How does multiple powder recycling cycles affect the sintering behavior of metal powders in SLS?

Multiple powder recycling cycles in SLS (Selective Laser Sintering) with metal powders can alter the sintering behavior due to several factors. Firstly, each cycle exposes the powder to high temperatures, potentially causing changes in particle size distribution due to sintering necks forming, smaller particles agglomerating, and oxidation. This can lead to reduced powder flowability and packing density. Secondly, repeated heating can alter the powder's chemical composition due to the buildup of trace contaminants from the environment or the loss of volatile elements. Thirdly, the powder's morphology can change, with particles becoming more rounded or irregular. These changes collectively affect how the powder absorbs energy from the laser, influencing the sintering process and potentially leading to variations in part density, surface finish, and mechanical properties. Therefore, it's essential to monitor and control the powder's characteristics with each recycling cycle and to refresh the powder with virgin material to maintain consistent sintering behavior.