The Effect Of Fe On The Microstructure And Mechanical Properties Of Ti-Al-Sn-Zr-Mo-Nb-Si High Temperature Titanium Alloy

With the development of aerospace industry,novel short-term high temperature titanium alloys with good combination property are developed for high-speed aircraft.The composition design of short-term high temperature titanium alloys mainly focuses on adjusting the type and content of the ? stable elements.Fe is a common ? stable element,its adverse effect on creep limits the use in long-term high temperature titanium alloys.However,short-term high temperature titanium alloys do not require excellent long-term creep properties.Therefore,it is of great significance to systematically study the effect of Fe on the microstructure and mechanical properties of short-time high temperature titanium alloys.Based on the previous research,Ti-6.5Al-2Sn-4Zr-1.5Mo-2Nb-xFe-0.2Si(x=0/0.25/0.5)high temperature titanium alloys were designed and studied in this paper.The effects of Fe and heat treatment on microstructure and mechanical properties of the alloys were investigated.In addition,the deformation and fracture behavior of the alloys during high temperature tensile process wre analysed.The main conclusions were as follows:After annealing at(Tp-20)?,the alloys got bimodal structure.With the increase of the content of Fe,the microstructure of the alloys did not change significantly,only the volume fraction of the residual ? phase increased,which improved the plasticity of the alloy at room temperature.At 650?,the strength decreased and the plasticity increased.After tensile deformation at room temperature,a lot of slip lines and stacking faults appeared in the ?p phase,and the addition of Fe reduced the degree of dislocation entanglement and weakened the effect of working hardening.Dynamic recovery and dynamic recrystallization occurred simultaneously during the 650? tensile process.The addition of Fe increased the size of ?2 phase precipitated from theap phase,which reduced the strengthening effect of a2 phase.The high temperature fracture mode of the alloy was transformed from the intergranular and transgranular fracture mode of OFe and 0.25Fe alloy to the pure intergranular fracture mode of 0.5Fe alloy.The temperature and cooling rate of single stage annealing affect the microstructure and properties of the 0.5Fe alloy.After annealing in ?+? region(950?990?),the 0.5Fe alloy got bimodal structure.With the increase of annealing temperature,the volume fraction of ?p phase decreased,the size of a colony,the thickness of as lamella increased.During this stage,the strength at room temperature decreased and the elongation increased slightly.As the annealing temperature continued to rise,the size of ?t structure,the width of ? colony and the thickness of ?s lamella increased,the volume fraction of the ?p phase decreases rapidly.When the annealing temperature up to 1040?,the 0.5Fe alloy got Widmannstatten structure with no ?p phase.During this stage,the strength at room temperature increased and the elongation decreased significantly.At 650?,the strength of the 0.5Fe alloy increased and the plasticity decreased.With the increase of the cooling rate,the content and size of as decreased.The alloy with as lamella obtained by air cooling had the best combination property.