The Influence of Nb, Zr, and Zr + Hf on the Lattice Parameters and Creep Behavior of β-Solidifying γ-TiAl Alloys

X-ray diffraction (XRD) analysis was used to study the effect of alloying with 5 at.% Nb, 5 at.% Zr and 5 at.% (Zr + Hf) on the lattice parameters of the γ(TiAl) and α2(Ti3Al) phase in the intermetallic alloys based on Ti-44Al-0.2B (at.%). Before XRD analysis near the same duplex structures were obtained in the alloys under study. The XRD data were used to calculate the tetragonal distortion (cγ/aγ) of the γ phase, the cα2/aα2 ratio of the α2-phase and the γ/α2 lattice misfits in the alloys. The cγ/aγ ratio and the γ/α2 lattice misfits were found the highest in the base alloy, followed by the Nb-, (Zr + Hf)- and Zr-containing alloy. The cα2/aα2 ratio in the alloys was the highest in the Nb-containing alloy, followed by the base alloy and the Zr- and (Zr + Hf)-containing alloy. As was revealed in our previous work, the Ti-44Al-0.2B-based alloys doped with Zr and Zr + Hf demonstrated appreciably higher creep resistance than the alloy doped with Nb and the base alloy. It is assumed that the lower cγ/aγ and cα2/aα2 ratios obtained for the (Zr + Hf)- and Zr-containing alloys contributed to the decrease and the increase in the creep resistance, respectively. The fact that the (Zr + Hf)- and Zr-containing alloys showed higher creep resistance than the Nb-containing alloy should be mostly attributed to the lower lattice misfits in the (Zr + Hf)- and Zr-containing alloys and the higher solution hardening due to doping with Zr + Hf and Zr. Therefore, the impact of alloying on the creep resistance in the β-solidifying γ-TiAl alloys should be considered taking into account the changes of the lattice parameters of the γ and α2 phase, which have the influence on physical factors affecting the creep behavior.