【作者】 王蕊宁；

【导师】 奚正平； 赵永庆；

【作者基本信息】 西安建筑科技大学 ， 材料学， 2008， 博士

【摘要】 对合金热加工性的研究是合理制定热加工工艺,有效控制合金组织性能从而提高制品质量的重要依据。本文通过对近α钛合金Ti53311S,颗粒增强钛基复合材料TP650和Zr-4合金在较宽范围进行热压缩试验,全面、系统的研究了该三种合金的高温变形行为,利用数值模拟计算本构关系并建立流变模型,求出变形激活能,确定了该三种合金试验变形条件范围内流变应力与应变、应变速率及变形温度之间的关系;运用光学显微镜、透射电镜分析该三种合金的微观组织,研究变形温度、变形速率、变形程度对其组织的影响,并分析其变形机理,建立加工参数与显微组织演变的对应关系;运用系统稳定性分析原理,基于动态材料模型（DMM）构造出近α钛合金Ti53311S,颗粒增强钛基复合材料TP650和Zr-4合金的热加工图,结合高温变形组织对加工图进行综合分析,深入研究其热加工性并制定最优的热加工工艺参数,研究出最有利于材料变形的稳定加工区域,为工艺制定的一般原则和可行工艺参数范围的选择提供了理论依据。最后基于上述Ti53311S,TP650和Zr-4合金的变形机理分析和加工图建立了该三种合金的热变形机理图,来探明其加工参数和变形组织的关系,为该三种合金热加工工艺参数的选择、组织控制和性能优化提供理论指导,及以后类似钛、锆合金的加工提供理论参考。主要研究结果如下:根据Ti53311S、TP650和Zr-4合金的热变形特征分别采用幂指数和双曲正弦函数本构关系求得Ti53311S合金在相变点之下和相变点之上变形激活能（Q）的值分别为507和241KJ/mol,TP650合金在相变点之下和相变点之上变形激活能（Q）的值分别为691KJ/mol和202KJ/mol,Zr-4合金的变形激活能为387KJ/mol。并首次建立了Ti53311S、TP650、Zr-4合金的流变应力模型,拟和精度较高,Ti53311S合金对应变速率较为敏感。在两相区低应变速率0.001s^-1加工可以得到细小均匀的超塑性等轴组织,而中等应变速率0.1～1s^-1变形时,可以得到具有良好的塑性和疲劳性能的球化组织,随变形程度增加,其球化程度增加。在高温两相区980℃低应变速率0.001-0.1s^-1变形时主要发生了动态再结晶,而且再结晶核心的形成与位错的重新分布和再结晶前的多边形化形成亚晶有关;而在相变点之上,由刃位错的攀移、螺位错的交滑移控制的动态回复是Ti53311S合金的主要软化机理。TP650合金在900～980℃,应变速率为0.001～0.01^-1的区域,主要发生了超塑性。应变速率0.01-10s^-1变形时发生了动态再结晶以及部分α相球化,其中α相的再结晶主要与亚晶的形成、转动和聚合成核有关。TiC颗粒的加入对界面有钉扎和拖曳作用,因此有利于位错胞结构的形成和稳定基体中的细晶及亚晶。而在相变点之上,低应变速率0.001s^-1时主要的软化机理为动态回复,应变速率为0.01-10s^-1软化机理主要为动态再结晶。高温β区域TP650合金的变形特征主要由钛基体决定。Zr-4合金在α相区和低温α+β相区变形都发生了α-Zr为主的完全动态再结晶,形核机制为晶间弓出形核,晶界沉淀析出相Zr（CrFe）₂,阻碍界面迁移,引起界面弯曲,对Zr-4合金再结晶形核非常有利。而高温α+β相区,应变速率对其变形机理有重要影响,低应变速率0.005-0.05s^-1变形时,主要为β转变组织覆盖的粗大晶粒,软化机理无法判断,而当应变速率升高到0.5s^-1时,则发生晶内再结晶。变形机理和加工图的研究表明在Zr-4合金加工过程中,为形成均匀的组织,应避免在高应变速率成形。对Ti53311S和TP650合金的研究表明近α钛合金及其复合材料在两相区具有较宽的加工范围。而TP650合金由于TiC颗粒的加入对其晶界迁移有拖曳作用,影响基体中各滑移系的相互作用,使其再结晶区域较大。低温高应变速率变形容易形成绝热剪切带,由于钛合金的低热传导性,使高应变速率下变形热效应较为显著,塑性变形产生的热量传递不均造成局部温升过高在Ti53311S合金中发生相变剪切带。更多还原

