Selective laser melting of W-Ni-Cu composite powder: Densification, microstructure evolution and nano-crystalline formation

As the typical refractory metal, the W-Ni-Cu alloy faces severe challenge in machining of complex shapes. To deal with the problem, we use selective laser melting (SLM) additive manufacturing to consolidate W-10%Ni-10%Cu composite powder. The effects of laser parameters on densification, microstructural evolution and nano crystalline formation were studied. With the increase of laser energy density, the absolute density increases apparently and the surface unevenness is slightly alleviated. Except the typical W and Ni-Cu solid solution phases, interestingly, the amorphous W-Ni solid solution was detected in the SLM processed sample. The typical microstructure contains un-melted W region, W dendrite region with the melting of W and Ni-Cu region. The W solidification microstructure adjacent to the un-melt W presents cellular grain and then transforms into columnar dendrite, until it finally becomes equiaxed dendrite. A large number of W-based nanocrystals formed during the solidification process, which was caused by Marangoni migration that the Ni-Cu phase tends to break the liquid W into small ones, yielding the formation nano-crystalline. Better understanding of the corresponding metallurgical mechanisms will help pave the way towards newly refractory metal design for additive manufacturing application.