| Ti(CxN1-x) whiskers and the novel kinds of LTW series ceramic cutting tools were fabricated successfully by means of carbothermal synthesizing technology. The new design thought for carbothermal synthesized whisker toughening ceramic cutting tools was proposed. The carbothermal reduction process, whisker growth mechanism, mechanical properties, microstructure, toughening and strengthening mechanism, cutting performance were studied systematically. The design scheme for the synthesis of Ti(CxN1-x) whiskers by carbothermal reduction process was also proposed. According to the characteristics of the Ti(CxN1-x) continuous solid solution, Ti(CxN1-x) series whiskers where x value is various were successfully fabricated by controlling the molar ratio of C and Ti. This research laid the foundation of the further application of Ti(CxN1-x) whiskers and the LTW series ceramic cutting tools.The process for fabricating carbothermal synthesized whisker toughening ceramic cutting tool preforming powders was investigated. The study focused on the process parameters of carbothermal process parameters, and the optimization and selection of flux and catalyst. The novel whiskers such as TiC0.3N0.7, TiC0.5N0.5 and TiC0.7N0.3 were prepared successfully, which laid a foundation for developing Ti(CxN1-x) whisker toughening ceramic cutting tools.The growth mechanism of Ti(CxN1-x) series whiskers used in the ceramic tools was investigated. The theory of Ti(CxN1-x) whisker growth was analyzed and improved from the aspects of the basic process of whisker growth, thermodynamic principle, kinetics principle, whisker growth mechanism and the factors influencing the quality of whiskers. The V-S (Vapor-Solid) growth mechanism of Ti(CxN1-x) whisker was proposed and analyzed. The micro-growth mechanism model of V-S and V-L-S (Vapor-Liquid-Solid) growth mechanism of Ti(CxN1-x) whisker was established. The fabrication process and the mechanical properties of Ti(CxN1-x) whisker toughening ceramic cutting tools were studied. The novel kinds of whisker-toughening ceramic cutting tools such as LTW310 (Al2O3/Ti(C0.5N0.5)p/Ti(C0.3N0.7)w), LTW510 (Al2O3/Ti(C0.5N0.5)p/Ti(C0.5N0.5)w) and LTW710 (Al2O3/Ti(C0.5N0.5)p/Ti(C0.7N0.3)w were developed successfully. The flexural strength, fracture toughness and Vickers hardness of LTW310 are 752.5MPa,8.83MPa·m1/2 and 21.9GPa respectively. The flexural strength, fracture toughness and Vickers hardness of LTW510 are 812.9MPa, 7.64MPa·m1/2 and 20.0GPa respectively. The flexural strength, fracture toughness and Vickers hardness of LTW710 are 753.8MPa,8.12MPa·m1/2 and 20.2GPa respectively. The relationship between the microstructure and the mechanical properties was also investigated.The toughening and strengthening mechanism of the whisker toughening ceramic cutting tools was studied. The synergistic toughening mechanism model of Ti(C,N)w and Ti(C,N)p was established. The research results showed that the main toughening mechanism was the synergistic toughening and strengthening mechanism of Ti(C,N)w and Ti(C,N)p, whereas the assistant toughening mechanism was the toughening and strengthening mechanism by nano particle.The cutting performance of the carbothermal synthesized whisker toughening ceramic cutting tools was studied. The cutting speed for continuously turning the quenched alloy steel 40Cr was 600m/min, and the cutting speed for intermittent turning the quenched carbon steel 45# was 300m/min. The wear resistance and the fracture resistance of novel series tools LTW was good and similar to the compared commercial ceramic cutting tool LT55. The wear mechanisms were mainly controlled by crater wear on rake face and furrow wear on flank face, and the fracture mechanisms were mainly controlled by the conchoidal flaking-off on flank face and the breakage on the main cutting edge. |
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