From existing knowledge about high-temperature cavitation mechanisms, necessary conditions were discussed for the suppression of cavitation failure during superplastic deformation in ceramic materials. The discussion,...From existing knowledge about high-temperature cavitation mechanisms, necessary conditions were discussed for the suppression of cavitation failure during superplastic deformation in ceramic materials. The discussion, where special attention was placed on the relaxation of stress concentrations during grain-boundary sliding and cavity nucleation and growth, leaded to a conclusion that cavitation failure could be retarded by the simultaneous controlling of the initial grain size, the number of residual defects, diffusivity, dynamic grain growth and the homogeneity of microstructure. On the basis of this conclusion, high-strain-rate superplasticity （defined as superplasticity at a strain rate higher than 0.01 s^-1） could be intentionally attained in some oxide ceramic materials. This was shown in tetragonal zirconia and composites consisting of zirconia, a-alumina and a spinel phase.展开更多
A chemical co-precipitation strategy was employed to synthesize a series of(Gd_(0.95−x)Lu_(x)Eu_(0.05))_(3)Al_(5)O_(12)(x=0.1−0.95)powder phosphors,followed by vacuum sintering to achieve transparent garnet ceramic ph...A chemical co-precipitation strategy was employed to synthesize a series of(Gd_(0.95−x)Lu_(x)Eu_(0.05))_(3)Al_(5)O_(12)(x=0.1−0.95)powder phosphors,followed by vacuum sintering to achieve transparent garnet ceramic phosphors.The density functional theory indicated Lu_(3)Al_(5)O_(12) was formed in priority compared with Gd_(3)Al_(5)O_(12) during solid-phase reaction.Upon high-temperature sintering,the Lu^(3+)substitution for Gd^(3+)suppressed point mass diffusion leading to a smaller grain size.The in-line transmittances of bulk specimens with x=0.1,0.3,0.5,0.7,and 0.95 nm were~83.5%,80.1%,68.8%,73.7%,and 82.2%at 710 nm(Eu^(3+)emission center),respectively,among which the sample of x=0.1 exhibited the optical grade with near-zero optical loss in agreement with the defect-free single crystal(~100%of the theoretical transmittance).The resulting particle and ceramic materials both presented characteristic Eu^(3+)emission arising from 5D0→7FJ(J=1−4)transition,where the dominant far-red emission at~710 nm arising from ^(5)D_(0)→^(7)F_(4) transition overlapped with the absorption of phytochrome(PFR).The photoluminescence excitation and photoluminescence intensities of(Gd_(0.95−x)Lu_(x)Eu_(0.05))_(3)Al_(5)O_(12) powders and ceramics generally increased at a higher Gd^(3+)/Lu^(3+)ratio.Lu^(3+)dopants delayed the fluorescence lifetime while the bulk samples had shorter lifetime compared to the particle counterparts.The transparent(Gd_(0.85)Lu_(0.1)Eu_(0.05))3Al_(5)O_(12) ceramic phosphor exhibited good thermal stability with a high thermal quenching temperature above 533 K.The designed ceramic phosphor-converted light-emitting diode had a saturation injection current of 435 mA and a current-dependent color rendering index.More importantly,our report marked the developmental stage of transparent ceramic materials towards zero optical loss.展开更多
Tribological property of c-axis textured shell-like Ti3AlC2 ceramic was investigated using reciprocating sliding balls (SUS304) under loads of 1,5,and 9 N.It was found that the textured top surface (TTS),corresponding...Tribological property of c-axis textured shell-like Ti3AlC2 ceramic was investigated using reciprocating sliding balls (SUS304) under loads of 1,5,and 9 N.It was found that the textured top surface (TTS),corresponding to the (000l) plane,shows the lowest mean coefficient of friction in comparison with those measured on the textured side surface (TSS),where the sliding directions are parallel (TSS-1) and perpendicular (TSS-2) to c axis,under the same load.Among all the tested orientations,the TSS-2 exhibited the lowest wear rate of 1.51 × 10-3 mm3/(N·m) under the load of 9 N.The worn mechanisms on the TTS and TSS-1 were delamination,grain fracture,and grain spalling-off.On the TSS-2,plowing effect against balls was the dominating mechanism.This work suggests the criteria to maximize the wear resistance in the load range of 1-9 N.展开更多
Single-phase Y_(4)Al_(2)O_(9)(YAM)powders were synthesized via solid-state reaction starting from nano-sized Al_(2)O_(3) and Y_(2)O_(3).Fully dense(99.5%)bulk YAM ceramics were consolidated by spark plasma sintering(S...Single-phase Y_(4)Al_(2)O_(9)(YAM)powders were synthesized via solid-state reaction starting from nano-sized Al_(2)O_(3) and Y_(2)O_(3).Fully dense(99.5%)bulk YAM ceramics were consolidated by spark plasma sintering(SPS)at 1800℃.We demonstrated the excellent damage tolerance and good machinability of YAM ceramics.Such properties are attributed to the easy slipping along the weakly bonded crystallographic planes,resulting in multiple energy dissipation mechanisms such as transgranular fracture,shear slipping and localized grain crushing.展开更多
基金supported by a Grant-in-Aid for Scientific Research B21360328 from JSPSGrant-in-Aid for Scientific Research on Priority Areas 474-19053008 from MEXT,Japan
文摘From existing knowledge about high-temperature cavitation mechanisms, necessary conditions were discussed for the suppression of cavitation failure during superplastic deformation in ceramic materials. The discussion, where special attention was placed on the relaxation of stress concentrations during grain-boundary sliding and cavity nucleation and growth, leaded to a conclusion that cavitation failure could be retarded by the simultaneous controlling of the initial grain size, the number of residual defects, diffusivity, dynamic grain growth and the homogeneity of microstructure. On the basis of this conclusion, high-strain-rate superplasticity （defined as superplasticity at a strain rate higher than 0.01 s^-1） could be intentionally attained in some oxide ceramic materials. This was shown in tetragonal zirconia and composites consisting of zirconia, a-alumina and a spinel phase.
