Strength vs temperature for refractory complex concentrated alloys (RCCAs): A critical comparison with refractory BCC elements and dilute alloys

Abstract

To support the development of refractory complex, concentrated alloys (RCCAs), a clear understanding of the effect of temperature on strength is needed. Body-centered cubic (BCC) refractory metals and dilute refractory alloys show a strong temperature dependence of yield stress (σy) at low and high temperatures, with a relatively temperature-independent regime in between. RCCAs may introduce important changes in deformation and strengthening mechanisms, so it is not clear if RCCAs will show the same thermal dependencies. The objective of this work is to answer the question, “Is the temperature dependence of strength similar or different for RCCAs compared to BCC refractory elements and dilute refractory alloys ?” We evaluate σyvs. temperature for 61 RCCAs by analyzing data curated from the literature. We find that σy increases progressively from refractory BCC elements, to dilute alloys, to single- and multi-phase RCCAs. Single-phase RCCAs show the same three thermal regimes, but the stresses are higher and the intermediate plateau is shorter and is sometimes steeper. The thermal dependence of σy in multi-phase RCCAs shows more substantial differences. Six factors that contribute to the higher σy of RCCAs are discussed: (i) higher solute concentration; (ii) dispersion in atomic sizes; (iii) the shear modulus magnitude; (iv) the type of principal elements; (v) the solvus temperature of predicted secondary phases; and (vi) microstructure. Based on the present observations and analyses, suggestions for future research are made, especially regarding improved models for the effect of temperature on strength.