The Fundamental Research On MoS₂/Zr Self-lubricating Coated Tools

MoS₂/Zr self-lubricating coated tools were developed by medium-frequency magnetron sputtering combined with multi-arc ion plating technique on cemented carbide and high speed steel substrates. Tribological behaviors and wear mechanisms were detailed studied as well as its design theory, coating structures, deposition process parameters, mechanical properties and cutting performance.The finite element method (FEM) modeling for thermal residual stress analysis of the coatings was established and used to analyze physical compatibility of coating and substrate. The effect factors of the residual stress inside the coated tools such as substrates' physical parameters and deposition temperature were analyzed. Results indicated that residual stresses of coated tools are mainly affected by substrates' thermal expansion coefficient and Young's modulus, while substrates' Poisson ratio has little effect to residual stress. The optimum substrate materials matched with MoS₂ coating were selected afterwards, they were YT15 cemented carbide and M2 high speed steel, respectively. The FEM analysis results indicated that the residual stress on interface of the coated tools could be decreased by using suitable interlayer material. For MoS₂ coating deposited onto YT15 cemented carbide substrate, the residual stress with Zr interlayer is much smaller than that with Ti or Cr interlayer, while for MoS₂ coating deposited onto M2 high speed steel substrate, any interlayer (Ti/Cr/Zr) was not advised used.The soft coated MZ-1 (MoS₂/Zr+YT15) and MZ-2 (MoS₂/Zr+M2) tools were successfully developed by medium-frequency magnetron sputtering coupled with multi-arc ion plating technique. The optimum parameters (working gas (Ar) pressure: 0.45Pa; substrate bias: -200 V; MoS₂ target voltage: 700 V; Zr target arc current: 60 A; deposition time: 120 min; deposition temperature: 200℃=(for MZ-1) and 150℃(for MZ-2)). Fore treatment process of coated tools was studied. The results indicated that fore treatment process of polishing and ultrasonic cleaning can improve adhesion strength between the coating and substrate.The physical and mechanical properties of MZ-1 and MZ-2 coated tools were roundly studied. The structure of MZ-1 and MZ-2 coated tools is dense and coating elements are distributed equably. The coating micro-hardness is 10.0 GPa and 9.4 GPa both of which are higher than that of pure MoS₂ coating, and the adhesion strength is 60 N and 63 N, respectively, corresponding to MZ-1 and MZ-2 tools. The coating thickness of MZ-1 and MZ-2 is 2.4 and 2.6 urn, respectively. The interface adhesion mechanism of MZ series coatings and substrates is an interaction of mechanical occlusion and diffusion.The effect of load and friction distance on the friction and wear behavior of MoS₂/Zr coated materials sliding against 45# steel and Al₂O₃ ball was studied, respectively. The experiment results showed that the friction coefficient of MoS₂/Zr coated materials increases with increasing of friction distance, and decreases with increasing load. The wear rate increases with increasing load. Both friction coefficient and wear rate are much smaller than that of pure M0S2 coating. EDX analyses for the surface of coated tools and counterpart ball indicated that there was transfer layer formed, which was found to play an important role in reducing the friction coefficient and wear rate of MoS₂/Zr coated tools.The cutting performance of MoS₂/Zr coated tools was studied, and compared with YT15 cemented carbide and M2 high speed steel uncoated tools. The experimental results indicate that deposition of MoS₂/Zr soft coating onto YT15 and M2 tools shows decreased friction coefficient and flank wear compared with those of uncoated tools when dry cutting 45# quenched steel. Cutting speeds were found to have a profound effect on the wear behaviors of MoS₂/Zr coated tools. In case of low speed cutting, the MoS₂/Zr coated tools showed much better cutting performance compared to the uncoated tools, in high speed cutting processes, delamination of coating occurred owing to the elevated cutting temperature, which may initiate the loss of the coating from the rake face, and lead the increase of the tool wear.