【作者】 王岩；

【导师】 甄良； 邵文柱；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2008， 博士

【摘要】 本文研究了GH4169合金中δ相的静态溶解演变规律,分析了δ相的静态溶解过程并探讨了其动力学机制。通过热模拟试验,分别建立了固溶态和δ相时效态GH4169合金的本构关系方程,探讨了δ相对GH4169合金热加工性能的影响。利用光学显微镜（OM）、扫描电镜（SEM）、电子背散射衍射（EBSD）技术和透射电镜（TEM）等分析手段,研究了不同变形条件下固溶态和δ相时效态GH4169合金的微观组织演化过程,分析了其动态再结晶机制,并探讨了δ相对GH4169合金高温变形动态再结晶行为的影响。根据动态材料模型,分别得出了固溶态和δ相时效态GH4169合金的热加工图,确定了两种状态合金热加工的稳定区和失稳区,并提出了建议的工艺参数。研究结果表明,在温度为980℃和1000℃时,δ相的溶解量可达到稳定值;而在温度为1015℃、1025℃和1035℃时,δ相持续溶解。针状δ相在溶解过程中的形貌特征变化分为两个阶段,初期的变化主要表现为长针状δ相溶解成为短针状乃至球状,后期的溶解过程主要为短针状及球状δ相尺寸的减小。长针状δ相的溶解主要受Ni或Nb原子的长程扩散过程所控制,可用一维原子扩散动力学模型来描述;球状δ相的溶解主要受界面反应过程所控制,可用三维界面反应动力学模型来描述。固溶态和δ相时效态GH4169合金的高温压缩热模拟试验结果表明,双曲正弦函数适合于描述两种状态合金流变应力与变形条件之间的关系,其变形激活能分别为443kJ/mol和467kJ/mol。预析出δ相降低了GH4169合金高温变形的稳态流变应力和峰值应变,提高了合金峰值应力后的流变软化程度。固溶态GH4169合金的高温变形机制是以动态再结晶为主,伴随着位错的攀移过程;预析出δ相改变了GH4169合金的高温变形机制,提高了合金高温变形的表观激活能和表观激活体积。同时,预析出δ相提高了GH4169合金的高温变形延伸率,对合金高温成型性能起到有益作用。固溶态GH4169合金高温压缩变形试样的微观组织分析结果表明,合金的动态再结晶晶粒尺寸d_DRX和大角晶界频率f_HAB均可用Z参数来定量描述。合金的动态再结晶形核机制与Z参数值密切相关。在低Z值条件下,其主要形核机制为伴随着孪生的原始晶界的弓出机制;在高Z值条件下,原始晶界附近的动态再结晶形核机制主要为伴随着亚晶旋转的弓出机制,原始晶粒内部的形核主要集中在形变带上;同时,连续动态再结晶也会在合金的局部区域发生。δ相时效态GH4169合金高温压缩变形试样的微观组织分析结果表明,δ相在高温变形条件下的动态溶解速度远大于其在静态条件下的溶解速度。预析出δ相在一定程度上减小了GH4169合金动态再结晶的晶粒尺寸。预析出δ相改变了GH4169合金高温变形的动态再结晶机制,δ相时效态GH4169合金中的动态再结晶形核机制主要有δ相诱发动态再结晶形核和晶界弓出形核。固溶态和δ相时效态GH4169合金的热加工图分析结果表明,两种状态合金在中、低应变速率区均具有三个典型的动态再结晶区域。固溶态GH4169合金的始锻建议在应变速率为10^-2.7-10^-1.5s^-1、变形温度为1087.5-1100℃的区域内进行;终锻建议在应变速率为10^-2.5-10^-1.5s^-1、变形温度为1000-1065℃的区域内进行。在应变速率为10^-0.25-s^-1、变形温度为950¹100℃的区域,固溶态GH4169合金发生流变失稳,失稳的发生与局部塑性流动引发的裂纹形成有关。δ相时效态GH4169合金的热加工建议在应变速率为10^-2.5-10^-1.5s^-1、变形温度为950-1015℃的区域内进行;δ相诱发动态再结晶的发生对合金低温变形条件下（T=950℃）耗散效率的提高起较大作用;在高温低应变速率区出现的高耗散效率极大值,与δ相溶解对动态再结晶的促进作用有关;合金在应变速率为10^-0.351s^-1、变形温度为950¹100℃的区域发生的流变失稳与局部的剪切带有关。更多还原

