Numerical Analysis And Experimental Study Of Modified Al-Si Coating By Laser Melt Injection CeO₂ Particles

The improvement of oxidation and corrosion resistance of metallic bond coat is a hot topic in the field of thermal barrier coatings?TBCs?under extreme conditions.With the continuous increase of working temperature and the increasing complexity of service environment,it will inevitably lead to higher and higher requirements for the corrosion resistance of metallic bond coat.In this paper,based on the review of the current research status at home and abroad and the technical of laser melt injection CeO₂ particles proposed by our previous research results,the GH4169 superalloy is used as the matrix,and the Al-Si coating is the research object.The numerical analysis and experimental study of modified Al-Si coating by laser melt injection CeO₂ particles were systematically investigated in order to provide a reference for the development of new metallic bond coat which can meet the working requirements under extreme conditions.The main work and achievements of this paper are as follows:?1?The process,microstructure and properties of A-Si coating on the surface of GH4169superalloy were studied.The optimum process parameters under the experimental conditions were obtained by orthogonal experiments.The microstructure and hardness of Al-Si coating were investigated,and the mechanism of solid powder embedding of Al-Si coating was also clarified.The results show that the optimal parameters of infiltrating agent are 20wt.%Al powder,10wt.%Si powder,68wt.%Al₂O₃ powder and 2wt.%NH₄Cl.The optimal parameters of infiltrating process are heating at 850?C holding for 4 h,then heating at 1050?C holding for 6 h.The thickness of Al-Si coating is about 250?m,and its surface quality is good.The main phases of coating are NiAl phase and Ni₂Al₃ phase.The structure of coating is compact and the surface hardness distribution is uniform,which can meet the needs of modification by laser melt injection CeO₂ particle.?2?The numerical analysis of temperature field of laser melt injection CeO₂ particle modified Al-Si coating was carried out.The temperature field model of laser melt injection CeO₂ particle modified Al-Si coating was established by COMSOL simulation software.The influence of laser process parameters on the temperature field and change law of temperature field under the same line energy were analyzed.The optimal process parameters were obtained.The results show that with the increase of laser power,the melting amount of CeO₂particles and the depth of molten pool increase,and with the increase of laser scanning speed and defocusing amount,that decrease.At the same time,the influence of laser power is greatest,the scanning speed is the second,and the defocusing amount is the smallest.The optimal process parameters obtained by the numerical analysis of temperature field in this paper are as follows:laser power is 600 W,scanning speed is 400 mm/min and defocusing amount is 0 mm.?3?The numerical analysis of stress field of laser melt injection CeO₂ particle modified Al-Si coating was carried out.Based on the analysis of temperature field,the stress field model was further established.The distribution of stress field was analyzed,and the influence of different laser process parameters on stress field and change law of stress field under the same line energy were studied.The results show that the stress change trend of the surface of preset layer is similar to that of the Al-Si coating.In the laser action stage,the stresses in the X,Y and Z directions first show tensile stress and then changes to compressive stress.In the cooling stage,the residual stress in the X direction is the smallest and the Y direction is the largest on the surface of preset layer,while the residual stresses in the X and Y direction are the smaller than that in the Z direction on the surface of Al-Si coating.Meanwhile,with the increase of laser power,the Von Mises stress on the coating surface also increases,while with the increase of laser scanning speed and defocusing amount,the Von Mises stress decreases.In addition,the laser power has the greatest influence on the stress field,followed by the scanning speed,and the defocusing amount is the smallest.?4?The experimental study on laser melt injection CeO₂ particle modified Al-Si coating was carried out.Based on the numerical analysis and the previous exploratory experiments,orthogonal optimization experiments were carried out to obtain the optimal laser process parameters.The phase composition,microstructure,element distribution and hardness changes of modified Al-Si coating were analyzed by SEM,EDS,XRD,OM and microhardness tester.Moreover,the hot corrosion behavior of Al-Si coating and modified Al-Si coating in chlorinated sulphate at 1050?C was investigated.The results show that the optimal process parameters under the experimental condition are as follow:laser power is 650W,laser scanning speed is 350 mm/min and defocusing amount is-1 mm.The CeO₂ particles were successfully injected into the coating,and the microstructure of modified Al-Si coating was refined and present cell-like growth.The high temperature corrosion resistance of modified Al-Si coating by laser melt injectin is better than that of Al-Si coating.