Abstract
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 β 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 β+α 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.
Highlights
Tie6Ale4V alloy was firstly developed in 1954 [1] and has been the workhorse in the titanium industry
The trace addition of Fe is capable of boosting the performance of fracture toughness in TC4
Since the non-uniform local misorientation in microstructure can be caused by the inhomogeneous deformation and thereafter influence fracture toughness, EBSD has been employed to mapping the intragrain misorientation in TC4 and TC4F which is capable of evaluating retained plastic deformation in the heat-treated bþa lamellar microstructure
Summary
Tie6Ale4V alloy was firstly developed in 1954 [1] and has been the workhorse in the titanium industry. More than high strength and workability, the alloy design concept of damage tolerance has been more and more widely accepted [17] It requires that titanium components have the ability to sustain defects safely until a repair can be effected. Tie6Ale4V ELI (extra low interstitials) grade alloy provides improved fracture toughness comparing to grade 5 Tie6Ale4V alloy [20]. It has low contents of O 0.13 and Fe 0.25 [21]. Tie6Ale4V DT has been designed via mediating O content between ELI and commercial grades [23], showing a maximum oxygen content of 0.12 wt % against 0.20 wt % in commercial grade Tie6Ale4V It combines moderate strength, high toughness and low crack propagating rate. The effect of Fe addition on the fracture toughness of Tie6Ale4V and the underlying mechanisms behind the experimental phenomena are attempted to figure out
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