Fatigue crack growth behavior of SLM 316L stainless steel

Abstract

Additive manufacturing (AM) has the ability to change the way we design and manufacture products. The technology enables the manufacture of complex parts in one process by adding layer-upon-layer of material, with practically no material waste. AM has a broad range of applications and is already being used in the aerospace, automotive and biomedical industries. Knowledge of crack growth behavior of AM products is therefore of utter importance. Additive manufactured parts often suffer from inherent imperfections and weaknesses due to the complexity of the AM processing. These imperfections act as stress raisers under loading and can lead to premature failure of the component. Despite this, there is a lack of research on the fatigue crack growth behavior of AM components. As such, the focus of this thesis is to investigate the fatigue crack growth behavior of selective laser melted (SLM) 316L Stainless Steel. Fatigue crack growth tests were performed on SLM 316L samples in their as-built condition following two build strategies. Crack growth rates in both stable and in near-threshold crack growth regions were obtained. Stress relieving, annealing-furnace cooling and annealing-water quenching heat treatments were performed. Crack growth rates were obtained for these samples and compared to the as-built samples. Microstructure analysis was conducted the interpret the obtained results. It was found that the stress relieving treatment had no effect on the crack growth behavior of the samples. The annealing-furnace cooling treatment did slightly increase the crack growth resistance. Annealed water-quenched samples displayed high crack growth resistance compared to the two previous heat treatments.