The Effects of Heat Treatment on Tensile and Thermal Expansion Behavior of Laser Powder-Bed Fusion Invar36

This study is concerned with the effects of heat treatments and build orientation on the coefficient of thermal expansion (CTE) and tensile behavior in the context of laser powder-bed fusion of Invar36. Tensile and CTE samples printed in the x, y, and z orientations were annealed, hot isostatic pressing (HIP)-treated, and subsequently characterized for porosity, thermal expansion, and tensile behavior. Porosity was determined through computed tomography and showed that HIP closed most of the pores. Some anisotropy in tensile strength was statistically identified both before and after HIP and was not found to completely depend on porosity. The CTE was found to depend on build orientation and porosity; the CTE values determined (average 1.47 ± 0.06 µm/m °C for 30-100 °C) were lower than typical for conventionally manufactured Invar36. Most importantly, HIP after annealing was found to reduce the porosity levels and affect neither the tensile properties nor the CTE values.