AVS 62nd International Symposium & Exhibition
    Advanced Surface Engineering Monday Sessions
       Session SE+AS+NS+TR-MoM

Paper SE+AS+NS+TR-MoM8
Crystallographic Stabilization of δ-WC Thin Films by Alloying with B, using Reactive Magnetron Sputtering of W in Trimethylboron (CH3)3B

Monday, October 19, 2015, 10:40 am, Room 212A

Session: Nanostructured Thin Films and Coatings
Presenter: Hans Högberg, Linköping University, Sweden
Authors: H. Högberg, Linköping University, Sweden
L. Tengdelius, Linköping University, Sweden
M. Samuelsson, Linköping University, Sweden
G. Greczynski, Linköping University, Sweden
F. Eriksson, Linköping University, Sweden
L. Hultman, Linköping University, Sweden
Correspondent: Click to Email
The hardness, oxidation resistance, and high temperature stability of hexagonal δ-WC (Bh) in cemented carbide is a key component in metal cutting. Such a property envelop suggest many potential thin film applications. However, the literature shows that thin film growth of δ-WC by for instance magnetron sputtering is complicated typically resulting in the deposition of films containing the phase γ-WC (B1) with a carbon content lower than nominal, i.e. WC1-x. As the properties of this phase is less favorable compare to those of δ-WC, growth of WC1-x must be avoided in an optimized thin film material. In this study, we attempt to promote the formation of δ-WC films by alloying with B. Our hypothesis is that the preferred growth of WC1-x films depends on the preference of C to occupy octrahedral sites found in the B1 structure and where the larger B atom may act to stabilize the Bh structure by better filling out the larger trigonal prism interstitials in this structure. We use reactive magnetron sputtering of W, using trimethylboron (CH3)3B (TMB) as C and B precursor. The 5 min depositions were carried on Si(100) substrates in a Kr plasma held at a constant pressure of 0.53 Pa. The gaseous TMB was introduced close to the substrates. The influence of TMB flow, ranging from 1-10 mln, was studied for a growth temperature of 500 °C. Also, the influence of growth temperature, from room temperature to 900 °C, was investigated for a constant TMB flow of 10 mln. X-ray photoelectron spectroscopy shows that the content of B and C scales with the flow into the plasma with no B and ~3 at.% C at 1 mln and 6.5 at.% B and 17.8 at.% C at 10mln. In contrast, temperatures up to 600 oC show no impact on the B and C content in the films, while higher temperatures give a solid state reaction with the substrate. X-ray diffraction shows broad peaks indicative of small grain sizes and with peaks at 2θ angles matching those of the phases WC1-x or W. In the in the temperature range 300 to 600 oC, 100-textured WC1-x films are deposited and with a shift to a weak 111 orientation at lower temperatures. At 500 oC, TMB flows of 5 to 10 mln results in the growth of 100-textured WC1-x films, while lower flows yield W films. Films are deposited with thicknesses up to ~1000 nm, corresponding to a deposition rate of 3.3 nm/s. The microstructure is generally fine-grained, but with broken columns at 500 and 600 oC and a TMB flow of 1 mln. The mechanical properties of the films will be reported.