A Study Of Microstructure And Properties Of Carburized Or Aluminized High Entropy Alloys

High entropy alloy(HEA),as a new developed material,which has many particular properties, has drawn much attentions.Recently,the studies in this arae has been concentrated on the correlation between alloy components and its structure and properties,while the surface treatment of the alloy is seldom investigated.In this article,the traditional chemical heat treatment was adopted to treat two HEAs, Al Co Fe Cr Ni was treated by solid aluminization,and Cu Co Fe Cr Ni was treated by solid carbonization and aluminization respectively.The structure and properties of the treated alloy was investigated.Here are the conlusions below:(1) After carbonization,the precipitation of a mount of carbides occurs in the Cu Co Fe Cr Ni alloy substrate.In carbonization process, the carbon diffusing into the alloy followed two means, lattice diffusion and grain boundary diffusion, and the latter one is faster.The lattice diffusion of carbon leaded to the fine carbides in dendrites.And some of the carbon diffued along grain boundary precipitated out in the form of carbides in the indendrite,the others diffused into dendrite,which caused the precipitation of acicular carbides thereon which has obvious growth orientation.The carbides which played a roll of dispersion strenthening,improved the hardness and wear resistance of alloy,but degraded the oxidation risistance.(2) After aluminizing at 850℃,a single aluminide coating that consisted of one phase formed on Al Co Fe Cr Ni alloy,while a outter-innner-layer coating formed after aluminizing at 950℃.The inner layer was equivalent as the former one,and outter layer consisted of Al-rich phase.The aluminide coating&inner layer formed at 850℃ grows by inward diffusion of Al,of which growth was controled by diffusion process,while the outter layer grows by outward alloy elements diffusion. The formed alumide coatings which has high hardness is brittle,could improved the wear resistance under light load only.Howerer,it did improved the oxidation resistance because fo high content of Al.(3) After aluminizing at 850℃and 950℃,two distinctive coatings formed on Cu Co Fe Cr Ni alloy. The coating synthesized at 850℃,which was one-layer structure,growed by inward diffusion of Al.And the growth of coating synthesized at 950℃,which consisted of an outter layer and an inner layer, involved both inward Al and ouward alloy elements diffusion.The coatings formed at 850℃ and 950℃ that have high hardness, are too brittle to improved the wear resistance,but contributed to improvement of oxidation.