Study On The Interdiffusion Behavior Of Nickel Base Single Crystal Superalloy And Platinum Aluminum Coating

With the requirement of high thrust-to-weight ratio of aero engines,the environment where the materials of the hot end parts of the engines are working is becoming more and more severe.As one of the key components of an aero engine,the blade must have a protective coating on its surface to meet service requirements.The platinum-modified aluminide coating is widely used in aero-engine blades due to its advantages such as simple fabrication and good oxidation resistance.However,it is found in practical application that the interdiffusion between the substrate and the coating seriously affects the service life of the substrate and the coating,so it is necessary to study the interdiffusion process.In this paper,N5 and IC21 nickel-based single crystal superalloys with different thicknesses are selected as the base material,and platinum-modified aluminide（Pt Al,Re Pt Al）coatings are prepared on the base,and the coated samples are at 1100℃and 1150℃Perform static oxidation.X-ray diffractometer（XRD）analysis,scanning electron microscopy（SEM）observation,X-ray energy spectrometer（EDS）analysis,electron probe（EPMA）analysis,and transmission electrons are performed on the prepared sample and the sample at different times of static oxidation Microscope（TEM）observation to study the interdiffusion behavior between the substrate and the coating during static oxidation and the effect of the substrate thickness on the interdiffusion.The main findings are as follows:（1）After the coating sample is thermally diffused,there is an interdiffusion zone（IDZ）between the substrate and the coating.As the oxidation time increases,the interdiffusion thickness changes little,and refractory metal elements gather;the thickness of the secondary reaction zone becomes thicker,and the hard phase gradually grows.（2）After static oxidation of 1100℃for N5 substrate/Pt Al coating samples,it was found that dense Al₂O₃ was first formed inside the Pt Al coating,and spinel-like oxides with low density were formed on the surface of the N5 alloy.It is not strong,and the platinum-modified aluminide coating can be used in the design of the coating to achieve the purpose of anti-oxidation.The interdiffusion mechanism between the N5 matrix and the Pt Al coating:the phase transition occurring inside the platinum-aluminum coating isβ-（Ni,Pt）Al→γ′-Ni₃Al;the phase transition occurring in the matrix is:γ-Ni/γ′-Ni₃Al→β-（Ni,Pt）Al;during the diffusion process,the Ni element vacancies in the matrix are occupied by refractory elements,and the TCP phase is precipitated.At the same time,the Al element in the coating is detached from the original position,forming a Kirkendal cavity,the above changes Cause the system’s antioxidant performance to decline.（3）During the static oxidation of the IC21 substrate and the Pt Al coating sample at 1150°C,the Pt Al coating experienced aβ-（Ni,Pt）Al/β-Ni Al→γ′-Ni₃Al phase transition.During the phase transition,the coating Al₂O₃and Ni Al₂O₄ are formed on the surface.The protective aluminum oxide film cannot be continuously covered due to the consumption of Al element.Ni Al₂O₄ causes the coating surface to wrinkle and fall off.When the thickness of the substrate is 1.0 mm,the surface results are the best.The following changes occur in the cross-section of the system due to the diffusion of elements.The appearance and disappearance of the off-white structure.The surface dissipation of the Mo element leads to a decrease in the thermal corrosion resistance of the matrix.Thermal evolution and growth.Among the elements,the diffusion rate of Ni element is the fastest,and the diffusion rate of refractory metal element is slow.（4）The static oxidation of the IC21 substrate and the Re Pt Al coating sample at 1150℃shows that when the substrate thickness is 0.6mm,the damage caused by the oxidation of the coating surface is small,and the cross-sectional Re barrier diffusion band prevents Mo from diffusing into the coating.The highest content of elements in the Re band is 39.47%;when the substrate thickness is 1.0mm,the coating surface peeling phenomenon is the most serious.When the substrate thickness is 1.5mm,aluminum oxide is generated in the Re resistance diffusion zone,and the oxidation reaction proceeds to 75h.The length of the needle-like TCP phase is about 1800 nm,and the width is about 200 nm.At this time,the refractory metal in the matrix forms a large amount of new phase precipitation.An oxide film is formed on the surface of the coating while consuming the Al element.The Al content in the coating decreases and the phase structure changes.The phase structure of the coating surface gradually changes from theβ-Ni Al phase to theγ’-Ni3Al phase.