylindrical instead of conical interface As the analytical model yields the ballistic performance in the closer proximity of experimentally obtained, it can be considered to be an approximation to evaluate the ballistic performance of targets.展开更多
Silicon carbide (SiC) ceramics is a good structural ceramics material, which have a lot of excellent properties such as superior high-temperature strength up to a temperature of 1 350 ℃, chemical stability, good resi...Silicon carbide (SiC) ceramics is a good structural ceramics material, which have a lot of excellent properties such as superior high-temperature strength up to a temperature of 1 350 ℃, chemical stability, good resistance to thermal shock and high abrasion resistance. The silicon carbide ceramics material has so far been used widely for manufacturing various components such as heat exchangers, rolls, rockets combustion chamber. Sintering of ceramics structural parts have many technological method, the reaction-bonded is one of important sintering technology of ceramics structural parts. The preparation of reaction-bonded silicon carbide (RBSC) is based on a reaction sintering process, whereby a compacted body of α-SiC and carbon (graphite) powders is heated in contact with liquid silicon or gas silicon, which impregnates the body, converting the carbon (graphite) to β-SiC which bonds the original alpha grain. This process is characterized by low temperature and a short time sintering, and being appropriate to the preparation of large size and complex-shaped components, and so on. Besides, during compacting process of reaction sintering, it can maintain a stable dimension of ceramics parts. Therefore, the method of reaction-bonded silicon carbide ceramics has been identified as a technology suitable for producing complicated and highly exact dimensions’ ceramics parts. In this paper, the method of reaction-bonded silicon carbide was applied to the manufacturing of a complex-shaped spacecraft combustion chamber of SiC ceramics. SiC and carbon powder of 4～30 μm were chosen as the raw materials, green compacts containing appropriate wt.% carbon were formed using the mold press method, sintering was performed in a graphite electric furnace under an argon atmosphere. It was introduced in detail that the technological parameters and technological flow of reaction sintering silicon carbide ceramics. At the same time, physical and mechanical experiments such as bending strength, coefficient of thermal expansion, coefficient of thermal conductivity, gastight property, heat resisting property etc. have been carried out. The results demonstrated that spacecraft combustion chamber made from reaction sintering of silicon carbide ceramics is feasible and the results of experiment is satisfactory. The strength of high-temperature structural parts made by reaction sintered SiC varied with silicon content; Under the this article testing condition, the optimum silicon content is 10.5% for the part investigated. The method of reaction sintered SiC ceramics is suitable for manufacturing of complicated spacecraft parts with a working temperature of 1 500 ℃.展开更多
Aluminium hybrid functionally graded metal matrix composites(FGMMCs),meet growing demands for supreme tribo-mechanical performance in automotive and aviation industry.This research experimentally compares the influenc...Aluminium hybrid functionally graded metal matrix composites(FGMMCs),meet growing demands for supreme tribo-mechanical performance in automotive and aviation industry.This research experimentally compares the influence of carbide ceramics(B_(4)C,SiC,TiC)as reinforcements,in improving reciprocating tribology performance and mechanical strength of A333 hybrid composites against alloy.Hollow cylindrical samples of A333/6 wt%B_(4)C/4 wt%TiC and A333/6 wt%B_(4)C/4 wt%SiC hybrid FGMMCs were developed using horizontal centrifugal casting.Metallography analysis on both composites revealed increasing ceramic gradient distribution towards outer composite wall.Particle rich zone of A333/B_(4)C/SiC hybrid FGMMC showed maximum micro-hardness(198.9 HV)and tensile strength(267.9 MPa).Elemental mapping confirmed effective distribution of ceramics and detected elemental composition of both composites.Particle rich layer of A333/B_(4)C/SiC hybrid FGMMC exhibited improved wear resistance in comparison with all three layers of A333/B_(4)C/TiC hybrid FGMMC and alloy.Third-body abrasion and tribo-chemical wear were the predominant mechanisms revealed for both composites during worn surface analysis.展开更多
With OLYMPUS PMG3 metallograph, an abnormal three-layer gradient structure, i. e. coarse grain zone, binder enrichment zone and normal structure zone from surface to inner, was observed in Cr3C2 based cemented carbide...With OLYMPUS PMG3 metallograph, an abnormal three-layer gradient structure, i. e. coarse grain zone, binder enrichment zone and normal structure zone from surface to inner, was observed in Cr3C2 based cemented carbide. In the binder enrichment zone, three different shapes of anomalous coarse carbides were observed. It is shown that the transverse rupture strength can be raised remarkably, up 20.7%from the alloy with abnormal gradient structure by removing the abnormal gradient structure. The results suggested that the abnormal gradient structure in the surface, especially the anomalous coarse carbides in the binder enrichment zone is the main reason for the lower strength展开更多
