The 8% （mass fraction） yttrium-partially-stabilized zirconia （8YSZ） ceramic was fabricated via liquid phase sintering at 1 200-1 400℃ by adding different mass ratios of CuO-16.7%TiO2 （molar fraction） as sinteri...The 8% （mass fraction） yttrium-partially-stabilized zirconia （8YSZ） ceramic was fabricated via liquid phase sintering at 1 200-1 400℃ by adding different mass ratios of CuO-16.7%TiO2 （molar fraction） as sintering aid. Relative density, microstructure, Vickers hardness and bending strength as a function of sintering temperature and additive content were investigated. The experiment results show that liquid phase sintering at low temperature can be realized through adding CUO-16.7% TiO2 to 8YSZ. The Vickers hardness and bending strength of samples with sintering aid are generally much higher than those of samples without sintering aid for all sintering temperatures, and increase with the increase of sintering temperature. When the addition content of CUO-16.7% TiO2 is beyond 0.5%, the relative density, Vickers hardness and bending strength decrease with the increase of the mass ratio of sintering aid. Low additions of sintering aid are beneficial to aiding densification; high additions of sintering aid are detrimental to the sintered properties mainly due to greater amounts of pores generated by the volatilization of oxygen with the eutectic reaction between copper oxide and titanium dioxide. It is found that the fine grain size and high relative density are two main reasons of the high bending strength and Vickers hardness of the materials.展开更多
Ni Fe2O4 ceramics were prepared in different sintering atmospheres. The phase compositions, microstructures and mechanical properties were studied. The results show that the stoichiometric compound Ni Fe2O4 cannot be ...Ni Fe2O4 ceramics were prepared in different sintering atmospheres. The phase compositions, microstructures and mechanical properties were studied. The results show that the stoichiometric compound Ni Fe2O4 cannot be obtained in vacuum or atmospheres with oxygen contents of 2×10-5, 2×10-4 and 2×10-3, respectively. All the samples sintered in above-mentioned atmospheres contain phases of Ni Fe2O4 and Ni O. With increasing oxygen content, Ni Fe2O4 content in the ceramic increases, while Ni O content appears a contrary trend. In vacuum, Ni Fe2O4 ceramic has average grain size of 3.94 μm, and bending strength of85.12 MPa. The changes of the phase composition and mechanical properties of Ni Fe2O4 based cermets are mainly caused by the alteration of their properties of Ni Fe2O4 ceramic.展开更多
ZrB2 ceramics with various hexagonal BN(hBN)additions up to 37 vol%were reactively densified by spark plasma sintering using powder mixtures containing ZrB2,ZrN and boron.ZrN-boron based additives effectively promoted...ZrB2 ceramics with various hexagonal BN(hBN)additions up to 37 vol%were reactively densified by spark plasma sintering using powder mixtures containing ZrB2,ZrN and boron.ZrN-boron based additives effectively promoted the densification process,ZrB2 ceramics reached>99%relative density at 2000℃and an applied pressure of 60 MPa with only 5 vol%in-situ formed hBN,whereas the relative density of pure ZrB2 was only 91.2%at the same conditions.Increasing thehBN contents,the morphology of hBN grains gradually changed from quasi-spherical to flake dominated,which has substantial influence on their mechanical properties.In-situ ZrB2-10 vol%hBN ceramics demonstrated high flexural strength of 597±22 MPa,relatively low Young’s modulus of 406 GPa and good machinability,especially for the impressively large strain to failure(1.47×10^-3)which is superior to most of their counterparts in the ZrB2 based particulate reinforced ceramics.展开更多
Ceramic composites Al_2O_3/(W, Ti)C/Cr_3C_2 with different contents of Cr_3C_2 and (W, Ti)C particles, and with the additive Y_2O_3, were fabricated with hot-pressing technique at 1700 ℃ under 28 MPa pressure for 30 ...Ceramic composites Al_2O_3/(W, Ti)C/Cr_3C_2 with different contents of Cr_3C_2 and (W, Ti)C particles, and with the additive Y_2O_3, were fabricated with hot-pressing technique at 1700 ℃ under 28 MPa pressure for 30 min in N_2 atmosphere. The mechanical properties were tested, and the microstructure was investigated by environment scanning electron microscope (ESEM), transmission electron microscope (TEM), energy dispersive analysis using X-ray (EDAX) and optical microscope (OM). Results indicate that the incorporation of Cr_3C_2 and (W,Ti)C particles can suppress the grain growth of the others, and the toughening and strengthening effects mainly originate from nano-particles, dispersion toughening and solidification strengthening. The multiphase composite ceramic material Al_2O_3/10%Cr_3C_2/20%(W,Ti)C shows good mechanical properties, especially the fracture toughness increases from 4.0 MPa·m 1/2 (Monolithic Al_2O_3 ceramic) to 8.92 MPa·m 1/2, the flexural strength from 260～340 MPa (Monolithic Al_2O_3 ceramic) to 496 MPa, due to incorporation of the suitable contents of Cr_3C_2 and (W,Ti)C particles.展开更多
