Influence of Cu-liquid content on densification and microstructure of direct laser sintered submicron W–Cu/micron Cu powder mixture

The direct metal laser sintering (DMLS) was used to consolidate a composite powder system consisting of submicron W–Cu powder and micron Cu powder. The influence of Cu-liquid content on densification response of direct laser sintered W–Cu components was investigated. It was found that a proper increase of Cu elemental fraction to 60 wt.% yielded a high densification of 94.8% theoretical density, due to a favorable viscosity of liquid–solid mixture and the resultant sufficient rearrangement of W particles. However, a further increase in Cu content deteriorated laser sintered density, because of “balling” effect. The effect of Cu-liquid content on microstructural features of laser-processed components was also studied. It showed that at a suitable Cu elemental content of 60 wt.%, a series of regularly shaped W-rim/Cu-core structures were formed after laser sintering. The metallurgical mechanisms for the formation of such a novel structure were proposed. It shows that the combined action of the thermal Marangoni flow and the solutal one, which are induced by temperature gradient and concentration differences at solid-liquid interfaces, accounts for the formation of the W-rim. The “particle pushing” effect during rapid solidification of Cu melt prevents the W-rim from merging and, thus, remains the Cu-core after solidification.