Cracking mechanism and control of Hastelloy X prepared by laser powder bed fusion

Abstract

In this study, orthogonal experiments were carried out under different processing parameters to tackle the cracking issue of Hastelloy X (HX) fabricated by laser powder bed fusion (LPBF). The metallurgical defects, molten pool characteristics, cracking and residual stresses under various parameters were studied. The results show that when the volume energy density (VED) is controlled within the range of 83.33–200.00 J/mm3, the as-built samples have a greater density and a smoother surface. Cracking propagation occurs mostly along high-angle grain boundaries, and Mo6C carbides develop at cracks and between dendrites, which are liquation cracking characteristics. Cracks can be effectively suppressed by altering the morphology of the molten pool and minimizing residual stress. The cracking density of as-built HX can be lowered by 93% after optimizing the process settings so that the produced samples with nearly full density and minimal surface roughness can be obtained.

Keywords

• Hastelloy X superalloy
• Laser powder bed fusion
• Liquation cracking
• Process optimization
• Residual stress