This paper presented the microstructure, mechanical properties and oxidation behavior of silicon nitride obtained by both conventional sintering and sintering followed by hot isostatic pressing （HIP）. Silicon nitrid...This paper presented the microstructure, mechanical properties and oxidation behavior of silicon nitride obtained by both conventional sintering and sintering followed by hot isostatic pressing （HIP）. Silicon nitride with additives such as 5 wt.% Al2O3 and 5 wt.% Ln203 （Ln= La, La concentrate, Gd or La＋Gd） were studied. The results revealed that Gd203 additions increased the formation of elongated grains of β-Si3N4, the fracture toughness and oxidation resistance. La2O3 additions led to higher densification and hardness values, while addition of La2O3 concentrate promoted the formation of materials with intermediate properties, compared to the other studied compositions. Hot isostatic pressing increased the hardness but decreased the fracture toughness of the material, mainly because it allowed residual pores to close and also reduced the average aspect ratio of β-Si3N4 grains.展开更多
Ti-Modified (Na0.5K0.5)(TixNb1-x)O3 (NKNT) piezoelectric ceramics were fabricated by double-layer buried powder process at 1020°C for 2 h. The microstructures,and piezoelectric and dielectric properties of the le...Ti-Modified (Na0.5K0.5)(TixNb1-x)O3 (NKNT) piezoelectric ceramics were fabricated by double-layer buried powder process at 1020°C for 2 h. The microstructures,and piezoelectric and dielectric properties of the lead-free NKNT ceramics were investigated. X-ray diffraction re-sults indicated that Ti4+ had diffused into the (Na0.5K0.5)NbO3 lattices to form a solid solution with a perovskite structure. The introducing of Ti into the (Na0.5K0.5)NbO3 solid solution effectively reduced the sintering temperature and...展开更多
Hot-pressed sintering was employed to prepare the sodium super ionic conductor (Na1+xZr2SixP3-xO12, 1.8≤x≤2.2) ceramics and compare with the sample obtained from normal-press sintering. The phase formation, density,...Hot-pressed sintering was employed to prepare the sodium super ionic conductor (Na1+xZr2SixP3-xO12, 1.8≤x≤2.2) ceramics and compare with the sample obtained from normal-press sintering. The phase formation, density, and conductivity of the hot-press sintered and the normal-press sintered samples were investigated in detail. Results show that the density of NASICON ceramics and the degree of crystallization can be improved by hot-press process efficiently. The density of the sample sintered by normal sintering is obviously lower than that sintered by hot press. XRD analysis indicates all the hot press sintered samples contain mainly monoclinic NASICON and no ZrO2 phase was found. The ionic conductivity of normal-press sintered sample is much lower than that of hot-press sintered sample. When the composition is close to Na3Zr2Si2PO12, the dc conductivities of the hot press sintered samples were in the order of 10-3 S·cm-1. The variation of the ac conductivity with frequency in the high frequency region agrees with the power law feature of σ(ω)∝ωn(0<n<1).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
文摘This paper presented the microstructure, mechanical properties and oxidation behavior of silicon nitride obtained by both conventional sintering and sintering followed by hot isostatic pressing （HIP）. Silicon nitride with additives such as 5 wt.% Al2O3 and 5 wt.% Ln203 （Ln= La, La concentrate, Gd or La＋Gd） were studied. The results revealed that Gd203 additions increased the formation of elongated grains of β-Si3N4, the fracture toughness and oxidation resistance. La2O3 additions led to higher densification and hardness values, while addition of La2O3 concentrate promoted the formation of materials with intermediate properties, compared to the other studied compositions. Hot isostatic pressing increased the hardness but decreased the fracture toughness of the material, mainly because it allowed residual pores to close and also reduced the average aspect ratio of β-Si3N4 grains.
基金the National Natural Science Foundation of China (No. 50842028)the National High-Tech Research and Development Program of China (No. 2006AA03Z436).
文摘Ti-Modified (Na0.5K0.5)(TixNb1-x)O3 (NKNT) piezoelectric ceramics were fabricated by double-layer buried powder process at 1020°C for 2 h. The microstructures,and piezoelectric and dielectric properties of the lead-free NKNT ceramics were investigated. X-ray diffraction re-sults indicated that Ti4+ had diffused into the (Na0.5K0.5)NbO3 lattices to form a solid solution with a perovskite structure. The introducing of Ti into the (Na0.5K0.5)NbO3 solid solution effectively reduced the sintering temperature and...
文摘Hot-pressed sintering was employed to prepare the sodium super ionic conductor (Na1+xZr2SixP3-xO12, 1.8≤x≤2.2) ceramics and compare with the sample obtained from normal-press sintering. The phase formation, density, and conductivity of the hot-press sintered and the normal-press sintered samples were investigated in detail. Results show that the density of NASICON ceramics and the degree of crystallization can be improved by hot-press process efficiently. The density of the sample sintered by normal sintering is obviously lower than that sintered by hot press. XRD analysis indicates all the hot press sintered samples contain mainly monoclinic NASICON and no ZrO2 phase was found. The ionic conductivity of normal-press sintered sample is much lower than that of hot-press sintered sample. When the composition is close to Na3Zr2Si2PO12, the dc conductivities of the hot press sintered samples were in the order of 10-3 S·cm-1. The variation of the ac conductivity with frequency in the high frequency region agrees with the power law feature of σ(ω)∝ωn(0<n<1).
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.
