Effect of Gd addition on phase composition, structure, and properties of beta-solidifying TiAl-based alloy with Zr and Cr content variability

The aim of the present work was to study the influence of Gd microaddition on the sequence and temperatures of phase transformations as well as on the microstructural evolution and properties of a new six-component TiAl-based alloy Ti-44.5Al-2V-1Nb-xZr/yCr-(0 … 0.1)Gd (at.%) with variable Zr (x = 0.5–1.5 at.%; eq. 1.2–3.5 wt%) and Cr (y = 1.5–2.5 at.%; eq. 2.0–3.5 wt%) content in the as-cast condition using thermodynamic calculations in Thermo-Calc software and experimental methods including differential scanning calorimetry, in-situ high-temperature X-ray diffraction analysis, optical, scanning, and high-resolution transmission microscopy. It was demonstrated that in all compositions of the studied alloy the sequence of phase transformations at high temperature interval includes L→β, β→α, and α→γ transformations, passing through the single-phase β and α fields. These are then followed by a three-phase eutectoid reaction α→α2+γ in Zr-containing compositions and further by a four-phase α→α2+γ+β reaction in Cr- and (Zr+Сr)-containing compositions. It has been revealed that the addition of 0.1 at.% Gd does not change the sequence and temperatures of these phase transformations. Nevertheless, the formation of nano-particles, identified as base-centered monoclinic Gd2O3 oxide located in Zr-containing compositions inside the γ lamellae and in Cr- and (Zr + Cr)-containing compositions on the boundaries of the γ lamellae and inside the β phase interlayers and being coherent with the β0 phase, results in reduction of (α2+γ) colony size in the as-cast condition (VAR + VAR + VIM) down to 100 ± 10 μm. It has been also found that ultimate tensile strength and plastic elongation in Zr- and Cr-containing compositions of the studied alloy in the as-cast condition measured at room temperature are 473 ± 8 MPa, 1.1 ± 0.1% and 513 ± 10 MPa, 1.4 ± 0.1%, respectively. The addition of 0.1 at.% Gd results in plastic elongation increasing to (1.3–1.6)±0.1%, while remaining the strength unaffected. •Gd (0.1 at.%) doesn't change sequence and temperatures of L.→β, β→α, α→γ, and eutectoid reactions in a new TiAl-alloy.•Formation of nano-size Gd2O3 particles is observed inside and on boundaries of γ-lamellae.•Addition of Gd increases plasticity while remaining the strength unaffected in as-cast condition.