Evaluation of Heat Treatments for the Nickel-Based Superalloy Haynes® 282® Manufactured by Selective Laser Melting : A Study Based on Microstructural Examinations and Mechanical Testing

Sammanfattning: Nickel-based superalloys have a wide range of applications, mainly in gas turbines for power generation and aircraft propulsion. They are superior to competing alloys in maintaining excellent mechanical properties for extended durations at extreme temperatures and loads, all while resisting corrosion and oxidation. Haynes 282 is a new age-hardenable nickel-based superalloy that is reported to have a remarkable combination of creep strength, thermal stability, weldability and formability that gives it potential for new applications. Additive manufacturing (AM) is often referred to as 3D printing and the term comprises a number of techniques with the commonality of producing components layer-by-layer with a 3D CAD model as basis. The AM methods allow for unprecedented design freedom and the possibility of replacing complex multi-part components with single part components. The AM methods also enable shorter lead times in many cases and repairs where only part of a component can be replaced instead of replacing the whole component. Selective laser melting (SLM) is a metal AM method that involves a metal powder bed and a laser beam that fuses the powder by melting it according to the predefined geometry. The aim of this project was to evaluate the effect of different heat treatments for Haynes 282 components produced by SLM and it was done by microstructural studies and mechanical testing. Comparisons were made between literature reports on the conventionally produced material, the as-manufactured SLM material and three different heat treatments of 1120-2h-WQ+1010-2h-AC+788-8h-AC, 1170-8hWQ+1010-2h-AC+788-8h-AC and 1170-8h-WQ+1010-4h-AC+788-8h-AC. The first one is recommended by Haynes for conventionally produced material. The microstructural studies focused on identifying occurring phases and their distribution. The grain boundary carbide precipitation after heat treatment was shown to be rather different from the conventionally produced material both in terms of carbide types and their distributions. Grain boundary carbide networks were formed after all the heat treatments. A fine intragranular distribution of a titanium-rich phase that could not be identified was found in all examined SLM specimens. The mechanical testing consisted of tensile testing at room temperature and 600°C, impact testing and hardness testing. The heat treated specimens exhibited remarkable strength but significant embrittlement that was believed to be caused by the grain boundary carbide networks.