Sialon结合刚玉材料凝胶注模成型及其性能

研究了Sialon结合刚玉耐火材料浓悬浮体的流变性能和稳定性能.固相体积分数79%的悬浮体,在中等剪切速率时表现剪切变稀特征,剪切速率10～100 s-1范围表现出突出的"切稀"行为,符合凝胶注模成型的要求.计算了在剪切速率10～20s-1范围内的Bingham值为22960Pa,建立的流变模型为:σ=22960 391 γ.凝胶注模成型后的坯体具有3.11g/cm3的体积密度和14MPa的抗折强度.烧结材料的物相组成为刚玉和Sialon,六方柱状Sialon晶体发育完整,具有均匀一致的显微结构,性能达到了使用机械成型产品的性能,高温抗折强度提高3.8倍.     

Effects of nitrogen and fluorine on crystallisation of Ca-Si-Al-O-N-F glasses

The effect of nitrogen and fluorine substitution on the crystallisation of a new generation of oxyfluoronitride glasses in the Ca-Si-Al-O-N-F system has been studied. Glasses were nucleated for 5 h at the nucleation temperature of Tg + 50 °C and crystallised for 10 h at the maximum crystallisation temperature (900-1050 °C depending on the glass composition) determined from differential thermal analysis. For the oxide glass, crystallisation results in formation of wollastonite (CaSiO₃), gehlenite (Ca₂Al₂SiO₇) and anorthite (CaAl₂Si₂O₈) along with a small amount of residual glass. For crystallisation of oxyfluoride glasses (0 equiv.% N), when fluorine content increases, cuspidine (Ca₄Si₂O₇F₂) is the major crystalline phase at the expense of gehlenite while in oxyfluoronitride glasses containing 20 equiv.% N, gehlenite is always the dominant crystalline phase at different fluorine contents. At constant fluorine content (5 equiv.%), an increase in nitrogen content favours the formation of gehlenite rather than anorthite or wollastonite suggesting that this phase may be able to accommodate N into its crystal structure. While a small amount of nitrogen substitution for oxygen can be assumed in the gehlenite structure, the residual glass in the glass-ceramic is expected to be very N-rich. In terms of properties, hardness is shown to be more sensitive to changes in microstructure, phase morphology and crystal size compared with elastic modulus which is related to the amounts of constituent phases present.     

cBN reinforced Y-α-SiAlON composites

Dense α-Sialon–cBN composites were produced by FAST/SPS–sintering at 1575–1625 °C. The hardness of the materials increases only up to 21 GPa for materials with 10 vol.% cBN. On the other hand the fracture toughness increases up to nearly 8 MPa m^0.5 with 30 vol.% cBN. The reason for the increase in fracture toughness is attributed to crack deflection at cBN grains due to the weak bonding of the grains in the matrix. The weak interfaces are also responsible for the moderate increase in hardness. Detailed investigation of the interface between cBN and the matrix was carried out by TEM.     

Assessment and Prediction of Thermodynamic Functions of Compounds in Sialon System

According to the quasi-paraboloid rule, a computer program was developed and the Gibbs free energy functions of some compounds in Sialon system were assessed and predicted. It makes the theoretical design of the Sialon materials possible.     

Sialon固溶体Z值是粒状态的相关性

利用ＳＴＥＭ和ＥＤＡＸ对Ｓｉａｌｏｎ晶粒的生长形貌在溶体Ｚ值进行分析发现，不同发育形态六方晶型Ｓｉａｌｏｎ晶粒及晶粒内不同位置均具有不同的ＡＩ＾３＋固溶含量，该研究结果表明，根据原料配比中或烧结体中的ＡＩ＾３＋含量来计算Ｓｉａｌｏｎ材料的固溶Ｚ值是不确切的。     

Al2O3和Sialon陶瓷中LiTaO3第二相的断裂行为

将LiTaO3压电陶瓷颗粒分别添加到Al2O3和Sialon结构陶瓷基体中,通过对复相陶瓷试样断口形貌和裂纹扩展路径的观察,研究了Al2O3和Sialon结构陶瓷基体中LiTaO3第二相的断裂行为.研究结果表明:Al2O3和Sialon陶瓷基体的断裂均为沿晶断裂,LiTaO3压电陶瓷颗粒的断裂为穿晶断裂,在LiTaO3第二相的断口上,观察到了许多断裂台阶,这些断裂台阶是由于试样断裂时,裂纹扩展过程中遇到LiTaO3晶粒内的90°电畴发生裂纹偏转和分支引起的.     

