The role of shot peening on liquation cracking in laser cladding of K447A nickel superalloy powders over its non-weldable cast structure

A novel strategy with shot peening (SP) pretreatment was proposed to prevent heat-affected zone liquation cracking during laser cladding of K447A nickel-based superalloy powder over its non-weldable cast structure. High dislocation density accumulated by the SP pretreatment drove the high-temperature zone of the heat-affected zone to recrystallize during the laser cladding process, as a result, the coarse columnar grain with an average dendrite stem and secondary dendrite arm width of 102.67 ± 4.24 μm was transformed into a fine equiaxed grain with an average size of 10 μm. SP could effectively inhibit liquation cracking. With the increase of SP duration, the tendency of the liquation cracking reduced. Compared with no SP BM, the total length of the liquation cracking in the longitudinal section of the laser cladding sample reduced from 1649 μm to 248.8 μm. In-situ experimental observation and process simulation were opted to study the evolution behavior of recrystallization. Recrystallization firstly developed in the region of the intergranular zone at ~1214 °C and gradually the base metal recrystallized between 1232 and 1242 °C except for the region with γ/γ′ eutectic structure. As the temperature rose further, a fine liquid film network developed in the range of 1260–1267 °C. Finally, the stress and strain-based criteria were exercised to evaluate the crack susceptibility of the liquid film. The fine liquid film network adequately constrained the liquation cracking by reducing the driving stress applied to the liquid film as well as by lowering the pressure drop of the liquid film caused by driving strain.