Study On The Microstructure And Electrochemical Properties Of Nickel Base Single Crystal Superalloy With Different Crystal Faces

Due to its excellent corrosion resistance and intentionally high temperature performance,Ni-based single crystal alloy is a key material for producing cash turbine engine blades.At present,there are few researches on the corrosion properties of Ni-based single crystal superalloys with different crystal faces and in marine environment.In this experiment,the microstructure and electrochemical properties of different crystal plane samples after casting and heat treatment were studied.The results showed that the dendrite morphologies of as-cast SRR99 Ni-based single crystal superalloy with different crystal planes were different.（001）crystal plane was"+"shape,（110）crystal plane was asymmetrical"+"shape,（111）crystal plane was"×"shape.In the as-cast samples,the morphologies ofγ’phases of each crystal plane were irregular.The eutectic morphologies of three different crystal planes were similar.The carbide morphology of as-cast SRR99 Ni-based single crystal superalloy was Chinese characters,and the type of carbide was MC.According to the fitting analysis of the Tafel polarization curves measured in the as-cast samples,the corrosion behaviors of the three crystal planes in the passive region were different.（001）crystal plane had the highest thermodynamic stability,the slowest electrochemical corrosion rate and the strongest corrosion resistance.The thermodynamic stability of samples at low withdrawal rate was higher than that with high withdrawal rate.The electrochemical corrosion resistance of samples at low withdrawal rate was better than that of samples at high withdrawal rate.According to the fitting analysis of EIS impedance curve,the electrochemical corrosion processes of the three crystal planes were the same.The electrochemical corrosion resistance of（001）crystal plane was the best,and the corrosion resistance of low withdrawal rate samples was better than that of high withdrawal rate samples.CV cycle curve showed that the electrochemical corrosion behavior was irreversible and the reaction was unidirectional.After heat treatment,the dendrites became blurred due to the diffusion of elements.The shape ofγ’phase became regular.Theγ’phase of the（001）plane had a cubic structure,theγ’phase of the（110）plane had a triangular prism structure,and theγ’phase of the（111）plane had a triangular pyramid structure.The eutectic structure disappeared after heat treatment.After heat treatment,the carbide decomposed at high temperature,the size of carbide decreased,and the types of carbide changed from MC to M₆C.The results of the fitting analysis on the Tafel polarization curve and EIS impedance spectrum were basically consistent with those of the as-cast samples.（001）crystal plane had the best thermodynamic stability and electrochemical corrosion resistance.The CV cycle curve after heat treatment showed that the electrochemical corrosion behavior was irreversible and unidirectional,and the oxidation peak was more obvious and the reaction was more thorough.