On the state of stress in the surface of ground cemented carbide before and after metal ion implantation

Abstract The residual stress and strain distribution in each phase of as-ground cemented carbide, before and after metal ion implantation, has been studied using parallel beam glancing angle X-ray diffraction down to a maximum depth of penetration of about 1 μm. In as-ground material, the residual stress is constant at depths beyond about 0.5 μm, assumed to correspond to bulk material, and is compressive in WC and the cubic carbide, and assumed tensile in the Co binder which contains both α and β modifications. The grinding operation introduces tensile stresses into the WC and cubic carbide phases extending down to a depth of about 0.2 μm, with parallel increases in the strain distributions. Only α-Co is found near the surface down to a depth of about 0.5 μm, and the lattice parameter is reduced from the bulk value with an increase in the strain distribution. The effect of a NiTi dual metal ion implantation is threefold: (i) within the zone where the implanted 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 μm deep) the tensile stresses and strain distributions in both carbide phases are reduced down to the bulk values, i.e. the effect of the grinding operation is removed, as is the stress in α-Co (β-Co is not present near the surface); (iii) in the bulk (at least down to the depth of 1 μm available for study here), the compressive residual stress in WC is reduced to about half of the value in the as-ground material, confirming the “long range effect” of metal ion implantation as extending well beyond the implanted zone.