Dilatometry: a powerful tool for the study of defects in ultrafine-grained metals

Grain boundary excess volume and defect annealing of copper after high-pressure torsion

“…The experimental data, plotted as a dilatometric length change curve $\mathrm{\Delta }l/l_0$, represents the difference signal between the specimen and the reference (so-called difference dilatometry). The length change is directly related to the defect volume via the relation $3\times \mathrm{\Delta }l/l_0=\mathrm{\Delta }V/V_0$, assuming an isotropic distribution and annealing of defects [12]. The temperature of the maximum defect release rates can be determined from the minima of the derivative $d(\mathrm{\Delta }l/l_0)/\mathit{dT}$ of the length change curve with respect to temperature.…”

Direct measurement of vacancy relaxation by dilatometry

“…4 A powerful tool for measuring the volume associated with lattice vacancies is dilatometry. An overview on the various measuring principles of dilatometry is for instance given by Sprengel et al 5 In the classical technique of differential dilatometry, the change of macroscopic length DL/L is measured simultaneously with the change of the lattice constant Da/a upon thermal formation of vacancies at high temperatures. 1,6 However, since vacancy relaxation affects the macroscopic length and the lattice constant in the same way, 7 the vacancy concentration C V determined from the difference (C V ¼ 1=3ðDL=L À Da=aÞ) is independent from the vacancy relaxation.…”

Structural anisotropy in equal-channel angular extruded nickel revealed by dilatometric study of excess volume

“…The dilatometric measurements were performed by means of a vertical high-precision difference dilatometer (Linseis, model: L75VD500 LT) under a flow of 5 l h -1 of high-purity argon (99.999 %) (for details of the technique see, e. g., Sprengel et al [1]). The length changes DL=L 0 quoted in the following (Table 1, see below) denote net length changes determined as the difference to the pre-annealed reference sample prepared in the same orientation from the same rod.…”

“…In the past few years, difference dilatometry has proven a powerful absolute technique in order to quantify the amount of excess volume in ultrafine grained metals prepared by severe plastic deformation (SPD) [1,2] 1 . In particular, the absolute concentration of deformation-induced lattice vacancies and the grain boundary (GB) expansion as well as issues of structural relaxation, defect kinetics and aggolomeration could be determined focusing on SPD-processed Ni [4 -6] and Cu [7,8].…”