Unravelling the competitive effect of microstructural features on the fracture toughness and tensile properties of near beta titanium alloys

The competitive effect of microstructural features including primary alpha (alpha(p)), secondary alpha (alpha(s)), grain boundary alpha (alpha(GB)) and beta grain size on mechanical properties of a near beta Ti alloy were studied with two heat treatment processes. The relative effect of beta grain size and STA (solution treatment and ageing) processing parameters on mechanical properties were quantitatively explored by the application of Taguchi method. These results were further explained via correlating microstructure with the fracture toughness and tensile properties. It was found that large numbers of fine as precipitates and continuous alpha(GB) played greater roles than other features, resulting in a high strength and very low ductility (<2%) of STA process samples. The beta grain size had a negative correlation with fracture toughness. In the samples prepared by BASCA (beta anneal slow cooling and ageing) process, improved ductility and fracture toughness were obtained due to a lower density of alpha(s) precipitates, a basket-weave structure and zigzag morphology of alpha(GB). For this heat treatment, an increase in prior beta grain size had an observable positive effect on fracture toughness. The contradictory effect of beta grain size on fracture toughness found in literature was for the first time explained. It was shown that the microstructure obtained from different processes after beta solution has complex effect on mechanical properties. This complexity derived from the competition between microstructure features and the overall sum of their effect on fracture toughness and tensile properties. A novel table was proposed to quasi-quantitatively unravel these competitive effects. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

The study investigated the competitive effects of microstructural features on the mechanical properties of a near beta Ti alloy, revealing the complex impact of microstructure on fracture toughness and tensile properties under different heat treatment processes. The competition between microstructural features and their overall effects on fracture toughness and tensile properties were quantitatively explored, providing insights into the contradictory effects of beta grain size on fracture toughness for the first time.