Influence of α+β solution treatments on Ti65 ultrathin sheets: Silicide precipitation, mechanical behaviour and novel twinning system
(1. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China;
2. Innovation Center, NPU·Chongqing, Chongqing 401135, China;
3. National & Local Joint Engineering Research Center for Precision Thermoforming Technology of Advanced Metal Materials, Northwestern Polytechnical University, Xi’an 710072, China;
4. Baoti Group Ltd., Baoji 721014, China;
5. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China)
2. Innovation Center, NPU·Chongqing, Chongqing 401135, China;
3. National & Local Joint Engineering Research Center for Precision Thermoforming Technology of Advanced Metal Materials, Northwestern Polytechnical University, Xi’an 710072, China;
4. Baoti Group Ltd., Baoji 721014, China;
5. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China)
Abstract: To cope with the urgent demands of the aerospace industry for lightweight and excellent high-temperature performance titanium alloy components, the microstructure evolution, silicide precipitation and mechanical behaviour of a novel high-temperature Ti65 titanium alloy ultrathin sheet with different heat treatments were systematically investigated. Submicron (Ti,Zr)6Si3 silicides are observed after solution treatments followed by air cooling, leading to a decline and significant fluctuations in tensile properties. For furnace cooling samples, (Ti,Zr)5Si3 silicide crossing grain boundaries and (Ti,Zr)6Si3 silicide near grain boundaries are observed after solution treatment at 950 ℃. When the solution temperature increases to 1010 ℃, the third silicide (Ti,Zr)3Si appears near dislocations. The combined effect of the strong size effect of the alloy ultrathin sheet and silicide precipitation results in great performance fluctuation, sharp drop of ductility and even brittle fracture. In addition, silicide precipitation differs little with various holding time during low-temperature solution treatment. Moreover, novel twins appear after the rolling process at 990 ℃ and are only inside coarse basal texture α grains, with an axis-angle pair of 65° .
Key words: titanium alloy; ultrathin sheet; silicide; mechanical property; size effect; twinning