ON THE STATE OF STRESS IN THE SURFACE OF GROUND CEMENTED CARBIDE BEFORE AND AFTER METAL-ION IMPLANTATION

The residual stress and strain distribution in each phase of as-ground cemented carbide, before and after metal ion implantation, has been s tudied using parallel beam glancing angle X-ray diffraction down to a maximum depth of penetration of about 1 mu m. In as-ground material, t he residual stress is constant at depths beyond about 0.5 mu m, assume d to correspond to bulk material, and is compressive in WC and the cub ic carbide, and assumed tensile in the Co binder which contains both a lpha and beta modifications. The grinding operation introduces tensile stresses into the WC and cubic carbide phases extending down to a dep th of about 0.2 mu m, with parallel increases in the strain distributi ons. Only alpha-Co is found near the surface down to a depth of about 0.5 mu m, and the lattice parameter is reduced from the bulk value wit h an increase in the strain distribution, The effect of a Ni-Ti dual m etal ion implantation is threefold: (i) within the zone where the impl anted material resides (some 60 nm deep), compressive stress is found in WC and the cubic carbide, with very high strain distributions, and with a reduction in the stress and strain distribution in Co; (ii) in the zone affected by the grinding operation (some 0.2 mu m deep) the t ensile stresses and strain distributions in both carbide phases are re duced down to the bulk values, i.e. the effect of the grinding operati on is removed, as is the stress in alpha-Co (beta-Co is not present ne ar the surface); (iii) in the bulk (at least down to the depth of 1 mu m available for study here), the compressive residual stress in WC is reduced to about half of the value in the as-ground material, confirm ing the ''long range effect'' of metal ion implantation as extending w ell beyond the implanted zone.