Alternatives to Reduce Hot Cracking Susceptibility of IN718 Casting Alloy Laser Beam Welds with a Mushroom Shape

Abstract

Reducing hot cracking is essential for ensuring seamless production of nickel superalloys, which are extensively used in welded structures for aircraft engines. The prevalence of hot cracking in precipitation-strengthened alloy 718 is primarily governed by two factors: firstly, the chemical composition and the coarse microstructure formed during solidification, and secondly, the activation of hot cracking mechanisms, which is particularly critical in mushroom-shaped welding morphologies. In this study, different nickel-based superalloys welded using laser beam welding (LBW), more specifically bead on plate welding (BoP), specimens are compared. The cracking susceptibility of both wrought and two investment casting 718 alloys with tailored chemical compositions is examined through the application of both continuous and pulsed LBW. Additionally, various pre-weld treatments, including with and without Pre-HIP (hot isostatic pressing), are analyzed. The influences of chemical composition, LBW parameters and pre- and post-welding treatments on both internal and external cracks determined by conventional and advanced non-destructive tests are studied. A clear reduction of hot cracking susceptibility and overall welding quality improvement was observed in a tailored 718 alloy with relatively high Ni (55.6% wt) and Co (1.11% wt) contents.

Keywords

• hot cracking
• Ni superalloys
• alloy 718
• laser beam welding
• mushroom shape
• Co contents