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

Abstract

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.