Evolution mechanism of interface cohesion for the coating inducing by laser cladding YSZ@Ni core-shell nanoparticles: Experimental and theoretical research

Stainless steel coated by multi-layers of YSZ@Ni core-shell nanoparticles was sintered by laser cladding. Microstructure shows that the coating by laser cladding YSZ@Ni core-shell nanoparticles has a nanometer microstructure with stratification feature. Therein to cladding layer, amount of chromium atoms appear, and the Ni atoms are diffused largely in matrix layer, which results in the original YSZ@Ni core-shell nanoparticles translated into Cr crystal arming YSZ ceramics crystal. Such influence of variable bonding mechanism on ceramics/metal interface was studied deeply by first principle and molecular dynamics simulation. The results show that in diffusion process of solid state, the element diffusion of Zr↔Ni and Fe↔Ni are both hard to happen. But in Cr↔Ni diffusion process, it is hard only when they are at the nearest neighbor. Diffusion process in cooling process before liquid→solid phase transformation, the diffusion coefficient of Fe, Cr and Ni is D_Fe > D_Cr > D_Ni. But in nucleation process, its trend becomes D_Ni > D_Fe ≈ D_Cr, although all of them are too small. Deeply investigating on their electronic structure, the different distribution of Fe and Cr in cladding layer is originated from their trend of Mulliken population Q_O-Cr > Q_O-Fe. As a result, such weaken bonding of ZrO₂/Cr has destroyed the initial purpose on the Ni as the excellent transition layers between ceramics enforcing phase and metal matrix phase. Thus comparing the connective and diffusive processes, our findings open an avenue for detailed and comprehensive studies of laser cladding process in producing composites.