RADIATION EFFECTS OF COPPER SINGLE CRYSTALS UNDER STRESS Masao Doyama, Y. Kogure and T. Nozaki Teikyo University of Sci. & Tech. JAPAN

RADIATION EFFECTS IN SOLIDS UNDER STRESS ARE QUITE IMPORTANT Most simulations are performed under no stress. In electron microscopic observation, behavior of radiation damage has been reported. Interstitial clusters move during observation under irradiation.

UNDER HIGH PRESSURE The activation energy for the motion of a vacancy increases as the pressure becomes higher.

SIMULATION UNDER STRESS Most simulations have been performed under no stress. In this work, behavior of interstitials and vacancies under uni-axial stress is reported.

INTERATOMIC POTENTIAL Embedded Atom Potential Etotal=Ei (1) rij =｜ri—rj ｜ (2) EI=(1/2)Σ(rij)+F(i) (3) F(i) = D i ln (4) i = Σ f (r ij) (5)

(rij) = A 1 ( r c1 − r ij)2 exp( − c 1 rij) (6) f (r ij) = A 2 ( r c2 − r ij)2 exp( −c 2 rij) (7) are assumed. f (rij) and (rij) are smoothly truncated at rc1 and rc2, respectively. rc1 was chosen to be 1.65d, where d is the nearest neighbor distance. (rij) was chosen to be 1.95 d.

These are determined to reproduce the Born stability, cohesive energy, elastic constants c11, c12, and c44, the formation energy of a vacancy, and stacking fault energy. For copper, A1 = 8.28945997705×103/d2, A2 = 1.83251035107×10-2/d2, C1 = 10.72729128641/d, C2 = 0.319759369823/d, D = 13.07921251628. Here d is the nearest neighbor distance in angstroms (2.882), and the energies are in eV.

SPECIMEN 6a x 6a x 6a a = Lattice Parameter Center: 500 atoms Relaxed Outer: 872 atoms Fixed Total: 1372 atoms

MOLECULAR DYNAMICS Molecular Dynamics Time Step = 1 x 10-15 s Temperature gradually reduced to 0K. The Crystal Energies are the same to 8 digits after 80,000 cycles. No Periodic Boundary Conditions Are Used.

INTERSTITIALS USING MORSE POTENTIAL

INTERSTITIALS UNDER NO STRESS

UNDER NO STRESS DISTANCE BETWEEN TWO SPLIT ATOMS 100-Split 0.758d d= nearest neighbor distance

UNDER NO STRESS Activation energy for the motion of 100-split interstitial is 0.073eV at (0.4a, 0.2a, 0)

2% COMPRESSION 001-split is the most stable.

2% COMPRESSION Activation energy for the motion from a 100-split interstitial to a 010-split on (001) is 0.085eV. Activation energy for the motion from a 100-split to a 001-split is 0.087eV. Activation energy for the motion from a 001-split to a 100-split is 0.071eV.

2% COMPRESSION On (001)

2% COMPRESSION on (010)

ELONGATION 2% 100-split is the most stable. This is different from the case for compression.

MOTION OF 100-SPLIT INT. (2% Elongation) The activation energy for the motion of 100-split interstitial=0.046eV <0.073eV

ELONGATION 2%

MOTION OF 001-SPLIT INT. On (010) Plane 1.02a/2

MOTION OF 001-SPLIT INT. (2% Elongation) Alternate motion of 100-split and 001-split interstitials. The activation energies for the motion are also alternate, 0.046ev from 100-split to 001-split and 0.029eV from 001-split to 100-split. 1.02a

VACANCIES UNDER STRESS

UNDER NO STRESS Activation energy for motion of a vacancy = 0.58eV

UNDER 2% COMPRESSION (1) Motion energy = 0.70eV (2)Motion energy Compare Under no stress =0.58eV (1) (2)

UNDER 2% ELONGATION (1) EMV ＝0.52eV (2) EMV = 0.61eV Remember Under no stress =0.58eV (1) (2)

CONCLUSIONS It was clearly shown that Activation energies for the motion of interstitials and vacancies are greatly affected by stress. This could lead important interpretations of experimental results.

Thank you very much for your attention