1.Introduction B_(4)C ceramics have high potential for use in aerospace,military,nuclear energy,and other fields owing to their excellent properties such as low density,high melting point,high hardness,high chem-ical ...1.Introduction B_(4)C ceramics have high potential for use in aerospace,military,nuclear energy,and other fields owing to their excellent properties such as low density,high melting point,high hardness,high chem-ical stability,excellent wear resistance,and good neutron absorp-tion ability[1-3].However,the fracture toughness(1.9 MPa·m^(1/2))of B_(4)C is poor[2].Furthermore,the low diffusion coefficient asso-ciated with the strong covalent bond of B_(4)C makes it very difficult to achieve densification through traditional pressureless sintering.For example,after the pressureless sintering of B_(4)C at 2375℃ for 1 h,Roy et al.[4]achieved a relative density of only 87%.展开更多
Digital light processing(DLP)is a crucial additive manufacturing(AM)technique for producing high-precision ceramic com-ponents.This study aims to optimize the formulation of Si_(3)N_(4)slurry to enhance both its perfo...Digital light processing(DLP)is a crucial additive manufacturing(AM)technique for producing high-precision ceramic com-ponents.This study aims to optimize the formulation of Si_(3)N_(4)slurry to enhance both its performance and manufacturability in the DLP process,and investigate key factors such as particle size distribution,photopolymer resin monomer ratios,and dispersant types to im-prove the slurry’s rheological properties.Through these optimizations,a photosensitive Si_(3)N_(4)slurry with 50vol%solid content was de-veloped,exhibiting excellent stability,and low viscosity(2.48 Pa·s at a shear rate of 12.8 s^(-1)).The effects of gas-pressure sintering on the material’s phase composition,microstructure,and mechanical properties were further explored,revealing that this technique significantly increases the flexural strength of the green sample from(109±10.24)to(618±42.15)MPa.The sintered ceramics exhibited high hard-ness((16.59±0.05)GPa)and improved fracture toughness((4.45±0.03)MPa·m^(1/2)).Crack trajectory analysis revealed that crack deflec-tion,crack bridging,and the pull-out of rod-likeβ-Si_(3)N_(4)grains,are the main toughening mechanisms,which could effectively mitigate crack propagation.Among these mechanisms,crack deflection and bridging were particularly influential,significantly enhancing the frac-ture toughness of the Si_(3)N_(4)matrix.Overall,this research highlights how monomer formulation and gas-pressure sintering strengthen the performance of Si_(3)N_(4)slurry in the DLP three-dimensional printing technique.This work is expected to provide new insights for fabricat-ing complex Si_(3)N_(4)ceramic components with superior mechanical properties.展开更多
Nitrogen gas pressure sintering was successfully employed to achieve the in-situ formation of Si_(3)N_(4)-bonded MgO-C refractories.The primary objective was to investigate the influence of different gas pressures on ...Nitrogen gas pressure sintering was successfully employed to achieve the in-situ formation of Si_(3)N_(4)-bonded MgO-C refractories.The primary objective was to investigate the influence of different gas pressures on the mechanical properties and microstructure of MgO-C refractories.The results indicate that higher nitrogen pressure promotes the transformation of silicon nitride from theαphase to theβphase.This phase transition positively impacts the mechanical properties of Si_(3)N_(4)-bonded MgO-C refractories,leading to an enhancement in their overall strength.Notably,when the nitrogen pressure was set at 3 MPa,exceptional compressive strength of 109.7 MPa and an elastic modulus of 142.4 GPa were achieved by these prepared refractories.These findings highlight the great potential for utilizing gas pressure sintered Si_(3)N_(4)-MgO-C refractories.展开更多
As an important A_(2)B_(2)O_(7)-type ceramic,(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy pyrochlore pos-sesses promising properties such as high melting point,high chemical durability,and low...As an important A_(2)B_(2)O_(7)-type ceramic,(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy pyrochlore pos-sesses promising properties such as high melting point,high chemical durability,and low thermal conductivity.However,the low sintering ability limits its application in thermal barrier coating and radioactive waste immobilization.It usually needs long-term high-temperature soaking to achieve full density,but with inevitable grain growth.In this work,dense and grain-refined nanocrystalline(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramics were prepared with ultra-high pressure sintering(UHPS)method under 10 GPa at a low temperature of 800℃.The densification behavior,microstructure evo-lution,and properties of the UHPS-ed samples were then investigated.The grain size of as-prepared(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramic was only 151 nm,which is 40%smaller than that of raw pow-der.In addition,it exhibited advantageous properties including both high hardness and aqueous durabil-ity.Plastic deformation under ultra-high pressure was believed as the dominant densification mechanism responsible for grain refinement and property improvement.