The cermet composites WC-20wt%Co/ZrO2（E6）with four different comtents of ZrO2（3Y）were prepared by normal vacuum sinter processing;the optical microscope and SEMwere used to characterize their microstructures.The h...The cermet composites WC-20wt%Co/ZrO2（E6）with four different comtents of ZrO2（3Y）were prepared by normal vacuum sinter processing;the optical microscope and SEMwere used to characterize their microstructures.The hardness.bending strength and impact toughness of the specimens were determined.The experimental results show that ZrO2（3Y） particles in WC-20wt%Co matrix are sphcrical particles in different sizes which are distributed uniformly in Co phases and WC phases,the bending strength and impact toughness of the WC-20wt%Co cermet composites added ZrO2（3Y）improve remarkably.but the hardness values have little change.展开更多
Phase relation and microstructure evolution in the pressure-less sintered TiB_(2)‒TiC ceramics preceded with mechanical alloying were systematically studied by a combination of SEM analysis.WC debris from milling ball...Phase relation and microstructure evolution in the pressure-less sintered TiB_(2)‒TiC ceramics preceded with mechanical alloying were systematically studied by a combination of SEM analysis.WC debris from milling balls promotes sintering by dissolving into the TiC phase to achieve dense microstructures at 1600℃.Variation of W solution in TiC grains exposes two types of core-rim structures,with no or more W in dark and white cores respectively but with common medium W in both rims.Diminishing whitecores reveal an exchange reaction between WC and TiC via mechanical alloying to form the Ti_(1-z)W_(z)C phase prior to sintering.The dark-cores inherit from the as-milled TiC power to further enable the reprecipitation of rims from a mixed liquid-phase,which facilitated also the anisotropic growth of TiB_(2) grains.The dark-cores grow persistently in the second-step at 2000℃ enabled by this liquid-phase,which coarsens the TiB2 grains too.With more alloyed phase,sintering was insufficient at 1500℃ with only the surface fluidity from the primary powders,and the second-step sintering increased the fluidity in the liquid-phase to fully densify the binary microstructure.Re-distribution of the alloyed W by two-step sintering rationalizes the evolution process of the binary microstructures and leads to better understanding of the mechanical behaviors.展开更多
以纳米ZrO 、微米Al O 为原料,采用无压烧结方式制备了ZTA 复相陶瓷。结果表明:nano-ZrO 的 2 2 3 2加入有利于制备细晶ZTA 复相陶瓷。此外,nano-ZrO 的加入对 Al O 陶瓷的显微结构也产生影响,ZrO ...以纳米ZrO 、微米Al O 为原料,采用无压烧结方式制备了ZTA 复相陶瓷。结果表明:nano-ZrO 的 2 2 3 2加入有利于制备细晶ZTA 复相陶瓷。此外,nano-ZrO 的加入对 Al O 陶瓷的显微结构也产生影响,ZrO 颗粒以 2 2 3 2“晶内型”和晶界型两种形式存在。合理的配方组成及制备工艺有利于 Z r O 以四方亚稳相存在。Z r O 含量为 2 23 0 w t % 时,其四方相含量可达 6 9 %,有利于应力诱导相变增韧,该 Z T A 复相陶瓷的抗弯强度、断裂韧性分别达到 604MPa、6.87MPa·m1/2。展开更多
The preparation of dense ZrB_(2)-based ceramics typically requires high temperatures and long sintering time,which often result in significant grain coarsening and thus deterioration of mechanical properties.Ultrafast...The preparation of dense ZrB_(2)-based ceramics typically requires high temperatures and long sintering time,which often result in significant grain coarsening and thus deterioration of mechanical properties.Ultrafast sintering techniques offer a solution to inhibit grain coarsening by reducing the processing time.However,the ultrafast preparation of dense ZrB_(2)-based ceramics remains a challenge.In this work,we successfully fabricated dense ZrB_(2)-based ceramics in just a few minutes using heavy continuous direct current(DC)Joule heating and pressing.Notably,the densification rate peaked at 1218℃,and the densification process was nearly complete at a relatively low temperature of 1500℃.The application of heavy continuous direct current not only promotes the densification of the ceramics but also enhances the texturization of ZrB_(2).This results in optimally aligned ZrB_(2) grains that form a three-dimensional bonded skeletal network.These unique microstructures can effectively induce multi-stage fracture surfaces during failure,which helps synergistic strengthening and toughening of the ceramics.The ceramics exhibit remarkable comprehensive mechanical properties,with flexural strength and fracture toughness values reaching 773±114 MPa and 5.88±0.08 MPa·m^(1/2),respectively,surpassing those of conventional hot pressed samples.This technique is expected to be applied to other ultra-high temperature ceramics,providing a promising approach for the development of thermal protection materials.展开更多
