Study On Alumina Ceramic Surface Laser Alloyed With Copper-based Alloy Powder

Ceramic materials have many excellent Properties, and they were widely applied to Power machine, mechanical trade, aerospace, heat exchanger, large-scale integrated circuit and electronic devices and components, etc. But because of its unavoidable disadvantage, the ceramic further extensive applications have been limited. so it is necessary to improve properties of ceramic surface and join to metal into complex part, and it is the main way extending their application.The ceramic surface layer modifyed by surface modification technology can be directly used not only as the middle layer in brazing or diffusion bonding, and surface treatment can change ceramic surface's crystal lattice structure, crystal defects, surface energy and surface stress state, wich can play an important role in improving the wettability of ceramic surface, the element diffusing capacity, in lowering welding temperature and increasing joint strength, etc.Copper alloying on the alumina ceramics was carried out by Nd:YAG pulsed laser, and analyzes the relationship between the alloy layer thickness and laser processing parameters. The test results shows that weld width and penetration have increase with the increased laser power or decreased scanning speed. The optimal parameters for the pulse width is 3 ms, voltage 75 V, frequency 20 Hz, defocus 11 mm, scanning speed 5 mm·s-1,with Argon as the protection gas, protection methods is the coaxial and the side protection, gas flow was 25 mm·s-1, 15 mm·s-1. A layer of copper alloy with good profile was deposited on the surface of alumina ceramics. the bonding between the copper alloy layer and the substrate is excellent, The thickness of alloy layer is relatively uniform with the average thickness of 40～50μm.α-Al2O3 and CuAlO2 was detected in the alloy layer, The CuAlO2 can substantially improve wettability between the copper and alumina ceramics. Because a large number of copper was burned, copper content is less than 20% in the alloy layer.The objective of this work is the development of a laser-supported process that allows to modify the properties of ceramics on a local scale. The principle of the process is based on local melting of the ceramic by a 5Kw continuous cross-flow CO2 laser and application of an copper additive to the molten area on the surface. The injection process and the pre-coating process have been established for embedding secondary phases in a substrate material by a laser surface modification process. The pre-powder method's optimum parameter for the laser power is of 450 W, scanning speed 10 L·min-1, defocus 20 mm, with Argon as the protection gas, protection methods is the side protection, gas flow was 15 mm·s-1. A layer of copper alloy with good profile was deposited on the surface of alumina ceramics, and the average thickness is of 150μm. CuO andα-Al2O3 was detected in the alloy layer, the CuO can substantially improve wettability between the copper and alumina ceramics. The injection process's optimum parameters for laser power is of 500 W, scanning speed 10 L·min-1, defocus 20 mm, with Argon as the protection gas, gas flow 12 L·min-1. Copper layer thickness can reach 180μm, including the copper area and metallurgical areas, copper is mosaic structure in ceramics, embedded depth is of 60μm. the alloy layer has a significant metal performance. As the ceramic substrate and the copper melting point is too large different, test analysis found that a lot of copper burned in the pre-powder method, and the injection process can avoid this phenomenon.In this study the mechanism of cracks was analyzed. The tin-bronze alloy powder was used to instead of pure copper powder, the test results show that alloy layer crack slowed for using the bronze.