展开更多
Dense nanocrystalline BaTiO3 ceramics with a homogeneous grain size of 30 nm was obtained by pressure assisted sintering. The ferroelectric behaviour of the ceramics was characterized by the dielectric peak at around ...Dense nanocrystalline BaTiO3 ceramics with a homogeneous grain size of 30 nm was obtained by pressure assisted sintering. The ferroelectric behaviour of the ceramics was characterized by the dielectric peak at around 120 ℃, the P-E hysteresis loop and some ferroelectric domains. These experimental results indicate that the critical grain size for the disappearance of ferroelectricity in nanocrystalline BaTiO3 ceramics fabricated by pressure assisted sintering is below 30 nm. The ferroelectric property decreasing with decreasing grain size can be explained by the lowered tetragonality and the ＇dilution＇ effect of grain boundaries.展开更多
Polycrystalline cubic boron nitride(Pc BN)compacts,using the mixture of submicron cubic boron nitride(c BN)powder and hexagonal BN(h BN)powder as starting materials,were sintered at pressures of 6.5–10.0 GPa and temp...Polycrystalline cubic boron nitride(Pc BN)compacts,using the mixture of submicron cubic boron nitride(c BN)powder and hexagonal BN(h BN)powder as starting materials,were sintered at pressures of 6.5–10.0 GPa and temperature of1750℃without additives.In this paper,the sintering behavior and mechanical properties of samples were investigated.The XRD patterns of samples reveal that single cubic phase was observed when the sintering pressure exceeded 7.5 GPa and h BN contents ranged from 20 vol.%to 24 vol.%,which is ascribed to like-internal pressure generated at grain-to-grain contact under high pressure.Transmission electron microscopy(TEM)analysis shows that after high pressure and high temperature(HPHT)treatments,the submicron c BN grains abounded with high-density nanotwins and stacking faults,and this contributed to the outstanding mechanical properties of Pc BN.The pure bulk Pc BN that was obtained at 7.7 GPa/1750℃possessed the outstanding properties,including a high Vickers hardness(~61.5 GPa),thermal stability(~1290℃in air),and high density(~3.46 g/cm^(3)).展开更多
Ultra-high temperature ceramics (UHTCs) are most recently getting much attention for structural parts of hypersonic missiles with their cruising speed of more than Mach 5. Most of the UHTCs are poor sinterability carb...Ultra-high temperature ceramics (UHTCs) are most recently getting much attention for structural parts of hypersonic missiles with their cruising speed of more than Mach 5. Most of the UHTCs are poor sinterability carbides, nitrides, and borides. Therefore, they have been studied and developed for a long time. However, there are still many problems to solve. In this paper, based on the solid-state reaction presented as an equation of (x + y)·ZrC + 2·y·B → x·ZrC + y·ZrB<sub>2</sub> + y·C, three-phase ZrC/ZrB<sub>2</sub>/C composites have been fabricated from ZrC and amorphous B powders using pulsed electric-current pressure sintering at 1373 to 2173 K for 6.0 × 10<sup>2</sup> s under 50 MPa in a vacuum. ZrC/ZrB2/C = 30/70/C~70/30/C vol% composites with the relative densities D<sub>r</sub> of 96.6 to 98.7% were obtained at 2073 K. The 60/40/C vol% composite revealed high bending strength σ<sub>b</sub> (554 MPa), Vickers hardness H<sub>v</sub> (19.2 GPa) and moderate fracture toughness K<sub>IC</sub> (5.25 MPa·m<sup>1/2</sup>) at room temperature. Furthermore, all composites showed elastic deformation up to 1873 K and revealed σ<sub>b</sub> more than 600 MPa at this temperature, in addition, some composites showed higher σ<sub>b</sub> than 900 MPa at the same temperature. These high mechanical behaviors are discussed with those of the simple binary ZrC/ZrB<sub>2</sub> composites which were fabricated under the same conditions except for their starting materials. The best mechanical properties of binary composites were σ<sub>b</sub> (474 MPa), H<sub>v</sub> (18.5 GPa), and K<sub>IC</sub> (4.45 MPa·m<sup>1/2</sup>) at room temperature, and σ<sub>b</sub> of 400 - 700 MPa at 1873 K. Overall, three-phase composites, nevertheless including soft carbon, have higher mechanical properties than the binary composites.展开更多
