A simple kinetic parameter indicating the origin of the relaxations induced by point(-like) defects in metallic crystals and glasses
AS Makarov and RA Konchakov and YP Mitrofanov and MA Kretova and NP Kobelev and VA Khonik, JOURNAL OF PHYSICS-CONDENSED MATTER, 32, 495701 (2020).
Computer simulation shows that an increase of the volumeVdue to point defects in a simple metallic crystal (Al) and high entropy alloy (Fe20Ni20Cr20Co20Cu20) leads to a linear decrease of the shear modulusG. This diaelastic effect can be characterized by a single dimensionless parameterK= dlnG/dlnV. For dumbbell interstitials in single crystalsK approximate to -30 while for vacancies the absoluteK-value is smaller by an order of magnitude. In the polycrystalline state,K approximate to -20 but its the absolute value remains anyway 5-6 times larger than that for vacancies. The physical origin of this difference comes from the fact that dumbbell interstitials constitute elastic dipoles with highly mobile atoms in their nuclei and that is why produce much larger shear softening compared to vacancies. For simulated Al and high entropy alloy in the glassy state,Kequals to -18 and -12, respectively. By the absolute magnitude, these values are by several times larger compared to the case of vacancies in the polycrystalline state of these materials. An analysis of the experimental data on isothermal relaxations ofGas a function ofVfor six Zr-based metallic glasses tested at different temperatures shows thatKis time independent and equals to approximate to-43, similar to interstitials in single-crystals. It is concluded thatKconstitutes a important simple kinetic parameter indicating the origin of relaxations induced by point(-like) defects in the crystalline and glassy states.
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