Effect of phase transformation on mechanical properties of Al16.80Co20.74Cr20.49Fe21.28Ni20.70 high entropy alloy coatings processed by laser cladding

Abstract

Eight Al16.80Co20.74Cr20.49Fe21.28Ni20.70 high entropy alloy (HEA) coatings were fabricated by laser cladding with different laser scanning speed. The mechanical properties caused by phase transformation and microstructure evolution of Al16.80Co20.74Cr20.49Fe21.28Ni20.70 HEA coatings were investigated. The experimental results showed that the volume fraction of the FCC phase and the BCC phase in each coating were different depending on laser scanning speed. High laser scanning speed will increase the number of BCC phase. BCC phase was composed of alternate A2 and B2 structure formed by spinodal decomposition. All coatings exhibited a polycrystalline structure composed of uniform equiaxed grains. The grain size of equiaxed grains reduced from 185 to 42 µm with increased laser scanning speed. The phase-mechanical properties connection at nano-scale were established by nano-hardness mapping and elastic modulus mapping. Furthermore, the micromechanical properties of individual FCC phase and BCC phase were studied by analyzing nanoindentation data statistically. The BCC phases were found to have a higher nano-hardness and elastic modulus than the FCC phases. Therefore, the increment of the BCC phase could significantly enhance the strength and wear resistance of coatings. The optimum wear resistance was obtained in V17, owning a higher volume fraction of BCC (>90%) and finer grains (75 µm). In addition, the strengthening mechanism has been discussed. Grain boundary strengthening makes a great contribution to the excellent performance of coatings.