| Nickel-based self-fluxing alloys have good wear resistance,corrosion resistance,and oxidation resistance due to their excellent deoxidation and wetting properties.NiCrSi alloy is one of the NiCrBSi series nickel-based self-fluxing alloys and is widely used in parts with severe wear.Therefore,the detection and improvement of the wear resistance of NiCrSi alloy is the research focus of this paper.In this paper,Laser melting deposition technology(LMD)was used to successfully prepare NiCrSi(X)(X＝0,Y2O3,Mo)series nickel-based self-fluxing alloys.The microstructure and different wear temperature(25℃,250℃ and 400℃)tribological properties of NiCrSi(X)alloys were systematically studied.In addition,NiCrSi,NiCrSi(0.5Y),NiCrSi(5Mo)three alloys with excellent wear properties were subjected to different post heat treatments,and the effects of different heat treatment methods on the microstructure and tribological properties of these three alloys were studied.The micro-scratch test verified the results of friction and wear performance of three alloy samples after different heat treatment methods.The results show that the microstructure of the NiCrSi alloy prepared by LMD technology is mainly composed of a y-Ni matrix,γ+Ni3B eutectic structure,and Cr-rich carbide M 7C3.After the addition of Y2O3,the microstructure changes of NiCrSi(Y)alloy are mainly reflected in the increase of the eutectic structure proportion,and the second phase precipitates in the inter-eutectic region increase.Among them,the maximum eutectic fraction of NiCrSi(1Y)sample is 34.5%,which is 1.8 times the eutectic fraction of NiCrSi alloy.The increase of the eutectic fraction leads to the refinement of grain size and the improvement of alloy properties.Microhardness test results show that NiCrSi(0.5Y)has the highest hardness,reaching 491.2 HV0.5,and NiCrSi alloy has the lowest,only 378.4 HV0.5.The results of friction and wear experiments show that the friction coefficient curves of NiCrSi(0.5Y)at room temperature of 25℃,service temperature of 250℃,and extreme working temperature of400 ℃ are relatively stable,and have excellent wear resistance.The wear rates are 5.307,16.610,and 16.121(10-8mm-3/N·m)，respectively,compared with the wear rate of NiCrSi 2.654,18.990,26.898(10-8mm-3/N·m),it has good wear resistance at service temperature and extreme working temperature.The carbide precipitates in the microstructure of NiCrSi(Mo)alloy prepared by LMD increased,and Mo2C precipitated in the sample when NiCrSi(5Mo.However,due to the high melting point and poor solubility of Mo,the pores in NiCrSi(Mo)alloys increased during the preparation of LMD,and the density decreased.The minimum reached 87.58%at NiCrSi(5Mo).Therefore,the addition of Mo element cannot be excessive.The results of wear at different temperatures show that the NiCrSi(5Mo)sample has the best wear resistance,the friction coefficient curve has the smallest fluctuation,and the wear rate is the lowest,1.792,4.543,and 8.565(10-8mm-3/N·m),respectively.The microstructures of the three alloys NiCrSi,NiCrSi(0.5Y),and NiCrSi(5Mo)prepared by LMD were significantly different from those of the untreated alloys afterHT1,HT2,and HT3,respectively.It roughly shows the same trend:after theHT1,the grain boundaries were destroyed,the eutectic structure was partially remelted,Cr7C3 carbides were distributed in the structure;in the HT2,the element B in the eutectic position was re-melted in the matrix,and the Ni3Fe compound was generated in the interdendritic regions;the hard phase of the sample is uniformly distributed at the eutectic boundary after HT3.The annealing microhardness of the NiCrSi,NiCrSi(0.5Y),and NiCrSi(5Mo)three alloys are 304.91,514.11,and 607.1 HV0.5,respectively.The friction and wear test results show that the three alloys subjected HT3show excellent wear resistance at 25℃,250℃,and 400℃.The abrasion resistance of the samples after HT1 and HT2 was the worst,and the untreated samples showed great wear resistance at 25℃.The micro-scale wear performance was tested by micro scratch test.The residual depth curves and scratch friction coefficient curves of three unheated samples of NiCrSi,NiCrSi(0.5 Y)and NiCrSi(5Mo)show that under fixed load,the addition of the element 0.5Y2O3 and the alloy element 5Mo makes the curve fluctuation smaller.AfterHT3,the scratch width of the three alloy samples under 200 mN and 1000 mN load is the narrowest,and the surface of the scratch groove is relatively smooth.The scratch friction coefficient curves of the HT3 samples have small fluctuations under different loads,and the residual depth curve also shows the smallest fluctuation and the shallowest depth.It indicates that the NiCrSi(X)series of self-fluxing nickel-based alloy subjected annealing treatment hold excellent micro-wear performance. |
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