Study On Preparation Of NiCr/Al High Temperature Coating By Surfacing And Spraying Composite Method

With the rapid development of aviation technology,the performance of materials at high temperature continues to put forward new performance requirements.High temperature oxidation of the working environment,far more than the general use o f materials and alloys limit temperature,so the preparation of high temperature oxidation of new materials has become an important direction of material research.Thermal spraying technology plays an important role on the field of aviation.Spraying high temperature oxidation resistance coating on the metal substrate can increase the heat resistance and high temperature strength of the materials,so as to improve the reliability,to reduce the loss and to prolong the life of the materials.Firstly,TIG welding method was used to deposit NiCr layer on the stainless steel surface,and then arc spraying technique was used to spray a layer of Al coating.Then the coatings were heated at the temperature of 1100? in the resistance furnace.Scanning electron microscopy(SEM),X-ray diffraction analysis(XRD)and energy spectrum analysis(EDS)were used to study the oxidation resistant coating composition and microstructure.Taken advantage of thermal gravimetric analysis technique stud ied the anti-oxidation mechanism and high temperature oxidation coatings failure mechanism.Then the diffusion mechanism by means of Fick's second law was analyzed.The diffusion coefficient of element was calculated by least squares method.From the NiCr/Al coatings results,it shows that NiCr coating and the substrate form a good metallurgical bond,but the Al coating present s some small pores during spraying process.In the process of oxidation,a dense oxide film is formed on the surface of the coating,and spray coating of Al element diffuse to the NiCr surfacing layer.Throughout the heating process,NiCr surfacing layer oxygen element is almost not found,so it proved that the outer coating plays better protection.By calculating the Al diffusion coefficient,the diffusion coefficient decreases from 3.15 × 10-15 m / s to 0.8 × 10-15 m / s with the diffusion depth increasing.The test results show that the surfacing and spraying NiCr/Al composite coating at a constant temperature of 1100? oxidation kinetics meet Wagner parabolic law,and it has good resistance to high temperature oxidation and hot corrosion.It can solve the thermal barrier coating failure problem of single layer which was caused by the diffusion of the Al element to surface coating.