Microstructure of d.c. magnetron sputtered TiB2 coatings

TiB2 coatings were deposited onto cemented carbide substrates by d.c. magnetron sputtering using different substrate bias voltage, both positive and negative. Transmission electron microscopy, TEM, was used to investigate how the microstructure relates to deposition parameters. All coatings investigated were found to be crystalline with dense grain and grain boundaries, i.e. no pores or voids were detected. It was concluded that the (0001) planes were preferentially oriented perpendicular to the growth direction for all coatings, independent of substrate bias voltage. However, the orientation of the grains was more random during the initial nucleation. The main mechanism for development of this (0001) texture of d.c. magnetron sputtered TiB2 coatings is proposed to be due to a rapid growth in the [0001] direction. There is a change in coating morphology as the substrate bias changes from negative (−110 V) to positive (+50 V). The negatively biased coatings have a columnar structure with a grain size that increases with coating thickness, while coatings grown with positive bias have a dense fibrous morphology, with smaller and more uniform grain size.