SIALON陶瓷材料的合成与改性

本文作者结合大量的文献资料及多年从事Ｓｉａｌｏｎ陶瓷材料研究的实践，介绍了Ｓｉａｌｏｎ材料的由来，对Ｓｉａｌｏｎ的生成机理与合成方法进行了较为详尽的探讨。着重介绍Ｓｉａｌｏｎ材料的几种改性方法，添加剂的加入，相变与纤维复合材料的引入以及复相陶瓷设计。     

BEHAVIOUR OF BUFFER LAYER IN JOINING OF SIALON CERAMICS TO STEEL 40Cr

The buffer layer material itself may be influential to the bond strength between active brazingfiller and ceramics.For Ag_(57)Cu_(38)Ti_5 filler metal,Cu or Ta is excellent buffer layer material,but Kovar or Ni-15Cr-15Co is worse.It was important to design a layer of soft buffer,suchas Cu,to relax interfacial stress rather than hard buffer layer,such as Mo,to avoid stress.There is an optimum thickness range of soft buffer layer,saying h/L=0.02—0.1. It was agood solution to the interfacial stress problem to use soft/hard buffer layer to increasemetal/ceramics joint strength.Finally,an idea of designing gradual materials as buffer layerbetween metal and ceramics was suggested.     

Recycling of coal ash for production of dense β-Sialon/ZrN/ZrON-based ceramics without sintering aids via pressureless sintering

β-Sialon(z = 2, Si₄Al₂O₂N₆)/ZrN composite powders have been synthesized from coal ash, zircon, and active carbon at 1550°C for 6 hours, and β-Sialon(z = 2)/ZrN/ZrON-based composite ceramics (SZZCCS) have been prepared from as-synthesized β-Sialon/ZrN composite powders via pressureless sintering process. The effects of sintering temperatures (1450, 1500, 1550°C) on the phase compositions, microstructures, linear shrinkage ratio, bulk density, and oxidation characteristics of the SZZCCS were investigated in detail, and the oxidation process was also analyzed. It was found that the dense SZZCCS could be prepared at 1550°C for 1 hour, and they mainly consisted of β-Sialon(z = 2), ZrN, and ZrON. The ZrN and ZrON particles were uniformly distributed on the β-Sialon matrix. The sintering properties of the SZZCCS were greatly improved with increasing the sintering temperature. The SZZCCS sintered at 1550°C for 1 hour possessed excellent oxidation resistance at 900°C for 6 hours due to their dense microstructures.     

Influence of β-Si3N4 particle size and heat treatment on microstructural evolution of α:β-SiAlON ceramics

In the present study, we report the effects of starting β-Si₃N₄ particle sizes and post-sintering heat treatment on microstructure evolution and mechanical properties of prepared α-β SiAlON ceramics. Three different β-Si₃N₄ starting powders, with particle sizes of 2, 1 and 0.5 μm were used to prepare α-β SiAlON ceramics by gas-pressure sintering. Elongated β-SiAlON grain morphology was identified in the samples prepared using 0.5 μm particle size β-Si₃N₄ powder. Low-aspect ratio grain morphology was observed in samples prepared from starting powders with coarse particles (2 μm and 1 μm). The sintered samples were further heat treated to develop desired microstructure with elongated grains. The hardness and indentation fracture toughness values of sintered and heat treated samples were found to lie in the range of 12.4-14.2 GPa and 5.1-6.4 MPa m^1/2 respectively. It was revealed that fracture toughness increases with decrease in particle size of starting β-Si₃N₄ powder.