Pb(Zr,Ti)O_(3)-Pb(Zn_(1/3)Nb_(2/3))O_(3) (PZT-PZN) based ceramics, as important piezoelectric materials, have a wide range of applications in fields such as sensors and actuators, thus the optimization of their piezoe...Pb(Zr,Ti)O_(3)-Pb(Zn_(1/3)Nb_(2/3))O_(3) (PZT-PZN) based ceramics, as important piezoelectric materials, have a wide range of applications in fields such as sensors and actuators, thus the optimization of their piezoelectric properties has been a hot research topic. This study investigated the effects of phase boundary engineering and domain engineering on (1-x)[0.8Pb(Zr_(0.5)Ti_(0.5))O_(3)-0.2Pb(Zn_(1/3)Nb_(2/3))O_(3)]-xBi(Zn_(0.5)Ti_(0.5))O_(3) ((1-x)(0.8PZT-0.2PZN)- xBZT) ceramic to obtain excellent piezoelectric properties. The crystal phase structure and microstructure of ceramic samples were characterized. The results showed that all samples had a pure perovskite structure, and the addition of BZT gradually increased the grain size. The addition of BZT caused a phase transition in ceramic samples from the morphotropic phase boundary (MPB) towards the tetragonal phase region, which is crucial for optimizing piezoelectric properties. By adjusting content of BZT and precisely controlling position of the phase boundary, the piezoelectric performance can be optimized. Domain structure is one of the key factors affecting piezoelectric performance. By using domain engineering techniques to optimize grain size and domain size, piezoelectric properties of ceramic samples have been significantly improved. Specifically, excellent piezoelectric properties (piezoelectric constant d_(33)=320 pC/N, electromechanical coupling factor kp=0.44) were obtained simultaneously for x=0.08. Based on experimental results and theoretical analysis, influence mechanisms of phase boundary engineering and domain engineering on piezoelectric properties were explored. The study shows that addition of BZT not only promotes grain growth, but also optimizes the domain structure, enabling the polarization reversal process easier, thereby improving piezoelectric properties. These research results not only provide new ideas for the design of high-performance piezoelectric ceramics, but also lay a theoretical foundation for development of related electronic devices.展开更多
An increase in RE element content in Mg alloys promotes the grain boundary precipitate,which affects the mechanical properties.However,the influence of grain boundary precipitates on microstructure of Mg-RE alloys dur...An increase in RE element content in Mg alloys promotes the grain boundary precipitate,which affects the mechanical properties.However,the influence of grain boundary precipitates on microstructure of Mg-RE alloys during ageing and their role on ductility of the aged alloy is unclear.In this work,hot extrusion and ageing treatment were performed for Mg-9Gd-2Y-xNd-0.2Zr(x=1 wt.%and 3 wt.%)alloys,and grain boundary precipitates were formed in the extruded Mg-9Gd-2Y-3Nd-0.2Zr alloy due to the increase of Nd content.The extruded alloys exhibit a complete dynamic recrystallization(DRX)microstructure and a texture with the<0001>orientation parallel to the extrusion direction(ED).In addition,a large amount of fiber microstructures distributed by the second phase along the ED were formed in the Mg-9Gd-2Y-3Nd-0.2Zr alloy,while only a small amount of the second phase was observed in the Mg-9Gd-2Y-1Nd-0.2Zr alloy.After ageing treatment,a large amount ofβ'phase precipitated inside the grains.The strength of the Mg-9Gd-2Y-1Nd-0.2Zr alloy increased from 202 MPa to 275 MPa but the elongation decreased from 12.8%to 2.6%,and the strength of the Mg-9Gd-2Y-3Nd-0.2Zr alloy increased from 212 MPa to 281 MPa but the elongation decreased from 13.7%to 6.2%.Among them,the Mg-9Gd-2Y-3Nd-0.2Zr alloy showed good overall mechanical properties,especially the elongation of the aged alloy was 58%higher than that of the Mg-9Gd-2Y-1Nd-0.2Zr alloy.The increase in ductility of the aged Mg-9Gd-2Y-3Nd-0.2Zr alloy attributed to the grain boundary precipitate promotes the formation of a large number of precipitation free zones(PFZs)with widths of 130-150 nm during ageing treatment.展开更多
This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-...This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-and molybdenum-free high-nitrogen austenitic stainless steel(HNASS).FSW at 400 rpm and 30 mm/min resulted in finer grains(4.18μm)and higher coincident site lattice(CSL)boundaries(32.3%)at the top of the stir zone(SZ)due to dynamic recrystallization(DRX).PWHT at 900℃for 1 h led to grain coarsening(12.91μm the bottom SZ)but enhanced CSL boundaries from 24.6%to 30.2%,improving grain boundary stability.PWHT reduced the kernel average misorientation(KAM)by 14.9%in the SZ-top layer and 20.4%in the SZ-bottom layer,accompanied by a 25%decrease in hardness in the SZ-top layer and 26.7%in the SZ-bottom layer,indicating strain recovery and reduced dislocation density.Potentiodynamic polarization tests(PDP)showed a 18%increase in pitting potential and a 76%reduction in corrosion rate after PWHT.The improvement in corrosion resistance is attributed to the increase inΣ3 twin boundaries,which enhance grain boundary stability and reduce susceptibility to localized corrosion.These findings highlight the role of PWHT in refining the microstructure and strengthening corrosion resistance,making HNASS a promising material for demanding applications.展开更多