基金The National Natural Science Foundation of China(Grant Nos.523B2063 and 52376089)。
文摘Boron-based fuels,recognized for their high energy density and potential in energetic applications,encounter challenges such as long ignition delays and incomplete combustion,which result in reduced combustion efficiency and limited performance in aerospace propulsion.In this study,boron carbide(B4C)is investigated as an alternative fuel to pristine boron due to its favorable gas-phase combustion.Both metal oxide(nickel oxide(NiO))and metal fluoride(nickel fluoride(NiF_(2)))are selected as oxidizing modifiers to enhance the reactivity of B4C.A method combining laser ignition with optical diagnostics is employed to investigate the enhancing effects of different oxidizers on the ignition and combustion characteristics of B4C.Both NiO and NiF_(2)can significantly increase the combustion radiation intensity and reduce the time to maximum intensity of B4C.Differential scanning calorimetry,in-situ X-ray diffraction,and Fourier transform infrared spectroscopy were used for simultaneous thermal analysis of the B4C composite powders.Combined thermal analysis showed that the effects of NiO and NiF_(2)on promoting B4C combustion is mainly achieved via the formation of NimBn and the release of a large number of gas products.It is reasonable to speculate that the phase separation at the B2O3/NimBn interface forms new pathways for oxygen diffusion and reaction with the B core.The difference in the combustion mechanism of B4C with NiO and NiF_(2)lies in the gas phase products,i.e.,CO_(2)and BF3,respectively,thus leading to significant differences in their reaction processes.
基金Project(2012AA03A503) supported by the National High Technology Research and Development Program of China
文摘The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 ℃to 1080 ℃ with strain rate of 1-20 s-1. The activation energy（Q） for the tested steel is calculated to be around 682.99 k J/mol at a deformation strain of 0.6. Microstructural analysis by SEM shows that the dynamic recrystallization（DRX） behavior is dependent sensitively on the deformation strain, temperature and strain rate, while an exponential relationship between DRX grain size and Z parameter is obtained from the computational formula. Moreover, the M6C-type carbides（〈1 μm） act as the main prohibitor of grain coarsening, and the polynomial regression relationship between them is worked out. With electron backscatter diffraction（EBSD） observation, DRX is the main nucleation mechanism responsible for the formation of new grains during hot compression. In conclusion, the interaction between DRX affected by hot deformation parameters and carbides precipitation determines the ultimate grain size refinement.
文摘A method, doping WC with La(NO 3) 3, of producing cemented carbide with rare earth was introduced. The effects of lanthanum on the mechanical properties and microstructure of WC 9(Co 75%Ni) cemented carbide were studied and a rock drilling experiment was carried out.The experimental results show that both transverse rupture strength (TRS) and hardness of WC 9(Co 75%Ni) rare earth cemented carbides can match that of WC 9Co cemented carbide, when La 2O 3 / (Co+Ni) ratio is 0.3%, the abnormal growth of WC grain in the cemented carbide can be restrained effectively, the homogeneity of grain size in microstructure and the wear resistance are improved, which can be matchable to that of WC 9Co cemented carbide for mining.
基金Project(20180550242)supported by the Liaoning Science and Technology Plan,China。
文摘The electrodeposition of nickel-silicon carbide coatings on a copper electrode was done by mixing SiC particles in the nickel electrodeposition solution.The influence of surfactants and silicon carbide particle size on uniformity and quantity of silicon carbide particles in nickel-silicon carbide composite coatings was investigated.It was found that particle size affects the nucleation overpotential,with 40 nm silicon carbide nanoparticles more effective in promoting nickel nucleation than 500 nm particles due to an increase in active nucleation sites.In terms of surfactants,anionic surfactant sodium dodecyl sulfate(SDS)produced better dispersion of 40 nm silicon carbide particles than cationic surfactant cetyltrimethyl ammonium bromide(CTAB),but little difference was found between the two when 500 nm silicon carbide particles were used.Thus,although the suspension of silicon carbide particles can be improved and their co-deposition can be promoted with a cationic surfactant CTAB,it is less effective than an anionic surfactant SDS in terms of surface finish.
