Evaluation of solidification and microstructure in laser cladding Inconel 718 superalloy

Abstract The development of directional or completely equiaxed microstructures by the laser cladding process can determine the final properties and applications of Inconel 718 alloys. The main purpose of this study is to investigate the effect of laser cladding process parameters on the solidification and final microstructure of Inconel 718 alloy. In this study, Inconel 718 powder was cladded on the Inconel 718 substrate by Nd: YAG laser using laser power of 150–300 W, scanning rate of 4–6 mm/s and powder feeding rates of 150, 200, 250, 300 and 400 mg/s and the effect of them on the solidified microstructure at three zones of the interface, middle and surface of coating was studied. The dendritic secondary arms spacing was calculated and the cooling rate was determined in each zone. The structural defects including cracks, porosity and segregation and finally phase analysis were examined. The results showed that with increasing laser power from 150 to 300 W and also laser scanning rate from 4 to 6 mm/s due to decrease in the G/R ratio, so that the more part of microstructure was equiaxed. In addition, by taking distance from the interface, the dendrite secondary arms spacing decreased from 1.08 to 0.98 and the cooling rate increased from 2.3649 × 104 k/s to 3.2641 × 104 k/s. With increase in the powder feeding rate the equiaxed zone increases. However, the effect of the powder feeding rate cannot be directly and specifically determined. The all samples were free crack but, the small amount of porosity was observed in cladding sample. Results showed that between the laser parameters and the percent of porosities were not exist of the clear relation.