2008 NSTI Nanotechnology Conference and Trade Show - Nanotech 2008 - 11th Annual

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Clean Technology 2008

Universal Mechanisms of Dislocation Motion/Multi Plication

V.P. Kisel
Institute of Solid State Physics, R A S, RU

Keywords:
nanoscale characterization, nanostructured materials, devices

Abstract:
The effect of applied compressive/extension stresses, ( = 0.6 o to 95 o, where o is the resolved shear stress) and stress rates (10 to 1 000 000 MPa/sec) on dislocation dynamics was investigated in pure NaCl and InSb single crystals (SC) in the temperature range T = 0.004 to 0,945 Tmelt, Tmelt is the melting point. The general damping character of dislocation unpinning, motion and multiplication (work-hardening of crystals,WH) under various tests (the interrupted loadings are included) manifests in the ultimate mean path lengths of individual dislocations (UMPID). It is shown that the jumping motion of dislocation groups and the serrated macroflow of crystals are of the same origin and they are determined by the correlated cross-slip, conservative motion of jogs-superkinks, climb of jogs (lattice defects production) and the Orowan bowing of superkinks-segments between the pinning points (jogs-impurity precipitates, dislocations, etc.) under external stress [3]. Having covered a certain UMPID determined by the pinned jogs of cross-slips (due to crystal prehistory and test parameters), the dislocations exposed to successive acts of multiplication thus forming the slip lines, bands, subgrains, low/high-angle/nanograin boundaries (GB) in series (multiplication of GB) in all the materials [1,3]. The dependences of the UMPID vs creep, impulse, impact stresses and temperature are topologically similar to the conventional macroscopic strain-stress curves for the same crystals. This means the strict scaling of the flow stresses for dislocation motion, multiplication and deformation at fixed strains in SC and nanostructured crystals (NSC) up to fracture [1,3]. This confirms the above conclusions about the same micromechanisms for individual dislocations, their ensembles and macroscopic WH, i.e. they are the same for various levels of stress and deformation [1] up to their ultrahigh values (severe deformation of NSC). It is extremely important to note that the WH varies nonmonotonously to crystal softening according to the pulse length of the unloadings (restore time), and these dependences are the same for dislocations and macrodeformation (this work) as well as for NSC [2]. The same micromechanisms of correlated conservative motion of jogs-superkinks explains the internal-friction double low-temperature peaks (the Bordoni-Niblett-Wilks peaks), double high-temperature peaks (the Ke-Mash-Hall grain-boundary relaxation in polycrystals), recrystallization peaks in NSC [4] and the macrorecrystallization in NSC [2]. 1. V.P. Kisel. Physica Status Solidi (a), v. 149, No 1, pp 61-68 (1995). 2. R.Z. Valiev, I.V. Aleksandrov, Doklady Akad.Nauk, v. 380, No 1, pp 34-37 (2001). 3. N.S. Kissel, V.P. Kisel Mater. Sci. Eng. A, v. 309-310, pp 97-101 (2001). 4. Gondi P., Nognato R., Evangelista E. Physica Status Solidi (a), v.33, p. 579 (1976).


Nanotech 2008 Conference Program Abstract