Palmqvist test method for Ti-based cermets and WC-CO hardmetals

Experiments were performed to assess the measurement uncertainty in the Palmqvist method for toughness determination which is based on measuring the length of cracks generated at the corners of Vickers hardness indentations. It was found that although the use of an optical microscope separate from that on the hardness machine gave slightly longer total crack lengths and indentations, the difference was barely greater than the measurement uncertainty. The use of a field emission SEM gave high crack lengths, but low indentation diagonal measurements were obtained due to the difficulty in defining the corners of indentations in the SEM. When Palmqvist measurements were made on a range of cermets and hardmetals, it was found that the differences in the Palmqvist parameter from specimen to specimen in the materials examined were less than the experimental uncertainty measured in the early part of the study. Annealing the specimens resulted in the measurement of longer crack lengths and indentation diagonals, and gave a significant reduction in the values of Palmqvist parameters. (Copyright (c) Crown Copyright, 1991.)