The microstructure, texture and mechanical property evolution of the extruded Mg-x Y(x = 1, 5 wt.%) alloys during equal channel angular pressing(ECAP) were systematically investigated using an optical microscope, elec...The microstructure, texture and mechanical property evolution of the extruded Mg-x Y(x = 1, 5 wt.%) alloys during equal channel angular pressing(ECAP) were systematically investigated using an optical microscope, electron backscatter diffraction(EBSD) and uniaxial tensile test. The Mg-Y alloys exhibited a weakened basal texture before the ECAP, and the texture was further weakened with the max basal poles dispersed along ~45° between the extrusion direction and the transverse direction after the ECAP. The Mg-5 Y alloys always exhibited a finer grain size comparing to that of Mg-1 Y for the same ECAP process. With a proper ECAP process, both the strength and elongation of Mg-5 Y alloy could be improved simultaneously after the ECAP, i.e., the yield strength(273.9 ± 1.2 MPa), ultimate strength(306.4 ± 3.0 MPa),and elongation(23.9 ± 1.0%) were increased by 10%, 6%, and 72%, respectively, comparing to that before the ECAP. This was considered to be arose from the combined effects of grain refinement, significant improved microstructure homogeneity and solid solution hardening.In addition, it was found that Mg-Y alloy with better comprehensive properties could be obtained by the decreasing-temperature ECAP processes. The yield strength-grain size relationship could be well described by the Hall-Petch relation for all the ECAPed Mg-Y alloys,which was consistent with that the texture changes did not significantly affect the average Schmid factors of basal, prismatic and pyramidal slips for both Mg-Y alloys.展开更多
The damping behavior of extruded Mg-xY(x=0.5,1.0,3.0 wt.%)sheets were investigated in detail concerning the effects of Y addition and temperature,and the relationship between damping capacity and yield strength was di...The damping behavior of extruded Mg-xY(x=0.5,1.0,3.0 wt.%)sheets were investigated in detail concerning the effects of Y addition and temperature,and the relationship between damping capacity and yield strength was discussed.At room temperature(RT),with Y content increasing from 0.5%to 3.0%,the damping capacity(Q-1)significantly decreased from 0.037 to 0.015.For all the studied sheets,the relationship between strain amplitude and Q-1 fitted well with the Granato and Liicke(G-L)dislocation damping model.With temperature increased,the G-L plots deviated from linearity indicating that the dislocation damping was not the only dominate mechanism,and the grain boundary sliding(GBS)could contribute to damping capacity.Consequently,the Q-1 increased remarkably above the critical temperature,and the critical temperature increased significantly from 50℃ to 290℃ with increasing Y contents from 0 to 3.0wt.%.This result implied that the segregation of Y solutes at grain boundary could depress the GBS,which was consistent with the recent finding of segregation tendency for rare-earth solutes.The extruded Mg-IY sheet exhibited slightly higher yield strength(Rp0.2)and Q-1 comparing with high-damping Mg-0.6Zr at RT.At an elevated temperature of 325℃,the Mg-IY sheet had similar Q-1 but over 3 times larger Rp0.2 than that of the pure Mg.The present study indicated that the extruded Mg-Y based alloys exhibited promising potential for developing high-performance damping alloys,especially for the elevated-temperature application.展开更多
Single crystals of(1x) Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3)(PMN-xPT)near their morphotropic phase boundaries(MPBs)are under extensive investigations for their extraordinary high dielectric and piezoelectric behavior.Ap...Single crystals of(1x) Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3)(PMN-xPT)near their morphotropic phase boundaries(MPBs)are under extensive investigations for their extraordinary high dielectric and piezoelectric behavior.Applications of those single crystals facilitated the breakthrough in ultrasonic transducer materials and devices.Ferroelectric materials are known to be fragile which often leads to various reliability failures in applications involving electric loadings.In a mechanical sense,the failure modes concern the fracture under an intensive electric field,and the fatigue crack propagation under an alternating electric field.In an electrical sense,the failure is exhibited by degenerated hysteresis loop by shrinking the remnant polarization and expanding the coercive field.All these modes degrade the performance for ferroelectric devices.As a departure from the tetragonal TÞferroelectric materials,exemplified by BaTiO_(3) and Pb(ZrTi)O_(3),the domain structures of PMN-PT around the MPB are versatile and intricate,depending sensitively on the composition variation,orientation and previous loading history.In this review,the attention is mainly focused on three aspects.First,the phase fragility and multiphase coexistence are presented for both[100]-and[101]-oriented PMN-PT single crystals.Second,investigations on electric field-induced fatigue crack propagation are described,along with the orientation effect on the crack propagation behavior.Third,the inverse effects of the phase transition and fatigue crack growth on the polarization behavior,or the interaction between the mechanical and electrical degradations will be elucidated.The review aims for better understanding the underlying mechanism for the ultrahigh performance of the PMN-PT single crystals,to bridge the studies of ferroelectric materials from the mechanical and electrical senses,as well as to evaluate the reliability of PMN-PT single crystals under device applications.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51401172 and 51601003)Sichuan Science and Technology Program(2019YJ0238)+1 种基金Fundamental Research Funds for the Central Universities(2682020ZT114)open funding of International Joint Laboratory for Light Alloys(MOE),Chongqing University。
