The orientation dependence of dislocation slip in NaCl single crystals

1986

MRS Proc.

Self Cite

Pulsed nuclear magnetic resonance proved to be a new complementary technique for the study of moving dislocations in Al-base alloys. Spin-lattice relaxation measurements clearly indicate that fluctuations in the quadrupolar field caused by moving dislocations in Al-base alloys are different compared to those in ultra-pure Al. From the motion induced part of the spin-lattice relaxation rate the mean jump distance of mobile dislocations has been determined as a function of strain. Measurements have been performed on Al-Cu, Al-Li and Al-Zn binary alloys. As a typical illustration of the strength of this technique, this paper reports the results obtained of Al-(1-2 at%) Zn solid solution.

“…Detailed information of certain NMR experiments along these lines on metallic (Al-base alloys) and ionic crystals can be obtained from ref. [5][6][7][8][9][10][11][12].…”

Section: Methodsmentioning

confidence: 99%

Dislocation Dynamics Investigated by Means of Nuclear Magnetic Resonance a Complementarynew Technique

Hosson

1986

MRS Proc.

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“…Rowland and Fradin [5], Kanert [1] and others were thus able to evaluate the impurity diffusion in alloys. These techniques, in addition, made it possible to probe the jumping dislocations in situ during deformation in a non-interactive fashion [6][7][8]. We have recently reported an investigation of the superimposed effects of deformation on spin-lattice relaxation time (of Z3Na) in the rotating frame, T10, in singlecrystalline pure (~ 1.5p.p.m.…”

Section: -2461 9 1996 Chapman and Hallmentioning

confidence: 99%

In situ nuclear magnetic resonance study of defect dynamics during deformation of materials

Murty

Detemple

JOURNAL OF MATERIALS SCIENCE

et al. 1996

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Nuclear magnetic resonance techniques can be used to monitor in situ the dynamical behaviour of point and line defects in materials during deformation. These techniques are non-destructive and non-invasive. We report here the atomic transport, in particular the enhanced diffusion during deformation by evaluating the spin lattice relaxation time in the rotating frame, Tip, in pure NaCI single crystals as a function of temperature (from ambient to about 900 K) and strain-rate (to ~ 1.0 s-1) in situ during deformation. The strain-induced excess vacancy concentration increased with the strain-rate while in situ annealing of these excess defects is noted at high temperatures. Contributions due to phonons or paramagnetic impurities dominated at lower temperatures in the undeformed material. During deformation, however, the dislocation contribution became predominant at these low temperatures. The dislocation jump distances were noted to decrease with increase in temperature leading to a reduced contribution to the overall spin relaxation as temperature is increased. Similar tests with an improved pulse sequence (CUT-sequence), performed on ultra-pure NaCI and NaF single crystals revealed slightly different results; however, strain-enhanced vacancy concentrations were observed. The applicability of these techniques to metallic systems will be outlined taking thin aluminium foils as an example.

“…In Eq. [19], M 0 is the initial magnetization at the beginning (t ϭ 0) of the locking field, which is often taken to be the signal height (M 0 ) following the /2 pulse, whereas in reality it may be quite different from M 0 . Moreover, in order to measure M (t) at different times, one has to repeat the experiment varying the period of the locking pulse ( Figure 2).…”

Section: Methodsmentioning

confidence: 99%

“…These techniques, in addition, made it possible to investigate the dislocation jump distances in situ during deformation in a noninvasive fashion. [18,19,20] We have recently reported an investigation of the superimposed effects of deformation on spin-lattice relaxation times in the rotating frame (T 1 ) in single crystalline pure (Ϸ1.5 ppm impurity) NaCl and NaF at varied temperatures and strain rates, [1] from which the strain-induced excess vacancy concentration was derived. In this study, both the classic T 1 and the new CUT-sequence methods were used, while the data analyses were based on the vacancy production due to both the thermal and mechanical jogs.…”

Section: Introductionmentioning

confidence: 99%

In-situ nuclear magnetic resonance investigation of strain, temperature, and strain-rate variations of deformation-induced vacancy concentration in aluminum

Murty

Detemple

et al. 1998

Metall Mater Trans A

Self Cite

Critical strain to serrated flow in solid solution alloys exhibiting dynamic strain aging (DSA) or Portevin-LeChatelier effect is due to the strain-induced vacancy production. Nuclear magnetic resonance (NMR) techniques can be used to monitor in situ the dynamical behavior of point and line defects in materials during deformation, and these techniques are nondestructive and noninvasive. The new CUT-sequence pulse method allowed an accurate evaluation of the strain-enhanced vacancy diffusion and, thus, the excess vacancy concentration during deformation as a function of strain, strain rate, and temperature. Due to skin effect problems in metals at high frequencies, thin foils of Al were used and experimental results correlated with models based on vacancy production through mechanical work (vs thermal jogs), while in situ annealing of excess vacancies is noted at high temperatures. These correlations made it feasible to obtain explicit dependencies of the strain-induced vacancy concentration on test variables such as the strain, strain rate, and temperature. These studies clearly reveal the power and utility of these NMR techniques in the determination of deformationinduced vacancies in situ in a noninvasive fashion.