Convection heat transfer coefficient and air pressure drop in sinter layer are important factors for the design of sinter cooling craft. Due to the lack of necessary data, the two parameters are studied by experimenta...Convection heat transfer coefficient and air pressure drop in sinter layer are important factors for the design of sinter cooling craft. Due to the lack of necessary data, the two parameters are studied by experimental method. The experimental results show that heat conduction of sinter impacts the measurement of convection heat transfer coefficient. Convection heat transfer increases with the increase of air volumetric flow rate. Sinter layer without small particles(sample I) gives higher convection heat transfer coefficient than that with small particles(sample II). Under the considered conditions, volumetric convection heat transfer coefficient is in the range of 400-1800 W/(m3·°C). Air pressure drop in sinter layer increases with the increase of normal superficial velocity, as well as with the rise of air temperature. Additionally, air pressure drop also depends on sinter particle size distribution. In considered experimental conditions, pressure drop in sinter sample II is 2-3 times that in sinter sample I, which resulted from 17% small scale particles in sinter sample II.展开更多
（Bi_2Te_3）_（0.2）（Sb_2Te_3）_（0.8） thermoelectric material was sintered via a field activated and pressure assisted sintering（FAPAS） process.By applying different current intensity（0,60,320 A/cm^2） in the si...（Bi_2Te_3）_（0.2）（Sb_2Te_3）_（0.8） thermoelectric material was sintered via a field activated and pressure assisted sintering（FAPAS） process.By applying different current intensity（0,60,320 A/cm^2） in the sintering process,the effects of electric current on the microstructure and thermoelectric performance were investigated.This demonstrated that the application of electric current in the sintering process could significantly improve the uniformity and density of（Bi_2Te_3）_（0.2）（Sb_2Te_3）_（0.8） samples.When the current intensity was raised to 320 A/cm^2,the preferred orientation of grains was observed.Moreover,positive effects on the thermoelectric performance of applying electric current in the sintering process were also confirmed.An increase of 0.02 and 0.11 in the maximum figure of merit ZT value could be acquired by applying current of 60 and 320 A/cm^2,respectively.展开更多
W/ Cu functionally gradient materials （FGMs） containing 1% La2O3 and 1% TiC were prepared using graded sintering under tdtra-high pressure （GSUHP）. The specimens have been found to exhibit low porosity （11.57% an...W/ Cu functionally gradient materials （FGMs） containing 1% La2O3 and 1% TiC were prepared using graded sintering under tdtra-high pressure （GSUHP）. The specimens have been found to exhibit low porosity （11.57% and 11.35%, respectively）. Shearing strength of the specimens between layers is good. Moreover, the specimens have still demonstrated good performance in testing thermal-shock resistance. When power density of laser is 200MWm^-2, the specimens have been tested for thermal-shock resistance （1000 times）; the specimens that contained 1%La2O3 were not subjected to damage, whereas those that contained 1%TiC began to crack. Finally, effect of additives on thermal-shock resistance was also preliminarily discussed.展开更多
基金supported by the National Natural Science Foun-dation of China(No.52372061)the Project of the Education Department of Jilin Province(No.JJKH20231163KJ).
文摘1.Introduction B_(4)C ceramics have high potential for use in aerospace,military,nuclear energy,and other fields owing to their excellent properties such as low density,high melting point,high hardness,high chem-ical stability,excellent wear resistance,and good neutron absorp-tion ability[1-3].However,the fracture toughness(1.9 MPa·m^(1/2))of B_(4)C is poor[2].Furthermore,the low diffusion coefficient asso-ciated with the strong covalent bond of B_(4)C makes it very difficult to achieve densification through traditional pressureless sintering.For example,after the pressureless sintering of B_(4)C at 2375℃ for 1 h,Roy et al.[4]achieved a relative density of only 87%.
基金supported in part by the National Natural Science Foundation of China.(Nos.62461160259,92360307 and 92267103).
