Study On Fabrication And Cutting Performance Of TiC-TiB₂ Cermet Cutting Tools

TiC based composite material is a promising cutting tool material, however, at present many studies show that usually only a single mechanical property of this material can be improved with their fabricating process, few research shows that can improve the comprehensive properties. According to the design principle of composite cutting tool materials, two kinds of TiC-TiB2 composite cermet tool material with Ni and Mo as sintering additives were successfully fabricated by the vacuum hot-press sintering technology in this paper. The new fabricated TiC-TiB2 cermet cutting tool materials can not only ensure the high hardness, but also have high flexural strength and fracture toughness, namely, it possesses the high comprehensive mechanical properties. The high temperature properites of the cutting tool material and its evolution law were studied under the cutting conditions in service. The cutting performance and failure mechanisms of the new developed cutting tool in turning difficult-to-machine materials were investigated. The achievements of the research have the significance of providing the theory foundation for the development of advanced ceramic tool materials and wide application of new ceramic cutting tool.The contents of Ni and Ni-Mo as sintering additives of the TiC-TiB2 cermet cutting tools were optimized. The research results showed that the cermets with 5wt%Ni (TBN5) and 4.45wt%Ni+3.55wt%Mo (TBNM8) had relatively high mechanical properties and fine microstructures. The holding stage, heating rate, sintering temperature and holding time of TBN5 and TBNM8 were optimized. The optimum fabrication process was as follows:two holding stages, a heating rate of 50℃ /min, a sintering temperature of 1450 ℃, a holding time of 30 min under a pressure of 32 MPa. The flexural strengths, Vickers hardness, fracture toughness were 932.3±70 MPa,20.14±1.1 GPa and 6.86±0.60 MPam1/2 for TBN5, and 921.2±140 MPa,22.4±1.0 GPa and 7.18±0.5 MPa-m1/2 for TBNM8 respectively. The strengthening and toughening mechanisms were crack deflection, crack bridging and crack branching resulted from the mixed fracture mode of intergranular fracture and transgranular fracture.The flexural strength and fracture toughness of TBN5 and TBNM8 cermet cutting tools at elevated temperatures and the increment/degradation mechanisms were investigated. The research results showed that with an increase in the temperature, the flexural strengths of TBN5 and TBNM8 decreased while the fracture toughness increased first and subsequently decreased. The flexural strengths and fracture toughness of TBN5 and TBNM8 still maintained higher than 400 MPa and 6 MPa-m1/2 respectively at 1000 ℃, indicating that TBN5 and TBNM8 had good high-temperature mechanical properties and suited for the application of cutting the hard-to-cut materials.The cutting performance of TBN5, TBNM8 and the commercial LT55 cutting tools when cutting martensitic stainless steel (17-4PH) and austenitic stainless steel (321) was comparably studied. The results showed that the advanced cermet cutting tools TBN5 and TBNM8 had great cutting performance when continuously wet-turning martensitic stainless steel (17-4PH). The failure modes of the cermets cutting tools were rake face microchips and flank face wear. The wear mechanisms were diffusion wear, adhesive wear and oxidation wear. Howerver, the tool lives of both TBN5 and TBNM8 when continuously dry-turning martensitic stainless steel (17-4PH) were short. The failure modes were rake face rupture, flank face wear and cutting edge tipping. The wear mechanisms were diffusion wear, adhesive wear and oxidation wear. Compared with the wet cutting, the results showed that the advanced cermet cutting tools TBN5 and TBNM8 had preferable cutting performance when continuously dry-turning austenitic stainless steel (321). The failure modes of TBN5 were cutting edge rupture and flank face chips. The wear mechanisms were abrasive wear, diffusion wear and oxidation wear. The failure modes of TBNM8 were microchips and cutting edge tipping. The wear mechanisms were abrasive wear, adhesive wear, diffusion wear and oxidation wear.