Study On Advanced Self-Toughening Silicon Nitride Matrix Nanocomposite Ceramic Tool Materials And Properties

Aimed at the difficult problems of the lower fracture toughness and flexural strength of ceramic tools, the self-toughening and strengthening mechanisms of Si₃N₄ ceramics and the toughening and strengthening mechanisms of nano-scale composites were used to successfully develop the advanced self-toughening Si₃N₄ matrix nanocomposite ceramic tool materials. Their toughening and strengthening mechanisms, dispersing technology of nano-scale composite powders, the compositions of the ceramic tool materials, hot pressing technology, mechanical properties, microstructure, sintering theory, anti-oxidization theory and cutting performance were deeply investigated. The successful development of advanced self-toughening Si₃N₄ matrix nanocomposite ceramic tool materials has established a base for further development and application of ceramic tool with higher mechanical properties.The dispersing technology for advanced self-toughening Si₃N₄ matrix nano-scale composite ceramic powders was proposed and the Si₃N₄ matrix nano-scale composite ceramic powders without agglomeration was successfully prepared. According to the characteristics of α-Si₃N₄, nano-scale α-Si₃N₄, nano-scale Ti(C₇N₃) and nono-scale TiN powder, the deionized water and PMAA-NH₄ were respectively used as dispersing medium and dispersant. By means of ball milling, ultrasonic stirring, modulating pH value and adding dispersant, the optimal parameters such as the dispersing pH value and dispersant content of single-phase powder and composite powders were achieved. And the homogeneous and stable dispersing suspension of single phase and composite powders were prepared.The nano-scale TiN toughened Si₃N₄ matrix composite ceramic cutting tool material GT1(Si₃N₄/TiN) was fabricated successfully. Its optimum fabricating technology is a sintering temperature of 1650°C, a duration time of 40min and a sintering pressure of 30MPa. And its flexural strength, fracture toughness and Vickers hardness are 1079.8MPa, 9.1MPa·m^1/2and 15.47GPa respectively. The research results indicated that nano-scale TiN can improve the sintering activity of composite powders, decrease the sintering temperature and enhance the mechanical properties. The homogeneous elongated Si₃N₄ grains can contribute to the improvement of the flexural strength and fracture toughness. A lot of intragranular nano-scale...