| In this paper,Ni-Cr-Mo alloy coating was prepared on the surface of H13 steel by Nd3+:YAG laser,and the phase composition,microstructure,microhardness and thermal stability of the coating were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,energy dispersive spectroscopy?EDS?,microhardness tester,etc.The high temperature wear test of Ni-Cr-Mo alloy coating and H13 steel under different experimental temperature and load conditions were carried out by MMU-5GA pin-disk vacuum high temperature friction and wear tester.The wear resistance and wear behavior of Ni-Cr-Mo alloy coating were mainly studied.The formation an'd action of the friction layers as well as wear mechanism were discussed.The research has a theoretical significance and an engineering application value.The test results showed that a good metallurgical bond was formed between the Ni-Cr-Mo alloy coating and the substrate.The main phases of coating 1 were?-Fe,?-Fe,and the main phase of both coating 2 and coating 3 was?-Fe.There were also a small amount of intermetallic compounds dispersed in the matrix.The coating consisted of a cladding zone,a bonding zone,and a matrix heat-affected zone.Equiaxed grain was formed in the cladding zone;relatively coarse columnar dendrites formed perpendicular to the bonding surface and the bonding zone.The hardness of the coating was greatly improved.The hardness of the coating 1 reached about 660HV0.2,and the hardness of the coating 2 and the coating 3 was between 740-760 HV0.2.The thermal stability of the three Ni-Cr-Mo coating are greatly improved compared to H13 steel,especially coating 3.The wear test shows that the wear loss of the three Ni-Cr-Mo alloy coatings and H13 steel increases with the increase of temperature and load.At 400-500°C,the wear loss between Ni-Cr-Mo alloy coatings and H13 steel was low and their difference was small.H13 steel presented slightly higher wear loss than coatings,in which the wear loss of coating 1 was the lowest.Even at 500°C,the wear loss of the coatings and H13 steel approached one another.This meant that Ni-Cr-Mo alloy coatings and H13steel possessed good wear resistance at 400-500?.However,at600°C,the wear-loss difference of Ni-Cr-Mo alloy coating and H13 steel becames larger.Especially as the load increased to 150N,the wear loss of Ni-Cr-Mo alloy coating and H13 steel rapidly rose;the wear resistance of H13 steel became worse with about 23times wear loss of the coating.The coating 1 presented the least wear loss with the best wear resistance.It was suggested that the Ni-Cr-Mo alloy coatings possessed superior high-temperature wear resistance than H13 steel with the coating 1 for the best.It was found that friction oxide layers were formed on the worn surfaces of Ni-Cr-Mo alloy coatings and H13 steel under different temperatures and loads conditions,and affected the wear behavior and mechanism.At 400°C,there are a lot of furrows and a small amount of black smooth areas on the worn surfaces of Ni-Cr-Mo alloy coatings and H13 steel..The thin friction layer provided the protective function.The wear mechanism was mainly oxidative mild wear and abrasive wear.At500°C,the worn surfaces of Ni-Cr-Mo alloy coating and H13 steel surface represented fish scale-like adhesion marks and large area black smooth area with thick friction protective layer.The wear mechanism was mainly oxidative mild wear and adhesive wear.At 600°C,50-100N,the worn surfaces of Ni-Cr-Mo alloy coating and H13 steel surface represented large area black smooth area.As the load reached 150N the H13 steelsoftened and friction layers severely peelled off.In this case,H13steel presented serious extrusive wear.While for the Ni-Cr-Mo alloy coating,the friction layer on the worn surface exfoliated and formed a multi-layer structure.In this case,the wear fell in a mild-to-severe transition zone of oxidation wear. |
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