Preparation And Properties Of The Laser Cladding High Entropy Alloy Coatings

High entropy alloys with excellent properties have received extensive attention and research. But the elements of high entropy alloys are mostly expensive, such as Co, Cr and Ni, the cost of bulk high entropy alloys preparation is high. Therefore, it is quite significant to prepare high entropy alloys on low cost steel substrate for expanding the application of high entropy alloys. According to the theory of high entropy alloy design and the traditional experience of laser cladding Ni-base alloy coating, FeCoCrNiB and FeCoCrNiCu high entropy alloy coatings with different WC content were prepared by the continuous wave CO2 laser. The microstructure of high entropy coatings was investigated by optical microscope, scanning electron microscope and X-ray diffraction, the hardness and wear resistance of coatings were respectively measured by vickers hardness tester and wear tester. Effects of WC particles on microstructure and properties of high entropy coatings were investigated. Meanwhile, effects of high temperature annealing on microstructure and properties were also studied. The results show:High entropy alloy coatings with flat suface, well forming quality, appropriate dilution and high hardness could be obtained when the laser cladding parameters were as follows:1.6 KW laser power,150 mm/min scanning,4 mm beam diameter and 50% lapping rate.Bottom of FeCoCrNiB cladding layer is composed of granular structure and matrix structure. With the increasing of the distance from interface, the transformation from granular structure to rod-like structure happened. Rod-like structure was the typical structure of FeCoCrNiB coating, which is composed of rod-like M3B phase and fcc matrix. Along with the rising of annealing temperature, M3B phase content increased, fcc phase content reduce, but phase composition was unchanged. After annealing at 900℃ and 1000℃, some granular and short rod-like M3B phase precipitated in coating. After annealing at 1150℃, rod-like, granular and short rod-like structure disappeared, blocky M3B phase formed, the microhardness of blocly phase is 1188HV. The coating exhibits excellent resistance to high temperature softening, coating after annealed at 1150℃ has the best wear resistance. The decrease of microhardness is only about 7% and 9% after annealed at 900℃ and 1000℃.The addition of WC particles have a great influence on the microstructure and properties of the FeCoCrNiB coating. With the addition of 5% WC particles, M3C and fee phase eutectic structure generates, which the coating is composed of M3B phase, M3C phase and fee phase. When WC content is 10%, the microstructure changes to dendrite structure, which the dendrite is M23(C,B)6 phase and some fine mesh M7(C,B )3 phase is distributed in interdendritic. When WC content is 20%, the mesh M7(C,B)3 phase disappears and the coating remains dendrite structure, which the coating is composed of M23(C,B)6 phase and fee phase. With the increasing of WC content, the hardness and wear resistance of the coating improve.The high entropy alloy coatings with different WC content are all composed of fee and bcc solid solution phases, the addition of WC did not cause the formation of complex carbide phases. Most of WC particles dissolved into the bcc phase and only small part of WC particles dissolved into the fee phase. With the increasing of WC content, bcc phase content increase and fee phase content decrease, The increasing of WC content lead to grain refinement, microhardness and wear resistance increase.