Effect Of Microstructure Of BT25 Titanium Alloy On Mechanical Properties

BT25 titanium alloy was developed by the former Soviet union,it is a kind of giving priority to with alpha titanium alloy which Belonging to Markov shape ?+ ? two-phase titanium alloys.Test data show that BT25 titanium alloy has superior stability of microstructure and creep strength. Its nominal composition is Ti-6.5Al-2Mo-1Zr-1Sn-1W-0.2Si, its Chinese brand is TC25.By adding Metal elements tin(Sn) and tungsten(W),The heat-resistance and high temperature strength of BT25 titanium alloy was improved,And prolonged the service life. BT25 titanium alloy has good high temperature mechanical properties,its working time can reach 6000 h Under 500 ?,When 550 ? its working time can reach 6000 h.So it is suitable for manufacturing aeroengine compressor parts.In order to obtain good overall performance aircraft components, the paper by changing the solution temperature and cooling rate to achieve the purpose of controlling the microstructure of the alloy.Because the microstructur of titanium is key factor to determine its performance.Heat treated microstructure of a phase and ? phase morphology, size, and volume fraction are varies greatly with the heat treatment process minor changes, so that the microstructure of titanium alloy presences diversity.This paper through the microscope, scanning electron microscope and Micro Hardness Tester testing methods comparative analysis the effects of different solution heat treatment temperature(990??1000??1010??1020?)on the microstructure of titanium alloy bars.And more different when different organizations at different cooling rates(0.1 ?/s, 1 ?/s, 10 ?/s, 20 ?/s, 50 ?/s) to room temperature obtained from the single-phase ?-phase region organizations carries on tensile properties test, discussing the correspondence between the BT25 alloy microstructure and tensile properties.Mechanical properties and deformation capacity of the two-phase titanium alloy relies heavily on its microstructure.The fine grain equiaxed has good room temperature ductility and fatigue properties.However, due to too stable organization titanium sheet steel can not be obtained with the same fine equiaxed grains by annealing cycle.So the study two-phase titanium alloy obtained other organizations as well as the axis of the sheet-like ? phase decomposition law by thermal deformation is very necessary.In this paper, B?hr DIL805 A / D high-precision differential dilatometer, the first shaft having uneven tissue changes wrought organized into the same sheet thickness lamellar, carry on lamellar structure test of BT25 titanium alloy deformation of 20%, 40% and 60% and deformation temperature of 940 ?, strain rate, respectively 0.01s-1, 0.1s-1,0.001s-1 hot compression experiment through unidirectional heat compressions.Then we observed and analysised the organization through the after heat compression by OM, SEM and Image-Pro Plus software,deriveing the law that the thermal deformation process lamellar structure to equiaxed structure and obtain and analyze the true stress-true strain curve.Hot compression true stress-strain curves exhibit a softening primarily by promoting phase transformation deformation and dynamic recrystallization caused.It found that the degree of deformation has an important influence on the process of BT25 Titanium equiaxed lamellar microstructure through the observation of hot compressed microstructure analysis.With the increase of the amount of deformation, dynamic recrystallization grains increasing the volume fraction and crystal fraction alkylene decrease, increasing lamellar equiaxial degree.The ultimate conclusion that we reach two mechanisms of equiaxed titanium alloy BT25 :(1) ? lamellar wedges dynamic recrystallization grain boundary or grain boundary equiaxed grains of ? phase, the sheet ? decomposing into several smaller sheet, and then through a small atomic diffusion sheet realize equiaxed.(2) the direction parallel to compressive stress that flaky lamellar ? phase occurs bent due to instability, bent so that ? is too large slice into several small slice, and then through the small atomic diffusion achieve equiaxed.