Simultaneous enhancement of powder properties, additive manufacturability, and mechanical performance of Ti–6Al–4V alloy by 2D-nanocarbon decoration

Abstract

Poor understanding of composite powder properties is a bottleneck in the design of high-performance metallic components via laser powder bed fusion (L-PBF). Traditional particle- or fiber-like fillers are known to result in reduced powder flowability and the uncontrollable morphology of composite powders. In this work, we demonstrate a first example of improving the powder properties and L-PBF manufacturability of metallic powders decorated by two-dimensional (2D) nanofillers. 0.5 wt% graphene oxide (GO) sheets were uniformly adhered onto the surface of Ti–6Al–4V (Ti64) powders via an electrostatic self-assembly, with their spherical morphology and particle size uncompromised. The notably enhanced quality of the GO-decorated Ti64 (GO@Ti64) powder bed, indicated by the results of a novel centrifugal separation testing and a recoating experiment, was attributed to the significant reduction in powder/powder and powder/substrate adhesive forces. Moreover, while the thermal conductivity of the GO@Ti64 powders was found to decrease, the laser absorptivity increased as a result of multiple local absorptions of wrinkled GO. The optimal process zone of GO@Ti64 powders was therefore shown to have been extended and to have become wider, enhancing L-PBF printability. High-resolution transmission electron microscopy inspections revealed that the GO/Ti64 build fully consisted of ultrafine α’ martensite structures with a lath width of ∼91 nm. This novel structure was attributed to the high-temperature, nonequilibrium densification of L-PBF; the complete dissolution of the 2D GO nanosheets into the Ti64 matrix generated a novel carbon-supersaturated, precipitation-free structure. The grain refinement and solid-solution strengthening behaviors led to an increase in the yield strength of the GO/Ti64 build from 1375 MPa to 1793 MPa, and also an increase in its compressive strength, from 1796 MPa to 2032 MPa. The results of this investigation contribute to a better understanding of composite powder properties and can be seen as a significant step toward the preparation of high-performance metallic components via L-PBF.