Theory of solid solution strengthening of BCC Chemically Complex Alloys

Abstract An analytic model describing substitutional solid solution strengthening in body-centered cubic (BCC) complex, concentrated alloys (CCAs) based on a/2 screw dislocation mobility is developed and presented. At lower temperatures it is assumed that dipole dragging is the rate limiting strengthening mechanism, and as the temperature increases this changes to a jog dragging mechanism. While both mechanisms are contained in Suzuki's classical model for substitutional solid solution strengthening developed for BCC alloys significant modifications are required to apply such a model to the refractory CCA's. First, two approaches for incorporating the net effects of the complex solute chemistry are developed and contrasted using a ternary NbTaTi alloy and four quaternary alloys, MoNbTaTi, WNbTaTi, CrMoNbTi and CrMoTaTi . Our model is extended to higher temperatures and applied to analyze experimental yield data as a function of temperature (0.15–0.7TL, where TL is the absolute liquidus temperature) and strain rate (10−5 to 10−2/s) in a range of BCC chemically complex alloys including stoichiometric NbTiZr and HfNbTaTiZr. We find that the model, based on just these two mechanisms, gives excellent agreement with experimental yield data in both these BCC CCAs, NbTiZr and HfNbTaTiZr. The experimental yield data of these two BCC CCA's as well as NbTaTi and four quaternaries are also analyzed using Maresca's edge dislocation model developed for these types of alloys. The screw model presented is useful in predicting BCC CCAs with adequate high temperature strength, which will accelerate development of high temperature, high strength BCC alloys for aerospace applications.