Temperature-dependent tensile behaviors and strain localization of TC17 high temperature titanium alloys with bimodal microstructure

Abstract

TC17 (Ti-5Al-2Sn-4Mo-4Cr) titanium alloys are extensively applied under high temperature environment, necessitating a comprehensive understanding of their high-temperature mechanical properties and deformation mechanisms. In this study, we systematically investigated the temperature-dependent tensile behaviors and deformation features of TC17 alloys with representative bimodal microstructure using multiple measurement and characterization techniques. It is intriguingly found that the alloy ductility remains nearly unchanged as the tensile temperature is raised from 25 °C to 400 °C although normal softening occurs concurrently. This phenomenon in ductility is closely associated with a reduction in uniform plastic strain during tension, leading to premature necking at elevated temperatures. Microstructural characterizations indicate that plastic deformation predominantly occurs within α_p-domain at ambient temperature, resulting in significant dislocation piling-up and even large crystallographic misorientations. However, as the testing temperature increases, this specific deformation gradually shifts towards the β_trans-domain, inducing pronounced deformation localization in the fashion of strain localization bands (SLBs). Since the bimodal microstructure comprises a soft α_p-domain and a hard β_trans-domain, it can essentially be classified as a heterostructure, which potentially imparts back-stress work hardening to prevent necking and thus enhance global ductility at ambient temperature. However, elevated temperatures weaken the effect of back-stress working hardening while promoting deformation transition into the β_trans-domain, thereby activating strain localization and accelerating necking onset. These findings enrich our fundamental understanding on high-temperature mechanical behaviors of TC17 alloys, and also provide implicit guidance for advancing material performance at elevated temperatures.