Aspects of room temperature compression tests for WC/Co Hardmetals

Hard materials, particularly tooling compositions based on WC/Co structures, are predominantly designed for applications that take advantage of their extremely good properties in compression. There is a standard test method for obtaining compression properties (strength and ductility), ISO 4506:1979, but it is rather expensive to use, needing high capacity testing machines and, in some cases, quite complex testpieces to avoid problems with premature failure from parasitic tensile stresses at the platen/testpiece interface. Consequently, for the most part, the compressive properties of hardmetals are estimated through measurements of hardness; using techniques such as Rockwell (ISO 3738: parts 1–1982 and 2–1988) or Vickers (ISO 3878:1983). This paper discusses the correlation of hardness values with compression data and reviews the testing background, advantages and disadvantages of the test methods, together with comments on the underlying science and comparative studies by complementary researchers. The adoption of stiff compressive testing rigs at NPL for the measurement of almost 40 grades of hardmetals with a comprehensive spread of microstructures is used to comment on good testing practice.