Effect Of Ti C Addition On Microstructure And Properties Of CoCrFeNi High-entropy Alloy Coatings

The unique design concept of high-entropy alloy breaks through the limitations of traditional metal materials.The plasticity and strength of the alloy can be balanced by a rational composition design.For high-entropy alloys with FCC structure,the plasticity is higher but the hardness and wear resistance are poor.It is difficult to use as a protective coating.By adding other alloying elements or hard particles,it is expected to significantly improve the mechanical properties of high-entropy alloy coatings.The CrFeCoNi-x TiC（x:mass fraction,x=5,10,15 wt.%）high entropy alloy composite coating was prepared by plasma cladding and plasma spraying methods.The purpose is to study the effect of the addition of different mass fractions of TiC ceramic particles on the microstructure and mechanical properties of the coating.Clarify the mechanism of coating formation and strengthening.The effect of TiC addition on the phase formation and structure of CrFeCoNi cladding layer was studied.The composition of the phase in the cladding layer after adding TiC was analyzed by means of X-ray diffractometer and electron backscatter diffraction.The analysis and judgment of the generated phase from the perspective of thermodynamics,and the enhancement mechanism of TiC and the precipitation phase were discussed.The study shown that the second phase strengthening and the dissolution desorption were the two main mechanisms for the strengthening of TiC coatings.The nanoscale TiC in the cladding layer was synthesized from the decomposed[Ti]and[C]atoms.Partially decomposed[C]atoms were combined with[Cr]atom to form C_rnC_m.The vickers hardness of Co Cr Fe Ni-TiC cladding layer increases with the increase of TiC ceramic particles,while the wear rate decreases with the increase of the mass fraction of TiC ceramic particles.Scanning electron microscope and energy dispersive spectrometer were used to analyze the morphology evolution process of TiC particles with different mass fractions in the cladding layer.The main reason for this transformation was the segregation of TiC in the high-entropy alloys.The effect of TiC ceramic particles on the microstructure and properties of the CrFeCoNi spray coating was studied.CrFeCoNi-TiC coatings were analysed at different treatment temperatures.Observation of the effects on phase composition,organization and properties before and after heat treatment.It can be seen that the addition of TiC ceramic particles effectively promotes the formation of Cr O phase in the CrFeCoNi high-entropy alloy coating,and the coating structure is mainly thin strips.The heat-treated CrFeCoNi-TiC coating still has the FCC structure.When the heat treatment temperature reaches 600℃,the formation of Cr O was effectively promoted,the FCC phase was suppressed.The volume fraction of Cr O in the coating reached the maximum.As the heat treatment temperature increased to 800℃,the Cr O phase was inhibited,and the formation of TiC and FCC phases could be effectively promoted at high temperature.The white area（rich Co-Ni）,gray area（rich Fe-Cr）and black area（TiC）of the coating structure were interdiffused in thin strips,and the structure gradually changed from thin strips to thick.Significantly improved porosity in coatings.The wear rate of Co Cr Fe Ni-TiC coatings decreases with the addition of TiC ceramic particles.The study found that the hardness of the coating first increased and then decreased after heat treatment,and reached a maximum value of 570HV at a temperature of 600℃.