| Thermal barrier coatings(TBCs)prepared technology is the third key technology in advanced aero-engine and heavy-duty gas turbine,which is as important as high-temperature structural materials and efficient cooling design.At present,there are two main industrial applications:atmospheric plasma spraying(APS)and electronic beam physical vapor deposition(EB-PVD).APS TBC has layered structure,good thermal insulation performance and low preparation cost,but its thermal cycle life is low;EB-PVD TBC has columnar crystal structure,high thermal cycle life,poor thermal insulation performance and high preparation cost.The limitations of the two processes limit their application.In recent years,suspension plasma sprayed(SPS)thermal barrier coating has the advantages of the two kinds of coating,such as high coating life,good thermal insulation,low preparation cost and not limited by equipment size,atmosphere and other conditions.It is considered as one of the potential thermal barrier coating preparation technologies,and has become a hotspot in the research field of TBCs.The fundamental difference between SPS and traditional APS is that the melting medium is changed from powder to slurry,which requires high power of plasma spraying equipment and high efficiency of slurry injection,and a good match between the two abilities is needed to prepare reliable coating.However,most of the current researches are limited to the research of the related process and coating performance under a specific equipment,and lack of hardware matching research.During radial feeding,the process parameters are sensitive due to lower power;or the different of slurry injection characteristics,their research results are different;In axial feeding,the SPS equipment is different from traditional plasma equipment,so it is not of universal significance.All of above limit the application of SPS.At present,there are no researchers to study the coupling effect of plasma and liquid injection,the influence of liquid injection on the coating structure,and no researchers to evaluate the radial feeding and axial feeding methods under a unified standard,pointing out the different direction of process optimization under the two forms.Aiming at the essential problem of the matching between plasma spraying equipment and feeding characteristics,this study simulated the influence of liquid injection characteristics on plasma field in two modes of axial feeding and radial feeding,and verified the relevant results by experiments.Finally,the expected TBC that have excellent structure and performance were obtained.The specific research contents and achievements are as follows:(1)With the help of Fluent software to deal with the computational fluid dynamics(CFD)related models,the three-dimensional transient mathematical model of spraying process is modeled and meshed in Meshing environment.The mathematical model of multiphase jet flow field formed by plasma spraying was established by Eulerian method,and the boundary conditions,thermophysical parameters and physical model settings of the model were determined.(2)The heat transfer and flow characteristics were simulated by using the established mathematical model.The effects of feed position,feed velocity and feed direction on plasma jet velocity and temperature were obtained;The influence of feeding speed on plasma jet velocity and temperature in axial feeding was studied.(3)The effects of radial feeding distance,liquid concentration and feeding speed on the microstructure of the coating were obtained;The effects of feeding distance,liquid concentration and feeding speed on the microstructure of the coating were investigated.The experimental results confirm the interaction between plasma and feed characteristics,which can be used to optimize the coating structure.(4)According to the calculation results,the expected coating structure is obtained,and the performance of the coating under the designed structure is verified:except that the thermal cycle life of the coating still has room to improve compared with the existing industrial level,the bonding strength,thermal shock performance and thermal shock performance of the coating are better than APS thermal barrier coating,and similar to EB-PVD Thermal barrier coating.(5)The influence of feeding characteristics on coating structure can guide the design of slurry feeding device.It can also guide the structure design and process optimization of the coating under the specific plasma spraying equipment and feeding mode. |
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