Special Seminar - Materials Science and Engineering: Prof. Zhan Chen

Powder-bed fusion selective laser melting (SLM) is the major form of metal additive manufacturing. The additive feature of SLM allows for parts of high shape complexity to be made but the liquid to solid transformation in the tiny and rapidly moving melt during SLM can result in microstructures that are not desirable for functional parts. Thus, how grain growth direction and cell/dendrite size may be affected and possibly be controlled by SLM parameters are important to be understood. In this presentation, firstly, our study on modes of solidification during SLM of metallic alloys will be described. How the major mode of solidification has limited the application of SLM to wider industrial alloys will be discussed. Secondly, the effect of increasing laser power on heating mode and thus the shape of melt track will be explained. The explanation will extend to the significance of the effect of track shape/size on grain size and growth direction. Thirdly, the extensive measurement of cell/dendrite size and track geometry related growth rate combining the use of primary cell/dendrite spacing model for the calculation of thermal gradient and cooling rate will be presented. These estimated thermal quantities will be plotted in solidification map to estimate how thermal condition may need to be adjusted for the more favorable solidification mode.