Hardness variation in inconel 718 produced by laser directed energy deposition

Abstract

Directed energy deposition (DED) of Inconel 718 is of critical importance for the repair of aerospace components, which have tight tolerances for certification, particularly on mechanical properties. Significant hardness variation has been seen throughout DED manufactured Inconel 718 components, suggestive of variation in mechanical properties, which must be understood such that the variation can either be removed, or implemented within the design in line with regulatory guidance. In this work, γʹ precipitation was theorised to be the cause of hardness variation throughout the component, despite Inconel 718 conventionally being regarded as a γʺ strengthened alloy. A simple precipitation potential model based on a moving heat source was found to correlate with the measured hardness and explain the hardness distribution observed. In addition, it has been shown that sections under a critical thickness of 2 mm never reach the peak hardness in the as-built condition. This understanding allows for the development of in-situ heat treatment strategies to be developed for microstructural, and hence, mechanical property optimisation, necessary for repair technologies where post processing steps are limited.