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

摘要: 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 that operate under high-temperature and stress environment. A major concern with the SLM precipitation hardenable is their high susceptibility cracking, which has been heavily documented in field welding. Weld cracking may occur either during processing (hot liquation ductility-dip cracking) or post weld heat-treatment stage (strain-age cracking). Due complex thermal history fabricated material there potential all these mechanisms be active. In this investigation, cuboidal coupons superalloy CM247LC were by argon gas atomised powder. Parametric studies performed investigate influence process parameters (laser scan speed, power spacing) on density morphology through conducting stereological study scanning electron microscope (SEM) micrographs. Further microstructural evidence presented, illustrating different crack morphologies observed as well suggesting responsible mechanisms. Finally postfabrication Hot Isostatic Pressing (HIP) treatment was its utility ‘healing’ internal cracks, providing route retro-fix problem heat production. findings highlight need models order understand structures observed. Introduction discipline additive layer (ALM) steadily growing since 1980’s now encompasses wide variety technologies. They share common feature producing three dimensional shape combining two ‘slices’ predetermined thickness. recent years, ALM technologies have developed push forward from ‘rapid-prototyping’ towards ‘rapid-manufacturing’ fully dense functional metallic components. terms fabrication are key rapid fully-dense components; Direct Laser Fabrication (DLF any ‘Blown Powder’ system) ‘Selective Melting Powder-Bed’ manufacturing. Comprehensive reviews methods can found elsewhere [1-4]. technology attracted interest aerospace manufacturers several reasons including: elimination expensive tooling associated forging investment casting; immediate recyclability unused metal powder, significant reduction ‘design-to-component’ time thus allowing actual physical testing many design iterations. present aims assess characteristics application. Cracking considered analogous continuous welding process. this, alloy weldability used indication processability SLM. Figure 1 [5] shows number typical plotted according Al Ti contents (γ′ forming elements). alloys lying above dotted line show volume fraction γ′ phase typically unweldable due susceptibility. This relationship between attributed hardening occurs within aging temperature alloy; reheating region (either part post-weld (PWHT)) results accompanied ductility leaving prone [5]. review relevant literature highlighted four superalloys, are: 1. Plot showing increasing elements (Al Ti) Alloys particularly susceptible PWHT. Solidification Also referred ‘Hot-Tearing’, reported solidifying melt pool (or mushy zone) where