DRY CUTTING PERFORMANCE OF HSS TWIST DRILLS COATED WITH IMPROVED TIALN

PVD TiAlN coatings have been known for 10 years, particularly because of their high oxidation resistance. This specific property favours the m in dry cutting operations. Ti0.4Al0.6N coatings grown by combined st eered arc!unbalanced magnetron (UBM) deposition show a considerable co ncentration of growth defects stemming from the adhesion enhancing cat hodic are TiAl metal ion-substrate etching prior to the UBM magnetron coating step. Thus the roughness of 3 mu m thick purely UBM deposited TiAlN coatings is enhanced from R-a=0.04 mu m to R-a=0.18 mu m. The ro ughness of these coatings may be reduced to R-a=0.05 mu m, if Cr is us ed as metal ion etching vapour instead of TiAl. The hardness of Ti0.4A l0.6N coatings can be increased from typically HK3000 to approx. HK330 0 by adding C (reactively) into the near surface region of the him. La boratory and industrially scaled dry drilling tests have been carried out in cast iron GG25. Reducing the surface roughness of the coatings doubles the lifetime of ADX drills when operated at 60 m min(-1) cutti ng speed. The lifetime is further doubled by the addition of C. In pro fessional and industrial drill tests the new ''smooth'' TiAlN coated d rills clearly outperform most of the purely are coated tools.