Application Of Thermal Shock Resistance Of Atmospheric Plasma Sprayed Thermal Barrier Coating

Since the 21st century,China’s automobile industry has achieved rapid development.Cars have quickly entered the homes of ordinary people,and the demand has increased year by year,which promotes the development of the automobile industry.In response to the green industrial revolution of carbon peak and carbon neutralization,it is urgent to increase the thermal efficiency of the engine,and only one third of the energy generated by the fuel in the engine is used for useful work.Therefore,people have conducted extensive research on how to reduce the loss of gas energy.Based on the thermal barrier coating has good thermal insulation characteristics,and increasing the piston surface temperature can improve the thermal efficiency of the engine,the thermal barrier coating is prepared on the piston and gas turbine surface by atmospheric plasma spraying process,and a series of performance tests are carried out to study the failure mechanism of the thermal barrier coating.The main research results are as follows:Firstly,the three-dimensional diagram of the piston is drawn by Solid Works,and then the steady-state thermal analysis simulation of the piston is carried out by ANSYS.The temperature field distribution of aluminum alloy and cast iron piston was studied.The results show that there is a difference in temperature before and after spraying thermal barrier coating,which shows that thermal barrier coating can play a good heat insulation effect.By referring to relevant literature,four kinds of bond coating materials are selected,namely Nickel clad aluminum powder(JZGR-502F),Ni Co Cr Al Ta Y(Amdry 997),Ni Cr Al Y(Amdry 962),nickel 5%aluminum(Metco 450NS),nickel 20%aluminum(Metco 404NS),and the ceramic coating material is 8YSZ.Thermal barrier coatings were prepared on the surfaces of aluminum alloy,cast iron piston and steel sheet by atmospheric plasma spraying process.The relevant characteristics of the powder and coating were observed by X-ray diffraction,scanning electron microscope and thermogravimetric differential thermal analyzer.Oxygen-acetylene flame impact test proves that thermal barrier coating has good thermal insulation,which can reduce the surface temperature of the piston and protect the piston crown.Through the thermal shock test of aluminum alloy piston and cast iron piston,the failure form and failure mechanism of coating are analyzed.It is found that the surface of aluminum alloy and cast iron piston does not fall off after 70 times thermal shock tests,indicating that the four bond coats materials can be used as the bond coating of thermal barrier coating,and can operate for a long time;the thermal shock test temperature was increased from 550~oC to 800~oC.After the thermal shock test of cast iron piston,it was found that the thermal shock life of thermal barrier coatings with bond coatings of Metco 404NS and Metco 450NS was shorter,only 12 and 19times,while that of thermal barrier coatings with bond coats of Amdry 997 and Amdry962 was 70 times,indicating that the high temperature resistance of these two bond coatings was better than that of Metco 404NS and Metco 450NS.There are two main failure modes of the coating in this thesis.One is the overall falling off between the bond coatings and the piston matrix.The reason for this phenomenon is that the edge angle at the top of the piston is relatively sharp,and the sprayed thermal barrier coating will produce the problem of stress concentration;in the process of thermal shock test,the temperature changes sharply,resulting in the formation of high temperature tensile stress and low temperature compressive stress between the substrate and the bond coats,which eventually leads to the fallen off of the interface between the substrate and the bond coats.The way of falling off is relatively rare,mostly due to the mismatch between the thermal expansion coefficient of the bond coats material and the piston substrate.The other failure mode is the interlayer fallen off between ceramic coats.The reason is that the prepared thermal barrier coating adopts atmospheric plasma spraying process.The coating is a typical layered structure,and there are microcracks,pores and other defects.With the continuous increase of the number of thermal shock tests,the thermal stress in the coating increases,and the main part of the stress is the defect in the coating,the crack at the defect expands further on the basis of thermal stress.When it exceeds a certain critical value,the coating will fall off.Finally,the thermal barrier coating is prepared on the surface of gas turbine parts,and the test run is carried out.The tensile test and hardness value of the prepared sample are tested.The results show that the coating does not fall off after the test run,and the bonding strength and hardness value of the thermal barrier coating meet the standard requirements,indicating that the thermal barrier coating can withstand high temperature environment and meet the requirements.