Evaluation via powder metallurgy of nano-reinforced iron powders developed for selective laser melting applications

Abstract

In this work, a gas atomised stainless steel AISI 316L powder was used as metal matrix and SiC was employed as a nano reinforcement. The powders were experimentally characterised to determine the effect of the morphology, size, and levels of reinforcement on the powder flowability. The powder was developed via the powder metallurgy route and the effect of material, process conditions and various levels of reinforcement were investigated through the microhardness of the sintered samples. Sintered samples produced from the 316L + SiC + PVA powder mixes presented improved hardness. Analysis of the Energy Dispersive X-ray measurements detected high intensity levels of carbon and silicon on the surface of the reinforced 316L particles. In terms of measured powder rheology, the 6 wt% SiC coated 316L provided the highest flowability of the prepared SiC coated 316L powders and a much higher flowability than the as received 316L powder. All prepared SiC coated 316L powders showed good flowability and highly repeatable powder rheology. The high degree of flowability was attributed to the particle spherical morphology, the narrow range of particle size distribution and also the coating of nano SiC particles on the 316L particles which were found to act in this case as a solid lubricant. A successful homogeneous and uniform reinforcement of SiC onto the surface particles was resultant from the established mixing technique. While the nano-SiC improved the powder fluidity, the obtained improvement in hardness was also due to the nano-SiC dissolution and resultant precipitates formed during the thermal treatment. Keywords: Selective laser melting, Metal matrix composites, Nano reinforcement, Powder metallurgy, Stainless steel, Powder rheology