Phase transformation pathways in a Ti-5.9Cu alloy modified with Fe and Al

Titanium alloys have been gaining importance in various industries due to their advantageous combination of strength, low density, excellent corrosion/oxidation resistance, and superior mechanical properties at elevated temperatures. Recently, eutectoid Ti-Cu alloys have been explored as promising candidates for advanced processes. This work investigates the effects of Fe and Al on a Ti-5.9Cu alloy using multi-scale characterization techniques. While Fe acts as a beta-stabilizing element (despite being a sluggish eutectoid former), Al acts as an alpha-stabilizer. This work focuses on the effects of combined addition of these elements, studied in different heat treatment conditions. The results show that a fine, equiaxed microstructure is obtained in the binary Ti-5.9Cu alloy, whereas the addition of 2 wt% Fe, or 2 wt% Fe combined with 2 wt% Al to the Ti-5.9Cu alloy deteriorates the effect of grain refinement and coarse, columnar grains result and a small amount of beta-phase is retained. Further, the microstructure resulting from the eutectoid decomposition is altered dramatically from a lamellar pearlitic in the binary alloy to a lath-like alpha-phase with diverse decomposition products in the ternary and quaternary alloys accompanied by increasing hardness values. Evaluation of the alpha misorientation suggests that a substantial amount of non-Burgers alpha is present in the Ti-Cu alloy in contrast to the results of the ternary and quaternary alloys. The observed Cu-rich intermetallic compound was identified as Ti2Cu phase with offstoichiometric composition. Results obtained explain how adding either Fe or Fe and Al leads to substantial hardening.