| Hard coatings have been widely used in the field of material processing to improve the properties and thus prolong the service life of cutting tools, due to their superior mechanical properties and thermal stability. However, a lot of heat was produced in contact area during the machining process, which would result in the wear failure of the cutting tools. Accordingly, many efforts have been made to develop the high temperature tribological performance of the hard coatings to improve the tools.Owing to the excellent high temperature oxidation resistance and mechanical properties, PVD Ti-Al-(X)-N coating, it has been commercialized in the field of cutting tools. Generally, the performance of the coating depends on its structure and composition. The Ti/Al ratio and other element incorporation (such as Si incorporation) have a great influence on the coating hardness, thermal stability, high temperature oxidation resistance and high temperature tribological performance. For instance, AlTiN coatings have higher levels of Al than TiAIN coatings. As the crystal structure keeps unchanged, higher levels of Al content can significantly improve high temperature oxidation resistance and mechanical properties of AlTiN coatings. On the other hand, it was reported that a certain content of Si added into the TiN coating can form the crystal structure (nc-TiN/a-Si3N4) where Si3N4 amorphous phase surrounds TiN grains by thermodynamic spiondal decomposition, which can not only increase hardness but also improve the high temperature stability of the coatings. In addition, the architecture design of multi-layer composite structure can also have been expected to greatly improve the performance of the coatings.In this paper, the influences of the Ti/Al ratio and Si incorporation on the high temperature tribological performance of the commonly used Ti-Al-N coatings were studied. Firstly, the TiAIN and the AlTiN/TiSiN multilayer nanocomposite coatings (referred to as the s-AlTiN/TiSiN) were deposited by arc ion plating (AIP) on high speed steel. To discuss wear behavior and wear mechanism of the TiAIN and the s-AlTiN/TiSiN coatings at different temperatures, the tribological properties of the TiAIN and the s-AlTiN/TiSiN coatings were investigated using a ball-on-disc high temperature tribometer at room temperature,400℃ and 600℃. Secondly, due to the hardness of high speed steel substrate was relatively low (58～62 HRC), the AlTiN and AlTiN/TiSiN multilayer coatings (referred to as the c-AlTiN/TiSiN) were deposited on cemented carbide to do friction test at 400℃,600℃and 800℃. Then the wear mechanisms were discussed carefully according to the wear behaviors of the AlTiN and c-AlTiN/TiSiN coatings at different temperatures. Finally, in order to study what friction velocity and load impacted the wear performance of the coating. The c-AlTiN/TiSiN coating was selected to do friction test under different friction velocitys (30 cm/s,40 cm/s, and 50 cm/s) and loads (5 N,8 N and 10 N) at 800℃.This paper focuses on the high temperature tribological behaviors of the coating at different temperatures. In addition, the microstructure and mechanical properties of the coatings were analyzed by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and nanohardness tester.The main results are as follows:(1) In comparison of the TiAIN coating and the s-AlTiN/TiSiN coating in the wear behaviors at different temperatures, the TiAIN coating had been worn out after 10000 times of friction at room temperature,400℃ and 600℃. However, the s-AlTiN/TiSiN coatings had not been worn out until 600℃, which illustrated that the high temperature wear performance of the s-AlTiN/TiSiN coating was better than that of the TiAIN coating. Both the TiAIN coating and the s-AlTiN/TiSiN coating showed the highest friction coefficient at 600℃ and the lowest friction coefficient at room temperature. In terms of wear mechanism, the failure form of the TiAIN coating was adhesive wear between the friction pair at room temperature, adhesive wear and oxidation wear mainly at 400℃and 600℃. The wear behaviors of the s-AlTiN/TiSiN coating were characterized by abrasive wear, adhesive wear and the fish-like cracking which caused by plastic deformation at room temperature, adhesive wear and oxidation wear mainly at 400℃.With increasing of oxidation wear and the effects of abrasive wear and adhesive wear at the same time, the s-AlTiN/TiSiN coating worn out eventually at 600℃.(2) When comparing high temperature friction behaviors of the AlTiN coating with that of the c-AlTiN/TiSiN coating at 400℃,600℃ and 800℃, neither of them was worn out. With the tendency of friction coefficient was similar to that of the coatings on the high speed steel substrate, the maximum value of the friction coefficients were shown at 400℃ while the lowest value were acquired at 800℃. In terms of wear mechanism, adhesive wear were the main wear behaviors of the AlTiN coating at 400 ℃. And adhesion wear, abrasive wear and oxidation wear were the main wear mechanisms of the AlTiN coating at 600℃ and 800 ℃. While oxidation wear and adhesive wear existed in the c-AlTiN/TiSiN coating during friction process at 400℃,600℃ and 800℃. Besides mild plastic deformation was the one of wear mechanisms of the c-AlTiN/TiSiN coating at 600℃.(3) As comparing the wear performances of the c-AlTiN/TiSiN coating at different friction velocitys and loads, it was found that the friction velocitys (30 cm/s, 40 cm/s, and 50 cm/s) and loads (5 N,8 N and 10N) had a little influence on the friction coefficient of the c-AlTiN/TiSiN coating at 800℃. But wear rate had a tendency to decrease with the increase of load and increase first and then decrease as the friction velocity. It indicated that increasing load and friction velocity appropriately could decrease the wear rate of the c-AlTiN/TiSiN coating under the condition of friction coefficient was constant. |
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