基金Project(51671217)supported by the National Natural Science Foundation of ChinaProject(2016YFB0700302)supported by the National Key Research and Development Plan of China。
文摘For developing new binder phase with high performance, Co-Ni-Fe alloy was used as binder in cemented carbides. The mechanical properties of WC-CoNiFe and WC-Co cemented carbides with different grain sizes were studied. The results show that the reprecipitation of WC-CoNiFe is inhibited compared with that of WC-Co during sintering process, and the grains in WC-CoNiFe cemented carbides are more of smooth shape, resulting in a slightly lower hardness and higher transverse rupture strength. With the increase of the grain size, the hardness of the two cemented carbides decreases, and the transverse rupture strength increases. However, the slope values of K in Hall-Petch relationship are higher in WC-CoNiFe than those in WC-Co, indicating the high toughness of medium entropy alloy Co-Ni-Fe.
基金Project(50574104) supported by the National Natural Science Foundation of China
文摘Three observation methods were used to investigate the existing form and the behavior of rare earth during the sintering process of high activity mischmetal （RE, with lanthanum and cerium） doped WC-8%Co-0.048%RE（mass fraction） alloy with low carbon-containing level by scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDXS）, considering the fact that the addition amount of rare earth in the alloy is very minute. The directional migration process and mechanism of cerium were discussed. First, the sinter skin （surface） is observed. oxide on the sinter skin, and lanthanum in these cerium observed, and lanthanum containing phase/micro-zone in It is shown that there exists a dispersedly distributed cerium containing enrichment positions is very minute. Secondly, the polished section is the alloy is identified. Finally, based on the fact that the fracture of cemented carbide is resulted from the heterogeneous phase or other defects within the microstructure, the fracture surface is observed and cerium containing phase/micro-zone in the fracture source approximately 260 μm from the surface is identified. These combined observations reveal adequately the fact that lanthanum and cerium get separated and cerium predominantly migrates towards the surface during the sintering process.
基金Project(E2016203256)supported by the Natural Science Foundation of Hebei Province,China
文摘The behaviors of the precipitation and decomposition of carbides in AISI M2 high-speed steel modified by nitrogen and mischmetal were investigated using DSC, XRD, SEM and TEM. The as-cast microstructure of the experimental steel consists of dendrites of iron matrix, networks of eutectic carbides and secondary carbides. The average distance between networks is about 34 μm. The carbides mainly include M_2C, M(C,N) and M_6C, and their relative contents are 58.5%, 30.3% and 11.2%, respectively. The average spacing between the M_2C fibers is 1.5 μm. The decomposition of M_2C occurs from 897.2 to 1221.5 ℃(heating rate of 200 ℃/h). Some precipitated carbide particles occur in the M_2C matrix after holding for 15 min at 1100 ℃. With increasing holding time, the carbide fibers neck down more and more obviously until they are broken down. The spectral peaks of M_2C almost disappear after holding for 60 min. The spectral peaks of M_6C gradually strengthen with the holding time, and the relative content of M_6C increases to 79.8% after holding for 60 min. After holding for 180 min, the carbide fibers disappear, and the decomposition products consist of fine carbide particles(about 300 nm) and short rod-like carbides(about 3.5 μm).
文摘Aluminium composites are inevitable in ship building,commercial and defence aircrafts construction due to their light weight,high strength to weight ratio,admirable properties and cost affordability.In this study,the microstructural characteristics of explosive cladded dissimilar grade aluminium(Al 1100-Al 5052) clad composites reinforced with silicon carbide(SiC) particles is presented.Microstructure taken at the interface by optical and scanning electron microscopes(SEM) revealed the formation of a silicon carbide layer between the dissimilar grade aluminium sheets.Though reaction layers were witnessed at few locations along the interface,the diffusion of atoms between the participant metals is not visible as confirmed by energy dispersive spectroscopy,elemental mapping,line analysis and X-ray diffraction(XRD).The variation in microhardness at various regions of the silicon carbide reinforced dissimilar aluminium explosive clad is reported.The increase in tensile strength of the SiC laced clad is also presented.
