Tensile behaviour of Inconel 718 alloys under extreme conditions of temperature and strain-rate

Abstract

Nickel-based superalloys are widely used in critical applications where structural components are subjected to harsh operating conditions such as elevated temperatures and high strain-rate. These alloys are also among the most hard-to-cut materials. For this reason, some critical components with complex geometrical features along with critical dimensions cannot easily manufactured by conventional technologies. A rising disruptive Additive Manufacturing (AM) technique, namely powder-based Laser Metal Deposition (LMD), is able to overcome these limitations in terms of manufacturing costs, tool wear, as well as lead time. As a consequence, the mechanical response under harsh condition of additively manufactured Nickel-based superalloys has to be accurately understood in order to guarantee the reliability of the structural parts made with them. Presently very few researches were addressed to study the dynamic tensile behaviour of Inconel 718 produced by additive manufacturing under high strain-rate combined with elevated temperature. To overcome this lack, the coupled effect of strain rate (0.001 s−1, 250 s−1 and 800 s−1) and temperature (20°C, 350°C and 550°C) on the tensile properties of Inconel 718 alloys produced through cast and additive manufacturing technologies has been experimentally studied. The experiments were also addressed to investigate and compare the flow stress behaviour in function of strain rate and temperature considering the differences in terms of microstructure. A modest strain-rate sensitivity has been observed for both as-cast and as-built material, as well as a moderate decrease of the mechanical strengths has been highlighted for increasing temperatures. Finally, comparable mechanical behaviour has been observed between additively manufactured samples produced with a power laser of 400W and as-cast samples.