基金Project(200805331062) supported by the Research Fund for the Doctoral Program of Higher Education of ChinaProject(2010FJ4061) supported by the Science and Technology Program of Hunan Province,China
文摘The 8% （mass fraction） yttrium-partially-stabilized zirconia （8YSZ） ceramic was fabricated via liquid phase sintering at 1 200-1 400℃ by adding different mass ratios of CuO-16.7%TiO2 （molar fraction） as sintering aid. Relative density, microstructure, Vickers hardness and bending strength as a function of sintering temperature and additive content were investigated. The experiment results show that liquid phase sintering at low temperature can be realized through adding CUO-16.7% TiO2 to 8YSZ. The Vickers hardness and bending strength of samples with sintering aid are generally much higher than those of samples without sintering aid for all sintering temperatures, and increase with the increase of sintering temperature. When the addition content of CUO-16.7% TiO2 is beyond 0.5%, the relative density, Vickers hardness and bending strength decrease with the increase of the mass ratio of sintering aid. Low additions of sintering aid are beneficial to aiding densification; high additions of sintering aid are detrimental to the sintered properties mainly due to greater amounts of pores generated by the volatilization of oxygen with the eutectic reaction between copper oxide and titanium dioxide. It is found that the fine grain size and high relative density are two main reasons of the high bending strength and Vickers hardness of the materials.
基金Project(2008AA030503)supported by the National High Technology Research and Development Program of ChinaProject(51474238)supported by the National Natural Science Foundation of China
文摘Ni Fe2O4 ceramics were prepared in different sintering atmospheres. The phase compositions, microstructures and mechanical properties were studied. The results show that the stoichiometric compound Ni Fe2O4 cannot be obtained in vacuum or atmospheres with oxygen contents of 2×10-5, 2×10-4 and 2×10-3, respectively. All the samples sintered in above-mentioned atmospheres contain phases of Ni Fe2O4 and Ni O. With increasing oxygen content, Ni Fe2O4 content in the ceramic increases, while Ni O content appears a contrary trend. In vacuum, Ni Fe2O4 ceramic has average grain size of 3.94 μm, and bending strength of85.12 MPa. The changes of the phase composition and mechanical properties of Ni Fe2O4 based cermets are mainly caused by the alteration of their properties of Ni Fe2O4 ceramic.
基金supported financially by grants from the National Natural Science Foundation of China(NSFC)(No.51972243 and 51521001)。
文摘ZrB2 ceramics with various hexagonal BN(hBN)additions up to 37 vol%were reactively densified by spark plasma sintering using powder mixtures containing ZrB2,ZrN and boron.ZrN-boron based additives effectively promoted the densification process,ZrB2 ceramics reached>99%relative density at 2000℃and an applied pressure of 60 MPa with only 5 vol%in-situ formed hBN,whereas the relative density of pure ZrB2 was only 91.2%at the same conditions.Increasing thehBN contents,the morphology of hBN grains gradually changed from quasi-spherical to flake dominated,which has substantial influence on their mechanical properties.In-situ ZrB2-10 vol%hBN ceramics demonstrated high flexural strength of 597±22 MPa,relatively low Young’s modulus of 406 GPa and good machinability,especially for the impressively large strain to failure(1.47×10^-3)which is superior to most of their counterparts in the ZrB2 based particulate reinforced ceramics.
文摘Ceramic composites Al_2O_3/(W, Ti)C/Cr_3C_2 with different contents of Cr_3C_2 and (W, Ti)C particles, and with the additive Y_2O_3, were fabricated with hot-pressing technique at 1700 ℃ under 28 MPa pressure for 30 min in N_2 atmosphere. The mechanical properties were tested, and the microstructure was investigated by environment scanning electron microscope (ESEM), transmission electron microscope (TEM), energy dispersive analysis using X-ray (EDAX) and optical microscope (OM). Results indicate that the incorporation of Cr_3C_2 and (W,Ti)C particles can suppress the grain growth of the others, and the toughening and strengthening effects mainly originate from nano-particles, dispersion toughening and solidification strengthening. The multiphase composite ceramic material Al_2O_3/10%Cr_3C_2/20%(W,Ti)C shows good mechanical properties, especially the fracture toughness increases from 4.0 MPa·m 1/2 (Monolithic Al_2O_3 ceramic) to 8.92 MPa·m 1/2, the flexural strength from 260～340 MPa (Monolithic Al_2O_3 ceramic) to 496 MPa, due to incorporation of the suitable contents of Cr_3C_2 and (W,Ti)C particles.
