Depth-sensing indentation tests in studying plastic instabilities

This review surveys the phenomenon of plastic instabilities occurring in depth-sensing indentation measurements. Investigations presented focus on the characterization of Portevin-Le Chatelier type instabilities observed in different metal alloys during indentation. The effect of some important factors such as solute concentration, the formation of Guinier-Preston zones, and grain size and orientation are described and discussed. The phenomenon of plastic instabilities as serrated flow recently observed in bulk metallic glasses is also briefly reviewed

Macroscopic and microscopic descriptions of the plastic deformation of Fcc metals over a wide range [-4pt] of strain and temperature

The plastic behavior of face-centered cubic metals was investigated over a wide range of strain and testing temperature. The experimental stress-strain data were described using both macroscopic and microscopic, well-established relationships. The characteristics of these descriptions are discussed and compared with each other. The analysis of the characteristics leads to a definition of the low and high temperature deformation regions, where the kinetics of both the dislocation-multiplication and the dislocation-annihilation (recovery) are different. For pure aluminum, it is shown that the boundary between these two regions occurs at a homologous temperature of the order of $\approx 0.5 T_{m}$ where $T_{m}$ is the absolute melting temperature. From this analysis, correlations are also drawn between the macroscopic parameters describing the stress-strain relationship and the fundamental characteristics of the microscopic processes both at room temperature and elevated temperatures

Microstructure decomposition and unique mechanical properties in an ultrafine-grained Al-Zn alloy processed by high-pressure torsion

An ultrafine-grained (UFG) Al-30wt.%Zn alloy was processed by high-pressure torsion (HPT) and then the mechanical and microstructural properties were investigated using depth-sensing indentations (DSI), focused ion beam (FIB), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Emphasis was placed on the microstructure changes due to HPT processing as well as the effects of grain boundaries and the unusually high strain rate sensitivity. The deformation characteristics are explained by the formation of a Zn-rich phase which wets the Al/Al grain boundaries and enhances the role of grain boundary sliding in this UFG alloy. The occurrence of intensive grain boundary sliding in this UFG alloy at room temperature was also demonstrated by deforming micro-pillars. It is shown that, as a result of grain boundary sliding, the plastic deformation process of the UFG samples remains stable even at the micro-scale without the intermittent flow and detrimental strain avalanches which are an inherent feature of micro-size conventional crystals. This result illustrates the advantage of using UFG materials for effective applications in micro-devices. <br/