AGING BEHAVIOUR OF INCONEL 718 PPREPARED BY LASER PROCESSING

Abstract

The inconel 718 is a commercially successful nickel-base superalloy widely used in nuclear reactors, heavy machinery and other high-temperature applications because of its good corrosion resistance, mechanical properties and structural stability up to 650⁰C. for high temperature application directionally solidified or single crystal is used because of its better creep resistance and thermo-mechanical fatigue behavior in the absence of grain boundaries. But the manufacturing cost of single crystal is more this is one of the major problems. Hence, there developed interest in finding an alternative route synthesizing inconel 718 by laser deposition on mild steel substrate. An intense laser heating of the powder feed followed by cooling of the metal powders (via substrate) leads to a dendritic microstructure in layer wise growth of the material: this subsequently gets exposed to further heating during multilayer growth of the material up to 28 mm in length and 15 mm in thickness. As it is known, precipitation of inter-metallic phases during heat treatment improves creep resistance in inconel 718. Prior to this, a solutionizing treatment is also necessary at 955⁰C for 1 hr. Thus, a microstructure comparison of the as-prepared sample was done with respect to the samples heat treated at 718⁰C for 8h (HT2) and another at 718⁰C for 8h+ 621⁰C for 18 h (HT1), as commercial practice.