Laser cladding of Ni–5Al powder on AISI 431 martensitic stainless steel

This study aims to investigate the microstructural characteristics, phase evolution, and hardness distribution of laser-preplaced Ni–Al cladding on AISI 431 stainless steel. Optical microscopy revealed the columnar grains adjacent to the interface that transformed into fine equiaxed structures toward the outer surface of the cladding. Solidification cracking was observed exclusively at the lowest duty cycle, attributed to a reduced liquid fraction, insufficient interdendritic backfilling, and elevated cooling rates during the final stages of solidification. Elemental line-scan analysis revealed interdiffusion of Fe, Cr, Ni, and Al elements across the interface, leading to the formation of a continuous partially melting zone (PMZ) and establishing a sound metallurgical bond. Phase identification indicated the likely presence of γ and γ′ phases within the cladding zone. In the interfacial region, α′ martensite, blocky M₇C₃ carbides, and eutectic α+M₇C₃ phases were observed. The average microhardness was approximately 180 HV in the cladding and about 500 HV in the substrate. Across the PMZ, a gradual increase in hardness from the cladding toward the substrate was observed, which correlated with the increasing Fe and Cr content and the progressive formation of Fe–Cr-rich carbides.