In-Situ Characterization Of Mechanical Properties Of EB-PVD Thermal Barrier Coatings Under High Temperature

Thermal barrier coatings?TBCs?,as important hot end protection components for aero engines and gas turbines,are widely used in engine nozzles,blades and other key parts,which can effectively increase their service temperature and greatly extend the service life of hot end components.With the continuous pursuit of high thrust and high thrust-to-weight ratio engines,the service temperature of thermal barrier coatings will continue to increase,which puts forward higher requirements for the reliability of thermal barrier coatings at high temperatures.Mechanical properties,as the basic properties of thermal barrier coatings,are indispensable key parameters for the reliability evaluation of coatings.At present,researchers have fully researched the mechanical properties of thermal barrier coatings at room temperature,but little is known about the research on the mechanical properties of thermal barrier coatings at high temperatures.With regards to this,this article independently built a three-point bending test platform under high temperature environment,combined with two advanced non-destructive testing techniques of acoustic emission testing technology and digital image correlation method,to achieve the load-displacement curve and the acquisition of critical parameters in the fracture process of the thermal barrier coating at high temperature,finally the key mechanical parameters of the thermal barrier coating were characterized in situ in real time by appropriate mechanical model,and the fracture process of the thermal barrier coating was analyzed by SEM.The main research contents include:1. Using the self-built high-temperature environment three-point bending test system as an experimental platform,the evolution law of Young's modulus of the substrate and EB-PVD thermal barrier coating with temperature was studied.The test results show that as the temperature increases,the Young's modulus of the GH536superalloy substrate gradually decreases,from 124.866 GPa at room temperature to77 GPa at 800?.The Young's modulus of the ceramic layer shows the same law.The Young's modulus of the ceramic layer gradually decreases from room temperature to 800?,respectively 64.013 GPa and 22.107 GPa.The test results show that the stiffness of the ceramic layer will decrease and the plasticity will increase at high temperature.2. Using the self-built high-temperature environment three-point bending test system as an experimental platform,the evolution law of the surface fracture toughness of the EB-PVD thermal barrier coating with temperature was studied.Since the ceramic layer of the EB-PVD thermal barrier coating has a typical columnar crystal structure,it was found during the experiment that the vertical surface cracks inside the coating were actually open columnar crystal gaps and formed after the bond coating cracked.As the temperature increases,the critical strain required to produce vertical cracks on the surface gradually increases.The surface fracture toughness showed the same law.With the increase of temperature,the surface fracture toughness increased from 1.96 MPa?m^1/2 at room temperature to 4.52 MPa?m^1/2 at 800?.During the experiment,it was found that the bond coating had toughness-brittle transition phenomenon.3. Using the three-point bending test system built under the high temperature environment as the experimental platform,the evolution law of the fracture toughness of the ceramic coating/bond coating interface of the EB-PVD thermal barrier coating with temperature was studied.Under the action of bending load,no cracks were found at the interface of the ceramic layer/adhesive layer,and transverse cracks appeared at the interface of the adhesive layer/substrate.The samples treated with oxidation at1100 ?for 50 h were found to have cracks in the interface between the ceramic layer and the bonding layer at room temperature.The critical energy release rate of the interface of the EB-PVD thermal barrier coating was 29.28 J/m² calculated by the Suo-Hutchinson model.As the temperature increases,the EB-PVD thermal barrier coating shows a higher resistance to bending load damage,and no interfacial cracks are found,which indicates that the EB-PVD coating has a higher critical energy release rate at high temperatures.