AlFeCrNiTiCu_x And Al_0.5FeCrCoNiTi_x High-entropy Alloys Coatings Fabricated By Laser Cladding

Traditionally, alloys have been designed following the rules that olny one or two major elements is the consitituents of them and then improve their properties by adding minor element or heat treatment. High entropy alloys(HEA) is a new kind of alloys which usually have at least five elements according to the mole ratio or similar to mole ratio of an alloy.Compared with traditional, due to high entropy, the forming of intermetallic compound phases was inhibited. At the time the forming of the single phase solidation was promoted. They have many excellent performance such as high hardness, good strength, excellent wear resistance and high corrosion resistance.AlFeCrNiTiCux (x=0,0.5,1.0) and Al0.5FeCrCoNiTix(x=0,0.25,0.5,0.75,1.0) high entropy alloy coatings were fabricated on Q235 steel substrate by laser cladding process.Microstructure of the coatings were detected detailedly by XRD, SEM, EDS. On the other hand, other properties were studied by Vickers, wearing test and electrochemical experiment.The result shows that:(1)AlFeCrNiTiCux high-entropy alloy coatings only have mixed simple structure of FCC and BCC. Due to the high cooling rate after laser cladding, the growth of the coatings' grain was inhibited and some micrometer scale axial dendritic structure were observed in the samples. Due to the positive mixing entropy of Cu and other alloy elements in the coating, the segregation of element Cu in intergranular region was observed. This promotes the forming of Cu-rich FCC phase in intergranular region. With the Cu content increasing, the forming of FCC solid phase was promoted. At the same time the forming of BCC phase were hampered.And the hardness and the wear resistance of the samples decreases. With the adding of Cu, the Ecorr increases while Icorr decreases. AlFeCrNiTiCu high alloy coating has the best corrosion property of that Ecorr=-0.413V,Icoor=-4.786x×10-7A/CM2.(2) Al0.5FeCrCoNiTix high-entropy alloy coatings presents equiaxed grains and they only have mixed simple structure of FCC1 and BCC. With Ti content increasing, the coatings had eutectic transformation and FCC2 structure appeared gradually. The coatings' grain was refined , the hardness and the wear resistance of the samples increases. The value of average hardness reaches maximum 1171HV when x=1. Because of the existing of Al, Ni, Cr elements,AIFeCrNiTiCux high-entropy alloy coatings are easy to generate passive film which is stable to protect the alloy coatings from continues corrosion in 3.5% NaCl solution. The pitting is slight. With the Ti content increasing, the Ecorr increase while Icorr decrease. AIFeCrCoNiTi high alloy coating has the best corrosion property of that Ecorr=0.502V,Icoor=-7.030×10-7 A/CM2.