文摘The cermet composites WC-20wt%Co/ZrO2（E6）with four different comtents of ZrO2（3Y）were prepared by normal vacuum sinter processing;the optical microscope and SEMwere used to characterize their microstructures.The hardness.bending strength and impact toughness of the specimens were determined.The experimental results show that ZrO2（3Y） particles in WC-20wt%Co matrix are sphcrical particles in different sizes which are distributed uniformly in Co phases and WC phases,the bending strength and impact toughness of the WC-20wt%Co cermet composites added ZrO2（3Y）improve remarkably.but the hardness values have little change.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51532006 and 51472060)Science and Technology Commission of Shanghai Municipality(16DZ2260601)the 111 Project(D16002)of the National Foreign Experts Bureau of China.
文摘Phase relation and microstructure evolution in the pressure-less sintered TiB_(2)‒TiC ceramics preceded with mechanical alloying were systematically studied by a combination of SEM analysis.WC debris from milling balls promotes sintering by dissolving into the TiC phase to achieve dense microstructures at 1600℃.Variation of W solution in TiC grains exposes two types of core-rim structures,with no or more W in dark and white cores respectively but with common medium W in both rims.Diminishing whitecores reveal an exchange reaction between WC and TiC via mechanical alloying to form the Ti_(1-z)W_(z)C phase prior to sintering.The dark-cores inherit from the as-milled TiC power to further enable the reprecipitation of rims from a mixed liquid-phase,which facilitated also the anisotropic growth of TiB_(2) grains.The dark-cores grow persistently in the second-step at 2000℃ enabled by this liquid-phase,which coarsens the TiB2 grains too.With more alloyed phase,sintering was insufficient at 1500℃ with only the surface fluidity from the primary powders,and the second-step sintering increased the fluidity in the liquid-phase to fully densify the binary microstructure.Re-distribution of the alloyed W by two-step sintering rationalizes the evolution process of the binary microstructures and leads to better understanding of the mechanical behaviors.
文摘以纳米ZrO 、微米Al O 为原料,采用无压烧结方式制备了ZTA 复相陶瓷。结果表明:nano-ZrO 的 2 2 3 2加入有利于制备细晶ZTA 复相陶瓷。此外,nano-ZrO 的加入对 Al O 陶瓷的显微结构也产生影响,ZrO 颗粒以 2 2 3 2“晶内型”和晶界型两种形式存在。合理的配方组成及制备工艺有利于 Z r O 以四方亚稳相存在。Z r O 含量为 2 23 0 w t % 时,其四方相含量可达 6 9 %,有利于应力诱导相变增韧,该 Z T A 复相陶瓷的抗弯强度、断裂韧性分别达到 604MPa、6.87MPa·m1/2。
基金supported by the Natural Science Basic Research Program of Shaanxi(Nos.2024JC-YBQN-0580 and 2020JM-599)Shaanxi Province’s Key Research and Development Project(No.2023-YBGY-172)+1 种基金the Scientific Research Program Funded by Education Department of Shaanxi Provincial Government(No.24JK0360)the Graduate Scientific Research Foundation of Shaanxi Univerisity of Technology(No.SLGYCX2401).
文摘The preparation of dense ZrB_(2)-based ceramics typically requires high temperatures and long sintering time,which often result in significant grain coarsening and thus deterioration of mechanical properties.Ultrafast sintering techniques offer a solution to inhibit grain coarsening by reducing the processing time.However,the ultrafast preparation of dense ZrB_(2)-based ceramics remains a challenge.In this work,we successfully fabricated dense ZrB_(2)-based ceramics in just a few minutes using heavy continuous direct current(DC)Joule heating and pressing.Notably,the densification rate peaked at 1218℃,and the densification process was nearly complete at a relatively low temperature of 1500℃.The application of heavy continuous direct current not only promotes the densification of the ceramics but also enhances the texturization of ZrB_(2).This results in optimally aligned ZrB_(2) grains that form a three-dimensional bonded skeletal network.These unique microstructures can effectively induce multi-stage fracture surfaces during failure,which helps synergistic strengthening and toughening of the ceramics.The ceramics exhibit remarkable comprehensive mechanical properties,with flexural strength and fracture toughness values reaching 773±114 MPa and 5.88±0.08 MPa·m^(1/2),respectively,surpassing those of conventional hot pressed samples.This technique is expected to be applied to other ultra-high temperature ceramics,providing a promising approach for the development of thermal protection materials.
