Structural investigation and wear resistance of submicron TiN coatings obtained by a hybrid plasma immersion ion implantation process

Ile ever increasing demands for high precision machining and increased cutt ing performance, in terms of cutting speed and lifetime, require wear resis tant tools of large dimensional accuracy that have very sharp cutting edges . All these requirements cannot be fulfilled by the classic PVD and CVD tec hnologies because they result in rather thick overlay coatings. In this rep ort, first experiments are presented on a hybrid plasma immersed ion implan tation process (PIII) for depositing thin TiN coatings on hardened and anne aled high speed steel or cemented carbides. The layers were produced using a d.c.-cathodic arc source with a titanium cathode and a nitrogen feed gas. As the cathodic arc generates additional to the metal plasma, a large amou nt of liquid metal droplets, the plasma was guided to the samples through a 90 degrees magnetic bending field avoiding the deposition of droplets on t he samples. The obtained layer thickness was below 1 mum for deposition tim es of 2 min. To improve the adhesion of the deposited layers on the substra te materials, sputter cleaning by energetic ions was used during the initia l phase of the process. Negative high voltage pulses in the range from zero to 5 kV have been applied to the samples during the deposition. The effect of the energy of these ions on the coating structure was also investigated by SEM, TEM and XRD. Mechanical and functional properties were investigate d by hardness measurements and fretting wear tests, respectively. Finally, cutting performance tests of PIII-treated drills were performed, revealing that a 0.8-mum thick TiN PIII-coating increased the lifetime of the drills by a factor of 2.5. (C) 2001 Elsevier Science B.V. All rights reserved.