Preparation, Microstructure And Mechanical Properties Of Tial Alloys Sheet

TiAl based alloys is regarded as one of the most promising high-temperatureStructure Materials due to its good properties. However, the intrinsic brittleness whichdecrease their deformation ability, and anti-oxidation properties decreasing above800℃limit their engineering applications. Kim et al. suggest a TiAl based alloy namedBeta-Gamma TiAl. This kind of TiAl alloys own better high-temperature deformationability than traditional TiAl based alloys, which can broaden the hot-deform windows ofTiAl based alloys. This paper concern about two kinds of Beta-Gamma TiAl alloysnamed Ti-43Al-9V-Y(at.%) and Ti-45Al-2Nb-1.5V-1Mo-0.3Y(at.%). These two alloyswere prepared by ingot metallurgy. What’s more, their microstructure andmechanical property were observed and investigated. We also studied the influence ofthermal treatment on these two alloys.Via the XRD, OM, BSE, EDS, EBSD, we studied the microstructure andphase composition of Ti-43Al-9V-Y alloy. There is no dynamic recrystallization inTi-43Al-9V-Y alloy sheet tissue. The rolling process of plate deformation mechanism isdislocation slip. Further more, we find the principal phase of Ti-43Al-9V-Y alloy sheetis γ phase which occupy nearly71.8%, and β/B2phase take up24.2%. The α/α2phaseoccupied the least, only at the edge of the gamma and beta grains where we can find alittle.Based on Ti-Al-V phase diagram results, we designed four temperature to studythe influence of thermal treatment on Ti-43Al-9V-Y alloy. The four temperature were1250℃,1280℃,1310℃,1340℃. The holding time were1h. Then we studied themicrostructure and phase composition of the four condition of Ti-43Al-9V-Y alloy.After the heat treatment at1250℃, we find the microstructure of Ti-43Al-9V-Y alloy isequiaxial structure, The recrystallization took place in Ti-43Al-9V-Y alloy plate; whenthe heat treatment finished at1280℃, the β/B2phase Hold dominant position, and γphase followed; when the thermal treatment ended at1310℃, thephase change processwere similar to the treatment at1280℃, just the γ phaseexisted more in the alloy sheet;the last one at1340℃, we found that not only γ phase and β/B2phase existed, but also there are some α2+γ lamellar at the edge of γ phase, and this microstructure arein favour of strength and other properties of Ti-43Al-9V-Y alloy sheet.By means of Electron microscopic hardness tester, The hardness of Ti-43Al-9V-Y alloy sheet before and after heat treatment were tested. We found that the hardness ofalloy relate to the content of β/B2phase. When the slipped β/B2phase increased, thehardness of alloy decreased. Via Instron-5569electronic universal material testingmachine, we tested the mechanical properties of Ti-43Al-9V-Y alloy sheet, and therate of extension all are10-4S-1. Before the heat treatment, at room temperature, thetensile strength is347.7MPa, yield strength is246MPa, and the percentage elongation is3.3%. When we do the test at700℃, wo get the mechanical properties oforiginalTi-43Al-9V-Y alloy sheet. The tensile strength is569.13MPa, and the yield strength is481.4MPa, the percentage elongation can reach up to13.58%. However, after theheat-treatment at1340℃, theirmechanical properties changed. At room temperature,the tensile strength arrived383.9MPa, but the elongation decreased to2.2%; at700℃,the tensile strength reach up to604MPa, and the yield strength is555MPa, but theelongation nearly reduce by a half. Additionally, we carried up another experiment totest the compression performance of our sheet. Due to this test, we found that in a wakeof the compression speed from0.5mm/min to0.05mm/min, the compressive strengthdecreased, and the compression ratio decreased.In the Ti-45Al-2Nb-1.5V-1Mo-0.3Y alloy plate, the γ iometric Dominate thedominance. And the microstructure give priority to with large angle grain boundaries.This shows that in the plate rolling process, the dynamic recrystallization took place andthe microstructure crushed. At the same time, we found that some crack inside the alloysheet which suggest the dislocation accumulation and internal stress concentration leadsto the cracks. At last, we measure the compression properties ofTi-45Al-2Nb-1.5V-1Mo-0.3Y alloy sheet. At the same speed, the compression strengthwere lower than Ti-43Al-9V-Y alloy sheet, yet the compression ratio similarly. Theresult maybe have something to do with the crack inside sheet.