Research On The Composition-Microstructure-Property-Performance Relationship Of Ultra-fine Grade Ti(CN)-based Cermets

This thesis is composed of five chapters. In the first chapter, the microstructure, properties of Ti(CN)-based cermet as well as its development history and application in metal cutting area were introduced. Meanwhile, the development trend of nanocomposite ceramics was also briefed.In chapter two, we discussed the composition-microstructure-property relationship of ultra-fine grade Ti (CN)-based cermets, and we focused on the investigation of how different starting powder particle size and raw material compositions affect the microstructure and mechanical properties of cermets. Results show that: 1) The hardness of cermet increases as the ceramic particle size decreases while its bending strength and fracture toughness shows an opposite trend to hardness. 2) If the raw material contains too much oxygen contaminates or too much TiN decomposes during sintering process, decarbonization will occur leading the formation of a new compound that can be denoted as (Ni₂Mo₂.5W₁.3 )Cx. The presence of this third phase seems to be beneficial to hardness, however, harmful to strength and toughness. 3) A new type white core/grayish rim structure appeared in cermets fabricated from sub-micron sized Ti (CN) starting powders. It was believed that promoted diffusional reaction caused by ultra-fine raw powders led to the formation of this new core/rim structure which helps to improve the strength and toughness of the material. 4) Mo addition played an important role in determining the microstructure of the cermets. 5) Since the wettability of Co to Ti(CN) is better than that of Ni, the binding strength between ceramic phase and binder phase could be strengthened when part of Ni was replaced by Co.Chapter four presents our research results of the cutting performance of experimental cutting inserts against AISI 1045 carbon steel, in which we mainly investigated the influence of cutting force and feed rate on the tool life and tool wear mechanism. Results show that in high speed turning, oxidative wear and diffusion wear two principal wear mechanisms.Chapter five summarized the whole thesis and gave some advice on future works.