文摘Digital light processing(DLP)is a crucial additive manufacturing(AM)technique for producing high-precision ceramic com-ponents.This study aims to optimize the formulation of Si_(3)N_(4)slurry to enhance both its performance and manufacturability in the DLP process,and investigate key factors such as particle size distribution,photopolymer resin monomer ratios,and dispersant types to im-prove the slurry’s rheological properties.Through these optimizations,a photosensitive Si_(3)N_(4)slurry with 50vol%solid content was de-veloped,exhibiting excellent stability,and low viscosity(2.48 Pa·s at a shear rate of 12.8 s^(-1)).The effects of gas-pressure sintering on the material’s phase composition,microstructure,and mechanical properties were further explored,revealing that this technique significantly increases the flexural strength of the green sample from(109±10.24)to(618±42.15)MPa.The sintered ceramics exhibited high hard-ness((16.59±0.05)GPa)and improved fracture toughness((4.45±0.03)MPa·m^(1/2)).Crack trajectory analysis revealed that crack deflec-tion,crack bridging,and the pull-out of rod-likeβ-Si_(3)N_(4)grains,are the main toughening mechanisms,which could effectively mitigate crack propagation.Among these mechanisms,crack deflection and bridging were particularly influential,significantly enhancing the frac-ture toughness of the Si_(3)N_(4)matrix.Overall,this research highlights how monomer formulation and gas-pressure sintering strengthen the performance of Si_(3)N_(4)slurry in the DLP three-dimensional printing technique.This work is expected to provide new insights for fabricat-ing complex Si_(3)N_(4)ceramic components with superior mechanical properties.
基金the financial support from the National Natural Science Foundation of China(U21A2057 and 52402034)the Key Research and Development Program of Hubei Province(2023BAB106).
文摘Nitrogen gas pressure sintering was successfully employed to achieve the in-situ formation of Si_(3)N_(4)-bonded MgO-C refractories.The primary objective was to investigate the influence of different gas pressures on the mechanical properties and microstructure of MgO-C refractories.The results indicate that higher nitrogen pressure promotes the transformation of silicon nitride from theαphase to theβphase.This phase transition positively impacts the mechanical properties of Si_(3)N_(4)-bonded MgO-C refractories,leading to an enhancement in their overall strength.Notably,when the nitrogen pressure was set at 3 MPa,exceptional compressive strength of 109.7 MPa and an elastic modulus of 142.4 GPa were achieved by these prepared refractories.These findings highlight the great potential for utilizing gas pressure sintered Si_(3)N_(4)-MgO-C refractories.
基金financially supported by the National Natu-ral Science Foundation of China(nos.92163208,51902233,and 51972243)the National Key Research and Development Plan of China(no.2021YFB3701400)the Independent Innovation Projects of the Hubei Longzhong Laboratory(no.2022ZZ-11).
文摘As an important A_(2)B_(2)O_(7)-type ceramic,(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy pyrochlore pos-sesses promising properties such as high melting point,high chemical durability,and low thermal conductivity.However,the low sintering ability limits its application in thermal barrier coating and radioactive waste immobilization.It usually needs long-term high-temperature soaking to achieve full density,but with inevitable grain growth.In this work,dense and grain-refined nanocrystalline(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramics were prepared with ultra-high pressure sintering(UHPS)method under 10 GPa at a low temperature of 800℃.The densification behavior,microstructure evo-lution,and properties of the UHPS-ed samples were then investigated.The grain size of as-prepared(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramic was only 151 nm,which is 40%smaller than that of raw pow-der.In addition,it exhibited advantageous properties including both high hardness and aqueous durabil-ity.Plastic deformation under ultra-high pressure was believed as the dominant densification mechanism responsible for grain refinement and property improvement.
文摘Dense nanocrystalline BaTiO3 ceramics with a homogeneous grain size of 30 nm was obtained by pressure assisted sintering. The ferroelectric behaviour of the ceramics was characterized by the dielectric peak at around 120 ℃, the P-E hysteresis loop and some ferroelectric domains. These experimental results indicate that the critical grain size for the disappearance of ferroelectricity in nanocrystalline BaTiO3 ceramics fabricated by pressure assisted sintering is below 30 nm. The ferroelectric property decreasing with decreasing grain size can be explained by the lowered tetragonality and the ＇dilution＇ effect of grain boundaries.
文摘Polycrystalline cubic boron nitride(Pc BN)compacts,using the mixture of submicron cubic boron nitride(c BN)powder and hexagonal BN(h BN)powder as starting materials,were sintered at pressures of 6.5–10.0 GPa and temperature of1750℃without additives.In this paper,the sintering behavior and mechanical properties of samples were investigated.The XRD patterns of samples reveal that single cubic phase was observed when the sintering pressure exceeded 7.5 GPa and h BN contents ranged from 20 vol.%to 24 vol.%,which is ascribed to like-internal pressure generated at grain-to-grain contact under high pressure.Transmission electron microscopy(TEM)analysis shows that after high pressure and high temperature(HPHT)treatments,the submicron c BN grains abounded with high-density nanotwins and stacking faults,and this contributed to the outstanding mechanical properties of Pc BN.The pure bulk Pc BN that was obtained at 7.7 GPa/1750℃possessed the outstanding properties,including a high Vickers hardness(~61.5 GPa),thermal stability(~1290℃in air),and high density(~3.46 g/cm^(3)).
