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Technology and application of alumina coatings by arc and magnetron sputtering

Alumina film has many excellent properties of materials, especially high temperature stability, chemical stability and low thermal conductivity. Now the alumina film is widely used as a wear resistant coating material on cemented carbide inserts. As with these excellent properties, but alumina film has not been widely applied to other areas, the main reason is the industry standards of today is still built on the basis of in the thermal chemical vapor deposition (CVD) technology.
Although the CVD process has many advantages, but there are obvious shortcomings, that is, the process requirements of the high temperature (1000 C). Weyerhaeuser company develops out a new technology, can in standard temperature of 350 to 600 DEG C by physical gas phase deposition sputtering PVDsputtering deposited alumina. This is greatly expand the its scope of application.
Since the 2005 Hauser in the European Machine Tool Exhibition emo announced Al2O3 PVD coatings made a major breakthrough, Hauser began with the world's major tool manufacturing business and alumina modulus cast mold the user cooperation projects to test. The coating properties are discussed, and the results of this new coating obtained by the combination of arc and magnetron sputtering techniques are presented.
Tool wear condition
During the process of machining, there are several kinds of tool wear. Tool itself must be able to withstand high temperature, high pressure, wear and thermal shock. During the cutting process, the edge temperature will be more than 1000. In this high temperature, the adhesive and other components of the tool will degenerate, and lead to harmful chemical reactions between the tool and the workpiece. Cutting process is always accompanied by the occurrence of friction, cutting tool and the workpiece when the pressure is greater than 140bar (2000PSI).
Heat shock - cutting tool is urgent and hot, which is a common occurrence in milling process. The blade is heated in the cutting process, cutting surface when cooling in the left. There is a mechanical impact on the surface of milling and cutting. Sometimes there will be mechanical impact in the turning, the specific operation and the conditions of the workpiece is different. Bond wear occurs when the work piece is bonded with the tool (producing a built-up edge).


CVD and PVD alumina coatings
Today CVD alumina coated inserts are widely used in industry, and the properties of CVD alumina coatings are widely recognized. Due to the high hardness (especially in the high temperature), high oxidation temperature (>1000 degrees C), chemical inertia and low thermal conductivity, the performance of the alumina coated tool has been greatly improved. However, CVD process usually needs to be carried out at a high temperature of 800 degrees Celsius to 1000 degrees Celsius, which limits the application of CVD technology on the base of hard alloy. Due to the hard alloy tool brittle will lead to the reduction of toughness. PVD process for its 400 to 600 DEG C low deposition temperature, compared with the CVD process has obvious advantages.


In a PVD process production alumina coating the main limiting factor lies in the deposition process of insulating layer deposition within the coating system on all surfaces, which comprises a bottom base and the bottom of the base and target erosion surface outside the target and vacuum chamber wall. This will lead to the target of "poisoning" and the anode and cathode bias power disappear caused (ARC) unstable power supply. The two techniques to solve this problem are: RF (radio frequency) sputtering and BP-DMS (bipolar pulsed double magnetron sputtering).
Alumina coating equipment


PVD alumina system should be able to deposit a minimum of gamma alumina with a high deposition rate (short working cycle), and has a stable coating properties. The system should be able to operate at high temperature and the cost of technology itself is not high. It is best to use a single cathode system, so that the existing equipment can be upgraded to a coating of alumina coating equipment. Hauser, T - mode control system, the target surface in the oxidation deposition process in the transition state, which requires special cathode design and closed field unbalanced magnetron. In order to get the best reaction gas, a special control system is adopted. This system was verified on several production facilities in about two years.

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