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Numeric Simulation and Experimental Study of Rapid Processing of Copper Coatings on AIN Ceramics

Author: ShuFengYuan
Tutor: ZhaoHongYun
School: Harbin Institute of Technology
Course: Materials Processing Engineering
Keywords: AlN ceramics Rapid Preparation Copper cladding Laser Cladding Plasma spraying
CLC: TG66
Type: Master's thesis
Year: 2010
Downloads: 59
Quote: 0
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Abstract

To reach the the prepared copper cladding in AlN ceramic surface quickly prepared copper cladding purpose, the text of the calculated AlN ceramic surface quickly prepared copper cladding temperature conditions under which the laser cladding, laser cladding prior to the test The numerical simulation of laser cladding process, optimum test process parameters based on the laser cladding trials. After the test methods and process adjustments are made, using the lower heat source energy density plasma spraying process Preparation of copper cladding, and two preparation process results analyzed. (1) a protective gas in the flow of the material surface boundary layer and the thermal boundary layer thickness ratio 0.625; establishing and solving the basic equations of the surface of the material in high-energy heat source processing engineering the basic Newtonian fluid gas protection, thus deriving the thermal boundary the distribution law of the layer; protective gas inflow moment, the thickness of the thermal boundary layer of approximately 0.4mm, thermal conductivity of 600W / m or more, after which thermal conductivity is decreased rapidly, the minimum value of about 125W / m · K, the distribution of the radiation coefficient fitting, the radiation coefficient is the reciprocal of the high-order function on moving coordinates. Quantitative characterization of such dynamic convective heat transfer problem is transformed into a static heat conduction problems, providing new ideas for solving the high energy beam processing convective heat coefficient. (2) numerical simulation, dynamic simulation of laser cladding process. Identify the best range of process parameters in the effective laser power, scanning speed and preheating temperature were 750W, 7mm / s and 800K nearby. With the increase of the effective laser power, the node warming velocity becomes large and the cooling rate is reduced, the maximum principal stress becomes large, the stress is reduced speed; increasing preheat temperature can also reduce the heating rate and cooling rate, so that the maximum main stress value becomes larger, the stress-reducing speed; increase the scanning speed can be reduced the rate of temperature increase, but the cooling rate will become larger. Laser cladding AlN ceramics process can be taken to improve the process measures include the higher the preheating temperature, the smaller the laser power and the scanning speed is reduced by lowering the scanning speed, when the effective power is less than 738W can directly reduce The stress value, can reduce the maximum temperature change rate is used to improve the scanning speed when the effective power higher than 868W to indirectly reduce stress value. In addition, through numerical simulation preheated material and the end of the introduction of the starting point for the laser cladding process, the actual production slow cooling materials in order to reduce the likelihood of the occurrence of cracks. (3) Test findings with respect to plasma spraying, the energy density of the laser beam is great, resulting in the generation of micro-ablation role. Cause dilution of the copper cladding, also play a positive role in the transition layer thinning, you can achieve a combination of high-quality. Large energy density of the laser beam can lead to the AlN substrate burst, the combination of cladding sample can be obtained by adjusting the process parameters. Such as plasma spraying of cracks depends on the control of the plasma spraying process, the thicker side cladding layer prone to cracking between the substrate and the cladding layer, after the spraying process should try to ensure uniformity of the sprayed layer, preheat fully subjected to plasma spraying can be obtained not only the binding force to meet the actual needs of the sprayed sample, and also avoid the generation of cracks of the substrate, so it can be taken after the first spray of laser cladding method for the preparation of AlN surface copper cladding.

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