【作者】 张宏建；

【导师】 温卫东；

【作者基本信息】 南京航空航天大学 ， 航空宇航推进理论与工程， 2009， 博士

【摘要】 IC10合金是一种新型的多相Li₂型材料,由于具有优异的高温力学性能使其成为新一代航空发动机高温部件用结构材料之一。IC10的工作环境恶劣,受载情况复杂,而且具有异于传统无序材料的力学性能。但迄今为止,国内外对其力学特性及本构模型方面开展的研究工作还比较少。本文对IC10开展了相对系统的宏细观力学试验研究,研究了力学特性随温度和应变率的变化规律及力学特性的微细观机理;并基于试验结果,从细观和宏观两方面推导建立了适用于IC10这类材料的本构模型,用以描述IC10在各条件下的力学特性。研究工作和得到的主要结论如下:对IC10开展了系统的宏观力学性能试验研究和微细观机理观察研究,并分析力学特性参量的变化规律。本文在温度25～1100℃、应变率10-4～10-2/s范围内对IC10进行了率控制拉伸试验,获得其应力-应变、弹性模量、屈服应力和应变硬化率等材料数据,并研究了这些参数随应变率和温度变化的规律;同时,运用扫描电子显微镜（SEM）及透射电子显微镜（TEM）对IC10开展了断裂机理及细观机理观察试验研究。结果表明:应力-应变曲线在25～700℃范围内表现为应变硬化,800℃附近表现为动态回复,900～1100℃范围内表现为动态再结晶;屈服应力和应变硬化率均具有反常的温度相关性,在反常温度范围内它们随温度的升高小幅增大,且呈应变率弱敏感性,而超过该范围后它们随温度的升高大幅下降,且应变率敏感性很强;运用SEM对试件断口进行观察表明在25～800℃范围内,断裂机理主要为穿晶断裂;在900℃～1100℃范围内,断裂机理主要为韧窝聚集型断裂;在屈服反常温度范围内,IC10的强度升高等力学特性与其细观机制密切相关,该细观机制主要表现为八面体滑移系中螺位错被交滑移形成的KW锁锁住,从而使得产生原子之间位错需要更多的外部能量输入;在900℃～1100℃范围内IC10的应力-应变特性及应变率敏感性等力学特性与大量位错相互纠结形成胞状亚晶结构等现象相关。针对含γ′和γ多相Li₂型材料的力学性能及细观结构特征,提出并建立了一种细观本构模型及其数值解技术。该模型将含γ′和γ等相的混合单元体作为材料的细观特征单元体,并认为:材料的屈服和硬化由阻碍可动位错运动的点障碍所引起;螺位错的运动能力与其上超弯折的高度相关。根据总体位错密度的演化及超弯折的高度分布函数,推导建立了可动位错密度的演化方程和障碍密度的演化方程。基于所建立的模型、数值模拟技术和ABAQUS商用有限元分析软件,编制了本构模型的用户子程序（UMAT）。对25～700℃下的IC10应力-应变曲线预测结果与试验结果吻合良好,表明本文所提出的细观模型及其数值解技术是有效的。提出并建立了一种适用于描述含动态回复/再结晶行为的宏观本构模型。该模型将动态回复/再结晶行为的应力-塑性应变曲线分成峰值应力前的应变硬化和峰值应力后的应变软化这两部分,分别建立了硬化强度因子K_h、软化强度因子K_s、硬化指数n_h和软化指数n_s与材料屈服应力σ_0.2、临界应力σ_c ,临界塑性应变ε_c ,断裂应力σ_b和延伸率ε_b等宏观力学特性参数之间的函数关系。将本文模型分别应用于预测IC10在800℃的动态回复力学行为和900～1100℃的动态再结晶力学行为,并将预测结果与Cho模型的预测结果和试验值进行比较,结果表明本文模型能很好地预测IC10含动态回复/再结晶流变行为的力学特性,而且在使用上比Cho模型更方便。对L-H、J-C和ZA等三种常用于描述一般合金材料应变硬化的宏观本构模型进行了改进,发展了四种改进的宏观本构模型,即改进的L-H模型、改进的J-C模型、改进的ZA模型1和2。分别运用这四种改进模型对IC10在25～700℃范围的应力-塑性应变曲线进行了预测分析,与试验结果相比表明:改进L-H模型、改进J-C模型的形式简单,精度高、参数较少,更适用于工程应用。定义了应变率敏感度,对IC10进行应变率跳跃试验和应力松弛试验,定量分析了应变率敏感度和热激活体积的变化规律。分别对IC10在600～1100℃范围内进行了应变率跳跃试验和在600～1000℃范围内进行了应力松弛试验。试验结果表明:低于800℃时,IC10的力学特性对应变率的敏感性较弱,在800℃附近IC10的力学特性具有一定的应变率敏感性,而高于800℃时,IC10的力学特性对应变率非常敏感;热激活体积的量级较小,且随材料变形量的增加而降低;在600～900℃范围内热激活体积随温度的升高而下降,而在900～1100℃范围内随温度的升高而升高。更多还原

