Effects of Postprocess Thermal Treatments on Static and Cyclic Deformation Behavior of Additively Manufactured Austenitic Stainless Steel

As additive manufacturing advances towards use in structural applications which can also include fatigue-critical parts, the process-structure-property relationships must be fully characterized. Currently, most additive manufactured components go through extensive postprocessing including heat treatment to improve their microstructure and resulting fatigue performance. In this study, the effect of stress relief and solution annealing on the tensile and fatigue performance in force- and strain-controlled conditions was investigated. The results reveal that, while the strain-life fatigue behavior was not significantly affected by heat treatment, stress-relieved specimens showed remarkable enhanced stress-life fatigue resistance. Microstructural analysis suggested that the as-fabricated microstructure was beneficial to enhance the crack initiation resistance by shielding process-induced defects from excessive deformation. However, after solution annealing, the crack initiation mechanism shifted from nucleating at twin and high-angle grain boundaries to defects such as lack of fusion and gas-entrapped pores, negatively affecting the fatigue resistance.