| To achieve the purpose of rapid preparation of AlN ceramic surface coatingof copper , the article calculated the temperature of rapid preparation of AlNceramic surface coating of copper. Then the coating of copper was made bymeans of laser cladding and numerical simulation of laser cladding process wasused before the laser cladding technique test.The optimum test parameters wasthen obtained,by which laser cladding technique test was conducted.Manufactureing method and technique was then adjusted and lower energydensity heat source such as plasma spray was adopted as a result to prepare thecoating of copper and the results of the two methods was analysed at last.The thickness ratio of shielding gas between flow boundary layer andthermal boundary layer is 0.625.The fundamental equations of Newtonian fluidof gas which protects the surface of materials in the high-energy heat sourceheating process was established and then solved. The distribution of thickess offlow boundary layer was obtained and that of the heat boundary layer wasachieved subsequently.The moment the shielding gas flew in,the thickness ofthermal boundary layer is about 0.4mm and thermal conductivity coefficient(TCE)is more than 600W/m·K,then it decreased rapidly,the minimum is about125W/m·K.Then the distribution of the thermal coefficient was fitted, thermalcoefficient is reciprocal of high-order-function about moving coordinate.By thisway a dynamic convection heat transfer problem was transformed to be aresearch of quantitative characterization of static thermal conductivity, whichprovides a new ideas of for solving surface heat convection coefficient in a highenergy beam process.The numerical simulation realized the dynamic simulation of laser claddingprocess. It was found by analysing temperature and stress field of AlN substratethat optimum parameters as the effective laser power, scanning speed andpreheating temperature were around 750W, 7mm/s and about 800K.Heating rateof the nodes was made larger and cooling rate was decreased by increasing theeffective laser power and the maximum principal stress was made larger of whichthe dropping rate was accelerated;Increased preheating temperature resulted in reduced heating rate,reduced cooling rate,increased maximum principal stressand reduced dropping rate of the stress.Therefore,the measures taken in lasercladding process of AlN ceramic to improve the process included the adoption ofa higher preheat temperature or a smaller laser power.The maximum principalstress could be cut down directly by a smaller scanning speed when the effectivepower was larger than 738W or indirectly by a larger scanning speed when theeffective power was smaller than 868W as a result of a decreased maximumdropping rate of temperature.In addition, it was shown from numerical resultsthat for the laser cladding process, preheating materials at the beginning and slowcooling material at last should be introduced in actual production to reduce thelikelihood of cracks.It was found that, laser cladding was more likely to led to micro-ablationbecause of the significantly high energy density compared to plasmaspraying.The high energy density played an active role on thinning of thetransition layer resulting in a high quality bonding. High laser beam energydensity also led to a surface micro-cracks of AlN substrates.It was available toobtain good samples by adjusting the process parameters of the cladding process.Plasma spraying cracks was decided by the control of the plasma spray process.Itwas more likely to crack on the the thicker side of sprayed layer, therefore,uniform coating layer should be ensured in the spraying process.Samples withoutmatrix cracks that meets actual needs could be obtained by laser spraying afterfully preheated.The process of spraying followed by laser cladding wasrecommended to obtain surface preparation of copper.
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