Bias voltage and incidence angle effects on the structure and properties of vacuum arc deposited TiN coatings

TiN coatings were deposited on WC-Co bar substrates using a vacuum are plas ma gun connected to a cylindrical plasma duct in which an axial magnetic fi eld was imposed. During deposition, the cathode are current was 200 A, nitr ogen pressure was 0.67 Pa, and the substrate temperature was 420 degreesC. Substrate bias voltage (V-bias) was varied in the range of -40 to -600 V. T he coating structure and properties were studied both on the sample face su rface, i.e. normal to the plasma flux, and on its side surfaces. The struct ure and phase composition were studied using scanning electron microscopy ( SEM) and X-ray diffraction (XRD). Microhardness and scratch critical load w ere studied using Vickers micro-indentation and scratch tests, respectively . The TiN coatings had a single-phase cubic delta -TiN structure and consis ted of oriented columnar grains. No difference was observed in the preferre d grain orientation and grain size at the substrate-coating interface for t he coatings deposited on the face and the substrate side surface for every studied Vbias. The deposition rate decreased both on the face and the side surfaces, while the ratio between deposition rates on the face and the side surfaces increased from three to seven times when \V-bias\ increased from 40 to 600 V. With increasing \V-bias\, the preferred orientation of the col umnar grains changed from a mixture of (200) and (111) at -40 V to a strong (111) at -200 and -400 V. At -600 V, (111) remained dominant, while the (2 20) orientation also appeared. Increasing \V-bias\ increased the grain size on the coating surface. A zone of equiaxed grains was observed near the su bstrate-coating interface, whose thickness increased with increasing \V-bia s\. Possibly, the grain size growth was a thermal effect due to an increase in ion beam heating with increased \V-bias\ The grain size on the side sur faces was smaller than that on the face. The coating surface roughness and friction coefficient were smaller on the side surfaces than those on the fa ce, while no differences in microhardness were observed. (C) 2000 Elsevier Science S.A. All rights reserved.