LASER REMELTED Ni-Cr-B-Si COATING ON Al-Si ALLOY

The plasma sprayed coating zone (Ni-Cr-B-Si) on an Al-Si alloy surface was remelted by a 5 kW CO2 laser. SEM and TEM analysis showed that there is crystalline and amorphous coexistent region. As the annealing effects caused by heat transfer of following melt and latent heat of crystallizing, some Ni3Al nano-crystallites (2-5 nm) formed and some of them grew gradually into globular grains (0. 1-0.2μm). The hardness in amorphous region is up to HV 1235 which is 3 times as high as that of plasma sprayed coating zone.