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 ± 4.0HV _0.2 to 1055.9 ± 157.4HV _0.2 .