Exploitable results
The main aim of the project was to develop a range of coatings based on the C-B-N system which would have high hardness, low friction and low wear and that these coatings could be used for high speed machining where temperatures up to 800 degrees Celsius could be developed. The results achieved show that the coatings (carbon-based coatings) developed in this project satisfy most of the required properties, such as high hardness, good adhesion to substrate, very low friction and very low wear rate at very high load.
In addition, the coatings also provide protection of the opposing surface during sliding or moving between connecting partners. It is expected that these new coatings will certainly find application not only in cutting tools but also they will have wider range of applications (forming tools, dies, punches, gears, and other mechanical components) than the conventional hard coatings (TiN, TiC, or TiCN).
The coatings have been produced by unbalance magnetron sputtering. Process development was made on flat substrates and then extended to systems suitable for the large scale coating production on practical three-dimensional tools and other mechanical components. They were finally tested under working conditions on drilling and hobbing operations.
The most significant results achieved to date are the following:
- Carbon coatings have been deposited with hardness ranging from 1500 HV up to 4000 HV. It is possible to control the properties of these coatings by control of the deposition parameters in order to obtain the best tribological properties (low friction and low wear rate at high load). These coatings, as tested by high temperature pin-on-disc, are stable at temperature up to 400 degrees Celsius, comparing with TiN coating which failed at 200 degrees Celsius using the same conditions. At room temperature, it will hardly measure the wear of the pure carbon if the load is low (< 10 N);
- Carbon/chromium multi-layer coatings have been deposited with hardness around 2000 HV and tribological properties similar to carbon coatings, however, with a large improvement of the load bearing capacity and toughness. The most important tribological properties are low friction and low wear rate at high load (up to 140 N used for load in pin-on-disc);
- CBN coatings with metal additions (Cr, Ti), forming a composite (or multilayer) coating, have been deposited with hardness around 2300 HV, very good tribological properties and high load bearing capacity in dry and even better in plain water and oil. Also these coatings have very important tribological properties (low friction and low wear at high load);
- The coating system has been developed using three-fold rotation substrate turntable to produce uniform coatings on three-dimensional items such as drills and hobs. The deposition process has been scaled from small coating system to large coating system to produce the coating with similar properties;
- The drill tests in dry indicated these coatings outperformed commercial TiN coated drills by about 3.5 times. The hob tests in dry appeared to show the hobs with carbon based coatings were at least two times better than that with TiN coating in terms of cutting speed and feed rate.
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