Effect of ultrarapid cooling on microstructure of laser cladding IN718 coating

IN718 alloy clad coating cooled in liquid nitrogen was fabricated by high power diode laser. The microstructure of the coating was investigated using SEM equipped with energy disperse spectroscopy, and the precipitation phase was analysed using TEM after standard heat treatment. The results showed that the liquid nitrogen provided the clad coating an ultrarapid cooling rate during laser cladding. Laves in the ultrarapid cooled clad coating was refined, and Laves concentration and dendritic space were decreased compared with the air cooled clad coating. The ultrarapid cooling rate reduced the constitutional supercooling and restrained Nb segregation in the Laves during solidification. More Nb was distributed in austenite and precipitated as γ″-Ni₃Nb during the standard heat treatment to improve the mechanical properties of the clad coating.