Improved nanostructured diamond adhesion on cemented tungsten carbide with boride interlayers

Abstract

The application of diamond coatings for strengthening cemented tungsten carbide has been previously attempted, but suffers from delamination. Plasma enhanced chemical vapor deposition boriding improves the strength of cemented carbides by forming WCoB, W 2 CoB 2 , and/or CoB phases using controllable diborane stoichiometry;this research exploresthese borides as interlayers for nanostructured diamond coatings. Diamond deposition occurred between 600 °C and 1100 °C at 100 °C increments for 30 min to 4 hrs. Raman spectroscopy showed enhanced diamond growth compared to untreated WC-Co,however predominantlyWCoB and CoBphase interlayerssuffered from diamond film delamination. Examination by scanning electron microscopy and energy dispersive X-ray spectroscopy showed interfacial cobalt clusters on these interlayers. Predominantly W 2 CoB 2 phase interlayers showed improvement with a reduction in reactive cobalt, and improved adhesion of nanostructured diamond coatings. Diamond on W 2 CoB 2 was well adhered with deposition temperature dependentnanoindentationhardness ranging from 10 to 60 GPaand elastic modulus of 400 to 750 GPa. Scratch testing revealed cohesiveand adhesive failure of the diamond coatings at 5N ± 2N and 8N ±2N respectively and epoxy pull testing resulted in a surface adhesion tensile strength of 8.2 MPa ± .1MPa. The W 2 CoB 2 phaseis shown to be desirable as an interlayer for improved nanostructured diamondadhesion on cemented tungsten carbide.