Evolution of solidification and microstructure in laser-clad IN625 superalloy powder on GTD-111 superalloy

Nickel-based superalloys, especially GTD-111, are widely used in the aerospace industry. Due to the high amount of Cr, the IN625 superalloy can be a good option for the surface protection of GTD-111. In this study, IN625 powder was cladded on GTD-111 using a pulsed Nd: YAG laser. This study aimed to investigate the effect of laser process parameters such as power, scan speed, and powder feed rate on microstructure development, defects, and hardness of the cladded samples. The results of this study showed that with increasing laser power from 150 to 300 W, the solidification structure tends to form equiaxed grains due to the decreasing GR from 30,751 to 20,058 °C/s and G/R from 1230to 802 °C/mm2. While at the laser power of 300 W, the tendency to form liquated cracks is increased due to the expansion of HAZ and the consequent increase in the reaction of crack-sensitive phases such as γ′, γ-γ′, and MC within the matrix. The tendency to form an equiaxed/coaxial region in the clad zone (CZ) decreased with an increase in the powder feeding rate. The inclination to form lateral porosity increased due to the reduction of the laser time interaction with the sample surface. On the other hand, by increasing the scan speed from 4 to 7 mm/s, the tendency to form cracks in the interface of the clad-substrate and HAZ increases due to the increased stresses caused by cooling. Unlike scanning speed and laser power, with increasing powder feeding rate, the distance between dendritic arms at the bottom of the coating has decreased from 1.12 to 1.02 μm. In this study, it was found that with increasing the heat input, the solidification rate decreases and as a result, more time is created for increasing the coating dilution. The distance between the dendrites subsequently increases and coarsening of carbide particles also occurs.