Linear Versus Nonlinear Acoustic Probing of Plasticity in Metals: A Quantitative Assessment.

Carolina Espinoza,Vicente Salinas,Rodrigo Espinoza-González,Claudio Aguilar,Nicolás Mujica,Daniel Feliú,Fernando Lund

doi:10.3390/ma11112217

Abstract

The relative dislocation density of aluminum and copper samples is quantitatively measured using linear Resonant Ultrasound Spectroscopy (RUS). For each metallic group, four samples were prepared with different thermomechanical treatments in order to induce changes in their dislocation densities. The RUS results are compared with Nonlinear Resonant Ultrasound Spectroscopy (NRUS) as well as Second Harmonic Generation (SHG) measurements. NRUS has a higher sensitivity by a factor of two to six and SHG by 14–62%. The latter technique is, however, faster and simpler. As a main result, we obtain a quantitative relation between the changes in the nonlinear parameters and the dislocation density variations, which in a first approximation is a linear relation between these differences. We also present a simple theoretical expression that explains the better sensitivity to dislocation content of the nonlinear parameters with respect to the linear ones. X-Ray diffraction measurements, although intrusive and less accurate, support the acoustics results.

Highlights

Plastic behavior of metallic materials is determined by dislocations, with the transition from brittle to ductile behavior being of particular interest
One nonlinear acoustic experimental method that is widely used as a non destructive evaluation tool is Second Harmonic Generation (SHG) [25]
The relative sensitivity of Resonant Ultrasound Spectroscopy (RUS), Nonlinear Resonant Ultrasound Spectroscopy (NRUS) and SHG are presented and we show that nonlinear parameters are more sensitive to the presence of dislocations than the linear ones

Summary

Introduction

Plastic behavior of metallic materials is determined by dislocations, with the transition from brittle to ductile behavior being of particular interest. Oh et al [1] have reported in situ observations of dislocation nucleation and escape; Landau et al [2] have studied dislocation patterning; Zhang et al [3] have reported real-time correlation between flow stress and dislocation density; and Du et al [4] have reported observations of dislocation emission. These are destructive techniques and, in general, small, specially prepared samples are required.

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Conclusion