文摘At the present, the cutters used in button bits and rock bits are mainly cobalt tungsten carbide in our country. Because of its low abrasive resistance, the bit service life and drilling efficiency was very low when the hard and extremely hard formations were being drilled. Owing to its high abrasive resistance, the diamond composite material is widely used in drilling operations. However, its toughness against impact is too low to be used in percussion drilling, only can it be used in rotary drilling. In order to solve the problems encountered by DTH hammer in hard rock drilling, make bit life longer, increase rate of penetration and decrease drilling cost, a new type diamond enhanced tungsten carbide composite button with high abrasive resistance and high toughness against impact, which may be used in percussion drilling, has been developed. The key problems to make the button are to improve the thermal stability of diamond, to increase the welding strength between diamond and cemented tungsten carbide, and to lower the sintering temperature of tungsten carbide. All these problems have been solved effectively by pretreatment of diamond, low temperature activation hot-press sintering and high sintering pressure. (1) To plate tungsten on the surface of diamond. Diamond suffers easily from erosion in the environment of high temperature containing oxygen and iron family elements. There is very high energy between the interface of diamond and bonding metal and so the metallurgical bond can’t form at the interface between diamond and bond metal. This will lower greatly the bending strength and the toughness against impact of diamond enhanced tungsten carbide composite button. In order to improve thermal stability of diamond and increase the bonding strength of the interface between diamond and bond metal, to plate tungsten on the surface of diamond by vacuum vapor deposit is adopted. (2) To lower the sintering temperature by adding nickel, phosphorus and boron etc into conventional mixed powder. In general, the sintering temperature of cemented tungsten carbide is more than 1 350 ℃ in which diamond will suffer from serious heat erosion, so the sintering temperature must be lowered. To add nickel, phosphorus and boron etc into cobalt-base bond whose melting point is more than 1 350 ℃ will lower the sintering temperature to about 1 050 ℃. To add phosphorus can lower the temperature of liquid phase occurring and promote the densification of matrix alloy in advance because the co-crystallization temperature of Ni-P and Co-P is 880 ℃ and 1 020 ℃ respectively. The proper adding amount of nickel, phosphorus and boron etc is a key problem. To substitute nickel for partial cobalt can improve the toughness against impact of diamond enhanced tungsten carbide composite button and lower the sintering temperature. To add boron is helpful for sintering and improving the toughness against impact of diamond enhanced tungsten carbide composite button. (3) To increase the sintering press. Under the same sintering temperature, to improve the sintering press can improve the density and strength of sintering products. In this study to increase the sintering press 35 MPa in the usual conditions to 50～60 MPa in sintering diamond enhanced tungsten carbide button by adopting ceramic material as pressing rod has improved the sintering quality effectively. The properties of the button have been measured under lab conditions. The testing results show that its hardness is more than HRA86 and that its abrasiveness resistance is 100 times more than conventional cemented tungsten carbide, and its toughness against impact is more than 100J. All these data theoretically show that the button has very good mechanical properties that can meet the need of percussion drilling, and can solve the problems encountered with button bit of conventional cemented tungsten carbide.
基金the financial support received from the management of SSN。
文摘High velocity ballistic impact deformation behaviour of Titanium/GFRP Fiber Metal Laminates(FML)has been explored.Both single and multiple projectiles impact conditions were considered.Ti/GFRP FML targets were fabricated with addition of 5%and 10%weight percentage of boron carbide(B_(4)C)particles.Mechanical properties of Ti/GFRP FML targets were determined as per ASTM standards.High velocity ballistic experiments were conducted using Armour Piercing Projectile(APP)of diameter 7.62 mm and velocity ranging between 350 and 450 m/s.Depth of penetration of the projectile into the target was measured.The deformation behaviour of Ti/GFRP targets with and without the presence of ceramic powder(B_(4)C)was investigated.“Ductile hole growth”failure mode was observed for pure GFRP target when subjected to single projectile impact whereas“plugging”failure mode was noted for Ti/GFRP targets.The presence of B_(4)C(5%by weight)particles has significantly improved the ballistic resistance of the Ti/GFRP FML target by offering frictional resistance to the projectile penetration.Further addition(10%by weight)of B_(4)C has reduced the ballistic performance due to agglomeration.None of the targets showed‘brittle cracking’or‘fragmentation’failures.When compared to the published results of Aluminium(Al 1100/GFRP and Al 6061/GFRP)FMLs,Ti/GFRP FML showed lesser DoP which increases its potential application to aerospace industry.