基金National Natural Science Foundation of China (52202139, 52072178)。
文摘Pb(Zr,Ti)O_(3)-Pb(Zn_(1/3)Nb_(2/3))O_(3) (PZT-PZN) based ceramics, as important piezoelectric materials, have a wide range of applications in fields such as sensors and actuators, thus the optimization of their piezoelectric properties has been a hot research topic. This study investigated the effects of phase boundary engineering and domain engineering on (1-x)[0.8Pb(Zr_(0.5)Ti_(0.5))O_(3)-0.2Pb(Zn_(1/3)Nb_(2/3))O_(3)]-xBi(Zn_(0.5)Ti_(0.5))O_(3) ((1-x)(0.8PZT-0.2PZN)- xBZT) ceramic to obtain excellent piezoelectric properties. The crystal phase structure and microstructure of ceramic samples were characterized. The results showed that all samples had a pure perovskite structure, and the addition of BZT gradually increased the grain size. The addition of BZT caused a phase transition in ceramic samples from the morphotropic phase boundary (MPB) towards the tetragonal phase region, which is crucial for optimizing piezoelectric properties. By adjusting content of BZT and precisely controlling position of the phase boundary, the piezoelectric performance can be optimized. Domain structure is one of the key factors affecting piezoelectric performance. By using domain engineering techniques to optimize grain size and domain size, piezoelectric properties of ceramic samples have been significantly improved. Specifically, excellent piezoelectric properties (piezoelectric constant d_(33)=320 pC/N, electromechanical coupling factor kp=0.44) were obtained simultaneously for x=0.08. Based on experimental results and theoretical analysis, influence mechanisms of phase boundary engineering and domain engineering on piezoelectric properties were explored. The study shows that addition of BZT not only promotes grain growth, but also optimizes the domain structure, enabling the polarization reversal process easier, thereby improving piezoelectric properties. These research results not only provide new ideas for the design of high-performance piezoelectric ceramics, but also lay a theoretical foundation for development of related electronic devices.
基金Project(2021YFB3701103) supported by the National Key R&D Program of China。
文摘An increase in RE element content in Mg alloys promotes the grain boundary precipitate,which affects the mechanical properties.However,the influence of grain boundary precipitates on microstructure of Mg-RE alloys during ageing and their role on ductility of the aged alloy is unclear.In this work,hot extrusion and ageing treatment were performed for Mg-9Gd-2Y-xNd-0.2Zr(x=1 wt.%and 3 wt.%)alloys,and grain boundary precipitates were formed in the extruded Mg-9Gd-2Y-3Nd-0.2Zr alloy due to the increase of Nd content.The extruded alloys exhibit a complete dynamic recrystallization(DRX)microstructure and a texture with the<0001>orientation parallel to the extrusion direction(ED).In addition,a large amount of fiber microstructures distributed by the second phase along the ED were formed in the Mg-9Gd-2Y-3Nd-0.2Zr alloy,while only a small amount of the second phase was observed in the Mg-9Gd-2Y-1Nd-0.2Zr alloy.After ageing treatment,a large amount ofβ'phase precipitated inside the grains.The strength of the Mg-9Gd-2Y-1Nd-0.2Zr alloy increased from 202 MPa to 275 MPa but the elongation decreased from 12.8%to 2.6%,and the strength of the Mg-9Gd-2Y-3Nd-0.2Zr alloy increased from 212 MPa to 281 MPa but the elongation decreased from 13.7%to 6.2%.Among them,the Mg-9Gd-2Y-3Nd-0.2Zr alloy showed good overall mechanical properties,especially the elongation of the aged alloy was 58%higher than that of the Mg-9Gd-2Y-1Nd-0.2Zr alloy.The increase in ductility of the aged Mg-9Gd-2Y-3Nd-0.2Zr alloy attributed to the grain boundary precipitate promotes the formation of a large number of precipitation free zones(PFZs)with widths of 130-150 nm during ageing treatment.
文摘This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-and molybdenum-free high-nitrogen austenitic stainless steel(HNASS).FSW at 400 rpm and 30 mm/min resulted in finer grains(4.18μm)and higher coincident site lattice(CSL)boundaries(32.3%)at the top of the stir zone(SZ)due to dynamic recrystallization(DRX).PWHT at 900℃for 1 h led to grain coarsening(12.91μm the bottom SZ)but enhanced CSL boundaries from 24.6%to 30.2%,improving grain boundary stability.PWHT reduced the kernel average misorientation(KAM)by 14.9%in the SZ-top layer and 20.4%in the SZ-bottom layer,accompanied by a 25%decrease in hardness in the SZ-top layer and 26.7%in the SZ-bottom layer,indicating strain recovery and reduced dislocation density.Potentiodynamic polarization tests(PDP)showed a 18%increase in pitting potential and a 76%reduction in corrosion rate after PWHT.The improvement in corrosion resistance is attributed to the increase inΣ3 twin boundaries,which enhance grain boundary stability and reduce susceptibility to localized corrosion.These findings highlight the role of PWHT in refining the microstructure and strengthening corrosion resistance,making HNASS a promising material for demanding applications.
