摘要
通过改变退火温度获得了Ti-55531合金不同组织参数的全片层组织,利用带有不同缺口半径(R=0.13,0.25 mm)和光滑试样的拉伸实验测试了合金的缺口拉伸性能,通过不同的缺口拉伸性能计算其缺口敏感系数(NSR),研究了缺口半径对合金全片层组织的拉伸性能的影响规律,采用扫描电镜(SEM)分析了合金组织参数和断口形貌特征,研究了该合金的拉伸断裂机制。结果显示,随退火温度的升高,α片和α集束的尺寸都增大,导致光滑试样的强度降低,塑性升高。虽然缺口对合金的拉伸性能有显著的影响,但该合金没有表现出“缺口强化”效应(NSR皆小于1),与光滑试样相比,缺口使合金塑性明显下降且强度也降低。另外,随退火温度的升高,合金的缺口敏感系数增大;随缺口半径的增加,合金抗拉强度略有增加,但塑性几乎不变,且都很低。合金的拉伸断裂方式是沿晶断裂、韧窝和解理开裂组成的混合断裂模式,缺口的存在使合金的脆断倾向增加。
In recent years,high strength and toughness titanium alloy had become the object of many researchers because of its excellent performance in aerospace industry,and some of Ti-55531 alloy had been used to make the linkage between the wing and suspension slant of the Airbus-380.With the development of modern aviation aircraft in the direction of high speed and high maneuverability,the reliability and long life of high sight and thoroughness was more attentional of titanium alloy structural parts.Aerospace components often work in complex environments of multiple stresses,high temperature,long period and high radiation.Furthermore,engineering components often had all kinds of"notches"(such as shoulder steps,threads,keyways,etc.),which changed the stress distribution of the components under load.When the components were served,stress concentration at the notch would be easily loaded to the early initiation of cracks,and its service life was reduced finally.The performance index of smooth reflection couldnot direct the performance of actual components.In practical application,the data obtained by using smooth samples a small safety might lead to premature failure of components due to stress concentration at the notch and local actual stress exceeding the allowable stress of materials,thus caused aviation safety accidents.If a larger safety factor was adopted for safety,the mass of components would be too large,which contradicts the demand for weight reduction and wastes materials.Therefore,in order to ensure the safety and stability of aerospace vehicles and make full use of the properties of materials,it was very important to study the notch sensitivity and the influence of notch parameters on the deformation and fracture mechanism of high strength titanium alloy used for manufacturing its parts.Thus,in this paper,the fully lamellar microstructure of Ti-55531 alloy was obtained by solutionized at 860℃and then annealed at 610,640 and670℃for 3 h,respectively.The microstructural(including priorβgrain,αcolony andαplate)were observed and analyst by optical microscopy(OM),scanning electron microscopy(SEM)and image analysis software.Features indicated that the size ofαplate both width and length annealed at 610℃was the thinnest and shortest corresponding to three kinds of microstructures,which were about0.103 and 1.59μm,respectively.As the annealing temperature increased,the width ofαplates gradually coarsened to 0.258μm at670℃.The tensile properties of the alloy with different notch radius(R=0.13,0.25 mm)and no notch were tested.The notch sensitivity ratio was calculated by tensile properties of samples with different notch radius,and then the influence of the notch radius on tensile properties of the alloy with fully lamellar microstructure was researched.It could be found that the ultimate tensile strength(UTS)and yield strength(YS)of the alloy annealed at 610℃,were 1222 and 882.5 MPa,respectively,which was the highest among the three microstructures.The notch obviously reduced the plasticity of the alloy.The elongation of the smooth sample was 9.8%,and the elongation of the notch R=0.25 mm dropped sharply to 2.02%.The notch would reduce both the strength and plasticity of the alloy.It showed that the plastic deformation of Ti-55531 alloy was very sensitive to notch.According to the calculation of notch sensitivity coefficient,whether R=0.13 mm or R=0.25 mm,notch sensitivity ratio(NRS)was less than and not close to 1,which indicated that the alloy was sensitive to notch under these two notch radii.At the same annealing temperature,with the increase of notch radius,the tensile strength and notch sensitivity coefficient of the sample also gradually increased,indicating that the notch radius increased and the notch sensitivity of the sample decreased.At the same notch radius,the notch sensitivity coefficient gradually built up over the increase of annealing temperature,that was,the notch sensitivity of the sample also reduced.In a word,according to NRS judgment,when the notch radius of Ti-55531 alloy after solution annealing was 0.13 and 0.25 mm,the tensile fracture of the sample was very sensitive to the notch.The notch radius hada significant effect on tensile properties of Ti-55531 alloy of fully lamellar microstructure.However,there was no“notch strengthening”effect at notch tensile experiments of the alloy.To study the tension fracture mechanism of the alloy,microstructural features and tensile fracture morphology of the alloy were observed by SEM,and the results showed that the sizes of bothαlamellae andαcolony increased with increasing annealing temperature,which led to decrease of the strength and increasing of the plasticity for the smooth specimen.As the annealing temperature increased,the notch sensitivity coefficient increased.With the increase of the notch radius,the tensile strength of the alloy increased,but the plasticity kept a small.The tension fracture mechanism of the alloy was a mixed fracture mode,including inter-granular,dimples and cleavage cracking.Moreover,the notch made the alloy had a clear tendency of brittle fracture.
作者
王凤梅
黄朝文
雷旻
万明攀
温鑫
Wang Fengmei;Huang Chaowen;Lei Min;Wan Mingpan;Wen Xin(National&Local Joint Engineering Laboratory for High-Performance Metal Structure Materials and Advanced Manufacturing Technology,College of Materials and Metallurgy,Guizhou University,Guiyang 550025,China;Key Laboratory for Material Structure and Strength of Guizhou Province,Guizhou University,Guiyang 550025,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2022年第10期1269-1277,共9页
Chinese Journal of Rare Metals
基金
国家自然科学基金项目(51801037)
贵州省科技计划项目(黔科合基础[2020]1Y196,黔科合平台人才[2018]5781号)
贵州省教育厅青年科技人才成长项目(黔教合KY字[2018]104)
贵州大学引进人才项目(贵大人基合字(2017)02号)资助
作者简介
王凤梅(1993-),女,重庆奉节人,工程硕士,研究方向:高强韧钛合金组织性能,E-mail:1250865797@qq.com;通信作者:雷旻,教授,电话:15685172816,E-mail:amin_am@163.com
