Microstructural Refinement and Toughening Mechanism of Co Modified AlSiTiNi-WC Coatings Fabricated by Laser Cladding

Abstract

Laser cladding of metal matrix composites reinforced with WC often suffers from cracking due to inherent brittleness. This study investigates the addition of Cobalt (0, 5, 10 and 15 wt.%) to AlSiTiNi-WC coatings to mitigate cracking and enhance wear performance through microstructural tailoring. The results indicate that Co addition induces a significant microstructural transformation, shifting the matrix from coarse cellular dendrites to fine equiaxed grains.Co facilitates the formation of a robust “bimodal structure”, characterized by retained large WC particles and in-situ precipitation of fine Co-W-C and Ni₂Si carbides distributed within a toughened bcc/fcc matrix. This Co-induced structural modification significantly reduces crack initiation. The coating with 10 wt.% Co exhibited the optimal balance, achieving a maximum microhardness of 703.5 HV_0.2 and superior wear resistance (lowest friction coefficient and wear volume). The improvement is attributed to the synergistic effect of solution strengthening, grain refinement, and precipitation hardening inherent in the bimodal structure. Furthermore, Co addition shifted the dominant wear mechanism from severe brittle fracture and abrasive wear to mild abrasive and oxidative wear.