【Abstract】 In order to determine the hot working parameter,optimize the structure and property of alloy,hot work ability of the alloy must be studied.In this work,the near-alpha titanium alloy Ti53311S,TiC particles reinforced titanium matrix composite TP650 and Zr-4 alloy were hot compressed in a broad range of temperature.The flow behavior was described by the constitutive equation and numerical simulation,the deformation activation energy were calculated and the relationship between the flow stress and deformation parameters was studied systematically.The microstructure of the deformed specimens were studied by the optical microscope and the transmission electron microscope,the effect of deformation temperature,strain rate and deformation ratio on the microstructure of deformed specimens and the deformation mechanism were analyzed,and the relationship between the deformation parameter and the microstructure evolution was defined.The processing maps of Ti53311S,TP650 and Zr-4 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 observation,the hot work ability was studied profoundly and the deformation parameters were optimized,in order to select the "safety" regime and instruct the hot procedure.Lastly,the deformation mechanism map for Ti53311S, TP650 and Zr-4 alloy were plotted,which is the guide for the hot procedure of like-kind alloy.From this work,it was found that:The hot deformation behaviors of Ti53311S、TP650 and Zr-4 alloy were described by the power exponent and hyperbolic sine constitutive equation respectivly,and the deformation activation energy of Ti53311S alloy were calculated to be 507KJ/mol in （α+β）phase field and 241KJ/mol inβphase field,the deformation activation energy of TP650 alloy were calculated to be 691KJ/mol in（α+β）phase field and 202KJ/mol inβphase field,and the deformation activation energy of Zr-4 alloy were calculated to be 387KJ/mol.In addition,the flow stress model of Ti53311S、TP650 and Zr-4 alloy were established,and the fitting precision of which is satisfying.Ti53311S alloy is sensitive to the strain rate and different softening mechanism occurred at（α+β）phase.Superplasticity was observed at the strain rate of 0.001s^-1,it is mean that this alloy can be superplastic forged.At middle strain rate of 0.1～1s^-1,the microstructure of the specimens is spheroidization,and with the increase of deformation ratio,spheroidizing is strengthening.Dynamic recrystallization occurred at 980℃and 0.001-0.1s^-1,and the nucleation is related with the redistribution of dislocations and the subgrain which created by polygonization.However,dynamic recovery which controlled by climb motion and cross slip is the deformation mechanism of Ti53311S alloy above the transformation temperature.Superplasticity was observed in TP650 alloy also at 900～980℃and 0.001～0.01s^-1.Dynamic recrystallization and spheroidizing of small quantity ofαphase occurred at 0.01-10s^-1,and the dynamic recrystallization is related with the formation, rotation and aggregation of subgrain.The addition of TiC particles is help for the formation of structure cell and stabilization of subgrain and close grain by drageffect. Above the transformation temperature,the director softening mechanism is dynamic recovery at low strain rate of 0.001s^-1,dynamic recrystallization is the primary softening mechanism at 0.01-10s^-1,and the recrystal grain generated priority at the cross point and grain boundary.The deformation characteristic of TP650 alloy atβphase field is depending on the deformation of titanium matrix,it is due to the softening of matrix by the start of more slip system atβphase,the TiC particles turned in the matrix and the hardening effect is weakening.Dynamic recrystallization of Zr-4 alloy occurred inαphase and（α+β）phase,and the nucleation mechanism is intercrystal projection.The precipitated phase of Zr（CrFe）₂ play an important role in the recrystallization nucleation by hindering the interface migration.The effect of strain rate on the softening mechanism is important at high temperature rang of（α+β）phase,the softening mechanism is not obvious at low strain rate of 0.005-0.05s^-1and dynamic recrystallization occurred at high strain rate.When deformed in high temperatureαphase regime and middle strain rate,the higher efficiency of power dissipation is result form the inconsistent of the intercrystalline deformation,and the deformation shear zone is obvious at 850℃,50s^-1. Thus,in order to form the uniform structure,high strain rate should be avoided in the deformation of Zr-4 alloy.The research for Ti53311S and TP650 alloy showed that the good hot work ability of near-alpha titanium alloy and near-alpha titanium matrix composite can be obtained at（α+β）phase.The addition of TiC particles in near-alpha titanium alloy expended the field of dynamic recrystallization.Adiabatic shear zone is easy to occur at high strain rate and low temperature due to the low heat conductivity of titanium alloy.The non-uniform delivery of heat which produced by plastic deformation created phase transformation shear zone in Ti53311S alloy.更多还原