Diamond retention in sintered cobalt bonds for stone cutting and drilling

Thin (<1 mu m) coatings on diamond do not in influence segment density, clo sed porosity or bulk transverse rupture strength. None of these measures sh ow strong correlation to diamond saw performance. Diamond coatings influenc e the yield strength of the bond in shear, at the diamond-bond-matrix inter face, and more effectively utilize the compressive stress developed in bond fabrication to produce good retention. The improvement in retention, as ob served by differential hardness, in 100% cobalt bonds, is Cr-coated > Ti-co ated > uncoated. Since retention is only one attribute of a bond, the benef it of a coated crystal in tool performance is system- and condition-specifi c. Improvement in saw performance will come with reduction in blade angular fr iction derived from higher and more stable cutting point protrusion. To ach ieve higher protrusion will require higher retention from nominal or higher bond compressive stress combined with higher diamond-matrix friction. Diam ond coatings provide higher friction. Observing improvement in blade performance with a coated crystal requires t hat the condition/application be performance-limited by retention, not, for example, by acoustic impedance, blade stiffness or crystal crushing. (C) 1 999 Elsevier Science S.A. All rights reserved.