Dynamic Hall-Petch versus grain-size gradient effects on the mechanical behavior under simple shear loading of β-titanium Ti-25Nb-25Zr alloys

Abstract

Ti-25Nb-25Zr β-titanium alloys with both traditional (IP) and harmonic structure designed (HS) were submitted to monotonic simple shear tests. The HS alloy exhibited superior flow stress and strength. Yet, the strain to failure was very close for both materials as was the strain hardening rate evolution. Σ11 twin boundaries dominate the post-mortem microstructure of IP. Conversely, complete twinning inhibition was the main feature for HS alloy. Dynamic Hall-Petch-like effect and high density of geometrically necessary dislocation boundaries due to plastic incompatibility between the core and the ultrafine-grained shell of HS alloy, respectively, are invoked for the observed mechanical behaviors.