| Improving the surface hardness and wear resistance of titanium alloys plays an important role in expanding the engineering application scope of titanium alloys.Scholars at home and abroad have done lots of researches on preparation of wear resistant coating on titanium alloy surface,but the studies on the preparation of wear resistant coatings by plasma spray welding technology and take tempering treatment on the coating is rare,so lack of relevant research data.In this paper,Ni-based spray welding coating was prepared on the surface of TC4 titanium alloy with thickness of 8mm by plasma spraying technology,and the tempering treatments(air cooling)of Ni-based spray welding coating at 200?×1h,400?×1h,600?×1h was done,then analyze the microstructures,micro-hardness and wear properties of the welded and tempered samples,the results show that:The coating is composed of matrix,transition layer and strengthening layer,which is a typical structure of tough matrix + hard phase,and a metallurgical bonding was formed between the matrix and the coating.?-Ni is the matrix phase of the coating,which is soluted alloying elements like Cr,B and so on.The existence of carbides and borides hard phase like TiC,Cr7C3,CrB and Ti B2 significantly increased the micro-hardness of coating to 986.5HV0.5,which is about 3.5 times of TC4 substrate.Both the reciprocating friction wear test and the rubber wheel abrasive wear test show that the wear resistance of the spray coating is significantly higher than that of the TC4 substrate,there is no obvious adhesion signs on the coating worn surface,and only a slight abrasive wear characteristic was observed.Tempering treatment enhances the diffusion capacity of alloying elements,the thickness of transition layer increases with the increase of tempering temperature,when the tempering temperature is 600?,the thickness of the transition layer is up to 200?m,which is about 2 times of the welded.At the same time,the tempering treatment obviously improves the uniformity and densification of the transition layer,enlarges the size of the substrate transformation zone,changes the direction of the acicular structure from the original direction which is coincident with the heat flow to 45 degree angle,and the tempering treatment can also reduce the residual stress between substrate and coating,and improve the bonding ability of coating and substrate.At the tempering process of 200?×1h and 400?×1h,dispersion precipitation of carbides and borides take the dominant position,growth direction of carbides remains the same,comparing with the welded sample the hardness of coating surface increases.At the tempering process of 600?×1h,the coarsening of the substrate and aggregation growth of the hard phase takes the dominant position,the growth direction of carbides are disrupted,the hardness of coating surface decreases slightly.The wear tests show that in the reciprocating friction wear test,the wear resistance of samples was all improved.The wear resistance of coating with 400?×1h tempering treatment is the best,manifesting as the lowest friction coefficient of 0.5146 which decreased by 0.05 compared with welded sample,and the wear amount is 0.0078mm3 which is only 1/2 of the welded sample.In the rubber wheel abrasive wear test,the wear loss of the 200?×1h and 400?×1h tempering samples were reduced by 0.0039 g,0.0051 g respectively,which is slightly lower than that of the welded sample,so those two samples show a better wear performance.However,when the tempering treatment of sample is 600?×1h,with the coarsening of hard phase and weakening of substrate support the wear resistance decreased on contrary,its wear loss is increased by 0.0036 g compared with the welded sample. |
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