Through an investigation of the microstructure and mechanical properties of extruded Mg–5Bi–x Sn(BT5x, x = 0, 2, 4, and 6 wt%) alloys,this study demonstrates that the addition of Sn to an Mg–5Bi binary alloy signif...Through an investigation of the microstructure and mechanical properties of extruded Mg–5Bi–x Sn(BT5x, x = 0, 2, 4, and 6 wt%) alloys,this study demonstrates that the addition of Sn to an Mg–5Bi binary alloy significantly improves the tensile strength of the extruded alloy.All the extruded alloys exhibit a typical basal fiber texture and a partially dynamically recrystallized(DRXed) microstructure consisting of fine DRXed grains and coarse un DRXed grains. As the Sn content increases from 0 wt% to 6 wt%, the average size of the DRXed grains decreases from 4.2 to 2.8 μm owing to the increase in the amount of precipitates via their grain-boundary pinning effect. The extruded B5 and BT52 alloys contain numerous Mg_(3)Bi_(2) precipitates, but their size and number density are smaller and higher, respectively, in the latter alloy.Numerous Mg_(2)Sn precipitates as well as Mg_(3)Bi_(2)precipitates are present in the extruded BT54 and BT56 alloys, and the number density of the Mg_(2)Sn precipitates is higher in the latter alloy because of its higher Sn content. The addition of 2 wt% Sn to the B5 alloy significantly improves the yield strength(YS) and ultimate tensile strength(UTS) of the extruded alloy—by 76 and 57 MPa, respectively. This drastic improvement is the combined outcome of enhanced grain-boundary hardening, precipitation hardening, and solid-solution hardening effects induced by the refined DRXed grains, numerous precipitates, and Sn solute atoms, respectively. The further addition of 2 wt% or 4 wt% Sn to the BT52 alloy leads to moderate increments in the YS and UTS of the extruded alloy. Specifically, each addition of 2 wt% Sn increases the YS and UTS by ~26 and ~20 MPa, respectively, which is attributed mainly to the additional precipitation hardening effect induced by the Mg_(2)Sn precipitates.展开更多
In our previous study,we extruded Mg-5Bi-3Al(BA53,wt.%)alloy at a very high speed of 70 m/min,and the high-speed-extruded alloy exhibited an unusual fine grain structure.Since dynamic recrystallization(DRX)behavior de...In our previous study,we extruded Mg-5Bi-3Al(BA53,wt.%)alloy at a very high speed of 70 m/min,and the high-speed-extruded alloy exhibited an unusual fine grain structure.Since dynamic recrystallization(DRX)behavior determines the microstructure and corresponding mechanical properties of the extruded alloy,understanding its origin is crucial for further improvement and optimization of alloys.Herein,the DRX behavior during high-speed extrusion of the recently developed BA53 alloy was investigated in detail by analyzing the microstructure and texture of the extrusion butt along the extrusion path obtained by water quenching the remaining part of the billet immediately after extrusion.During the initial stages of extrusion with a high extrusion speed of 70 m/min and a high temperature of 400℃,tension twinning predominantly occurred in grains with a high Schmid factor(SF),switching the c-axis of the grains toward the transverse direction of the butt and causing the formation of a ring basal texture.In the intermediate stage,the microstructural changes were dominated by continuous and discontinuous DRX,resulting in the formation of fine recrystallized grains and orientation distribution originated from the parent grain.DRX was completed in the late stage wherein unrecrystallized grains with low SF for basal slip contributed to the late-stage recrystallization,strengthening the ring basal texture.Additionally,DRXed grains with favorable orientation for basal slip underwent lattice rotation,contributing to the formation of the obvious ring basal texture.Finally,preferential grain growth occurred after the DRX,leading to an increase in texture intensity and grain size of the extruded alloy.Therefore,the fine grain structure and ring basal texture obtained through high-speed extrusion were primarily attributed to the activated discontinuous DRX facilitated by a high strain rate and temperature.展开更多
Relaxor-PbTiO_(3)ferroelectric single crystals have drawn attention aiming at high-end piezoelectric applications thanks to their excellent piezoelectric properties.Like all the other ferroelectrics,relaxorPbTiO_(3)si...Relaxor-PbTiO_(3)ferroelectric single crystals have drawn attention aiming at high-end piezoelectric applications thanks to their excellent piezoelectric properties.Like all the other ferroelectrics,relaxorPbTiO_(3)single crystals can only be piezoelectrically active upon being electrically poled.However,this poled state is thermally unstable,limiting their uses because of their relatively low depolarization temperature.Here,we show that a non-destructible permanent poled state can be realized in relaxorPbTiO_(3)single crystals by forming a 0e3 composite in the presence of charged mobile point defects.We demonstrate this on solid-state grown 0.71 Pb(Mg1/3Nb2/3)O_(3)-0.29PbTiO_(3)single crystals doped with Mn(Mn-PMNT)as a donor with well-aligned and dispersed boron-rich MgO-based inclusions(MBIs).MnPMNTMBI sharing[001]axis with arrayed MBIs were spontaneously polarized during cooling across the Curie temperature without an external electricfield.The piezoelectric coefficient and dielectric permittivity of self-poled Mn-PMNTMBI crystals were as large as 90%of that achieved by a direct-current poling treatment at room temperature,and such poled state was reproducible against repeated thermal cycles.We expect that the poling-free high-performance piezoelectric relaxor-PbTiO_(3)single crystals offer an avenue for piezoelectric-based devices by removing the working temperature limit as one of the inherent fundamental limitations.展开更多
