Abstract: Wide-band laser cladding experiments of flame sprayed nickel based alloy coatings are carried out. Microstructures, phase compositions and hardness distribution of the cladding layers are characterized. Effects of process parameters on microstructures, bonding strength and layer hardness are ana-lyzed. Due to the emergency cooling and heating characteristics of laser cladding process, higher tensile strength often exists in the cladding layers. Simultaneously, because the laser cladding coatings of flame sprayed nickel based alloys are mainly com-posed of g(Fe, Ni) solutions and dispersedly distributed high- hardness brittle carbide phase, (Ni, B) and (Cr, Si) phases, the strength and hardness of the cladding layers are enhanced while the ductility decreases. Under the actions of internal residual stresses during the solidification process, the cladding layers are liable to crack. The cracks are transgranularly distributed, and are induced by the brittle and low ductility properties of the cladding layers. Through preheating of the substrate, holding and slow cooling after the process, temperature gradient can be effectively reduced and residual stresses can be released. With a preheating temperature of 300 ℃, cracks can be completely eliminated.

Key words: Cracking behavior, Flame spray, High hardness spray coating, Wide-band laser cladding