Flow properties of tool steel powders for selective laser melting – influence of thermal and mechanical powder treatments

In powder bed fusion additive processes the flow properties of the powder influence the quality of the final component and the efficiency of the process. In this investigation an attempt is made to identify flowability indicators which can describe the flow performance of the powder during the powder layering (i.e. recoating) step; common to all powder bed fusion processes. To this end, shear tests were performed by means of a powder rheometer. Bulk density, flow function and degree of cohesion were measured. The results suggest that there is a good correlation between the aforementioned parameters and the flowability of the powder during SLM processing. In addition, it was found that thermal treatments and tumbling enhance flowability. Thermal treatments were performed at 150, 200 and 250°C for a period of 10?min and in air.