基金Projects(50323008, 50574104) supported by the National Natural Science Foundation of ChinaProject (04JJ3084) supported by the Natural Science Foundation of Hunan Province, China
文摘The phase composition, phase transition and phase structure transformation of the wire-cut section of functionally graded WC-Co cemented carbide with dual phase structure were investigated by XRD phase analysis. It is shown that the composition of η phase in the core zone is Co_3W_3C (M_6 C type). The structure of cobalt based solid solution binder phase is fcc type. At the cooling stage of the sintering process, the phase transition of η phase, i.e. M_6C→M_12C and the martensitic phase transition of the cobalt based solid solution binder phase, i.e. fcc→hcp are suppressed, which facilitates the strengthening of the alloy. Because the instantaneous temperature of the discharge channel is as high as 10 000 ℃ during the wire cutting process, the processed surface is oxidized. Nevertheless, the oxide layer thickness is in micro grade. In the oxide film, η phase is decomposed into W_2C and CoO, and cobalt based solid solution binder is selectively oxidized, while WC remains stable due to the existence of carbon containing liquid organic cutting medium.
文摘Ultrafine tungsten carbide and fine cobalt as well as nano yttrium oxide powders were used as the raw materials. The effects of hot-press below the eutectic temperature and conventional liquid phase sintering on the structures and properties of WC-20Co-1Y2O3 cemented carbide were studied. It is shown that hot-pressed alloy has the character of isotropic properties and microstructure with homogeneous and ultrafine WC grains. However, the ultrafine and fully-densified structure is developed at the cost of the presence of large amount of cobalt-lake （unevenly distributed binder phase）, and thus lower strength. Yttrium oxide in the alloy cannot play the role of grain growth inhibitor fully when cemented carbide with high content of cobalt and ultrafine raw materials is sintered at high liquid phase sintering temperature. Peculiar platelet-enhanced bi-model structure is formed in WC-20Co-1Y2O3 cemented carbide by conventional liquid phase sintering, which points out that yttrium oxide in the alloy facilitates the formation of plate-like WC grain.
文摘Aluminium composites are inevitable in the manufacture of aircraft structural elements owing to less weight,superior corrosion resistance and higher specific properties.These composites reduce the weight of the aircraft,improve the fuel efficiency and enhance the maintenance duration.This study proposes the development of dissimilar grade aluminium(aluminium 1100-aluminium 5052)composites with different reinforcement’s viz.,stainless steel wire-mesh,silicon carbide(SiC)powders and SiC powder interspersed wire-mesh,by explosive cladding technique.Wire-mesh enhances the friction and restricts the movement of flyer plate to craft a defect free clad,while SiC particles form a band on the interface.Highest strength is obtained when SiC powder interspersed wire mesh is employed as reinforcement.The dissimilar aluminium explosive clad with SiC particle reinforcement results in lower strength,which is higher than that of the weaker parent alloy and that of the conventional dissimilar aluminium explosive clads without any reinforcement.
基金Project(2013GZX0146)supported by the Science and Technology Projects of Sichuan Province,ChinaProject(11DXYB096JH-027)supported by Chengdu Science and technology Program,China
文摘In order to investigate the effects of brazing temperature, heating rate and cooling methods on shear strength, hardness, magnetic saturation and coercivity of the ultrafine cemented carbide, the ultrafine cemented carbide was fabricated according to conventional powder metallurgical procedures, and then brazed to the stainless steel with silver-based filler alloy by supersonic frequency induction brazing. The microstructure was observed using scanning electron microscope （SEM）, energy dispersive spectroscopy （EDS） and the magnetic properties were tested utilizing coercimeter and cobalt magnetism instrument. The results show that no micro-crack is found in the cemented carbide after brazing because of silver-based sandwich compound used as filler alloy. In the melted silver layer, there is more carbon in the region adjacent to the cemented carbide. Varied shear strengths, hardnesses, magnetic saturations and coercivities are present under different brazing temperatures, heating rates and coolings. This phenomenon is correlated with some factors such as wettability and fluidity of filler alloy, brazing stress, oxidation of cemented carbide, and allotrope transition of cobalt. Shear strength reaches the maximum of 340 MPa and hardness of ultrafine cemented carbide remains 1879 HV at the brazing temperature of 730℃. The carbon increases with the of increase of the heating rate. What＇s more, and there is no r/phase found under this condition. content decreases with the increase of brazing temperature, and it the lowest magnetic saturation reaches 81.8% of the theoretic value,
