Fatigue strength and impact toughness dependence of powder bed fusion with laser beam-manufactured 316L stainless steel on orientation and layer thickness

Abstract

Additive manufacturing is an enticing way of producing complex geometries and optimized parts for special applications. Even though the achievable static properties for the printed material are usually good when compared to wrought materials, in many cases dynamic properties are known to be much worse. Often, the quality is sacrificed in respect of printing speed. Furthermore, printed materials have usually anisotropic behavior, caused by the remelting and fast cooling of each deposited layer. This means that the mechanical properties need to be measured in several directions in respect of the printing direction for attaining a more holistic approach to the achieved static and dynamic behavior. As a demonstration, this study focuses on determining the properties of 316L stainless steel-manufactured with laser powder bed fusion. A comprehensive set of samples for various testing methods were manufactured to investigate the effect of the layer thickness and printing orientation on the microstructure, mechanical properties, impact strength, and fatigue life. Fatigue performance of the material was evaluated in both axial and flexural bending comparing as-built and polished surface conditions. Bending fatigue testing revealed that a fatigue limit of 100 MPa at best can be achieved with the as-built surface quality, but with a polished surface and lower layer thickness, it could be doubled. Impact toughness and mechanical strength of the material are heavily dependent on the layer thickness, and while the best results were obtained with the lower layer thickness, the printing orientation can have a detrimental effect on it.