Comprehensive study on the formation of grain boundary serrations in additively manufactured Haynes 230 alloy

• Published in: Materials characterization Vol. 160; p. 110092
• Main Authors: Haack, Maximilian, Kuczyk, Martin, Seidel, André, López, Elena, Brueckner, Frank, Leyens, Christoph
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.02.2020
• Subjects: Additive manufacturing; EBSD; Grain boundary serration; Haynes 230; Laser metal deposition; Manufacturing Systems Engineering; Produktionsutveckling; Superalloy; Superalloy; Grain boundary serration; Laser metal deposition; Additive manufacturing; Haynes 230; EBSD
• ISSN: 1044-5803; 1873-4189; 1873-4189
• DOI: 10.1016/j.matchar.2019.110092

Recently, grain boundary serrations have been introduced in conventionally processed Haynes 230 through a slow-cooling heat treatment. The aim of this work was to utilize these heat treatments to introduce serrations in additively manufactured (Laser Metal Deposition) Haynes 230. Contrary to expectations, serrations already formed during the fast-cooling of the Laser Metal Deposition process. Electron Backscatter Diffraction was used to elucidate the underlying phenomenon for the emergence of serrations during fast-cooling. As a result, a hypothesis regarding a new mechanism responsible for the formation of grain boundary serrations was formulated. Additionally, specific characteristics of the Laser Metal Deposition process have been identified. This includes a columnar-to-equiaxed transition (CET) for slower feed rates, leading to smaller grains despite lower cooling rates; the observation of an abrupt increase in grain growth for a raised solution annealing temperature; the fact that serrations hinder uncontrolled grain growth and finally that the LMD-process leads to a finer carbide morphology compared to conventional manufacturing methods, potentially leading to an increased precipitation strengthening effect. •Haynes 230 is readily fabricable via Laser Metal Deposition•Grain Boundary Serrations already emerge through fast-cooling during deposition•Slower feed rates show finer grains due to a columnar-to-equiaxed transition (CET)•Carbides are much finer than for conventionally processed Haynes 230•A raised solution annealing temperature of 1280 °C shows an abrupt rise in grain growth compared to standard annealing temperature of 1230 °C