Microstructure And Properties Of CoCrFeMoNi High-entropy Alloy Prepared By Laser Cladding

High-entropy alloys（HEAs）exhibit excellent properties such as excellent strength,wear resistance,and corrosion resistance,but the application of HEAs is limitted by the expensive price in actual production.In this thesis,CoCrFeMoNi HEA-coating was fabricated on the surface of H13 steel with the laser cladding technology,respectively by the means of selective laser melting（SLM）and direct laser deposition（DLF）.The effects of laser power,scanning speed and powder feed rate on the single-track depositions’macro-morphology,dilution rate and powder efficiency were studied.the best process parameters of different laser cladding methods were selected to deposed multi-track coating,followed by aging-treatment.Finally,the microstructure,hardness,wear resistance and corrosion resistance of the cladding or aging HEA-coating were researched.The optimal process parameters for the SLM are laser power of 1600W,and scanning speed of 2mm/s.The laser power of 1600W,scanning speed of 1mm/s,and powder feeding rate of 6.56g/min are determined as the best process parameters of the DLF.The microstructure and micro-morphology of CoCrFeMoNi HEA-coating are not affected by the laser cladding method.All the coatings are composed of FCC phase,σphase,andμphase.The single-track coating is composed of long strips and petal-like eutectic structures,while the microstructure of the multi-track coatings transforms from columnar crystal to cellular crystal,and to equiaxed crystal from the interface of coating and matrix to the top of coating.The main component phase is FCC phase,and the Mo-richσandμphases are distributed at the grain boundary of FCC phase.After aging at 700-900℃for 24 hours,FCC and Mo-richσandμphases are still found in the SLM coating.With the increase of aging temperature,the simple tetragonal structuredσphase gradually changes to the rhombic trigonal structureμphase.Numerous acicularσphase structures are precipitated on the FCC substrate of the SLM coating after aging at700℃.With the increase of the aging temperature,the acicularσphase structure becomes coarse and the quantity ofσphase decreases.Meanwhile,Mo-rich pebble-likeμphase structure precipitates in the FCC substrate.The hardness of the laser cladding CoCrFeMoNi HEAs coating is approximately400HV,which is 85%higher than that of H13 steel（210HV）.The main strengthening mechanism of the coating is solid solution strengthening and precipitate strengthening.After aging at 700-900℃,the hardness of the aging-coating firstly increases then decreases,and a maximum value of 49.3HRC is achieved at 800℃.The wear mechanism of H13 steel is oxidation+adhesive abrasion,while the SLM coating shows a abrasive+peeling abrasion mechanism,compared to H13 steel,the wear rate of the coating reduces,but the aging treatment increases the wear rate of the SLM coating by 74%.In addition,the E_corr of SLM coating is 56%higher than that of H13 steel,which greatly improves the corrosion resistance.However,the large number ofσandμphases precipitated during aging treatment aggravates the galvanic corrosion in the coating and reduces the corrosion resistance of the aged-coating.