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New coating materials for high performance cutting tools

Deliverables

Films with different compositions within the B-C-N system have been grown by Ion Beam Assisted Deposition (IBAD) using two e-beam sources to evaporate simultaneously boron and carbon under concurrent N2+ assistance. This technique allows full control of the B, C, and N fluxes impinging to the substrate surface, so that a wide range of different BCN coating compositions can be obtained. Using this system, we have deposited coatings with the BCxN composition (x between 0.25 and 4) showing a hexagonal-like structure. These coatings show hardness values around 20 GPa, regardless the C content in the films. Higher hardness values (30 GPa) have been obtained for B4CNx films (i.e., B4C with increasing amounts of N). The wear rates of BCxN coatings with 1 m thickness decrease with the C content, from 10-6 mm3/cycle for 20 % C (i.e. close to TiN films) to 10-8 mm3/cycle for 80 % C ( ta-C films), with not delamination after 100.000 cycle in the wear tests. The friction coefficient in the BCxN coatings varied between 0.18 and 0.35, which is close to the values found in ta-C.
TEKNIKER focussed its work on multilayers based on CrN alternating with AlTiN and interlayers of CrAlTiN to improve the adhesion between them. This coating showed very good oxidation behaviour at temperatures in the range of 700?C-900?C. Adherence scratch tests showed critical load of 60N for TEK011 and about 80N for TEK012, in both cases no delamination or spalling was observed. Rockwell C adherence test corroborated these good results. Plastic hardness of the multilayer was about 50 GPa (taking account of the elastic recovery) with a Young/s modulus of 450 GPa and 66% of elastic recovery. Different AlTiN and AlTiN/CrN based multilayer processes were chosen to analyse the reliability of coating processes in terms of adherence, hardness and thickness. After scaling up the deposition processes to an industrial size PVD chamber, the variation ranges of these coating materials were established as follows. Chemical composition: Cr 25±2 at.%; Al 19±2 at.%; Ti 6±0.5 at.%; N ~50 at.% Thickness of each monolayer period: ~12 nm Total thickness: 2.6 ±0.1 μm Hardness: 26 ± 4 GPa.

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