Multi-scale dispersion strengthening for high-temperature titanium alloys: strength preservation and softening mechanisms

The long-lasting expectation “the hotter the engine, the better” calls for the development of high-temperature metallic alloys. Although the high specific strengths of titanium alloys are compelling for such applications, their deleterious softening beyond 600°C imposes serious limitations. Much has been known for decades regarding the phase metallurgy for precipitation strengthening design in titanium alloys, however, the other facile strength promotion mechanism, dispersion strengthening, remains comparatively less-explored and unutilized. The present research concerns the multi-scale dispersion strengthening in titanium alloys, with mechanistic emphases on the critical plasticity micro-events that affect strength preservation. Due to the simultaneous introduction of intragranular dispersoids and intergranular reinforcers, the current titanium alloys present superior engineering tensile strength of 519 MPa at 700°C. Throughout the examined 25-800°C temperature range, noticeable softening induced by the thermal activation occurs above 600°C, accompanied by evident strength loss. The temperature-dependence transition of dominated softening mechanisms from dynamic recovery to dynamic recrystallization has been clarified by theoretical calculations. Furthermore, the strengthening effect of multi-scale architectures is underpinned as the enhanced dislocation strengthening owing to the introduction of thermally-stable heterointerfaces, which could generically guide the design of similar heat-resistant titanium alloys.