| According to the types of defects in the microstructure of Ti(C,N)-matrix cermets and the demands of high speed machining for cutting tool materials, a definition for low defect Ti(C,N)-matrix cermet cutting tool material was proposed, the composition and fabrication technologies of Ti(C,N)-matrix cermets were designed and optimized, and then three kinds of low defect Ti(C,N)-matrix cermet cutting tool materials were successfully fabricated. At last, the cutting performance of three kinds of low defect Ti(C,N)-matrix cermet cutting tools were investigated in wet turning the hot die steel H13and the stainless steels17-4PH and1Cr18Ni9Ti.The mixing technologies of composite powder of Ti(C,N)-matrix cermet cutting tool material TWM6NC10were optimized. The results indicated that TWM6NC10material system had the best mechanical properties and microstructure when the mixing time was24h and the rotation rate for ball grinding process was350r/min, and the flexural strength, Vickers hardness and fracture toughness were1052±45MPa,19.58±0.34GPa and6.31±0.18MPa·m1/2, respectively.The contents of Mo and Ni-Co of Ti(C,N)-matrix cermet cutting tool materials were optimized. The results indicated that TWM4NC8material system had the best mechanical properties and microstructure, the flexural strength, Vickers hardness, fracture toughness and relative density were1243±86MPa,19.24±0.1G Pa,5.43±0.16MPa·m1/2and99.8%, respectively.The contents of WC, TaC and HfC of Ti(C,N)-matrix cermet cutting tool materials were optimized based on the TWM4NC8material system. The results indicated that TWMNCT6material system and TWMNCTH1material system had the best mechanical properties and microstructure, and the flexural strength were1382±144MPa and1281±100MPa, the Vickers hardness were19.11±0.15GPa and19.84±0.26GPa, the fracture toughness were5.45±0.21MPa-m1/2and5.24±0.31MPa·m1/2, and the relative density were99.4%and99.8%, respectively. The flexural strength of TMNC material system was300MPa higher than that of the TWM4NC8material system, the fracture toughness was improved a little and the hardness decreased a little. The flexural strength, Vickers hardness and fracture toughness of TMNC were1436±135MPa,18.81±0.15GPa,5.67±0.26MPa-m1/2, respectively.The sintering technologies of TMNC, TWMNCT6and TWMNCTH1were optimized. The results indicated that TMNC, TWMNCT and TWMNCTH all had the best mechanical properties and microstructure when sintered at a temperature of1400℃and a holding time of30min as well as a pressure of32MPa, and the flexural strength were1787±132MPa,1759±123MPa and1563±120MPa, respectively, the Vickers hardness were18.75±0.15GPa,18.55±0.16GPa and19.34±0.15GPa, respectively, and the fracture toughness were6.02±0.12MPa·m1/2,6.07±0.16MPa-m1/2and6.09±0.30MPa·m1/2, respectively.The cutting performance of three kinds of low defect Ti(C,N)-matrix cermet cutting tools fabricated in this study were investigated in wet turning the hot die steel H13and the stainless steels17-4PH and1Cr18Ni9Ti by orthogonal design with the optimization objectives of matrial removal of workpiece, surface roughness and tool life by wear. In turning the hot die steel H13, the optimal cutting parameters of cutting tools TMNC and TWMNCTH both were v=90m/min,ap=0.20mm and f=0.10mm/r, and those of TWMNCTH were v=90m/min, ap=0.15mm and f=0.10mm/r, respectively, and the tool lifes by wear were23.9min,25.5min and35.8min, respectively. The tool life by wear of TWMNCTH was22.1min, and that of the commercial tools LN10, CX50and JC215V were4.7min,8.0min and12.5min, respectively, at the cutting parameters of v=90m/min, ap=0.20mm and f=0.10mm/r. So three kinds of low defect eutting tools were better suitable for cutting hot die steel H13than three kinds of commercial tools.In turning the stainless steel17-4PH, the optimal cutting parameters of cutting tool TMNC were v=300m/min, ap=0.30mm and f=0.10mm/r, respectively, and those of the cutting tool TWMNCT were v=300m/min, ap=0.25mm and f=0.10mm/r, respectively. The tool lifes by wear of TMNC and TWMNCT were152.3min and169.2min, respectively. The tool lifes by wear of TWMNCTH and the commercial tool CX50were155.6min and66.7min, respectively, at the cutting parameters of v=300m/min, ap=0.30mm and f=0.10mm/r.In turning the stainless steel1Cr18Ni9Ti, the optimal cutting parameters of cutting tool TWMNCT were v=300m/min, ap=0.35mm and f=0.10mm/r, respectively. At these cutting parameters, the tool lifes by wear of TMNC, TWMNCT, TWMNCTH and the commercial tool LN10were66.7min,57.2min,55.6min and124.5min, respectively. The surface roughness (Ra) obtained by three kinds of low defect ceramic cutting tools all were less than1.2μm, and that of LN10was more than1.60μm after turning for55min. So three kinds of low defect ceramic cutting tools had better tool life by wear when the surface roughness was took into account.The failure modes and failure mechanisms of three kinds of low defect ceramic cutting tools in wet turning the hot die steel H13, the stainless steels17-4PH and1Cr18Ni9Ti were investigated, respectively. The results indicated that the main failure mode was tool flank wear and its main wear mechanisms were adhesive, oxidation and diffusion wear in wet turning three hard-to-cutting materials. The exfoliation caused by contact fatigue or thermal stress fatigue was found on the rake face of three kinds of low defect cutting tools in wet turning H13and17-4PH, serious boundary wear on the major flank were also found in wet turning two types of stainless steels, crater wear happened on the rake face in wet turning1Cr18Ni9Ti. |
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