文摘High speed machining (HSM) technology is one of important aspects of advanced manufacturing technology. Nickel-based superalloys have been widely used in the aircraft and nuclear industry due to their exceptional thermal resistance and the ability to retain mechanical properties at elevated temperatures of service environment over 700 ℃. However, they are classified as difficult-to-cut materials due to their high shear strength, work hardening tendency, highly abrasive carbide particles in the microstructure, strong tendency to weld and form built-up edge and low thermal conductivity. They have a tendency to maintain their strength at high temperature that is generated during machining. The Inconel 718 workpiece material used in the experiment was in the hot forged and annealed condition. The commercially available inserts (all inserts were made by Kennametal Inc.) were selected for the tests, a PVD TiAlN coated carbide, a CVD/PVD TiN/TiCN/TiN coated carbide and a CVD Al 2O 3/TiC/TiCN coated carbide were used at the cutting speed range about 50～100 m/min. Three kinds Sialon grade inserts with various geometry and cutting angles were used at the cutting speed range from 100 m/min to 300 m/min. For evaluating the inserts machinability when high speed cutting Inconel 718, Taylor Formula within certain cutting speeds, an high speed cutting experiment of tool life was carried out to establish the models of tool life by means of rapid facing turning test. The conclusions drawn from the turning of Inconel 718 with silicon nitride based ceramic; PVD and CVD coated carbide inserts are as follows: Studies on tool wear in high speed machining. The thorough investigations and studies were made on the tool wear form, wear process and wear mechanism in high speed cutting of difficult-to-machine materials with ceramic tools and with coated carbides. The major wear mechanisms of nickel-based alloys are interactions of abrasive wear, adhesion wear, micro-breakout and chipping. Optimization analysis on the application of high speed machining. Based on the experimental results, the optimal cutting parameters were determined for machining of Inconel 718 at high speed. The recommendation of tool inserts for high speed cutting inconel 718 were ceramic inserts of KY2000 with negative rake angle and KY2100 with round type, the PVD coated carbide insert KC7310 was recommended for its lower price.
文摘The oxidation behavior at 973 1 273 K and the effect of oxidation on the room temperature tribological properties of hot pressed boron carbide ceramic were investigated. Oxidized samples were studied by X ray diffractometer and scanning electron microscopy. It is demonstrated that the oxidation results in the formation of a thin transparent B 2O 3 film, and the oxide film is severely cracked during cooling due to the thermal expansion mismatch between the oxide film and B 4C substrate. B 2O 3 reacts with moisture in air to form boric acid, which is a kind of solid lubricant. The sliding friction factors of oxidized B 4C pair are about 0.05 0.08, compared to 0.25 0.35 of the as received B 4C pair. When the oxidation temperature is up to 1 273 K, severe unstability and increase of friction factor are observed. Visual inspection of the wear track reveals that the lubricant film is broken and some debris particles occur on and around the rubbing surfaces, because the friction interface is rough by the severe etching of grain boundaries.
基金Financial assistance from Armament research board,New Delhi,India
文摘High strength-to-weight ratio of non-ferrous alloys, such as aluminium, magnesium and titanium alloys, are considered to be possible replacement of widely accepted steels in transportation and automobile sectors. Among these alloys, magnesium is self explosive and titanium is costlier, and aluminium is most likely to replace steels. Application of aluminium or its alloys is also thought of as an appropriate replacement in defence field, especially to enhance the easiness in mobility of combat vehicles while maintaining the same standard as that of conventional armour grade steels. Hence most of the investigations have been confined to aluminium or its alloys as base material and open an era of developing the newer composite materials to address the major limitation, i.e. tribological properties. The surface composites can be fabricated by incorporating the ceramic carbides like silicon carbide, carbides of transition metals and oxides of aluminium using surface modification techniques, such as high energy laser melt treatment, high energy electron beam irradiation and thermal spray process which are based on fusion route. These techniques yield the fusion related problems, such as interfacial reaction, pin holes, shrinkage cavities or voids and other casting related defects, and pave the way to need of an efficient technique which must be based on solid state. Recently developed friction stir processing technique was used in the present investigation for surface modification of AA7075 aluminum alloy, which is an alternative to steels. In the present investigation, 160 μm sized boron carbide powder was procured and was reduced to 60 μm and 30 μm using high energy ball mill. Subsequently these powders were used to fabricate the surface composites using friction stir processing.Ballistic performance testing as per the military standard(JIS.0108.01) was carried out. In the present work, an analytical method of predicting the ballistic behavior of surface composites was developed. This method was based on energy balance, i.e., the initial energy of impact is same as that of energy absorbed by multi layers. An attempt also has been made to validate the analytical results with the experimental findings. Variation between the analytical and experimental results may be accounted due to the assumptions considering such as isotropic behavior of target and shearing area of contact as cylindrical instead of conical interface As the analytical model yields the ballistic performance in the closer proximity of experimentally obtained, it can be considered to be an approximation to evaluate the ballistic performance of targets.
