High-temperature Thermal Fatigue Damage Mechanism And Life Prediction Of NiCoCrAlY/AlSiY Coatings

Aiming at the problem of high-temperature oxidation damage of aero-engine turbine blades,this topic takes the Ni Co Cr Al Y/Al Si Y coating prepared by arc ion plating technology on TC4 titanium alloy substrate as the research object,and comparatively studies the thermal residual stress,thermal residual deformation and crack damage mechanism of the coating under different number of high-temperature thermal cycles,and makes life prediction,in order to comprehensively evaluate the Ni Co Cr Al Y/Al Si Y coating prepared by arc ion plating and its effect on the service life of TC4 titanium alloy blade.The study was carried out by a combination of experiments and finite element simulations.In this thesis,Ni Co Cr Al Y/Al Si Y high-temperature protective coating was prepared on TC4 titanium alloy substrate using arc ion plating technique according to the design concept of functional gradient anti-corrosion protective coating.It was found by scanning electron microscopy that the Ni Co Cr Al Y/Al Si Y coating generates axial microcracks under high temperature cyclic thermal loading,and the cracks will continue to expand along the axial direction as the number of thermal cycles increases;the finite element simulation results found that under the cyclic thermal loading,the radial residual thermal stress on the surface of Al Si Y coating increases from 1.29 MPa to 5.18 MPa as the number of cycles increases MPa,the stress gradient increased to 5.29 MPa,and the axial residual thermal stress and shear residual thermal stress were almost zero;the value of radial residual thermal stress at the Ni Co Cr Al Y/Al Si Y interface increased from 3.35 MPa to 13.43 MPa,and the stress gradient increased to 16.15 MPa;the shear residual thermal stress increased from 8.64 MPa to 34.64 MPa,and the stress gradient The surface crack extension along the axial direction mainly occurs in the warming stage,and is dominated by the radial thermal stress S11 when the crack is extended in the Al Si Y layer,and is jointly dominated in all directions when the crack is extended in the Ni Co Cr Al Y layer;the sprouting and extension of the Ni Co Cr Al Y/Al Si Y interface crack mainly occurs in the cooling moment,and is mainly dominated by the radial thermal stress S11;the predicted thermal fatigue life shows that the minimum life of the specimen is 118 times without coating and 260 times after coating.The following conclusions were obtained from the study: Ni Co Cr Al Y/Al Si Y coating under high temperature thermal cyclic loading,the large radial residual thermal stress existing on the surface will lead to the sprouting of surface cracks and expand along the axial direction under the radial thermal stress inside the coating,and the stress direction is perpendicular to the crack expansion direction,which is judged as type I cracks,and when the cracks expand in the Ni Co Cr Al Y layer,the type When the crack expands in the Ni Co Cr Al Y layer,the type is compound crack;the large radial residual thermal stress and shear residual thermal stress at the interface will prompt the sprouting of radial crack at the interface,and the crack expands in the radial direction under the radial thermal stress inside the coating,and the direction of crack expansion is parallel to the direction of stress,which is judged as type II crack;comparing the life time of the specimens with and without coating,the life time of the specimens with coating increased by 1.2 times,indicating that this coating can effectively extend the life time of TC4 titanium alloy.The research in this thesis provides a comprehensive theoretical support for the design,preparation and application of the coating to extend the service life of hot-end components,increase engine power and reduce fuel consumption.