Microstructure and Mechanical Properties of Rene 77 Alloy Manufactured by Laser Powder bed Fusion

Rene 77 is a precipitation hardened superalloy with high γ’ content, designed to service at a temperature between 730- 900 °C. It is often used in hot gas turbine engine parts, such as vanes blades and discs. Turbine blades of Rene 77 having coarse and inhomogeneous grain structure was commonly reported for conventional casting. Control of the microstructure is possible through control of solidification front velocity and cooling rate during solidification. Therefore, development of new processing techniques that would yield to finer microstructural features and better microstructural control for fabrication of these elements is possible and would be beneficial to achieve improved service life as well as room temperature and high temperature mechanical properties.

In this study, Rene 77, a high γ’ containing difficult to weld alloy was successfully fabricated by LPBF for the first time in literature. Crack free, dense parts were obtained after fabrication. Microstructural development during solidification and after age hardening heat treatment were investigated. Mechanical properties in both conditions were also studied by microhardness measurements along with room and elevated temperature tensile testing. Post fracture microstructure and fracture surfaces of the tested samples were conducted to understand the deformation behavior and microstructural change during elevated temperature testing.