Dynamic mechanical response and fracture behaviour of Ti–Ni–C composites fabricated by directed energy deposition

Abstract

This work studied the mechanical response and the associated microstructures and failure mechanisms of additively manufactured Ti matrix composites with in-situ synthesised Ti2Ni and TiCx reinforcements under a variety of loading rates. The composites were fabricated using directed energy deposition technique with Ti–6Al–4V (Ti64) and Ni coated graphite (NCG) powders. Different proportions of Ti64 and NCG were mixed to manufacture the specimens with different compositions. Compression tests were conducted at strain rates in the range of 10−3 to 800 s−1. Our results show that the metallurgical and mechanical properties of the composites change with the NCG fraction. The failure mechanisms of the composites are a combination of tensile fracture of brittle TiCx precipitates and shear of the Ti matrix. The composites with higher NCG content exhibit increased strength, reduced ductility and less strain rate sensitivity. Under high strain rate compression loading, the Ti–Ni–C composite can provide enhanced strength with the ductility unchanged, which make it a prospective material for the applications subjected to impact loads.