Improved fracture toughness by microalloying of Fe in Ti-6Al-4V

The widely used Ti-6Al-4V (TC4) titanium alloy has been modified through the micro-alloying of Fe. The microstructural features and mechanical properties of the designed alloy, TC4F, are compared with other alloys in Ti-6Al-4V class by combining experimental characterizations and thermodynamic calculations. TC4F alloy not only maintains strength, hardness, and elongation similar to baseline TC4 but also exhibits improved fracture toughness comparable to TC4_ELI and even superior to TC4_DT under the heat-treated condition. It opens up a new cost-reducing way to enhance fracture toughness in place of controlling interstitial contents, showing potential in engineering applications. The discerned mechanisms indicate that the trace addition of Fe gives rise to composition redistribution between V and Fe in the beta phase, boosts the lattice distortion and vibration, thereafter enhances Young's modulus and fracture toughness. It has been validated and verified by experiments, thermodynamic calculations, and Hahn-Rosenfield empirical research. The enhanced fracture toughness also benefits from the kinked beta+alpha lamellar microstructure at crack tip as well as the improved fracture surface due to the Fe addition. The enlarged plastic zone, redirected crack propagation, and more dimples with even-distributed size additionally contribute to the improvement of fracture toughness. (C) 2019 The Authors. Published by Elsevier Ltd.