Rapidly solidified nonequilibrium microstructure and phase transformation of laser-synthesized iron-based alloy coating

The rapidly solidified microstructural and compositional features, the precipitation and transformation of carbides during tempering, and the impact wear resistance of an iron-based alloy coating prepared by laser cladding are investigated. The clad coating alloy, a powder mixture of Fe, Cr, W, Ni, and C with a weight ratio of 10:5:1.1.1, is processed using a continuous wave CO, laser. Microstructural studies demonstrate that the coating possesses the hypoeutectic microstructure comprising the primary dendritic gamma-austenite and interdendritic eutectic consisting of gamma-austenite and M7C3 carbides. gamma-Austenite is a non-equilibrium phase with an extended solid solution of alloying elements. During high temperature tempering at 963 K for 1 h, the precipitation of M23C6, MC and M2C carbides in austenite and in situ carbide transformation of M7C3 to M23C6 and M7C3 to M6C respectively are observed. In addition, the microstructure of the laser-clad coating reveals an evident secondary hardening and a superior impact wear resistance.