Laser direct deposition Mo-Ni-ZrO₂ composited alloy gradient coating

The gradient composite Mo-Ni alloy powder with the different contents of 30-70wt%Mo and a small amount of ZrO₂ were designed, the Mo-Ni-ZrO₂ high temperature wear-resistant composite alloy coating were prepared on 3Cr2W8V steel by laser direct deposition technology. The microstructure, crack and pore elimination, phase composition and hardness of gradient coatings were studied by optical microscope, micro hardness tester, SEM, energy dispersive spectrometer and XRD. The results show that the MoO₃ is formed in the Mo-Ni composite alloy gradient coating because molybdenum is easily oxided under the laser action, MoO₃ tends to volatile when it's heated and can't escape timely in laser molten pool, so as to cracks and pores are produced in the gradient layer with 50wt%Mo, and its average microhardness is 287. The cracks and pores are reduced obviously because of ZrO₂ addition in Mo-Ni-ZrO₂ gradient layer with 50wt%Mo, the phase of the Mo-Ni-ZrO₂ gradient layer is composed of MoNi and reinforced such as Mo_1.24Ni_0.76, Ni₃Zr and a small amount of MoO₃, its average microhardness is 477. ZrO₂ has a favorable effect on elimination of the cracks and pores and improvement of the hardness in Mo-Ni high temperature gradient composite alloy coating.