An investigation of the plastic work to heat conversion of wrought and laser powder bed fusion manufactured Inconel 718

Abstract In this study, the conversion of plastic work to heat, also known as the Taylor-Quinney coefficient (β), of Inconel 718 (IN718) is investigated. Three material conditions are examined, specifically wrought IN718 and laser powder bed fusion (LPBF manufactured IN718 in the as-built condition and one that has been recrystallized through a solutionizing heat treatment. Adiabatic deformation conditions are achieved using a tension split-Hopkinson pressure bar. Infra-red thermography measurements are made during deformation such that the conversion of plastic work to heat can be determined for each material condition as a function of strain. Microstructure characterization was conducted using electron backscatter diffraction to measure grain size, morphology, and texture. From the experiments conducted, it was observed that wrought IN718 had the lowest conversion of plastic work to heat (β ≈ 0.2). The as-built LPBF IN718 had a slightly higher conversion of plastic work to heat (β ≈ 0.3), and the recrystallized condition had the greatest plastic work to heat conversion (β ≈ 0.45). The observed ordering of the plastic work to heat conversion efficiency is discussed in light of the microstructural similarities and differences of each material condition. Increasing grain size was found to be correlated with a decrease in β.