【作者】 王琛；

【导师】 张平祥； 毛小南；

【作者基本信息】 东北大学 ， 材料加工工程， 2013， 博士

【摘要】 TA19和TC17合金是两种航空发动机用钛合金。在热变形时,由于变形抗力大,难于变形,且对温度、应变和应变速率等热变形参数敏感,容易产生各类组织缺陷,从而影响材料的力学性能。利用热模拟压缩试验,通过加工图来研究两种合金的热变形行为及优化锻造工艺,可以把热加工、组织和性能联系起来,提高锻件的综合性能、降低成本和缩短研发周期。本文通过对近α钛合金TA19和近p钛合金TC17进行热模拟压缩试验,研究了两种合金的高温变形行为,获得了变形激活能,并分别建立了两种合金在(α+β)两相区和p单相区的流变模型；运用光学显微镜(OM)、扫描电镜(SEM)及透射电镜(TEM)分析观察两种合金的组织,研究了热变形参数对组织的影响；基于动态材料模型(DMM)构造出两种合金的热加工图,并结合组织对加工图进行分析,深入研究其热加工性并制订最优的热加工参数,为最佳工艺参数范围的选择提供了理论依据。主要研究结果如下：根据TA19和TC17合金的流变应力曲线,结合幂指数和双曲正弦函数获得了TA19合金在(α+β)两相区和β单相区的变形激活能分别为586KJ/mol和290KJ/mol; TC17合金在(α+β)两相区和p单相区的变形激活能分别为407KJ/mol和155KJ/mol。建立了TA19和TC17合金的流变应力模型。变形参数对TA19和TC1 7合金组织的影响较大,在(Ω+β)两相区变形时,随着变形量的增大,Ω相球化程度增大。当变形量增大到80%时,大部分组织发生了球化。TA19和TC17合金热变形时,应变速率越低,球化α含量越多,组织越均匀。低温高应变速率下,由于温升效应,容易形成绝热剪切带。TA19和TC17合金在(α+β)两相区的软化机制都是动态再结晶(球化),但因为初始片层a厚度不同,两种合金的球化机制不同。TA19合金在p单相区变形时,高应变速率下,主要软化机制是由位错滑移、交滑移产生的动态回复；低应变速率下,p相发生了动态再结晶；TC17合金在p单相区变形时,高应变速率下的主要软化机制也是动态回复：在低应变速率下,动态再结晶过程没有发生形核过程,主要软化机制是连续动态再结晶。TA19合金在温度范围为940-960℃℃,应变速率范围为0.01～0.1s-1时,峰值效率达到45%的区域内发生了球化；在980～1000℃℃,应变速率大约为0.01s-1,峰值达到35%,主要发生了β相的动态再结晶。TA19合金在温度为940～1000℃C,应变速率大于0.535s-1变形时,由于塑性变形产生的热量传递不均造成局部温升过高出现了绝热剪切带,在加工过程中应该避开这一区域。TC17合金在温度范围为820～850℃C,应变速率在0.01s-1附近,峰值功率耗散率达48%,该区域内发生了片状α相的球化；在温度范围为900～930℃C,应变速率大约在0.01～0.1s-1变形时,峰值功率耗散率达39%,主要发生了p相的动态再结晶。TC17合金在温度为820～880℃℃,应变速率大于0.415s-1变形时,出现了绝热剪切带,在加工过程中应该避开这一区域。TA19合金最佳加工的温度范围为940～960℃℃,应变速率范围为0.01～0.1s-1;TC17合金最佳加工的温度范围为820～850℃C,应变速率在0.01s-1附近。此时的功率耗散值都大于45%,为实现片层组织动态球化的理想热加工区域。更多还原

【Abstract】 TA19 and TC17 alloy are used for aeroengine and belong to difficult-to-deform materials, which show extremely sensitivity to the hot processing parameters, such as the temperature, strain and strain rate. It is easy for the formation of the defects during the deformation of these alloys, which will influence the mechanical properties of these alloys. The forging processes for these two alloys have been optimized by hot compression tests and using processing map technology, which have great signi-fycance in improve the properties of materials, depress cost and reduce research cycle.In this work, the high temperature deformation behavior of the near-alpha titanium alloy TA19 and the near-beta titanium alloy TC17 have been studied by hot compressing tests. The flow behavior was described by the constitutive equation, the deformation activation energy were calculated. The microstructures of specimens were studied by the optical microscope, the scanning electron microscope and the transmission electron microscope. The effect of the deformation temperature, strain and strain rate on the microstructure of specimens and mechanism were analyzed. The processing maps of TA19 and TC17 alloy were plotted by Dynamic Material Model and the principle of system stability analysis, and the different regime in processing map was analyzed by the microstructure, the hot work ability was studied profoundly and the deformation parameters were optimized. From this work, it was found that:The hot deformation behaviors of TA19 and TC17 alloy were described by the power exponent and hyperbolic sine constitutive equation respectively, and the deformation activation energy of TA19 alloy were calculated to be 586KJ/mol in α+β phase field and 290KJ/mol in β phase field. The deformation activation energy of TC17 alloy were calculated to be 407KJ/mol in α+β phase field and 155KJ/mol in β phase field. In addition, the flow stress model of TA19 and TC17 alloy were established.TA19 alloy and TC17 alloy are sensitive to the strain. The quantity of globular a phase increases with increasing strain under the Tp, and almost a phase from lamellar to equiaxed at the strain of 80%. The TA19 alloy and TC17 alloy are also sensitive to the strain rate, the quantity of globular a phase increases with decreasing strain rate. Adiabatic shear bands are easy to occur at high strain rate and low temperature field due to the low heat conductivity.Dynamic recrystallization (globularization) is the deformation mechanism of TA19 and TC17 alloy in α+α phase, though the globularized mechanisms are different. The dynamic recovery which controlled by climb motion and cross slip is the deformation mechanism of TA19 above the transformation temperature and at high strain rate, while the dynamic recrystallization is the deformation mechanism at low strain rate. The deformation mechanism of TC17 at high strain rate above the transformation temperature is also dynamic recovery, while the continuous dynamic recrystallization is the deformation mechanism at low strain rate.Globularization was observed in TA19 alloy at 940～960℃ and 0.01～0.1s-1, and the efficiency of power dissipation is 45%. The dynamic recrystallization of TA19 alloy was occurred at 980～1000℃ and the strain rate was 0.01s-1, and the efficiency of power dissipation is 35%. Adiabatic shear bands took place due to the low heat conductivity of TA19 alloy at 940～1000 ℃ and the strain rate was above 0.535s-1.At 820～850℃ and the strain rate was 0.01s-1, the microstructure of the specimens of TC17 alloy is spheroidization, and the efficiency of power dissipation is 48%. The dynamic recrystallization of TC17 alloy was occurred at 900～930℃ and 0.01～0.Is-1, and the efficiency of power dissipation is 39%. Adiabatic shear bands took place due to the low heat conductivity of TC17 alloy at 820-880℃ and the strain rate was above 0.415s-1.The optimized processing craft was obtained:the optimum processing temperature is in the range of 940～960 ℃ and the strain rate is in the range of 0.01～0.Is-1 for TA19 alloy. The optimum processing temperature is the range of 820-850℃ and the strain rate is about 0.01s-1 for TC17 alloy. The efficiency of power dissipations are above 45% in these regions.更多还原