New ternary equi-atomic refractory medium-entropy alloys with tensile ductility: Hafnium versus titanium into NbTa-based solution

• Published in: Intermetallics Vol. 107; pp. 15 - 23
• Main Authors: Wang, Shao-Ping, Ma, Evan, Xu, Jian
• Format: Journal Article
• Language: English
• Published: Barking Elsevier Ltd 01.04.2019; Elsevier BV
• Subjects: Alloys; BCC structure; Ductility; Electric arc melting; Medium entropy alloys; Refractory materials; Refractory metals; Solid solution hardening; Solid solutions; Solution strengthening; Tensile properties; Tensile strain; Titanium; BCC structure; Refractory metals; Medium-entropy alloys; Solid solution hardening; Tensile properties
• ISSN: 0966-9795; 1879-0216
• DOI: 10.1016/j.intermet.2019.01.004

We demonstrate that based on NbTa as the base solution, ternary equiatomic HfNbTa and TiNbTa single-phase body-centered-cubic (BCC) solid solutions are achieved at arc-melted alloy ingots. These add interesting new members into the group of ternary refractory medium-entropy alloys (RMEAs), previously available only in NbTiZr. Moreover, HfNbTa and TiNbTa are the first two ternary RMEAs that exhibit tensile ductility, with HfNbTa having a combination of yield strength and tensile strain on par with its high-entropy counterpart, the Senkov alloy TiZrHfNbTa. We also show that alloying Hf into the base NbTa solution manifests a much higher strengthening potency compared with Ti. This difference can be rationalized using empirical parameters and models accounting for the size and modulus misfits among constituent elements. [Display omitted] •Arc-melted equiatomic HfNbTa and TiNbTa alloys formed BCC solid solutions.•HfNbTa and TiNbTa are the first two ternary RMEAs that exhibit tensile ductility.•Alloying Hf into NbTa solution shows higher strengthening potency compared with Ti.•This difference can be rationalized using empirical parameters.•Fictive lattice model is also applicable to these RMEAs.