Dislocation internal friction and temperature dependence of yield stress in high‐purity molybdenum single crystals

Abstract

In honour of Professor B. I. VERKIN'S 70th birthday High purity molybdenum single crystals (residual resistivity ratio x 6 . lo4) were studied by means of computer-controlled internal friction technique at frequencies of about 100 kHz in the temperature range 6 t o 300 K. The amplitude dependences of decrement were measured within the vibrational strain amplitude lo-' t o It was established that the temperature dependence of ultrasonic amplitude providing a constant level of reversible dislocation deformation coincides well in relative units with the temperature dependence of the critical resolved shear stress at 20 t o 180 K.

Application of Internal Friction to Analysis of Plastic Behaviour of Crystals

“…If the temperaturedependent function in (9) has a form f i x exp [A T ] , then the stress at .cd=const will obey Eqn. (l l), frequently observed (see, for example, Fig.6) in experiments for microyield [26,27,37] and macroyield [82,83] stresses. The <u2> approach may be a basis for the similarity law.…”

“…The similarity law in zone refined MO single crystal [37] is valid at T 4 8 0 K (Fig.6). A deviation fkom the similarity is observed at D180K.…”

“…At present, the similarity law is observed in single crystals of different lattice structure and various purity: NaCI, NaF, LiF, MgO, W, Al [49,50], MO [37,49,50] and Al-Si-Fe [26,27] and in polycrystals: Mg [49,50], silicon bronze [25] and FeCr alloys [57]. It should be noted that there is no similarity between the microyield and macroyield stresses as a h c t i o n of the grain size (see Fig.8, where the data by Goto et al [38] for D, are compared in the HallPetch plot w i t h the data by Feltham and Meakin [58] for o,) and the impurity concentration [39,59].…”

Acousto-Optical Spectroscopy of Dislocations in Wide Band Gap Semiconductors

“…Amplitude dependent damping in crystals is considered as one of the methods of mechanical spectroscopy for investigating different mechanisms of dislocation anelastic phenomena. For a long time we studied dislocation -point defects interaction in ionic crystals, metals and alloys [1][2][3][4] using various models which described the phenomenon. But only for HgI 2 semiconductor crystal we were able to find out the origin of pinning points for vibrating dislocations.…”