Effect of Hot Isostatic Pressing and Sequenced Heat Treatment on the Mechanical Properties of Hybrid Additive Manufactured Inconel 718 Components

We report on the effect of hot isostatic pressing combined with solution and ageing treatment in different sequences on the mechanical properties of Inconel 718 specimens, which in turn have been fabricated by a hybrid additive manufacturing approach. The latter combines conventional laser powder bed fusion and in-situ high speed milling, yielding superior surface quality as being quantified by Ra about 1 μm. In a comparative study between hybrid additively manufactured parts and those built without milling, we find that, in general, any combination of heat treatment leads to a higher ultimate tensile strength and an improved endurance limit, while, however, hot isostatic pressing affects these figures of merit most. In addition, metallographic analysis reveals increased density and hardness for hot isostatic pressed parts due to precipitation hardening. These improvements of the mechanical properties are found to be even more pronounced when the printed parts are manufactured by the hybrid additive approach, i.e., for parts with improved surface conditions.