In-situ observation of hardmetal deformation processes by transmission electron microscopy. Part II: Deformation caused by tensile loads

摘要

In the 1st part of this article, hardmetal deformation processes caused by bending loads were examined in-situ by transmission electron microscopy. The major objective of this work is to examine hardmetal deformation processes in special thin hardmetal samples as a result of applying tensile loads in-situ directly in a transmission electron microscope with the aid of the push-to-pull method. Applying tensile loads to the samples results in the plastic deformation of the Co-based binder phase leading to the formation of different crystal lattice defects in the binder. Force-time and displacement-time curves recorded when loading the samples and maintaining the loads provide evidence for continuous processes of the formation and movement of crystal lattice defects, presumably dislocations, in the WC phase and Co-based binder leading to a high rate of the binder plastic deformation. After increasing the tensile loads up to a certain level leading to the severe plastic deformation of the binder phase, the samples suddenly fail as a result of the crack initiation and propagation at WC-Co interfaces. Presence of cobalt on the WC surface after the cracking suggests that the cracks propagate through the binder region adjacent to the interface rather than through the interface itself.