Achieving balanced mechanical and thermal expansion properties of Invar alloy prepared by hybrid laser directed energy deposition and post-heat treatment

The mechanical and thermal expansion properties of Invar alloy fabricated by in-situ rolling-assisted laser directed energy deposition (IR-LDED) combined with post-heat treatment were systematically investigated. The IR-LDED samples were subjected to either the three-stage heat treatment (HT1) or stress relief annealing (HT2) to enhance their mechanical and thermal expansion properties synergistically. The results revealed that the HT1 samples underwent complete recrystallization, while the HT2 samples exhibited low-energy dislocations with a few precipitates. The coefficient of thermal expansion (CTE), magnetic properties, and mechanical properties were also measured for both heat-treated samples. The CTE of the samples significantly increased after stress relief annealing, whereas samples subjected to the three-stage heat treatment exhibited an extremely low CTE due to the combined effects of numerous grain boundaries and low texture strength. Comparisons were made with samples produced by conventional and other additive manufacturing processes, focusing on the relationship between yield strength, ultimate tensile strength, elongation, and CTE. The reasons why the samples subjected to IR-LDED combined with heat treatment can achieve excellent comprehensive mechanical and thermal expansion properties were discussed.