Sub-micron grains and excellent mechanical properties of low-density Ti40Nb30Mo30-C refractory complex concentrated alloy reinforced with in-situ (Ti, Nb)C

A novel Ti40Nb30Mo30–C refractory complex concentrated alloy (RCCA) reinforced with in-situ (Ti, Nb)C carbide was fabricated via mechanical alloying (MA) and hot press sintering (HPS). The results showed that the alloy consisted of the BCC crystal-structured solid solution phase (TNM phase) and FCC crystal-structured carbide (Ti, Nb)C with submicron grain sizes of 0.79 μm and 0.62 μm, respectively. The ultra-fine microstructure benefitted from the inhabitation of in-situ (Ti, Nb)C on grain growth. The ab-initio calculations were conducted to study the formation process of in-situ composite carbide (Ti, Nb)C. Here, the lightweight alloy with a density of 7.04 g/cm3 exhibited promising compressive mechanical properties, such as yield strength of 2550 MPa at room temperature (RT), 1508 MPa at 800 °C, and 485 MPa at 1000 °C. According to the deformation microstructures at RT and 1000 °C, the dislocation-dominated deformation mechanism in TNM phase was invariable at different temperatures. A brittle-to-ductile translation of (Ti, Nb)C was found to happen at around 1000 °C supported by the stress-strain curve and TEM observation. The excellent mechanical properties of the alloy were attributed to the grain boundary strengthening and the strengthening effect of (Ti, Nb)C that hindered the movement of dislocations. The strategy that incorporating in-situ carbides into light RCCA system could broaden and inspire the design of lightweight and high-strength materials.