| TiAl alloy has the advantages of low density,high specific strength and stiffness,high temperature oxidation resistance,good creep resistance and so on.It has become a potential high temperature structural material.Among themany research directions of TiAl alloy,TiAl alloy sheet is considered to be one of the important research directions in the industrial application of TiAl alloy,which has broad development prospects in the automotive field and aerospace field.As a high temperature structural material,TiAl alloy honeycombsandwich structure has been successfully applied in reusable launch vehicles,as well as in low-pressure turbine blades of aero-engine Automobile exhaustpipe,etc.However,the traditional rolling process has the problems of rapid temperature drop and high stress,and it is easy to produce cracks in the rolling process.In view of these problems,researchers improve the formability of TiAl Alloy by alloying,heat treatment and thermomechanical treatment.Powder metallurgy is an effective method to prepare high quality TiAl alloy sheet because of its uniform structure and fine grain.In this paper,Ti-43Al-9V-Y pre alloyed powder was sintered by hot isostatic pressing at 1200?/140MPa/5h to obtain compact TiAl alloy bulk material.The slab with a thickness of 10mm was taken from the bulk material,and then it was wrapped with stainless steel,so that it could be rolled under near isothermal condition.The rolling speed was 200mm/s,the pass deformationwas 30%,and the starting rolling temperature was 1150?.In order to reducetheresidual stress,the plate was heated to900?for 10hours after rolling and then cooled to room temperature.Finally,the TiAl alloy plate with a thicknessof about 2.3mm and a complete surface without cracks was obtained.The microstructure of rolled sheet is composed of equiaxed grains?Grain,acicular?Phase,continuous block?In addition,there are a small amountof YAl2phase,which is equiaxed?.The average grain size is 10?m.The Y2O3particles in the structure are produced by the combination of oxygen andrare earth element Y in the process of hot isostatic pressing.The size of Y2O3particles ranges from 400 nm to 600nm.The number of small angle grain boundaries in rolled sheet accounts for19%,which indicates that there are more substructures in the sheet.board?The main texture types are copper Cu2{121}<1-11>,Brass B1{011}<2-11>,Goss G2{110}<001>,brass B2{110}<-112>,copper Cu1{112}<-1-11>.The tensile strength,yield strength and elongation of the sheet at room temperature are 766MPa,658MPa and 0.86%,respectively.At 750?,the yield strength can reach 526MPa and the plasticityis 54.7%.The excellent properties of the sheet can be attributed to the effectof uniform structure,fine grain,large number of substructures and strengthening of the second phase.The effects of different heat treatment temperature and time on the microstructure of the sheet were studied.With the increase of heat treatment temperature in the single-phase region,the volume fraction of lamellae increases,and the size of lamellae also increases?When the volume fraction of phase decreases,the grain size also decreases.However,when the temperature reaches1360?,the y-rich phase appears to gather and distribute in short line at the grain boundary.Prolonging the holding time of heat treatment plays a similar role as increasing the heat treatment temperature,that is,promoting the growth of the microstructure?2/?The formation of lamellae,but holding time is too long will cause high temperature?The grains grow rapidly,and finally get coarse lamellar structure.After heat treatment at 1320?/30min/FC and 1340?/30min/FC,the near lamellar structure and full lamellar structure were obtained respectively With the increase of heat treatment temperature,?2-phase content decreases and the number of large angle grain boundaries increases.The effect of heat treatment on tensile properties and nano hardness of the sheet was studied.The results show that the room temperature yield strength of the sheet increases with the increase of temperature in the heat treatment temperature range of 1260?,1280?,1300?and 1320?.When the heattreatment temperature is 1320?,the maximum strength is 684MPa,which is 26MPa higher than the room temperature strength before heat treatment.The yield strength of the other three groups of heat treatment samples is lower than that of the original sheet.The higher the heat treatment temperature is,the lower the elongation is.When the heat treatment temperature is 1320?,the lowest elongation is 0.36%.The yield strength of the plate at 700?increases with the increase of heat treatment temperature.When the heat treatment temperature is 1300?and 1320?,the strength of the plate is higher than that of the original plate,which is 583 MPa and 662MPa,respectively,which is 30MPa and 109MPa higher than that of the original plate.After heat treatment,there is no obvious change in microstructure The hardness of?0phase is about 7.41GPa,Thehardness of the?phase is about 5.65GPa,The hardness of?2/?is about 6.75GPa.The hardness of?2phase is higher than that of?phase This is different from the previous report about the hardness?-?TiAl.The hardness of each phase in TiAl alloy is different,but the hardness of ?0 phase is the highest. |
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