The Use of Ultrasound to Measure Dislocation Density

Abstract

Artículo de publicación ISIDislocations are at the heart of the plastic behavior of materials yet they are very difficult to probe experimentally. Lack of a practical nonintrusive measuring tool for, say, dislocation density, seriously hampers modeling efforts, as there is little guidance from data in the form of quantitative measurements, as opposed to visualizations. Dislocation density can be measured using transmission electron microscopy (TEM) and x-ray diffraction (XRD). TEM can directly show the strain field around dislocations, which allows for the counting of the number of dislocations in a micrograph. This procedure is very laborious and local, since samples have to be very small and thin, and is difficult to apply when dislocation densities are high. XRD relies on the broadening of diffraction peaks induced by the loss of crystalline order induced by the dislocations. This broadening can be very small, and finding the dislocation density involves unknown parameters that have to be fitted with the data. Both methods, but especially TEM, are intrusive, in the sense that samples must be especially treated, mechanically and chemically. A nonintrusive method to measure dislocation density would be desirable. This paper reviews recent developments in the theoretical treatment of the interaction of an elastic wave with dislocations that have led to formulae that relate dislocation density to quantities that can be measured with samples of cm size. Experimental results that use resonant ultrasound spectroscopy supporting this assertion are reported, and the outlook for the development of a practical, nonintrusive, method to measure dislocation density is discussed.Fondecyt 113038

Diffusion of elastic waves in a two dimensional continuum with a random distribution of screw dislocations

“…where M = (µb 2 /4πc 2 T ) ln(δ/ǫ) ≈ µb 2 /c 2 T , and we shall use the last approximation for estimates. These expressions coincide with (21) when B = 0, as required by the ISA to the WTI. The average that is implicit in (C2) can be ignored since it involves b 2 and the only remaining randomness (after having averaged over position to get proportionality to dislocation density n) is in the sign of b.…”

Acoustic Parameters as Criteria of Localized Deformation in Aluminum Alloys

“…The number of dislocations involved * corresponding author; e-mail: agl@ispms.tsc.ru in PLC band generation is order of 10 4 . The evaluation of dislocation assembly scope propagating in the form of PLC bands and their location along tested specimen can be carried out by the measurement of the velocity and the attenuation of ultrasound waves [9,10]. Theoretical ground of dislocation influence on the ultrasound velocity and attenuation was firstly presented by Granato and Lücke [11,12] as part of the internal friction theory.…”

Multiple scattering of elastic waves by pinned dislocation segments in a continuum

“…Leading order perturbation theory was used to obtain formulae relating change in the speed of wave propagation to dislocation density. These formulae have been used to show that ultrasound-more specifically resonant ultrasound spectroscopy (RUS)-can be used as a quantitative probe of dislocation density in aluminum 3 , with comparative advantages over X-ray diffraction (XRD) and transmission electron microscopy (TEM) 4 .…”