A new approach to the reasons for dependency of defects formation to the process parameters in laser powder bed fusion of IN625 on the IN738LC substrate

Abstract

Degradation is a common phenomenon in gas turbine components. Among additive manufacturing (AM) methods like direct laser deposition (DLD) and laser powder bed fusion (LPBF), DLD has been widely studied due to its ease in repair processes. However, LPBF offers higher dimensional accuracy, better surface quality, and reduced stress. This study employed LPBF of IN625 on an IN738 substrate for repair purposes. A wide range of process parameters (power at 100, 150, and 200 W and scan speeds between 100 mm/s to 2700 mm/s) was evaluated. The reasons behind process parameters' influence on defect formation, such as pores and cracks, were investigated, as these aspects have been less emphasized in prior studies. The relationship between process parameters, melt pool shape, pore formation, and changes in elemental concentration was explored. It was found that concentration peaks at the interface are the main factor in crack formation, enabling predictions of cracking behavior. Elements diffuse from rich to poor regions at the IN625/IN738 interface. At scan speeds ≤ 500 mm/s, increasing speed and power both increase elemental concentration at the interface, but speed promotes elemental accumulation behind the interface, while power enhances homogenization. The effect of process parameters on microhardness and cell size was also examined. It was determined that cracks do not form in softer nickel-based matrices where microhardness remains below the critical threshold of 256 HV.