Nonequilibrium microstructures and phase evolutions of an iron-based laserclad coating

The microstructural and compositional features of the laser-solidified micr ostructures and phase evolutions occurring during high temperature temperin g were investigated by using analytical electron microscopy with energy dis persive X-ray analysis. The cladded alloy, a powder mixture of Fe, Cr, W, N i and C with a weight ratio of 10:5:1:1:1, was processed with a 3 kW contin uous wave CO2 laser. The cladded coating possessed the hypoeutectic microst ructure of the primary dendritic gamma-austenite and interdendritic eutecti c consisting of (gamma+M7C3). The gamma-austenite is a nonequilibrium phase with extended solid solution of alloying elements. And, a great deal of fi ne structures, i.e., a high density of dislocations, twins, and stacking fa ults existed in austenite phase. During high temperature aging, the precipi tation of M23C6, MC and M2C in austenite and in situ transformation of M7C3 (+gamma) --> M23C6 and M7C3+gamma --> M6C occurred. The laser clad coating revealed an evident secondary hardening and superior impact wear resistance .