Additive manufacturing (AM) is a process where a digital model is converted into a component layer by layer fashion. Selective laser melting (SLM) being an AM process can be used to make complex metallic components from powder materials. During the SLM process, metal powder is spread on a substrate plate with each layer thickness of a few 10’s of microns. A high-energy laser beam scans the surface, melting and fusing the laid metal powder to form a solid layer. The process adds layers of material together, leading to the creation of a 3D component. SLM can accurately replicate the CAD model hence allowing for greater design freedom. SLM also permits the production of components without the need of expensive tooling or time consuming machining operations. As a result, SLM realises reduced lead time, manufacturing cost and material wastage. Hence, there is an increasing interest to employ SLM for the production of complex geometrical components, which cannot be made using traditional methods, from various industrial sectors i.e. aerospace, medical, oil & gas, marine etc.
There is currently a lack of knowledge regarding the influence of process variables on the mechanical properties and structural integrity of the as-fabricated SLM material. Hence, determining the unknown relationships between SLM processing as well as post-processing parameters and the resulting material properties is necessary to remove the barrier that prevents SLM technology from being extensively used, especially in safety critical applications. Establishment of these relationships will be necessary to provide a robust methodology to optimise the SLM process to produce complex-shaped parts with targeted design properties.
During the PhD research work, multiaxial and multiscale residual stresses caused by SLM in IN718 samples will be measured and characterized as functions of process parameters (i.e., laser power and beam traverse speed and their post-process steps such as hot isostatic pressing, heat treatment). The impact of the grain morphology and crystal orientation on mechanical behaviour under loading conditions will be investigated with the help of Electron Backscatter Diffraction (EBSD) and a gradient-enhanced crystal plasticity finite element (CPFE) model.