文摘The microstructure, texture and mechanical property evolution of the extruded Mg-x Y(x = 1, 5 wt.%) alloys during equal channel angular pressing(ECAP) were systematically investigated using an optical microscope, electron backscatter diffraction(EBSD) and uniaxial tensile test. The Mg-Y alloys exhibited a weakened basal texture before the ECAP, and the texture was further weakened with the max basal poles dispersed along ~45° between the extrusion direction and the transverse direction after the ECAP. The Mg-5 Y alloys always exhibited a finer grain size comparing to that of Mg-1 Y for the same ECAP process. With a proper ECAP process, both the strength and elongation of Mg-5 Y alloy could be improved simultaneously after the ECAP, i.e., the yield strength(273.9 ± 1.2 MPa), ultimate strength(306.4 ± 3.0 MPa),and elongation(23.9 ± 1.0%) were increased by 10%, 6%, and 72%, respectively, comparing to that before the ECAP. This was considered to be arose from the combined effects of grain refinement, significant improved microstructure homogeneity and solid solution hardening.In addition, it was found that Mg-Y alloy with better comprehensive properties could be obtained by the decreasing-temperature ECAP processes. The yield strength-grain size relationship could be well described by the Hall-Petch relation for all the ECAPed Mg-Y alloys,which was consistent with that the texture changes did not significantly affect the average Schmid factors of basal, prismatic and pyramidal slips for both Mg-Y alloys.
基金This work was supported by National Natural Science Foundation of China(Nos.51401172 and 51601003)National University Student Innovation Experimental Project(No.201710613005)Sichuan Science and Technology Program(No.2019YJ0238).
文摘The damping behavior of extruded Mg-xY(x=0.5,1.0,3.0 wt.%)sheets were investigated in detail concerning the effects of Y addition and temperature,and the relationship between damping capacity and yield strength was discussed.At room temperature(RT),with Y content increasing from 0.5%to 3.0%,the damping capacity(Q-1)significantly decreased from 0.037 to 0.015.For all the studied sheets,the relationship between strain amplitude and Q-1 fitted well with the Granato and Liicke(G-L)dislocation damping model.With temperature increased,the G-L plots deviated from linearity indicating that the dislocation damping was not the only dominate mechanism,and the grain boundary sliding(GBS)could contribute to damping capacity.Consequently,the Q-1 increased remarkably above the critical temperature,and the critical temperature increased significantly from 50℃ to 290℃ with increasing Y contents from 0 to 3.0wt.%.This result implied that the segregation of Y solutes at grain boundary could depress the GBS,which was consistent with the recent finding of segregation tendency for rare-earth solutes.The extruded Mg-IY sheet exhibited slightly higher yield strength(Rp0.2)and Q-1 comparing with high-damping Mg-0.6Zr at RT.At an elevated temperature of 325℃,the Mg-IY sheet had similar Q-1 but over 3 times larger Rp0.2 than that of the pure Mg.The present study indicated that the extruded Mg-Y based alloys exhibited promising potential for developing high-performance damping alloys,especially for the elevated-temperature application.
基金supports by the National Natural Science Foundation of China through Grant No.10772090National Basic Research Program of China through Grant No.2004CB619304,are greatly acknowledged.
文摘Single crystals of(1x) Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3)(PMN-xPT)near their morphotropic phase boundaries(MPBs)are under extensive investigations for their extraordinary high dielectric and piezoelectric behavior.Applications of those single crystals facilitated the breakthrough in ultrasonic transducer materials and devices.Ferroelectric materials are known to be fragile which often leads to various reliability failures in applications involving electric loadings.In a mechanical sense,the failure modes concern the fracture under an intensive electric field,and the fatigue crack propagation under an alternating electric field.In an electrical sense,the failure is exhibited by degenerated hysteresis loop by shrinking the remnant polarization and expanding the coercive field.All these modes degrade the performance for ferroelectric devices.As a departure from the tetragonal TÞferroelectric materials,exemplified by BaTiO_(3) and Pb(ZrTi)O_(3),the domain structures of PMN-PT around the MPB are versatile and intricate,depending sensitively on the composition variation,orientation and previous loading history.In this review,the attention is mainly focused on three aspects.First,the phase fragility and multiphase coexistence are presented for both[100]-and[101]-oriented PMN-PT single crystals.Second,investigations on electric field-induced fatigue crack propagation are described,along with the orientation effect on the crack propagation behavior.Third,the inverse effects of the phase transition and fatigue crack growth on the polarization behavior,or the interaction between the mechanical and electrical degradations will be elucidated.The review aims for better understanding the underlying mechanism for the ultrahigh performance of the PMN-PT single crystals,to bridge the studies of ferroelectric materials from the mechanical and electrical senses,as well as to evaluate the reliability of PMN-PT single crystals under device applications.
