Laser Powder Bed Fabrication of Nickel‐Base Superalloys: Influence of Parameters; Characterisation, Quantification and Mitigation of Cracking

Abstract

The use of a selective laser melting (SLM) powder-bed method to manufacture Ni-based superalloys components provides an economic approach for low production run components that operate under a high-temperature and stress environment. A major concern with the SLM of precipitation hardenable Ni-based superalloys is their high susceptibility to cracking, which has been heavily documented in the field of welding. Weld cracking may occur either during processing (hot cracking, liquation cracking and ductility-dip cracking) or during the post weld heat-treatment stage (strain-age cracking). Due to the complex thermal history of SLM fabricated material there is the potential for all of these mechanisms to be active.In this investigation, cuboidal coupons of the Ni-based superalloy CM247LC were fabricated by the SLM of argon gas atomised powder. Parametric studies were performed to investigate the influence of the process parameters (laser scan speed, power and scan spacing) on the cracking density and morphology through conducting a stereological study of scanning electron microscope (SEM) micrographs. Further microstructural evidence is presented, illustrating the different crack morphologies observed as well as suggesting the responsible mechanisms. Finally a postfabrication Hot Isostatic Pressing (HIP) treatment was performed to investigate its utility in 'healing' the internal cracks, and providing a route to retro-fix the cracking problem in the heat treatment stage of production. The findings highlight the need for process models of the SLM method in order to understand the thermal history and the laser fabricated structures observed.

Microstructure and Mechanical Properties of CMSX-4 Single Crystals Prepared by Additive Manufacturing

“…Recently, there is a strong research activity to qualify these kinds of alloys for processing by additive manufacturing. [13][14][15] In Reference 16 we have demonstrated that crack-free processing of CMSX-4 Ò via selective electron beam melting is possible. Even single crystals emerged directly from the powder bed by applying a suitable processing strategy.…”

Microstructural Evolution of Post-Processed Hastelloy X Alloy Fabricated by Laser Powder Bed Fusion

“…The LPBF process has been successfully employed for the fabrication of dense components made of various Ni-based superalloys such as Inconel 625 and Inconel 718 [9,12,13]. However, several Ni-based superalloys are prone to cracking during the LPBF due to their low weldability or the inappropriate selection of process parameters [2,4,14,15,16,17]. For instance, Hastelloy X (HX) alloy is characterized by susceptibility to crack formation when processed by LPBF [2,18,19,20,21,22,23].…”

Microstructure of the Nickel-Base Superalloy CMSX-4 Fabricated by Selective Electron Beam Melting

“…High c¢ volume fraction materials are susceptible to crack formation especially to strain age cracking and are typically considered as hard-or not weldable. [12][13][14] Because of their high cracking susceptibility, it is a challenge to process materials like CMSX-4 by additive technologies. [15,16] In the literature, investigations on IN625, IN738, and Rene142 as representative materials with high c¢ volume can be found.…”