Preparation of ultra-fine grain Ni-Al-WC coating with interlocking bonding on austenitic stainless steel by laser clad and friction stir processing

The ultra-fine structured Ni-Al-WC layer with interlocking bonding was fabricated on austenitic stainless steel by combination of laser clad and friction stir processing (FSP). Laser was initially applied to Ni-Al elemental powder preplaced on the austenitic stainless steel substrate to produce a coating for further processing. The as-received coating was subjected to FSP treatment, processed by a rotary tool rod made of WC-Co alloy, to obtain sample for inspection. Microstructure, phase constitutions, hardness and wear property were investigated by methods of scanning electronic microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) microanalysis, and X-ray diffraction (XRD), hardness test alongside with dry sliding wear test. The results show that the severe deformation effect exerted on the specimen resulted in an ultra-fine grain layer of about 100 μm in thickness and grain size of 1-2 μm. Synergy between introduction of WC particles to the deformation layer and deformation strengthening contributes greatly to the increase in hardness and friction resistance. An interlocking bonding between the coating and matrix which significantly improves bonding strength was formed due to the severe deformation effect.