【Abstract】 The evolution ofδphase in alloy GH4169 during static state dissolution were studied, and the dissolution process and its mechanisms were analyzed. The constitution equations describing the hot deformation behavior of the alloy at annealed state and the delta-processed state were established by thermal simulation compression tests, respectively. The effect ofδphase on the hot working performance of the alloy was discussed. Microstructure evolution of the alloy at the annealed state and delta-processed state under different deformation conditions were investigated by optical microscopy （OM）, scanning electron microscopy （SEM）, electron backscatter diffraction （EBSD） technique and transmission electron microscopy （TEM）. The mechanism of dynamic recrystallization for the alloy was analyzed, and the effect ofδphase on the hot deformation behavior of the alloy was also discussed. According to the dynamic materials model, processing maps of the alloy at the annealed state and delta-processed state were obtained, respectively. The stable and instable regions for hot working of the alloy at the different states were determined, and the suggested processing parameters were presented.The results show that the dissolution amount ofδphase reaches to stable values at temperatures of 980℃and 1000℃, and theδphase are continuously dissolved at temperatures of 1015, 1025 and 1035℃. The morphology change of needle-shapedδphase during dissolution process can be divided into two stages: from a long needle shape into a short needle and globular ones at the early stage, and the decrease in the dimension of short needle-shaped and globularδphase at the late stage. The dissolution of the long-needle-shapedδphase is mainly controlled by long range diffusion of Ni or Nb, which can be described by one-dimensional atomic diffusion dynamic model. The dissolution of the globularδphase is mainly controlled by interfacial reaction, which can be described by three-dimensional interfacial reaction dynamics model.The results of the thermal simulation compression tests show that the hyperbolic sine-type function is suitable for describing the relationship between the flow stress and the deformation condition for the alloy at both the annealed state and the delta-processed state. The activation energies for hot compression are 443 and 467 kJ/mol, respectively. After delta processing, the stable stress and the peak strain for hot compression of the alloy are decreased, and the flow softening degree after peak stress is enhanced. The deformation mechanism of the alloy at annealed state is mainly the dynamic recrystallization accompanied dislocation climbing. After delta processing, the mechanism for hot deformation of the alloy is different, and the apparent activation energy and activation volume are increased due to the pre-precipitatedδphase. Meanwhile, the elongation of the alloy is increased due to the pre-precipitatedδphase, which is beneficial to the processability.The results of the microstructure analysis for hot compressed samples at annealed state show that both the size of dynamic recrystallization grains and the frequency of high angle boundary can be quantitatively described by the Zener-Hollomon parameter. The nucleation mechanisms of dynamic recrystallization for this alloy are closely related to the value of Zener-Hollomon parameter. Under low Z conditions, the main nucleation mechanism is the bulging of original grain boundaries accompanied by twinning. Under high Z conditions, the main nucleation mechanism nearby original grain boundaries is the bulging of original grain boundary accompanied by subgrain rotation. The nucleations inside the original grains focus on the deformation bands, and the continuous dynamic recrystallization can also occur in the local region for the annealed alloy.The results of the microstructure analysis for hot compressed samples at delta-processed state show that the dissolution rate ofδphase under hot deformation conditions is much faster than that under static state conditions. After delta processing, the size of dynamic recrystallization grain decreases to some extend. The nucleation mechanisms of dynamic recrystallization for the alloy are different because of the pre-precipitatedδphases. The main nucleation mechanisms of dynamic recrystallization for delta-processed alloy include theδphase stimulated nucleation and the bulging of original grain boundaries.The results of the processing maps for the alloy at annealed state and delta-processed state show that three classic zones of dynamic recrystallization appear in the region with moderate and low strain rates. The starting forging for the alloy at annealed state are suggested to be at strain rates between 10^-2.7 and 10^-1.5s^-1 and temperatures between 1087.5 and 1100℃, and the final forging are suggested to be at strain rates between 10^-2.5 and 10^-1.5s^-1 and temperatures between 1000 and 1065℃. The flow instability occurring at the strain rates between 10^-0.25 and 1 s^-1 and the temperatures between 950 and 1100℃at the annealed alloy is related to the cracking induced by the local plastic flow. The hot working parameters for the alloy at delta-processed state are suggested to be at strain rate between 10-2.5 and 10^-1.5 s^-1 and temperature between 950 to 1015℃. The higher dissipation efficiency occurring at the lower temperature region （T=950℃） is closely related to the occurrence ofδphase stimulated nucleation of dynamic recrystallization. The higher value of dissipation efficiency occurring at the region with higher temperatures and lower strain rates for this alloy is associated with the acceleration of dynamic recrystallization due to the dissolution ofδphase. The flow instability occurring at the strain rates between 10^-0.35 and 1 s^-1 and temperature between 950 to 1100℃for the alloy at delta-processed state is related to the local shear bandings.更多还原