【作者】 胡南昌；

【导师】 尚丽娟；

【作者基本信息】 沈阳工业大学 ， 材料学， 2006， 硕士

【摘要】 应用电子显微分析技术,研究了单晶镍基高温合金蠕变三阶段的组织演化规律。分析了沉淀相γ的长大、形伐,位错的增殖、滑移、塞积,位错网的形成、破坏,空位的形成、聚集,微裂纹的形成、扩展,在合金蠕变过程中的影响和作用。据此,提出采用θ影射方法及其修正式对合金的蠕变行为进行预测,建立了方程中各参数与外在条件之间的函数关系。并对这两种方法的预测结果进行了分析。同时,结合单晶镍基高温合金蠕变特点,应用数学原理对预测精度较高的修正方程进行了数学理论推导。 由不同条件下实验数据的拟合结果,建立这两个方程中各参数与应力、温度或最小蠕变速率之间的函数关系,发现均满足线性关系。应用θ影射方法对单晶镍基高温合金在1100℃、120MPa条件下的蠕变行为进行预测。结果显示,该方程很好地再现了该合金蠕变过程的前两个阶段。用修正θ影射方法对1040℃、137MPa条件下蠕变行为进行预测,发现该方法不仅能够精确地预测蠕变过程的前两个阶段,而且能够描述出蠕变过程第三阶段的大部分内容。其预测精度可达96%。 经过对影响预测精度因素的分析发现,修正θ影射方法具有如此高的预测精度,其原因主要有以下三个方面:(1)所选择的本构方程符合单晶镍基高温合金蠕变过程的应变强化和应变弱化机制;(2)该方法的截断应变较高,包含了大部分蠕变实验数据,因而预测曲线能够更好地再现蠕变实验测量结果;(3)该模型中的强化项和弱化项曲线精确描述了蠕变的应变强化过程和应变弱化过程。 在金属蠕变理论的基础上,结合单晶镍基高温合金的蠕变特点,运用数学概念推导,可以得到与修正θ影射方法所用模型形式相同的数学表达式。这说明,修正θ影射方法是具有数学理论依据的。更多还原

【Abstract】 The regularity of the microstructure evolution of single crystal nickel-base superalloy during creep has been extensively studied by means of SEM and TEM analysis techniques. An investigation has been made into the effect of the precipitated phase γ’ growing and rafting, dislocation multiplication, slipping and piling up, dislocation network forming, vacancies forming and aggregating, microcracks forming and growing on the creep of single crystal nickel-base superalloy. According to the analysis results, the θ projection concept and its modified equation are proposed to describe creep curves measured. The equations of condition dependence of the material constants are established. The calculation results by these two methods are compared and analyzed. Then the equation of modified θ projection concept is derived from mathematic theory.The θ projection concept and its modified equation can well fit and reproduce creep curves measured with the single crystal nickel-based superalloy. According to the fitted curves under different condition, the models of temperature and stress dependence of the three material constants are established. And equations all are linearity. Creep curve under 1100℃, 120MPa is predicted. It is shown from the result that the first two stages of creep are predicted with high accuracy. While in the modified θ projection concept, creep curve (1040℃, 137MPa) is predicted with higher accuracy, to 96 percent of the rupture live.It is found that the prediction accuracy of the modified θ projection concept is improved because of three aspects. Firstly, a good constitutive creep equation is chose to well define the whole creep micro-mechanism;Secondly, cut off strain is higher, and including the most part of experiment result;Thirdly, the strain-hardening and weakening curves all accurately describe the strain harden and weaken processes of creep.The evolution of creep strain e with time is derived from mathematic theory, based on creep behavior of metal material. It is shown from the result that the expression of e with time determined by this method appears to be similar to that given by the modified 0 projection concept. So, the modified 0 projection concept is a right approach to predict the creep behavior of single crystal nickel-base superalloy.更多还原