文摘Ultra-high temperature ceramics (UHTCs) are most recently getting much attention for structural parts of hypersonic missiles with their cruising speed of more than Mach 5. Most of the UHTCs are poor sinterability carbides, nitrides, and borides. Therefore, they have been studied and developed for a long time. However, there are still many problems to solve. In this paper, based on the solid-state reaction presented as an equation of (x + y)·ZrC + 2·y·B → x·ZrC + y·ZrB<sub>2</sub> + y·C, three-phase ZrC/ZrB<sub>2</sub>/C composites have been fabricated from ZrC and amorphous B powders using pulsed electric-current pressure sintering at 1373 to 2173 K for 6.0 × 10<sup>2</sup> s under 50 MPa in a vacuum. ZrC/ZrB2/C = 30/70/C~70/30/C vol% composites with the relative densities D<sub>r</sub> of 96.6 to 98.7% were obtained at 2073 K. The 60/40/C vol% composite revealed high bending strength σ<sub>b</sub> (554 MPa), Vickers hardness H<sub>v</sub> (19.2 GPa) and moderate fracture toughness K<sub>IC</sub> (5.25 MPa·m<sup>1/2</sup>) at room temperature. Furthermore, all composites showed elastic deformation up to 1873 K and revealed σ<sub>b</sub> more than 600 MPa at this temperature, in addition, some composites showed higher σ<sub>b</sub> than 900 MPa at the same temperature. These high mechanical behaviors are discussed with those of the simple binary ZrC/ZrB<sub>2</sub> composites which were fabricated under the same conditions except for their starting materials. The best mechanical properties of binary composites were σ<sub>b</sub> (474 MPa), H<sub>v</sub> (18.5 GPa), and K<sub>IC</sub> (4.45 MPa·m<sup>1/2</sup>) at room temperature, and σ<sub>b</sub> of 400 - 700 MPa at 1873 K. Overall, three-phase composites, nevertheless including soft carbon, have higher mechanical properties than the binary composites.
基金Project(51306198)supported by the National Natural Science Foundation of China
文摘Convection heat transfer coefficient and air pressure drop in sinter layer are important factors for the design of sinter cooling craft. Due to the lack of necessary data, the two parameters are studied by experimental method. The experimental results show that heat conduction of sinter impacts the measurement of convection heat transfer coefficient. Convection heat transfer increases with the increase of air volumetric flow rate. Sinter layer without small particles(sample I) gives higher convection heat transfer coefficient than that with small particles(sample II). Under the considered conditions, volumetric convection heat transfer coefficient is in the range of 400-1800 W/(m3·°C). Air pressure drop in sinter layer increases with the increase of normal superficial velocity, as well as with the rise of air temperature. Additionally, air pressure drop also depends on sinter particle size distribution. In considered experimental conditions, pressure drop in sinter sample II is 2-3 times that in sinter sample I, which resulted from 17% small scale particles in sinter sample II.
基金Project support by the National Research Program of China(No.50975190)
文摘（Bi_2Te_3）_（0.2）（Sb_2Te_3）_（0.8） thermoelectric material was sintered via a field activated and pressure assisted sintering（FAPAS） process.By applying different current intensity（0,60,320 A/cm^2） in the sintering process,the effects of electric current on the microstructure and thermoelectric performance were investigated.This demonstrated that the application of electric current in the sintering process could significantly improve the uniformity and density of（Bi_2Te_3）_（0.2）（Sb_2Te_3）_（0.8） samples.When the current intensity was raised to 320 A/cm^2,the preferred orientation of grains was observed.Moreover,positive effects on the thermoelectric performance of applying electric current in the sintering process were also confirmed.An increase of 0.02 and 0.11 in the maximum figure of merit ZT value could be acquired by applying current of 60 and 320 A/cm^2,respectively.
文摘W/ Cu functionally gradient materials （FGMs） containing 1% La2O3 and 1% TiC were prepared using graded sintering under tdtra-high pressure （GSUHP）. The specimens have been found to exhibit low porosity （11.57% and 11.35%, respectively）. Shearing strength of the specimens between layers is good. Moreover, the specimens have still demonstrated good performance in testing thermal-shock resistance. When power density of laser is 200MWm^-2, the specimens have been tested for thermal-shock resistance （1000 times）; the specimens that contained 1%La2O3 were not subjected to damage, whereas those that contained 1%TiC began to crack. Finally, effect of additives on thermal-shock resistance was also preliminarily discussed.