基金supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science, ICT and Future Planning (MSIP, South Korea) (No.2019R1A2C1085272)by the Materials and Components Technology Development Program of the Ministry of Trade, Industry and Energy (MOTIE, South Korea) (No. 20011091)。
文摘Through an investigation of the microstructure and mechanical properties of extruded Mg–5Bi–x Sn(BT5x, x = 0, 2, 4, and 6 wt%) alloys,this study demonstrates that the addition of Sn to an Mg–5Bi binary alloy significantly improves the tensile strength of the extruded alloy.All the extruded alloys exhibit a typical basal fiber texture and a partially dynamically recrystallized(DRXed) microstructure consisting of fine DRXed grains and coarse un DRXed grains. As the Sn content increases from 0 wt% to 6 wt%, the average size of the DRXed grains decreases from 4.2 to 2.8 μm owing to the increase in the amount of precipitates via their grain-boundary pinning effect. The extruded B5 and BT52 alloys contain numerous Mg_(3)Bi_(2) precipitates, but their size and number density are smaller and higher, respectively, in the latter alloy.Numerous Mg_(2)Sn precipitates as well as Mg_(3)Bi_(2)precipitates are present in the extruded BT54 and BT56 alloys, and the number density of the Mg_(2)Sn precipitates is higher in the latter alloy because of its higher Sn content. The addition of 2 wt% Sn to the B5 alloy significantly improves the yield strength(YS) and ultimate tensile strength(UTS) of the extruded alloy—by 76 and 57 MPa, respectively. This drastic improvement is the combined outcome of enhanced grain-boundary hardening, precipitation hardening, and solid-solution hardening effects induced by the refined DRXed grains, numerous precipitates, and Sn solute atoms, respectively. The further addition of 2 wt% or 4 wt% Sn to the BT52 alloy leads to moderate increments in the YS and UTS of the extruded alloy. Specifically, each addition of 2 wt% Sn increases the YS and UTS by ~26 and ~20 MPa, respectively, which is attributed mainly to the additional precipitation hardening effect induced by the Mg_(2)Sn precipitates.
基金financially supported by the National Research Foundation of Korea(NRF)(Nos.2019R1A2C1085272 and RS-2023-00244478)funded by the Ministry of Science,ICT,and Future Plan-ning(MSIP,South Korea).
文摘In our previous study,we extruded Mg-5Bi-3Al(BA53,wt.%)alloy at a very high speed of 70 m/min,and the high-speed-extruded alloy exhibited an unusual fine grain structure.Since dynamic recrystallization(DRX)behavior determines the microstructure and corresponding mechanical properties of the extruded alloy,understanding its origin is crucial for further improvement and optimization of alloys.Herein,the DRX behavior during high-speed extrusion of the recently developed BA53 alloy was investigated in detail by analyzing the microstructure and texture of the extrusion butt along the extrusion path obtained by water quenching the remaining part of the billet immediately after extrusion.During the initial stages of extrusion with a high extrusion speed of 70 m/min and a high temperature of 400℃,tension twinning predominantly occurred in grains with a high Schmid factor(SF),switching the c-axis of the grains toward the transverse direction of the butt and causing the formation of a ring basal texture.In the intermediate stage,the microstructural changes were dominated by continuous and discontinuous DRX,resulting in the formation of fine recrystallized grains and orientation distribution originated from the parent grain.DRX was completed in the late stage wherein unrecrystallized grains with low SF for basal slip contributed to the late-stage recrystallization,strengthening the ring basal texture.Additionally,DRXed grains with favorable orientation for basal slip underwent lattice rotation,contributing to the formation of the obvious ring basal texture.Finally,preferential grain growth occurred after the DRX,leading to an increase in texture intensity and grain size of the extruded alloy.Therefore,the fine grain structure and ring basal texture obtained through high-speed extrusion were primarily attributed to the activated discontinuous DRX facilitated by a high strain rate and temperature.
基金the Technology Innovation Program funded by the Ministry of Trade,Industry&Energy(MOTIE,Korea)(20022441)JHK was supported by the Fundamental Research Program of Korea Institute of Materials Science(PNKA170).
文摘Relaxor-PbTiO_(3)ferroelectric single crystals have drawn attention aiming at high-end piezoelectric applications thanks to their excellent piezoelectric properties.Like all the other ferroelectrics,relaxorPbTiO_(3)single crystals can only be piezoelectrically active upon being electrically poled.However,this poled state is thermally unstable,limiting their uses because of their relatively low depolarization temperature.Here,we show that a non-destructible permanent poled state can be realized in relaxorPbTiO_(3)single crystals by forming a 0e3 composite in the presence of charged mobile point defects.We demonstrate this on solid-state grown 0.71 Pb(Mg1/3Nb2/3)O_(3)-0.29PbTiO_(3)single crystals doped with Mn(Mn-PMNT)as a donor with well-aligned and dispersed boron-rich MgO-based inclusions(MBIs).MnPMNTMBI sharing[001]axis with arrayed MBIs were spontaneously polarized during cooling across the Curie temperature without an external electricfield.The piezoelectric coefficient and dielectric permittivity of self-poled Mn-PMNTMBI crystals were as large as 90%of that achieved by a direct-current poling treatment at room temperature,and such poled state was reproducible against repeated thermal cycles.We expect that the poling-free high-performance piezoelectric relaxor-PbTiO_(3)single crystals offer an avenue for piezoelectric-based devices by removing the working temperature limit as one of the inherent fundamental limitations.
