Microstructural and mechanical properties of the laser-melted Inconel 718 nickel base superalloy

In this work, the microstructural development and the resulting mechanical properties of the nickel-based superalloy Inconel 718 processed in the SLM${}^{\circledR }$ (Selective Laser Melting) process were investigated. Subsequently, the influence of the HIP process (Hot Isostatic Pressing) on the porosity, microstructure and mechanical properties was analysed. Since the HIP process cannot close near-surface pores, selected samples were encapsulated with a Ni-20Cr coating by the Arc-PVD (Physical Vapor Deposition) process. Since the typical cell structures together with the γ${}^{\prime \prime }$ precipitates occur after solution annealing with subsequent precipitation hardening, the highest yield strength (Rp${}_{0.2}$) could be determined under quasi-static loading at room temperature (RT) as well as at 650°C. Under cyclic loading, the coated and hot isostatically pressed specimens show the lowest fatigue strength at RT, both before and after precipitation hardening. In the solution-annealed and subsequently precipitation-hardened condition, the material exhibits the highest fatigue life, especially at a low strain amplitude (Δε/2 = ±0.35 %), at 650 °C.