Creep Behavior Prediction Of Single Crystal Nickel-Base Superalloys

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.