Additive manufacturing of a Co-Cr-W alloy by selective laser melting: In-situ oxidation, precipitation and the corresponding strengthening effects

Additive manufacturing exhibits great potentials for the fabrication of novel materials due to its unique non-equilibrium solidification and heating process. In this work, a novel nano-oxides dispersion strengthened Co28Cr9W1.5Si (wt.%) alloy, fabricated by laser powder bed fusion (LPBF), was comprehensively investigated. During the layer-by-layer featured process, in-situ formation of Si rich, amorphous, nano-oxide inclusions was observed, whose formation is ascribed to the high affinity of Si to oxygen. Meanwhile, distinctive body-centered cubic (BCC) Co5Cr3Si2 nano-precipitates with an 8-fold symmetry were also confirmed to appear. The precipitates, rarely reported in previous studied Co-Cr alloys, were found to tightly bond with the in-situ oxidization. Furthermore, the morphologies, the size distributions as well as the microstructure of the interface between the matrix and the inclusions were investigated in detail and their influence on the tensile deformation was also clarified. The existence of transition boundaries between these inclusions and the matrix strongly blocked the movement of dislocations, thereby increasing the strength of the alloy. It was understood that when the plastic deformation proceeds, the fracture occurs in the vicinity of the oxide inclusions where dislocations accumulate. A quantitative analysis of the strengthening mechanism was also established, in which an additional important contribution to strength (∼ 169 MPa) caused by the effects of in-situ formed oxide inclusions was calculated.