Refractory high entropy alloys (RHEA), composed of high melting, passivating, and lightweight elements, show great promise for high-temperature structural applications [1]. They have demonstrated exceptional properties surpassing those of Ni-based superalloys and other refractory alloys, such as remarkable high-temperature strength and superior corrosion resistance [2]. However, the crucial aspect of creep resistance, essential for structural materials at elevated temperatures, has only been briefly addressed. A recent study by Gadelmeier et al. [3] investigated the tensile creep behavior of body-centered cubic (BCC) TiZrHfNbTa RHEA with a single-phase, polycrystalline microstructure at 980 °C and 1100 °C. The creep resistance at both temperatures was notably lower than that of a state-of-the-art, precipitation-strengthened, single-crystal Ni-based superalloy (CMSX-4). This discrepancy is attributed to phase decomposition during creep deformation and the BCC crystal structure of the alloy. Therefore, achieving a precipitation-strengthened condition is imperative for RHEA to exhibit competitive creep performance.

Several alloy concepts have been explored, including the 27.3Ta-27.3Mo-27.3Ti-8Cr-10Al (in at.%) RHEA, which exhibits a two-phase microstructure with a disordered A2 matrix and ordered B2 precipitates, resembling that of Ni-based superalloys [4,5]. It has been confirmed that the formation of B2 occurs through nucleation and growth-mediated precipitation, with a notably high solvus temperature of approximately 1055°C. Additionally, it maintains a stable microstructure even after prolonged exposure to elevated temperatures [5]. These findings suggest promising prospects for achieving high-temperature creep resistance in this alloy. Consequently, we present the current status of investigations into the creep behavior of the precipitation-strengthened 27.3Ta-27.3Mo-27.3Ti-8Cr-10Al alloy. Compression creep tests were conducted at elevated temperatures, including those close to the solvus temperature and above, with varying constant true stresses to unveil the creep deformation behavior and underlying mechanisms. Subsequently, scanning and transmission electron microscopy were employed to experimentally examine the deformed microstructures at different creep strains. The discussion will encompass the impact of the coherent interface between the matrix and precipitates.

References
[1] B. Gorr; Corrosion Science, 2020, vol. 166, p. 108475.
[2] C.J. Liu; Acta Materialia, 2022, vol. 237, p. 118188.
[3] C. Gadelmeier; Cell Reports Physical Science, 2022, vol. 3, p. 100991.
[4] S. Laube; Acta Materialia, 2021, vol. 218, p. 117217.
[5] S. Laube; Science and Technology of Advanced Materials, 2022, vol. 23, p. 692-706.