Design and preparation of low-cost α + β titanium alloy based on assessment of Ti-Al-Fe-Cr system

Abstract Previous investigations of the Ti-Al-Fe-Cr quaternary system and its related sub-systems were reviewed and summarized, then the thermodynamical database of the Ti-Al-Fe-Cr quaternary system was built up by directly extrapolating from the four sub-ternary systems using the Calphad method. The pseudobinary sections with Cr: Fe = 5.2:1 and Al = 0.0, 3.0, 4.5 and 6.0 wt% were calculated, combined with the empirical design criterion including aluminum and molybdenum equivalent, a novel α + β type titanium alloy Ti-3Al-8.5Cr-2Fe was proposed and successfully prepared. Microscopic observation showed that Ti-3Al-8.5Cr-2Fe contained α and β phase which was consistent with expectation, no segregation of the elements Cr and Fe existed in grain boundaries and C14 laves phase was not detected in Ti-3Al-8.5Cr-2Fe alloy. Mechanical properties were investigated using the universal testing machine and results showed that the average ultimate tensile strength (σ b ), 0.2% proof strength (σ 0.2 ) and elongation (EI) of this alloy in thermo-mechanical state can reach 985 MPa, 904.5 MPa and 19.6 Pct, respectively, which is similar to the Ti-4.3Fe-7.1Cr- 3.0Al(TFCA) and Ti-3Al-5Mo-4.5V(TC16). The SEM photographs of fracture surface showed that the fracture of Ti-3Al-8.5Cr-2Fe sheets after quenching process is plastic fracture.