TiC/a-C:H coatings were deposited using closed-field unbalanced reactive magnetron sputtering deposition from Ti targets. Different acetylene gas flow and substrate bias values were employed to vary the coatings' compositions and microstructures. The application of an external negative substrate bias increased the deposition rate of the plasma-enhanced chemical vapor deposition process from the reactive atmosphere. The sputtering of carbonaceous species from the poisoned targets surface was a minor source of C flux to the substrates. The application of an external substrate bias during deposition yielded films with a featureless cross-sectional structure, but the dominant parameter controlling the columnar growth was the chemical composition of the films. An explanation of this effect was formulated based on the microstructures observed and the deposition technique employed. (c) 2006 American Vacuum Society.