Splitting of tungsten wire in the knife-edge compression test

As-drawn tungsten wire has been known to split and rolled tungsten sheet to delaminate if mishandled. The mechanism of splitting of tungsten wire in a knife-edge compression test was studied for a number of tungsten wires of different diameter, composition, processing history, and origin. The micro-structure of these wires was examined by optical, scanning, and transmission electron microscopy. Grain boundary composition was determined by Auger electron spectroscopy. A correlation between the number of transverse boundaries in the microstructure and the split load in the knife-edge compression test was observed; the greater the number of transverse boundaries, the lower the load required to induce a split. This relationship held for all wires, regardless of the history of the wire. It was concluded that transverse grain or subgrain boundaries are responsible for initiating splits in the knife-edge compression test. The mechanism of splitting is discussed.