Contemporary Trends of the Development of Physics of Light Metals
V. G. Tkachenko
I. M. Frantsevich Institute for Problems in Materials Science, NAS of Ukraine, 3 Academician Krzhyzhanovsky Str., UA-03142 Kyiv, Ukraine
Received: 17.11.2008. Download: PDF
The results of original theoretical and experimental researches in a field of strength physics, microand nanoyield, kinetics and mechanisms of the delayed fracture and impurity embrittlement of light metals (h.c.p. Mg, h.c.p. Be, h.c.p. Ti and f.c.c. Al) are generalized. Some of them are concerned with scientific legacy of outstanding physicists–academicians V. N. Gridnev and A. A. Smirnov. It is deduced that existing traditional approaches to a problem of low-temperature brittleness of metals and their brittle strength based on power (athermal) criteria of the fracture nucleation do not provide valuable information for the understanding of an origin of the temperature dependences of true fracture stress to be observed in the temperature range of quasi-brittle transition in h.c.p. and b.c.c. metals, their solid solutions and eutectic metal-alloy systems. On the basis of the thermally-activated analysis of the microyield, which is predecessor and accompanying for the fracture propagation, another approach is proposed to an estimation of mechanical properties of light metals, which allows for athermal and thermally-activated contributions at a subcritical stage of the microcrack growth and interaction of the structural defects with a goal of improving the strength characteristics of these metal alloy systems. In terms of the newly developed physical (dislocation) theory of temperature dependence of the true fracture stress to be valid for b.c.c. and h.c.p. metals, the new basic (generalized) scheme of the quasi-brittle transition is constructed that includes the well-known Ioffe−Davidenkov’s scheme as a special case. Effects of deviations from classical (Arrhenius) behaviour in Mg−Ba and Al−Li systems to be observed at high temperatures are caused by a change of the diffusion mechanism in h.c.p. interstitial solid solutions such as h.c.p.-Be−C as well as by the nanoclustering of a structure in substitutional solid solution such as h.c.p.-Ti−H and h.c.p.-Mg−Ba oversaturated by excess vacancies. Physical principles of the precise alloying for the in situ bulk nanoclustering of a structure of the condensed metal systems (metal melts and their extended solid solutions) are formulated in order to solve the physical problem and thereby to reveal the origin of the cluster-induced photoemission centres responsible for the crucial increase (by two—three orders of magnitude) of quantum efficiency of simple light metals (h.c.p. Mg and f.c.c. Al) within the UV-spectrum range. The class of promising photoemission materials based on ternary Mg−Ba−Li and Al−Li−Ba alloy systems is developed with the goal of applying them as pulse bulk photocathodes in high-current electronics including the next RF-guns of FELs and electron accelerators. The new scopes of applying these materials containing nanoclusters with the intrinsic (shell) electronic structure are specified.
Keywords: strength, quasibrittle fracture, nanocluster, photoemission.
PACS: 61.72.jd, 62.20.Hg, 62.20.M-, 62.23.Pq, 66.30.J-, 79.60.Jv, 81.40.Np
Citation: V. G. Tkachenko, Contemporary Trends of the Development of Physics of Light Metals, Usp. Fiz. Met., 10, No. 1: 103—130 (2009) (in Russian), doi: 10.15407/ufm.10.01.103