A simple Rice-Ashby ductile–brittle transition temperature (DBTT) model based on dislocation mobility for body-centered cubic complex concentrated alloys

Schematic of the Ashby-Embury model for brittle and ductile fracture conditions in front of a crack tip. • A simple Rice-Ashby type model for ductile–brittle transition temperature (DBTT) of body-centered cubic ( bcc ) complex concentrated alloys is presented. Approximate condition for intrinsic ductile behavior is also given. • The DBTT model is shown to explain the DBTT behavior for four complex concentrated alloys: Nb 45 Ta 25 Ti 15 Hf 15 (NTTH), MoNbTaW. HfNbTaTiZr, NbTiZr and two simple bcc metals, Fe and W. • It is shown that within isotropic elasticity theory, intrinsically brittle bcc complex concentrated alloys with a yield stress >2 GPa are expected to be always brittle in transgranular cracking. A simple Rice-Ashby type model for ductile–brittle transition temperature (DBTT) of body-centered cubic ( bcc ) complex concentrated alloys (structures) is presented. The effect of accumulation of dislocation density on DBTT is also analyzed. The model results are compared with experimental yield stress vs . temperature data for four complex concentrated alloys: Nb 45 Ta 25 Ti 15 Hf 15 (NTTH), MoNbTaW, HfNbTaTiZr, NbTiZr and two pure bcc metals, Fe and W. It is shown that the DBTT behavior of these alloys and pure metals are in agreement with the simple ductility model presented in this manuscript. The DBTT model presented in this manuscript along with yield strength models for bcc complex concentrated alloys described in the literature should serve as a useful guide for designing such alloys with good high temperature strength and significant room temperature ductility.