Improvement of Adhesion Strength of the Sprayed Material

摘要

The effective way of enhancing resistance to deterioration of the parts is the change of surface properties due to coating with the required properties.Since the deposition process takes place at an elevated temperature,it is necessary to ensure the absence of phase and structural transformations in the metal,mixing of materials,changes in the chemical composition of the coating.The use of plasma spraying at the transport management facility showed a sufficiently high quality of the coating.However,the metallographic analysis showed the presence of discontinuities at the interface in the form of pores,oxide film and sections of decarburized steel.In the case of the process of melting-spraying,the overheating areas of the base metal are formed,which leads to disadvantages similar to the deposition process.To ensure the minimal thermal impact on the part,the thermal field calculations are required.For this purpose,the time of local melting of the part by a single-phase plasma jet was calculated.The temperature field of a part in which heat is transferred by thermal conductivity,the solution of the differential equation of thermal conductivity is described.The boundary conditions of three genera are formulated.The first kind is the distribution of temperature on the enclosing surfaces.The second kind-the task on the surface of the part of the heat flux density.The third kind-setting the temperature of the medium,which acts as a plasma jet,washing the surface of the part,and the intensity of heat exchange.The mathematical model of melting of the product is constructed.The formula for calculating the reflow time is derived.The temperature distribution expressions for the molten and solid zones are obtained by the solution of the problem with moving boundaries by the Fourier's method.On the basis of theoretical calculations it is proposed to increase the strength of the sprayed layer with the base to apply the process of plasma spraying with preliminary local melting by periodic exposure to a single-phase plasma jet.