文摘Silicon carbide (SiC) ceramics is a good structural ceramics material, which have a lot of excellent properties such as superior high-temperature strength up to a temperature of 1 350 ℃, chemical stability, good resistance to thermal shock and high abrasion resistance. The silicon carbide ceramics material has so far been used widely for manufacturing various components such as heat exchangers, rolls, rockets combustion chamber. Sintering of ceramics structural parts have many technological method, the reaction-bonded is one of important sintering technology of ceramics structural parts. The preparation of reaction-bonded silicon carbide (RBSC) is based on a reaction sintering process, whereby a compacted body of α-SiC and carbon (graphite) powders is heated in contact with liquid silicon or gas silicon, which impregnates the body, converting the carbon (graphite) to β-SiC which bonds the original alpha grain. This process is characterized by low temperature and a short time sintering, and being appropriate to the preparation of large size and complex-shaped components, and so on. Besides, during compacting process of reaction sintering, it can maintain a stable dimension of ceramics parts. Therefore, the method of reaction-bonded silicon carbide ceramics has been identified as a technology suitable for producing complicated and highly exact dimensions’ ceramics parts. In this paper, the method of reaction-bonded silicon carbide was applied to the manufacturing of a complex-shaped spacecraft combustion chamber of SiC ceramics. SiC and carbon powder of 4～30 μm were chosen as the raw materials, green compacts containing appropriate wt.% carbon were formed using the mold press method, sintering was performed in a graphite electric furnace under an argon atmosphere. It was introduced in detail that the technological parameters and technological flow of reaction sintering silicon carbide ceramics. At the same time, physical and mechanical experiments such as bending strength, coefficient of thermal expansion, coefficient of thermal conductivity, gastight property, heat resisting property etc. have been carried out. The results demonstrated that spacecraft combustion chamber made from reaction sintering of silicon carbide ceramics is feasible and the results of experiment is satisfactory. The strength of high-temperature structural parts made by reaction sintered SiC varied with silicon content; Under the this article testing condition, the optimum silicon content is 10.5% for the part investigated. The method of reaction sintered SiC ceramics is suitable for manufacturing of complicated spacecraft parts with a working temperature of 1 500 ℃.
文摘Aluminium hybrid functionally graded metal matrix composites(FGMMCs),meet growing demands for supreme tribo-mechanical performance in automotive and aviation industry.This research experimentally compares the influence of carbide ceramics(B_(4)C,SiC,TiC)as reinforcements,in improving reciprocating tribology performance and mechanical strength of A333 hybrid composites against alloy.Hollow cylindrical samples of A333/6 wt%B_(4)C/4 wt%TiC and A333/6 wt%B_(4)C/4 wt%SiC hybrid FGMMCs were developed using horizontal centrifugal casting.Metallography analysis on both composites revealed increasing ceramic gradient distribution towards outer composite wall.Particle rich zone of A333/B_(4)C/SiC hybrid FGMMC showed maximum micro-hardness(198.9 HV)and tensile strength(267.9 MPa).Elemental mapping confirmed effective distribution of ceramics and detected elemental composition of both composites.Particle rich layer of A333/B_(4)C/SiC hybrid FGMMC exhibited improved wear resistance in comparison with all three layers of A333/B_(4)C/TiC hybrid FGMMC and alloy.Third-body abrasion and tribo-chemical wear were the predominant mechanisms revealed for both composites during worn surface analysis.
文摘With OLYMPUS PMG3 metallograph, an abnormal three-layer gradient structure, i. e. coarse grain zone, binder enrichment zone and normal structure zone from surface to inner, was observed in Cr3C2 based cemented carbide. In the binder enrichment zone, three different shapes of anomalous coarse carbides were observed. It is shown that the transverse rupture strength can be raised remarkably, up 20.7%from the alloy with abnormal gradient structure by removing the abnormal gradient structure. The results suggested that the abnormal gradient structure in the surface, especially the anomalous coarse carbides in the binder enrichment zone is the main reason for the lower strength