基金supported by Zhejiang Provincial Natural Science Foundation of China(Grant No.LY23F050007).
文摘A chemical co-precipitation strategy was employed to synthesize a series of(Gd_(0.95−x)Lu_(x)Eu_(0.05))_(3)Al_(5)O_(12)(x=0.1−0.95)powder phosphors,followed by vacuum sintering to achieve transparent garnet ceramic phosphors.The density functional theory indicated Lu_(3)Al_(5)O_(12) was formed in priority compared with Gd_(3)Al_(5)O_(12) during solid-phase reaction.Upon high-temperature sintering,the Lu^(3+)substitution for Gd^(3+)suppressed point mass diffusion leading to a smaller grain size.The in-line transmittances of bulk specimens with x=0.1,0.3,0.5,0.7,and 0.95 nm were~83.5%,80.1%,68.8%,73.7%,and 82.2%at 710 nm(Eu^(3+)emission center),respectively,among which the sample of x=0.1 exhibited the optical grade with near-zero optical loss in agreement with the defect-free single crystal(~100%of the theoretical transmittance).The resulting particle and ceramic materials both presented characteristic Eu^(3+)emission arising from 5D0→7FJ(J=1−4)transition,where the dominant far-red emission at~710 nm arising from ^(5)D_(0)→^(7)F_(4) transition overlapped with the absorption of phytochrome(PFR).The photoluminescence excitation and photoluminescence intensities of(Gd_(0.95−x)Lu_(x)Eu_(0.05))_(3)Al_(5)O_(12) powders and ceramics generally increased at a higher Gd^(3+)/Lu^(3+)ratio.Lu^(3+)dopants delayed the fluorescence lifetime while the bulk samples had shorter lifetime compared to the particle counterparts.The transparent(Gd_(0.85)Lu_(0.1)Eu_(0.05))3Al_(5)O_(12) ceramic phosphor exhibited good thermal stability with a high thermal quenching temperature above 533 K.The designed ceramic phosphor-converted light-emitting diode had a saturation injection current of 435 mA and a current-dependent color rendering index.More importantly,our report marked the developmental stage of transparent ceramic materials towards zero optical loss.
基金'ChuYing' Program of Southwest Jiaotong University and Thousand Talents Program of Sichuan Province.Also,we thank for the supports of National Natural Science Foundation of China，Grant-in-Aid for Scientific Research B (No.23350104) from Japan Society for the Promotion Science,the Fundamental Research Program of Korean Institute of Materials Science，UK EPSRC Material Systems for Extreme Environments Programme Grant
文摘Tribological property of c-axis textured shell-like Ti3AlC2 ceramic was investigated using reciprocating sliding balls (SUS304) under loads of 1,5,and 9 N.It was found that the textured top surface (TTS),corresponding to the (000l) plane,shows the lowest mean coefficient of friction in comparison with those measured on the textured side surface (TSS),where the sliding directions are parallel (TSS-1) and perpendicular (TSS-2) to c axis,under the same load.Among all the tested orientations,the TSS-2 exhibited the lowest wear rate of 1.51 × 10-3 mm3/(N·m) under the load of 9 N.The worn mechanisms on the TTS and TSS-1 were delamination,grain fracture,and grain spalling-off.On the TSS-2,plowing effect against balls was the dominating mechanism.This work suggests the criteria to maximize the wear resistance in the load range of 1-9 N.
基金The present work was supported by“Chunlei Program”in Ningbo,“Hundred Talents Program”of the Chinese Academy of Sciences(No.KJCX2-EW-H06)National Natural Science Foundation of China(No.51172248/E020301)National Natural Science Foundation of China(Nos.50772072 and 51072129).
文摘Single-phase Y_(4)Al_(2)O_(9)(YAM)powders were synthesized via solid-state reaction starting from nano-sized Al_(2)O_(3) and Y_(2)O_(3).Fully dense(99.5%)bulk YAM ceramics were consolidated by spark plasma sintering(SPS)at 1800℃.We demonstrated the excellent damage tolerance and good machinability of YAM ceramics.Such properties are attributed to the easy slipping along the weakly bonded crystallographic planes,resulting in multiple energy dissipation mechanisms such as transgranular fracture,shear slipping and localized grain crushing.
