【作者】 尤振平；

【导师】 惠松骁； 叶文君；

【作者基本信息】 北京有色金属研究总院 ， 材料科学与工程， 2011， 博士

【摘要】 本文对TC4合金、TB10合金、TB8合金进行了分离式Hopkinson压杆(SHPB)实验,采用光学显微镜、SEM、TEM和XRD等技术对回收试样进行显微观察与分析,探讨了合金类型、典型组织状态、组织细节、织构特征及棒材尺寸规格对钛合金动态力学性能及绝热剪切敏感性的影响规律,并分析了冲击诱发相变对TB10合金的绝热剪切敏感性影响。主要研究结果如下：合金类型及典型组织状态对钛合金的动态力学性能影响较大。本实验选择的六组试样的绝热剪切敏感性的不敏感到敏感顺序依次为：TC4合金双态组织、TC4合金等轴组织、TB10合金两相区固溶+双级时效组织、TB10合金两相区固溶+时效组织、TB10合金β相区固溶组织、TC4合金魏氏组织。随TC4合金双态组织初生α相含量的增加,动态流变应力稍有降低,但其发生剪切失效前的均匀动态塑性应变增加幅度较大,在相变点以下50℃左右固溶(初生α相含量为38%左右)时,达到动态流变应力和均匀动态塑性应变的较好匹配,此时试样在剪切失效前所能吸收的能量较多。TC4合金相变点以下50℃固溶后炉冷获得的等轴α+晶间β组织,由于等轴α相彼此之间以及与基体之间取向任意,变形协调性好,可以通过自身的大变形有效协调塑性变形过程中的不均匀性,从而具有较低的绝热剪切敏感性和较好的抗绝热剪切失效能力。φ30 mm小规格棒材、φ165 mm中等规格棒材、φ350 mm大规格棒材的TC4试样在高应变率下的破坏规律大体相一致。但是,在加载条件相同的情况下,随着棒材尺寸规格的增大,试样的剪切变形和破坏程度相对较严重。两相区固溶+时效处理的TB10合金在剪切部位形成的绝热剪切带的过渡区由具有高位错密度的沿着剪切方向的宽度为20～50 nm的拉长组织构成,剪切带中心部位由大量低位错密度的直径为50～100 nm的晶粒组成,具有典型的再结晶组织特征,再结晶过程是晶粒机械碎化及晶界迁移、亚晶粗化共同作用的结果。β固溶状态的TB10合金在高应变率条件下,发生了冲击诱发相变,经标定为斜方马氏体α″；由于冲击相变过程吸收了一部分冲击功,使其未能达到材料本构失稳形成绝热剪切带的临界条件,且冲击诱发的斜方马氏体相具有相对较高的均匀伸长率和较大的塑性,因此晶粒在高应变率条件下能保持较好的均匀变形而不发生绝热剪切变形局域化。950℃轧制的TC4板材,无明显织构,其RD、TD、ND方向的动态力学性能及绝热剪切敏感性差别不明显。900℃轧制的TC4板材的主织构为{1219}<12 391>±30°RD,1050℃轧制板材的主织构为{1219}<1010>,由于织构强度较高,轧板存在明显的各向异性：TD方向的动态流变应力最大,ND次之,RD最低；RD方向发生绝热剪切失效前所吸收的能量最多,ND次之,TD最小,说明RD方向具有相对较低的绝热剪切敏感性和较好的抗绝热剪切失效能力。更多还原

【Abstract】 In this paper, a series of experiments on TC4, TB10 and TB8 alloys were carried out by split Hopkinson pressure bar(SHPB) in different strain rates. Microscope observation and analysis were carried out on samples by optical microscopy, SEM, TEM and XRD techniques, etc. The effect of microstructures and texture property on dynamic mechanical property and adiabatic shear sensitivity of titanium alloy was discussed. And the effect of impact-induced phase transformation on the adiabatic shear sensitivity of TB10 alloy was analyzed. The main results are as follows:The effect of microstructures of titanium alloy on dynamic mechanical property is lager. The energy absorbed by bimodal microstructure of TC4 alloy before adiabatic shear failure happening is the most, which of equiaxial microstructure of TC4 alloy, solution treated and aging microstructure of TB10 alloy and solution treated and diplex aging microstructure of TB10 alloy is less, and widmanstatten microstructure of TC4 alloy is more sensitive to the adiabatic shearing。With the increasing of primary a-phase in bimodal microstructure of TC4 alloy, the dynamic strength is slightly lower, and uniform dynamic plastic strain is enlarge. The dynamic plastic strain matches the uniform dynamic plastic strain better when solution treated below the phase transformation 50℃(the content of primary a-phase is about 38%). At this moment the energy absorbed before failure by the TC4 sample is the most, the adiabatic shear sensitivity is weaker and the ability to resist adiabatic shear failure is stronger.Exuiaxal a and intergranular (3 microstructure of TC4 alloy solution treated below the phase transformation 50℃and furnace cooling has excellent compatibility of deformation because the orientation between exuiaxal a-phase and matrix is random, which can compatibility the inhomogeneity effectively in the process of plastic deformation, and then has low adiabatic shear sensitivity and excellent ability to resist adiabatic shear failure.The failure law of TC4 bars ofΦ30 mm,Φ165 mm andΦ350 mm at high strain rate is generally consistent. However on the same loading condition the shear deformation and destruction of the samples were relatively more serious with the increase in bar size.With high strain rate, the transition zone between shear band and matrix of TB10 alloy by solution treated and aging is composed of grains of 20～50 nm in width with high dislocation density, and the grains were elongated along the shear direction. The center of shear band consists of a number of recrystallized grains with diameters of 50～100 nm and low dislocation density. The recrystallization is the result of grain mechanical fragmentation, crystal boundary migration and subgrain coarsening. With high strain rate loading, impact-induced phase transformation happened to the TB10 alloy treated ofβsolution, which calibrated to be martensite phase a". Because some shock energy was absorbed in the process of impact-induced phase transformation, it didn’t reach the critical condition of constitutive destabilization to formation adiabatic shear band. Therefore the deformation of grain is uniform at 3500 s-1 and there is no adiabatic shear localization phenomenon.The TC4 plate rolled in 950℃has no remarkable texture, and the difference of adiabatic shear sensitivity in rolling direction(RD), transverse direction(TD) and normal direction(ND) is obscure. The main texture of TC4 plate rolled at 900℃is {1219} <12 3 9 1>±30°RD whose intensity value is 10.577. And the main texture of plate rolled at 1050℃is {T219}(1010) whose intensity value is 15.333. TC4 rolled plate shows significantly anisotropic when texture intensity is high:The dynamic strength of TD is the highest, which of ND is lower and which of RD is the lowest. The energy absorbed before adiabatic shear failure occurring of RD is the biggest, which of ND is smaller, and which of TD is the least. And this indicates that the direction of RD has the lowest adiabatic shear sensitivity and excellent ability to resist adiabatic shear failure.更多还原