1. TiN and TiAlN coatings improve dry cutting
capability of the M2 HSS drills even under
aggressive machining conditions.
2. Although TiAlN coatings have high oxidation
resistance and relatively low friction
coefficient TiN coating was found to be
superiour than TiAlN coating as number of
holes drilled under the conditions used in this
study. It can be attributed to larger
compressive stress of TiAlN coating which
leadsearly coating layer abrading-off under
aggressive conditions.
3. However, the resulting holes formed by TiAlN
coated drills are a bit smoother than those
formed by TiN coated and uncoated drills.
4. Main wear mechanisms of the drills are
coating layer abrading-off, micro-cracking of
the cutting edges, chip clogging and breakage
of the drills.
5. As the cutting conditions are very changeable
in drilling operations further machining tests
have to be done to understand the wear
properties of these coatings better.