Contributions from point defects to the elastic constants of copper

Thesis/Dissertation · Fri Feb 01 04:00:00 EDT 1974

DOI:https://doi.org/10.2172/4317247· OSTI ID:4317247

Rehn, Lynn Eduard ^[1]

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1. Univ. of Illinois, Urbana, IL (United States)

The changes introduced in a complete set of independent copper elastic constants (C₁₁, C₄₄ and C') by irradiation with thermal neutrons below 4 deg K were measured. Simultaneous measurements of attenuation and resistivity were also performed, and the change in attenuation due to the introduction of defects was determined. The high degree of sensitivity achieved by using a pulse-echo superposition technique permitted a study to be made of the annealing of these effects through most of stage I. It was found that the contributions at liquid-helium temperatures from different stage I defects to a particular elastic constant were not the same, and the magnitude of the effect from a given defect was found to vary among different constants. Significant temperature dependent effects were also observed in all the elastic constants. The results are discussed in terms of four different effects: a small bulk effect; a larger polarization effect, which involves the stress induced internal displacement of certain defects; a thermally activated relaxation process; and a change in the vibrational spectrum of the lattice from the introduction of defect resonance modes. The indication of a small bulk effect is in agreemert with the range of reported theoretical estimates. The results obtained at 3.8 deg K for the recovery of the results during stage ID are qualitatively in agreement with a calculation by Dederichs of the polarizability of the (100)-split interstitial. The relaxation process previously reported by Nielson and Townsend was observed and attributed to the I_c defect. A model of this defect is proposed. No other relaxation of stage I defects was observed. The measurements indicate that both the I_D and I_E defects change the temperature dependence of the elastic constants by introducing resonance modes into the vibrational spectrum of the lattice. The frequency obtained from an analysis of stage I_D is believed to be 5 x 10¹² plus or minus 30% Hz, and is in reasonable agreement with the value of approximately 8 x 10¹² Hz obtained by Dederichs et al. with a computer simulation of a <100>-split interstitial in a copper lattice. The contribution from this effect to the temperature dependence of other physical properties (resistivity, specific heat and thermal expansion) is discussed. The results obtained are helpful in understanding apparent discrepancies in previously reported measurements of irradiation-induced changes in the elastic constants.

• Research Organization: Univ. of Illinois, Urbana, IL (United States)
• Sponsoring Organization: US Atomic Energy Commission (AEC)
• NSA Number: NSA-29-018982
• OSTI ID: 4317247
• Report Number(s): COO--1198-1036
• Country of Publication: United States
• Language: English

Related Subjects

*COPPER-- PHYSICAL RADIATION EFFECTS
36 MATERIALS SCIENCE
ELASTICITY
ELECTRIC CONDUCTIVITY
INTERSTITIALS
LATTICE VIBRATIONS
N50240* --Metals
Ceramics
&amp; Other Materials--Metals &amp; Alloys--Radiation Effects
NEUTRON BEAMS
POINT DEFECTS
RELAXATION
TEMPERATURE DEPENDENCE
THERMAL NEUTRONS
ULTRALOW TEMPERATURE