EVALUATION OF SOME TITANIUM-BASED CERAMIC COATINGS ON HIGH-SPEED STEEL CUTTING TOOLS

Titanium-based ceramic coatings, comprising Ti(B,N) and (Ti,Al)N, were produced by d.c. plasma-assisted electron beam physical vapour deposition and r.f.-magnetron sputtering on high speed steel (HSS) tools. Longitudinal turning tests were carried out using the international standard procedure ISO 3685-1977. HSS tool inserts were employed to cut calcium-treated (MoCN 206 M) cementation steel. The main cutting fluid was an emulsion with good cooling properties. Comparative drilling tests and turning tests with conventional (MoCN 206) cementation steel and aluminium alloy workpieces were also carried out as well as tests with a cutting fluid containing EP-additives. Reference materials in cutting tests were uncoated and commercially TiN coated HSS inserts. The new titanium-based coatings improved the tool life considerably even when compared with TiN coated tools. In particular, (Ti,Al)N coatings showed excellent resistance against flank wear in steel cutting conditions, improving the wear resistance of HSS tools two to three times when compared with TiN. Ti(B,N) coatings also had encouraging initial results, although variations in thickness and the brittle nature of the coating deteriorated their performance. The failure mechanisms of the new coatings differed to some extent from those observed with TiN coatings in metal cutting.