TB8合金的超塑性行为及两段超塑性研究

发布时间：2018-08-23 08:03

【摘要】：TB8钛合金具有优良的高温强度和抗蠕变性能、高淬透性、优良的抗氧化性能和耐腐蚀性能,固溶处理状态具有中等强度和高塑性,时效后具有较高的强度和断裂韧性。时效强化后抗拉强度可达到1450 MPa以上,是一种较为理想的航空结构材料。已有研究集中在TB8钛合金的板料成形和热压缩变形时的流变行为上,研究的内容主要在组织性能上。而TB8合金的超塑性及其变形机理尚未明确,两段超塑性行为也有待研究。本文对TB8钛合金进行超塑性变形,热处理之后再进行超塑性变形,及两段超塑性变形,研究了TB8钛合金的超塑性变形行为和其显微组织演变规律。主要研究内容和结论如下:(1)对TB8钛合金采用恒应变速率法进行超塑性变形,研究不同参数对其超塑性及流变行为的影响,研究显微组织的演变规律,建立相关流变应力数学模型。TB8钛合金的超塑性对温度和应变速率比较敏感,在应变速率一定时,超塑性变形的延伸率随着变形温度的升高先增大后减小,在变形温度一定时,超塑性变形的延伸率随着变形速率的降低而升高,在变形温度为840℃,应变速率为10-4s-1,得到最大延伸率356%。流变应力随着温度的升高或应变速率的降低而降低;变形过程中组织发生明显动态再结晶,随着变形温度的升高,或应变速率的降低,α相含量逐渐减少,动态再晶晶粒发生聚集长大。经过计算推导超塑性拉伸变形激活能和应力指数分别为251.25kJ/mol、2.3895,并采用Arrhenius模型建立了TB8钛合金应力-应变本构方程。(2)TB8钛合金固溶、预时效处理后进行超塑性变形,研究热处理参数对TB8钛合金延伸率、流变应力及其显微组织的影响。TB8钛合金在研究范围内固溶处理后,随着固溶温度的升高,流变应力降低,α相含量减少,超过相变点为β单相组织,超塑性变形后的延伸率有所降低,变形过程中发生明显的动态再结晶;预时效处理后,流变应力都有所降低,随着预时效温度的升高,超塑性变形后的延伸率先升高再降低,流变应力先降低再升高,变形过程中发生明显的动态再结晶;520℃预时效后延伸率达到最大值358%,晶粒部分细化。(3)对TB8钛合金进行两段超塑性变形,研究应变速率不同的两段超塑性和应变诱发最大m值法两段超塑性。TB8钛合金两段变形,第二段的变形抗力都显著降低,延伸率也有所降低;变形速度、变形量、保温时间对第一段变形的显微组织有影响,初速度为1.0mm/min、预应变量为0.5、保温时间为15min和初速度为1.5mm/min、预应变量为0.5、保温时间为5min时得到的组织较细小均匀;应变诱发最大m值法两段超塑性拉伸延伸率低的原因可能是第一段拉伸后的晶粒没有得到细化。
[Abstract]:TB8 titanium alloy has excellent high temperature strength and creep resistance, high hardenability, excellent oxidation resistance and corrosion resistance, medium strength and high plasticity in solution treatment state, and high strength and fracture toughness after aging. The tensile strength of TB8 titanium alloy after aging hardening can reach more than 1450 MPa. It is an ideal Aeronautical Structural material. Materials. Previous studies have focused on the rheological behavior of TB8 titanium alloy during sheet forming and hot compression, mainly on its microstructure and properties. The superplastic deformation behavior and microstructure evolution of TB8 titanium alloy were studied by deformation and two-stage superplastic deformation. The main research contents and conclusions are as follows: (1) Superplastic deformation of TB8 titanium alloy was carried out by constant strain rate method, and the effects of different parameters on its superplastic and rheological behavior were studied. The superplasticity of TB8 titanium alloy is sensitive to temperature and strain rate. When the strain rate is constant, the elongation of superplastic deformation increases first and then decreases with the increase of deformation temperature. At a certain deformation temperature, the elongation of superplastic deformation increases with the decrease of deformation rate, and at a certain deformation temperature, the elongation of superplastic deformation increases with the decrease of deformation rate. The maximum elongation is 356%. The flow stress decreases with the increase of temperature or the decrease of strain rate. The microstructure undergoes obvious dynamic recrystallization during deformation. With the increase of deformation temperature or the decrease of strain rate, the content of alpha phase decreases gradually and the dynamic recrystallization grains grow up. The activation energy and stress index of superplastic tensile deformation are 251.25 kJ/mol and 2.3895, respectively. The stress-strain constitutive equation of TB8 titanium alloy is established by Arrhenius model. (2) The superplastic deformation of TB8 titanium alloy after solution and pre-aging treatment is carried out. The effects of heat treatment parameters on the elongation, rheological stress and microstructure of TB8 titanium alloy are studied. With the increase of solution temperature, the rheological stress decreases, the content of alpha phase decreases, the elongation decreases after superplastic deformation and the dynamic recrystallization occurs during deformation. With the increase of aging temperature, the elongation of TB8 titanium alloy increases first, then decreases, the flow stress decreases and then increases, and the dynamic recrystallization occurs during the deformation process. The maximum elongation reaches 358% and the grain refines partially after pre-aging at 520 (?) TB8 titanium alloy has two stages of superplasticity, i.e. strain-induced maximum m-value method and strain-induced maximum m-value method. The microstructure obtained by strain-induced maximum m-value method is finer and more uniform when the pre-strain is 0.5 and the holding time is 5 minutes.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG146.23

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