Abstract
Microstructure and mechanical properties are key parameters influencing the performance of structural multi-phase alloys such as those based on intermetallic TiAl compounds. There, the main constituent, a γ -TiAl phase, is derived from a face-centered cubic structure. Consequently, the dissociation of dislocations and generation of stacking faults (SFs) are important factors contributing to the overall deformation behavior, as well as mechanical properties, such as tensile/creep strength and, most importantly, fracture elongation below the brittle-to-ductile transition temperature. In this work, SFs on the { 111 ) plane in γ -TiAl are revisited by means of ab initio calculations, finding their energies in agreement with previous reports. Subsequently, stacking fault energies are evaluated for eight ternary additions, namely group IVB–VIB elements, together with Ti off-stoichiometry. It is found that the energies of superlattice intrinsic SFs, anti-phase boundaries (APBs), as well as complex SFs decrease by 20–40% with respect to values in stoichiometric γ -TiAl once an alloying element X is present in the fault plane having thus a composition of Ti-50Al-12.5X. In addition, Mo, Ti and V stabilize the APB on the (111) plane, which is intrinsically unstable at 0 K in stoichiometric γ -TiAl.
Highlights
Titanium aluminides are intermetallic compounds and alloys with a wide reach for high-temperature applications
We presented the results of ab initio calculations of {111) stacking fault energies in γ-TiAl and ternary Ti-rich γ-Ti-Al-X alloys (X being a transition metal element)
Cross-checking various methodological aspects revealed that the results from various methods are consistent with each other, with the only exception being the scheme for the relaxation of atomic positions
Summary
Titanium aluminides are intermetallic compounds and alloys with a wide reach for high-temperature applications. These range from low-pressure turbine blades in the aircraft industry to turbocharger turbine wheels and valves in the automotive industry [1,2,3]. Their outstanding properties include low mass density, high specific strength and stiffness and good creep properties up to 750 ◦ C. They outperform titanium alloys by their good oxidation behavior and burn resistance [2]. The main constituent is the γ-TiAl phase, which fundamentally influences the alloy properties during processing, e.g., hot-forging and application
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