A comparative study of mechanical behaviour of heat-treated 3D printed In-718 and ASTM F75 alloys across multiple length scales

The hardness and strength of many alloys are frequently different when observed at nano, micro, and macroscopic scales. Hence, it is crucial to study the mechanical behaviour of important alloys across wide length scales. In this work, we present one such scenario, where two industrially important alloys, In-718 and ASTM F75, behave differently at micro and macroscopic levels. For the aerospace and petroleum industries, both alloys are promising candidates for similar applications. Both alloys were first 3D printed using selective laser melting (SLM) and then heat-treated in vacuum. The average yield strength and percentage elongation (along the build direction) of the In-718 alloy were 29% and 19% higher than those observed for ASTM F75 alloy. The difference between the UTS and Vickers hardness (at a load of 98 N) was almost negligible, i.e. < 5%. Contrary to Vickers hardness of 3.9 GPa and 3.8 GPa, the average nanohardness of In-718 and ASTM F75 alloys was 5.7 GPa and 7.6 GPa, respectively, and this was substantially higher than their Vickers hardness. Furthermore, ASTM F75 alloy also demonstrated much better wear resistance in ScanningWear tests performed using nanoindenter. The explanation for these differences and the similarities between macro and nanomechanical behaviour are presented in this work.