【Abstract】 Alloy IC10, one of the newly developed multiphase Li₂ alloys, is considered to be near-future candidate for advanced high temperature structure materials in aeroengine hot sections due to its excellent mechanical properties over a wide range of temperatures. IC10 is subjected to adverse and complex operating conditions and exhibits unusual thermo-mechanical flow behaviors. However, the studies on the mechanical properties and constitutive equations for IC10 are still very rare. In this thesis, the mechanical properties of IC10 were studied through both macro and micro tests. And the constitutive equations used to describe the flow behaviors of IC10 were developed through both phenomenological and physically scales. The main work done in this thesis includes:The tests on mechanical properties of IC10 were conducted. And the variation rules of mechanical properties were studied. In order to investigate the features of stress-strain curves and the mechanical properties （such as elastic moduli, elongation, yield stress and strain hardening rate）, the tensile tests were conducted over a wide range of temperatures （25～1100℃） and strain rates （10-4～10-2/s）. The fracture morphology and the micro-mechanisms of IC10 were studied based on the results of SEM and TEM tests. Experiments show: There are only work hardening behaviors in stress-strain curves over the range of 25～700℃. And the dynamic recovery behaviors are obvious in the stress-strain curves at 800℃. There are only dynamic recrystallization behaviors during the whole deformation above 800℃. IC10 exhibits the anomalous features of yield stress and strain hardening rate. During the special range of temperatures, yield stress and strain hardening rate are insensitive to strain rate and they increase slightly with temperature. Above the peak temperature of them, they drop off significantly and exhibit strong strain rate sensitivity. When the temperature is below 800℃, the fracture is transgranular cracking mixed with a few dimpled and intergranular fractures. The fracture is ductile cracking above 900℃. The TEM observations reveal that the macro mechanical properties are the reflections of the dominating long screws which are connected by superkinks and locked by KW locks.The mechanistic model and its numerical method were developed in this thesis. The mixed unit of the phase ofγ′andγis considered to be the micro-features unit of IC10. And two assumptions were proposed: the yield and hardening of IC10 are the net effect of point obstacles which resist the motion of mobile dislocations. The mobility of dislocations is connected with its superkink heights. The evolution of the mobile dislocation density was developed based on the evolution of whole dislocation density and the distribution of their superkink heights. And the evolution of obstacles density was derived from the evolution of the mobile dislocation density. The UMAT program of the model was written. And the flow behaviors over the range of 25～700℃were simulated by the model. The results show that the model is valid.A new constitutive equation, which can be used to describe the dynamic recovery/ recrystallization behaviors, was developed in this thesis. In the new model, the whole stress-strain curve is divided into the strain hardening part before the peak stress and the strain softening part after the peak point. The relationships between the model parameters （such as hardening factor K_h, softening factor K s, hardening exponent n_h and softening exponent n_s ） and the mechanical properties (such as yield stressσ_0.2,critical stressσ_c , critical plastic strainε_c ,broken stressσ_b and elongationε_b) were developed. The new model was used to predict the flow behaviors of IC10 above 800℃. Compared with the prediction of Cho’s model and the experiments, the new model is proved to be valid.The L-H model, J-C model and ZA model, which were widely used to describe the hardening flow behaviors, were modified, that is the modified L-H model, the modified J-C model, the modified ZA model 1 and 2. All these four modified models were used to predict the flow behaviors of IC10 during the range of 25～700℃. And the results show that: the modified L-H model and the modified J-C model are easy to use due to their simple formulation, few parameters and high accuracy.The strain rate sensitivity was defined in this thesis. The strain rate sensitivities and the thermal activation volume were analyzed quantificationally based on the strain rate jump tests and the stress-relax tests. The strain rate jump tests were conducted over the range of 600℃～1100℃. And the relax tests were conducted over the range of 600℃～1000℃. Experiments show that: the strain rate sensitivity is very low below 800℃. And it increases lightly at 800℃. It is apparent above 800℃. The thermal activation volume is very small. And the volume decreases with the increase of the deformation. At the range of 600～900℃, the volume decreases with the increase of the temperature. The volume increases with temperature at the range of 900～1100℃.更多还原