The Electroplastic Effect in Cermets

摘要

The crack propagation pattern and fracture toughness of carbide-based cermets subjected to high density current pulses were examined. The effect of high current density pulses, known as the electroplastic effect, on the plastic deformation behavior of metals and alloys is well-known. To study this effect in cermets, fracture toughness values were calculated using a modified Evans-Charles formula, data from microhardness tests and measurements of crack lengths resulting from Vickers indentatiom. Prior to experimentation, measurements were HK=1636+-24 kg/mm~2 and K_IC=21.25+-0.67 kg/mm~3/2 for average hardness and average fracture toughness, respectively. The influence of high density current pulses (800-1600 amps/mm~2 for 50-150 #mu#sec duration) on the extent of crack propagation was examined. Samples that were pulsed during Vickers indentation were observed to produce longer crack lengths than unpulsed samples. Indented samples that were pulsed prior to cyclic compression loading produced different crack extension patterns than unpulsed samples. Mechanisms influencing crack propagation behavior in these cermets during and after pulsing are discussed.