| γ-TiAl based alloys combine excellent properties such as high specific strength,high specific modulus,good creep resistance and oxidation resistance.It is widely regarded as a new generation of high temperature structural materials.It has a large potential especially in the aerospace and automotive fields.Beta-gamma TiAl alloy has excellent high temperature deformation ability and broadens the thermal processing window of TiAl alloy.Therefore,this paper takes a beta-gamma TiAl alloy Ti-43Al-9V-0.3Y as the research object,and prepares the sintered alloy by hot isostatic pressing technology.The microstructure and mechanical properties of the as-sintered Ti-43Al-9V-0.3Y alloy were investigated by means of XRD,SEM,EBSD,TEM and DSC,room temperature and high temperature tensile test.The microstructure and properties of the alloy during subsequent forging and heat treatment were studied.A commercial MSC.Marc software was used to simulate the hot isostatic pressing process of Ti-43Al-9V-0.3Y alloy powder billet.The radial and axial displacement and relative density of the powder body during hot isostatic pressing were studied.The influence of temperature,pressure and holding time on the densification process of the powder was analyzed,and the best hot isostatic pressing parameter of Ti-43Al-9V-0.3Y alloy is 1200 ℃/140 MPa for 5h.The powder displacement and relative powder density obtained under the optimal hot isostatic pressing process are analyzed.The densification process of the powder body can be divided into three stages.The density of the billet differs between the edge or the end and the core,but the difference is not obvious.In general,the relative density distribution of the alloy ingot is uniform and the sintering quality is good.Ti-43Al-9V-0.3Y alloy was prepared by pre-alloyed powder as raw material by hot isostatic pressing technique.The density measurement results of sintered alloy ingots at different positions were consistent with the results of finite element analysis,thus verifying the reliability of the finite element simulation methods in TiAl powder hot isostatic pressing simulation.The as-sintered Ti-43Al-9V-0.3Y alloy mainly contains equiaxed γ phase and a β phase distributed continuously in the grain boundary of γ grain and a bright white Y element precipitated phase,and a fine structure composed of γphase and β phase is formed.A good quality Ti-43Al-9V-0.3Y alloy forging cake with a size of Φ138mm×24mm was prepared at 1150℃ by a canned forging process.Themicrostructure of the as-forged Ti-43Al-9V-0.3Y alloy is still composed of massive γphase and β/B2 phase,and the β/γ layer structure is related to the phase transformation process of β phase to needle γ phase which occurs during the forging process.The difference in mechanical properties for the sintered Ti-43Al-9V-0.3Y alloy at the radial and axial directions is related to the hot isostatic pressing preparation method.The difference in mechanical properties of the alloy at different locations due to the density non-uniformity.After the forged state,the original micropores in the sintered alloy are eliminated,further increasing the density of the alloy and improving the alloy structure,so that the tensile properties of the forged alloy are greatly improved.The room temperature yield strength of the forged Ti-43Al-9V-0.3Y alloy reaches686-697 MPa,and the tensile strength of different parts is greater than 750 MPa,and the plasticity of the alloy is also greatly improved.At the same time,the yield strength and tensile strength of the alloy after being forged at 800 ℃ were slightly lower than those of the as-sintered alloy,and the elongation was significantly improved,reaching 70%.The fracture morphology of sintered Ti-43Al-9V-0.3Y alloy after tension at room temperature shows intergranular fracture,while the high temperature fracture mechanism is a mixed fracture mechanism of transgranular fracture and intergranular fracture,in which intergranular fracture is the main one.The tensile fracture mechanism of forged Ti-43Al-9V-0.3Y alloy at room temperature is intergranular and transgranular mixed fracture,and the proportion of transgranular fracture increases.Tensile fracture at800 ℃ is a mixed mode of intergranular fracture and transgranular fracture.The microstructure of the forged Ti-43Al-9V-0.3Y alloy was adjusted by different heat treatment processes,and the heat treatment was carried out in the temperature range of 1180-1300℃.It has undergone a process of change from the near gamma structure to the duplex structure,and then to the near lamellar structure and the fully lamellar structure. |
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