Effect of multiple thermal cycling on the microstructure and microhardness of Inconel 625 by high-speed laser cladding

Establishing the relationship between thermal cycling and the induced evolution of microstructures and cladding layer properties is crucial to achieving microstructural and performance control, given the complexity involved in high-speed laser cladding process. We hereby report our new findings from laser cladding of Inconel 625 on Q245R steel substrate using a high-speed laser cladding technique. The microstructure evolution and microhardness variations in the first cladding track with different thermal cycles were examined by XRD, SEM, EBSD, TEM, and microhardness tests in detail. Numerical simulation was also conducted to characteristically illustrate the complex thermal cycles during the laser cladding process. Our work revealed that the first six thermal cycles resulted in significant variations of microstructure in the laser cladding layers. The dislocation density and low angle grain boundaries (LAGBs) of the first cladding track decreased after two thermal cycles due to the high peak temperature (above 1000 °C) of thermal cycles and subsequently increased when subjected to further thermal cycles with low peak temperature (below 500 °C). The microhardness value increased from 220 HV0.2 to 320 HV0.2, mainly caused by the formation of precipitated phase during the first four thermal cycles, and through by the enhancement of dislocations after six thermal cycles.