Development Of Gradient Self-lubricating Ceramic Cutting Tools And Study On Their Cutting Performance

Ceramic tool materials have many advantages such as wear resistance,corrosion resistance,and good red-hardness.However,the disadvantage of large brittleness greatly limits the application range.Therefore,the toughening of ceramic tool materials was the focus of ceramic materials research.In this paper,TiB₂ and TiN were used as the matrix materials,WC was the reinforcing phase,?Ni,Mo?were used as the sintering aid,and the self-lubricating effect of the oxidation products of TiB₂and TiN at high temperature was utilized,gradient self-lubricating ceramic tool materials with different layer numbers and layer thickness ratios were successfully fabricated by combining gradient design ideas,and their mechanical properties,microstructure,friction and wear and cutting ability were studied.The residual stress analysis model of gradient self-lubricating ceramics was established,and the residual stress and distribution of different self-lubricating ceramics with different layers and layer thickness ratios were analyzed.It indicated that the residual compressive stress is formed in the outer layer of the material during sintering,and the residual compressive stress increased with the increase of the layer thickness ratio and the number of layers,and the residual compressive stress of the surface of T3-8,T7-1 gradient self-lubricating ceramic materials layer reached-338.21MPa and-193.61MPa,respectively.The residual compressive stress of the sample formed in a certain range close to the axis was relatively uniform after the hot press sintering,and the size of the region increases with the layer thickness ratios and the number of layers.Gradient self-lubricating ceramics with different layer numbers and layer thickness ratios were prepared by vacuum hot pressing sintering process,and their mechanical properties and microstructure were analyzed.The results showed that the fracture toughness and hardness of the surface of the gradient self-lubricating ceramic tool material increased with the increase of the number of layers and the layer thickness ratios,and the residual compressive stress has a good toughening and reinforcing effect.The fracture toughness and hardness of the surface of the seven-layer structure gradient self-lubricating ceramic material were 8.5 MPa.m^1/2,19.68 GPa,and the flexural strength was 974.8 MPa.The number of pores in the fracture surface of the gradient structure materials was slightly less than that of the homogeneous sample.The fracture mode of the surface material was the mixed fracture mode of transgranular fracture and intergranular fracture.More particle pullout can be observed in the fracture of the intermediate layer material,and the mode of the main fracture is an intergranular fracture.The dry sliding friction and wear test at room temperature was carried out on the reciprocating friction and wear tester by the pairing with the Si3N4 ball to study the friction characteristics of homogeneous and gradient structural materials under various speeds and loads,it indicated that the friction coefficients of G4,T3-1,T3-6and T5-1 materials showed a decreasing trend with the increase of friction load and speed,the lubricating film on the friction surface can be clearly observed,and gradient structural materials exhibit better friction properties than homogeneous materials.Through the comparative test of dry cutting 45#steel,the cutting performance of the surface homogen material tool and the gradient structure tool was explored,and the relationship between the compressive stress on the outer layer of the material and the anti-wear ability of the tool was explored,the results showed that:Due to the toughening and reinforcing effect of the compressive stress of the tool table,the gradient structure tool has better wear resistance than the homogenized tool material.Compared with the cutting speed of 60m/min,the cutting tool has better durability at a higher speed of 120m/min,this was mainly because the mechanical vibration was reduced when the cutting speed was high,and the temperature in the cutting zone was increased fastly,the increase of temperature was conducive to the formation of thermal oxidized lubricating film,and the lubrication effect was obvious.