Chemisorptive electron emission as a probe of plastic deformation in reactive metals

Abstract

The surface area created during tensile deformation and fracture of the reactive metals Ti, Zr, Mg, and Al is probed by real-time measurements of chemisorptive electron emission (CSE) due to oxygen adsorption. CSE is sensitive to the number of fresh metal atoms exposed at the surface as a consequence of plastic deformation. At constant strain rate, Ti, Zr, and Mg all display exponential increases in CSE intensities during loading, reflecting exponential increases in surface area prior to fracture. In Ti and Zr, CSE begins at the onset of unstable necking. In contrast, CSE intensities from Al reflect a nearly constant rate of surface area production during deformation at constant strain rate. Calibration of the Ti CSE intensities per unit surface area allowed determination of the total surface area produced during deformation and fracture. Atomic force microscopy of the necked region in strained Ti samples shows dramatic increases in surface roughness, in near agreement with the CSE results. A model is presented to account for these observations. The utility of CSE measurements as a probe of deformation and ductile fracture is discussed.