Investigating crack formation in IN738LC Ni-based superalloy fabricated by laser powder-bed fusion process

Abstract

Cracking is one of the most important challenges in the laser powder-bed fusion (LPBF) processing of high-γʹ nickel-based superalloys. In this work, crack susceptibility of the IN738LC superalloy fabricated by LPBF with different volume energy densities (VEDs) was investigated. It was observed that processing with medium VEDs (∼90 J/mm3) and higher scan speeds resulted in higher relative densities and lower defects. Cracks were mostly observed in grain boundaries with higher misorientation. Al oxide and MC carbides also were observed close to the crack area as stress concentration sites. Residual stress measurement using XRD also confirmed presence of tensile residual stresses in the as-built samples. Lower amount of residual stress in the sample associated with higher crack density was attributed to stress relaxation due to crack nucleation and growth. The majority of cracks in the IN738LC microstructure was found to be solidification cracks.

Keywords

• Laser powder-bed fusion
• IN738LC superalloy
• Crack susceptibility
• Cracking mechanism
• Residual stress