以稀土氧化物Lu_2O_3作为单一添加剂,研究在热处理过程中,稀土氧化物对氮化硅在粉体状态下相变的影响.指出氮化硅粉体的α→β相变率与稀土氧化物的添加量、粉体的热处理温度之间的关系.发现热处理温度在1650 ℃以下时,氮化硅粉体的相变率随着添加剂含量的异常变化.以上述制备的β-氮化硅晶种,在不进行化学处理的情况下直接用于氮化硅陶瓷的增韧,使得所制备的氮化硅陶瓷在保持原有的室温强度基本不变的情况下,断裂韧性得到大幅度提高.在此体系中研究了β-氮化硅晶种的增韧效果及机制.分析了晶粒尺寸及其分布与氮化硅陶瓷性能及显微结构之间的关系.研究表明:以Lu_2O_3为单一添加剂的自增韧氮化硅陶瓷,晶种的加入使材料在保持强度的同时,断裂韧性提高了10%～20%.
β-Si_3N_4 with completeness of phase transformation and pole-liked morphology was developed by means of heating the initial Si_3N_4 powder with certain additive of Lu_2O_3. The influence of Lu_2O_3 on phase transformation and seeds morphology was investigated. The result showed that the β-Si_3N_4 seeds with up to 95% a phase content could be gotten with 1 mol% Lu_2O_3 as additive contents at 1750 ℃ for 2 h. The microstructure and mechanical properties of hot-pressed Si_3N_4 ceramics, using 10 mol% of Lu_2O_3 additives were investigated by means of MTS measurements and Vickers indentation crack size measurements, as well as XRD and SEM. It was known that the high fracture toughness of Si_3N_4 ceramics was attributed to the rodlike morphology of β-Si_3N_4 grains. And the reinforcement effect and mechanism of β-Si_3N_4 seed were studied. It was found that the grain size and its distribution influence on the property and microstructure of Si_3N_4 ceramics were investigated. The improvement in the fracture toughness with the amount of additive was mainly attributed to elongated grain growth during the sintering process. By this method, self-reinforced Si_3N_4 ceramics with an increment of 10～20% of fracture toughness was fabricated.
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