Design And Development Of ZrN Coated Tools And Study On Its Cutting Performance

ZrN coated tool materials were developed by pulse biased arc ion plating technique deposition combined with ion bombardment. Tribological behaviors and wear mechanisms were detailed studied as well as its coating structures, design theory, coating process parameters, mechanical properties and microstructure.The modeling for residual stress analysis were established, it's used to analyze physical compatibility of coating and substrate, and the effect factors of the residual stress status inside the coated tools such as substrates' physical parameters and deposition temperature were analyzed. Results indicated that residual stresses of coated tools are affected by substrates' thermal expansion coefficient and Young's modulus. The change of substrates' Poisson ratio has little effect to residual stress. The optimum physical parameters matched with ZrN coating (thermal expansion coefficient: 6-7.5×10^-6/K; Young's modulus: 400-600 GPa) were obtained. The best match of substrate material to ZrN coating is YT15 cemented carbide. The effects of interlayer to the residual stress status inside coated tools were analyzed. The results indicated that the interlayer could decrease the residual stress on interface of the coated tools. The residual stress of ZrN coated tools with Zr interlayer is smaller than that with Ti interlayer.The ZrN coated tools (DZ, GZZ, and FZT) were successfully developed by pulse biased arc ion plating technique deposition combined with ion bombardment. The optimum parameters (substrate bias:-300 V; Zr arc current: 90 A; Ti arc current: 80 A; N₂ flow: 100 sccm; deposition time 55-75 min; deposition temperature: 250°C) were obtained through tests. Fore treatment process of coated tools was studied. The results indicated that fore treatment process such as polishing and sand-blasting can improve adhesion strength between the coating and the substrate. The interface adhesion mechanism of coating and substrate polished is intervenient between planar interface and diffusion interface, the adhesion strength is slightly low. The interface adhesion mechanism of ZrN coating and substrate after sand-blasting is an interaction of mechanical occlusion and diffusion interface. The physical and mechanical properties of DZ, GZZ, and FZT coated tools were roundly studied. The surface Vickers hardness of the DZ-1 coated tools is highest (28 GPa), the adhesion strength is 68 N. The bonding strength of GZZ-1 and FZT-1 coated tools are enhanced obviously to 72.6 N and 73.5 N. But their hardness was lower than DZ-1, 27 and 26.6 GPa. The coating thickness of GZZ-1, DZ-1 and FZT-1 is 5.4, 4.2 and 3 urn respectively. The hardness and bonding strength of coated tools deposited on YG6 cemented carbide are lower than coated tools deposited on YT15 cemented carbide. The structure of ZrN coated tools is dense and elements are distributed equably.The effect of load, sliding speed, friction distance and coating structure on the friction and wear behavior of ZrN coated materials was studied. The results indicated that the friction coefficient of ZrN coated materials decreases with increasing load. The wear rate increases with increasing load. Evaluation of the results show that the friction coefficient and the wear rate decrease with increasing sliding speed. At low speeds, the relation between the steel ring and ZrN block can be modeled by mechanical impact of micro-particles discontinuously. As a result, peeling of the surface coating occurs. This consequentially results in a significantly higher instance of wear. At high speeds, the area of contact between the steel ring and ZrN block increases exponentially, which causes high stiffness of this contact area. At high speeds, the relation between the steel ring and ZrN block is now modeled by repetitive mechanical friction force, giving rise to lower instances of wear. The friction coefficient of ZrN coated materials increases with increasing of friction distance, Analyses indicated that coating breakage will take place in 1000 m. Tribology tests show that the sliding speed has a predominant effect on the rate of wear. At low speeds, coating breakage is evident and implies a high rate of wear. Results of friction and wear tests show that wear resistance vary in ascending order of GZZ, DZ and FZT.The cutting performance of ZrN coated cutting tool was studied, and compared with YT15 cemented carbide and CN25 coated tool. The results indicate that the flank wear from high to low is YT15>FZT>DZ>GZZ when cutting 45# hardened steel; The GZZ-1's flank wear is smaller than that of CN25 during the process of cutting 40Cr hardened steel. Different modes of tool failure including abrasive wear, adhesive wear and coating breakage were observed when machining in this study. Among these tool wear patterns, abrasive wear was found to be the main mode of flank wear, while adhesive wear were the main rake face wear types. It is common that several tool wear patterns may appear simultaneously at the same time and have an effect on each other.