The Properties Of Ti(Cr,Al)Sic(O)N Coatings And The Coated Cemented Carbide Tools

Titanium alloys are widely used in aerospace, marine, machinery and biomedical engineering because of their excellent properties, such as high specific strength, high temperature and corrosion resistance. But it is well known that the titanium alloys machining process is difficult due to the material’s high-temperature strength, very low thermal conductivity, relatively low modulus of elasticity, chemical reactivity and high friction coefficient with other metals. And during dry cutting process, more cutting heat results in the higher cutting temperature and inereased tool wear which lead to low machining efficiency and short tool life existed in milling of titanium alloy. According to the characteristics of titanium alloys processing, in order to extend the service life of the tools for machining titanium alloys, the Ti(Cr,A1)SiC(O)N coatings are choosed as the study object in this paper so as to explore new coating materials for titanium alloy cutting and provide reference for the design and selection of tool coating material.In this paper, the mechanical and thermal stability of Ti(Cr,A1)SiC(O)N coatings (including TiSiCN、CrSiCN、CrAlSiCN、CrAlSiCCON、TiAlSiCN and TiAlSiCON) which were deposited on cemented carbide substrate using plasma enhanced magnetron sputtering method were evaluated. The CrAlSiCON, TiAlSiCN, TiAlSiCON coatings and cemented carbide substrate were undergone heat treatment at600℃during2h in air. The changes in structure, adhesion strength and hardness of the coatings and substrate vs. temperature have been analyzed using X-ray diffraction, scratch testing as well as hardness testing. The results indicated that the cemented carbide substrate was oxidized very obviously at600℃and the main oxidation products are WO3and COWO4generated by the WC and Co, and hardness drastically reduced. But all the above three coatings were not oxidation at600℃, and the adherence strength and hardness had not changed much. The TiSiCN, CrSiCN, CrAlSiCN, CrAlSiCON, TiAlSiCN, TiAlSiCON coatings and cemented carbide substrate were undergone heat treatment at700℃in air for2h in order to further investigate the coatings oxidation resistance, high temperature hardness and friction and wear behaviour. The results show:the substrate oxidation was more serious than at600℃and the formation of a homogeneous oxide layer in the substrate surface, approximately0.2mm thick, so the surface hardness was dropped from45GPa to2GPa. The TiSiCN and CrSiCN coating were slightly oxidized at700℃and the main oxidation products are TiO2and Cr2O3generated by the Ti and Cr. Compared with the CrAl-based and TiAl-based coatings, it can be found that TiAl-based coatings were oxidized at700℃and the main oxidation products are TiO2generated by the Ti but the Cr element in the CrAl-based coatings were not oxidation. It indicated that the Al element is significantly improved oxidation resistance of the CrAl-based coatings. The CrAl-based coatings still have a higher hardness at700℃. Friction and wear tests were carried out using pin-on-disc with Ti64balls at400℃; the CrAlSiC、CrAlSiCON、TiAlSiCN and TiAlSiCON coatings were used. The results show: The CrAlSiCN、CrAlSiCON、TiAlSiCN and TiAlSiCON coatings had a higher friction coefficient at400℃than at room temperature. And the oxygen-containing coatings friction coefficients were higher than the oxygen-free coatings. The wear resistance of CrAlSiCON coating was best at400℃.The cutting performance of the TiSiCN, CrSiCN, CrAlSiCN, CrAlSiCON, TiAlSiCN and TiAlSiCON coated K40UF cemented carbide end-mills were evaluated by milling Ti64alloy. The results showed that the TiSiCN and CrSiCN coated tools had a better cutting performance than other coated tools. The Cr based coatings had higher mlling temperature than the Ti based coatings. The TiAl-based and CrAl-based coatings had lower milling temperature than the Ti/Cr-based coatings. It indicated that the addition of A1element to Ti/Cr-based coatings can reduce milling temperature. The chip of cutting Ti64is the typical serrated chip. Different coated milling cutter had no significant effect on the morphology of chip.