Effect of Solutionizing Heat Treatment on Microstructure and Mechanical Behavior of Additively Manufactured Medium Gamma Prime Nickel Superalloy

Additive manufacturing (AM) of γ′-strengthened Ni-based superalloys is appealing for use in fabrication of high-temperature structural components. As AM produces unique microstructures and mechanical behaviors, a better understanding of microstructure development during post-printing heat treatment is important. An extensive set of experimental data of Rene65 printed by powder bed fusion-laser beam is reported. Effects of heat treatment on microstructure are characterized by scanning electron microscopy and electron-backscattered diffraction. Elevated temperature tensile testing, tension creep, and compression creep are conducted with samples loaded parallel and transverse to the build direction. Recrystallization occurs, resulting in an equiaxed grain structure, only with supersolvus heat treatments. There is no effect of supersolvus hold time on grain growth, a behavior different from that of wrought Rene65. Subsolvus heat treatments result in a coarse bimodal precipitate structure, while rapid cooling from supersolvus results in a fine homogenous structure. Comparable tensile behavior is seen regardless of heat treatment, apart from differences in elongation to failure due to loading direction. Creep behavior is improved with supersolvus heat treatment, although increased hold time has a detrimental effect. Based on the experimental results, the relation of microstructures to mechanical behaviors for additively manufactured Rene65 is discussed.