【作者】 刘敏；

【导师】 陈玉勇； 孔凡涛；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2020， 硕士

【摘要】 TiAl合金具有优异的高温性能和密度低的特点,是重要航天航空工业和汽车行业的高温结构材料。TiAl合金板材在600～900℃之间的热防护结构方面极具应用潜力,因此高质量的大尺寸TiAl合金板材成形是未来的发展方向。但是由于TiAl合金的热加工窗口窄、本征脆性大等缺点,导致TiAl合金板材的制备困难,且板材的后续热塑成形难度大。新型的β-γTiAl合金的热加工性能明显优于传统的γ-TiAl合金,研究β-γTiAl合金大尺寸板材制备有重要意义。本文通过优化工艺参数成功制得了大尺寸TiAl合金板材,研究了大尺寸TiAl合金板材不同截面的显微组织和织构,分析了板材力学性能各向异性,研究了TiAl合金板材加载速度、初始变形温度以及模具温度对板材热弯曲成形效果的影响。通过合理的工艺参数制备了尺寸为500mm×400mm×(2～3)mm的β-γTiAl合金板材。研究板材横截面、纵截面、轧面三个截面上的显微组织。大尺寸TiAl合金板材主要由少量的等轴γ晶粒、板条状γ晶粒、大量近似等轴的β/γ层片组织、β相和白色的析出物Y2O3组成。板材发生大量变形和充分再结晶能够明显细化合金的显微组织,绝大多数的γ晶粒尺寸集中在10μm范围内。板材不同截面的显微组织不同,在纵截面上γ相和层片组织呈长条状,呈现出明显的轧制流线性,轧面和横截面上的γ相和层片组织近似等轴状,没有明显的方向性。板材的织构密度低于3,由变形织构和再结晶织构组成,在不同截面上的织构均可以观察到<001>晶向平行于轧向。对大尺寸板材RD方向和TD方向在室温、700℃、750℃和800℃的力学性能进行研究。结果表明,该大尺寸板材制备工艺能够很好的改善TiAl板材的性能,RD方向和TD方向,室温屈服强度分别为947MPa和895MPa,延伸率为1.12%和1.09%。随着温度升高,屈服强度和极限抗拉强度下降,延伸率明显上升,RD方向温度升高到800℃时,极限抗拉强度仍有468MPa,塑性达到95.96%。TD方向在800℃时,抗拉极限强度为480MPa,延伸率超过100%。板材不同温度下力学性能均具有各向异性。由于显微组织的流线特征和织构影响,RD方向的力学性能在较低温度下优于TD方向的力学性能。在750℃以上拉伸会发生再结晶改变显微组织和织构类型,弱化变形织构的作用,在750℃和800℃时观察到的结果与室温下相反。通过DEFORM软件对Ti-43Al-9V-Y合金板材的热变形参数进行探索,研究了0.1mm/s、0.5mm/s和1mm/s加载速度,1000℃、1100℃、1200℃的板材初始变形温度和600℃、700℃、800℃的模具温度对板材V形弯曲变形行为的影响。通过控制变量法和正交实验法研究发现板材在1mm/s,初始变形温度为1100℃,模具温度为800℃时能够得到相对均匀的温度场分布和应力场分布。更多还原

【Abstract】 TiAl alloy has excellent high temperature performance and low density,and is an important high temperature structural material for the aerospace industry and the automotive industry.TiAl alloy sheet has great application potential in the thermal protection structure between 600℃and 900℃.Therefore,the formation of highquality large-size TiAl alloy sheet is the future development direction.However,due to the shortcomings of the TiAl alloy,such as a narrow thermal processing window and a large intrinsic brittleness,the preparation of the TiAl alloy sheet and the subsequent thermoplastic forming of the sheet are difficult.The thermal processing properties of the new β-γTiAl alloy are obviously superior to the traditional γ-TiAl alloy,and it is necessary to study the preparation of large-sized β-γTiAl alloy plates.In this paper,large-size TiAl alloy plates were successfully fabricated by optimizing the process parameters.The microstructure and texture of different cross-sections of large-size TiAl alloy plates were studied,anisotropy of the mechanical properties of the plates was analyzed.The influence of the loading speed,initial deformation temperature of the TiAl alloy plates and mold temperature on the effect of hot bending of sheet were studied.The β-γTiAl alloy sheet with dimensions of 500mm×400mm×(2～3)mm was prepared by reasonable process parameters.Study the microstructure of the three sections of the cross section,longitudinal section and rolled surface of the sheet.The large-sized TiAl alloy sheet is mainly composed of a small amount of equiaxed γ grains,lath γ grains,a large number of equiaxed β/γ lamellar structures,β phases and white precipitates Y2O3.A large amount of deformation and recrystallization of the sheet can obviously refine the microstructure of the alloy,and the majority of γ grain size is concentrated in the range of 10 μm.The microstructure of the different sections of the sheet is different.On the longitudinal section,the γ phase and the lamellar structure are elongated,showing obvious rolling flow linearity.The γ phase and the lamellar structure on the rolling surface and the cross section are approximately isometric.There is no obvious directionality.The texture density of the sheet is lower than 3,which is composed of deformed texture and recrystallized texture.The texture of different sections can be observed with the <001> crystal direction parallel to the rolling direction.The mechanical properties of RD and TD directions of large-sized sheet at room temperature,700°C,750°C and 800°C were studied.The results show that the largesize sheet preparation process can improve the performance of TiAl sheet well.The RD and TD directions,the room temperature yield strength are 947 MPa and 895 MPa,and the elongation is 1.12% and 1.09%.As the temperature rises,the yield strength and tensile strength decrease,in contrast the elongation increases significantly.When the temperature in the RD direction increases to 800°C,the ultimate tensile strength is still 468 MPa,and the shaping reaches 95.96%.When the TD direction is 800℃,the ultimate tensile strength is 480 MPa,and the elongation exceeds 100%.The mechanical properties of the plates are anisotropic at different temperatures.Due to the effect of the streamline characteristics and texture of the microstructure,the mechanical properties in the RD direction are superior to those in the TD direction at lower temperatures.Stretching above 750°C will cause recrystallization to change the microstructure and texture type,weakening the effect of deformed texture.The results observed at 750°C and 800°C are opposite to those at room temperature.The DEFORM software was used to explore the thermal deformation parameters of Ti-43Al-9V-Y alloy sheet,and the loading speeds of 0.1mm/s,0.5mm/s and 1mm/s were studied.The initial deformation temperature at the sheet was 1000℃,1100℃ and 1200℃ And the effect of mold temperature of 600℃、700℃、800℃ on the thermal effect of the sheet.Through the controlled variable method and orthogonal experiment method,it is found that the sheet can obtain a relatively uniform temperature field distribution and equivalent stress field distribution at 1 mm/s,the initial deformation temperature is 1100 ℃,and the mold temperature is 800 ℃.更多还原