Niobium carbide reinforced-Ti6Al4V composites via directed energy deposition

Abstract

Directed energy deposition (DED) was used to produce niobium carbide (NbC)-reinforced Ti6Al4V (Ti64) metal–matrix-composite (MMC) structures. The objective was to improve upon Ti64's wear and oxidation resistance. The characterization techniques consisted of scanning electron microscopy (SEM), backscattered electron (BSE) imaging, energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), Vickers micro- and nanoindentation-derived hardness, as well as tribological testing at varying normal loads. DED produced compositions were of Ti64, Ti64 + 5 wt.% NbC (5NbC), and Ti64 + 10 wt.% NbC (10NbC). Electron micrographs revealed crack- and delamination-free structures. Tribological analysis revealed a 25.1% reduction in specific wear rate. XRD and EDS results indicated the presence of a Ti-Nb solid solution. It was deduced that the NbC particles coupled with the Ti-Nb solid solution aided in increasing Ti64's resistance to plastic shear as the superficial microstructure remained unchanged compared to pure Ti64. Additionally, TGA displayed a reduction in total oxidation mass gain and suppressed oxidation kinetics to parabolic behavior with increased NbC. Application-based composite structures with site-specific mechanical properties were fabricated in the form of a composite cylinder, gear and compositionally graded cylinder. The graded cylinder displayed a 0%–45%NbC presence—end-to-end—equating to a hardness increase from 161.6 ± 4.0HV0.2 to 1055.9 ± 157.4HV0.2.