The dislocation relaxation by kink-pair formation on screw dislocations in high-purity molybdenum

Abstract

By means of low‐frequency internal‐friction measurements in an inverted torsion pendulum at 0.5 to 15 Hz, the so‐called γ‐relaxation in high‐purity molybdenum (occurring between 400 and 550 K) is investigated on predeformed single crystals with torsion axes 〈011〉 or 〈112〉. The sum of the formation enthalpy of widely separated kink pairs on a0〈111〉/2 screw dislocations, 2HkM, and of the migration enthalpy for the migration of the kinks along these dislocations, H kM, is obtained by the peak‐shift method and found to be 2Hk + H kM = (1.275 ± 0.03) eV. This agrees with the value 2Hk = 1.22 eV deduced earlier from the analysis of the strain‐rate and temperature dependence of the flow stress of pure molybdenum after cyclic deformation into saturation. The present results are in full agreement with the view that in refractory b.c.c. metals the kink‐pair formation on screw dislocations controls the γ‐relaxation as well as the plastic deformation at low and intermediate temperatures.

Progress and problems in the understanding of the dislocation relaxation processes in metals

“…Moreover, no viable suggestion for the role of hydrogen in bringing about the ␤-relaxation could be made. The specific difficulty was that, on the one hand, the ␤-relaxation [77], Holzwarth and Seeger [82], DeLima and Benoit [83], Seeger et al [84], Funk and Schultz [85], D'Anna and Benoit [86], Werner [87], Werner and Seeger [88], Schultz et al [89], Baur et al [90], Brunner and Diehl [79], Mizubayashi et al [91], Hollang et al [78], Suzuki and Seeger [81]. occurred at too high temperatures to be attributed to the interaction of hydrogen atoms with kinks on non-screw dislocations (i.e.…”

“…The activation enthalpy H ␥ was determined by torsion-pendulum measurements on high-purity molydenum single crystals (residual resistivity ratio RRR ≈ 2.5 × 10 4 ) of two different orientations ( 1 1 0 and 1 1 2 )[81]; for the references to the ␤-relaxation measurements see text.…”

Multiscale modeling of plastic deformation of molybdenum and tungsten. III. Effects of temperature and plastic strain rate

“…However, since for ! " = 0 the activation enthalpy is equal to 2H k , the energy of a kink can be estimated with high precision from experimental data of the temperature dependence of the flow stress at low stresses [44,45] and/or from studies of internal friction [46]. Values of 2H k determined in this way for Mo and W are presented in Table 2.…”

From Vernier Defects and Verhakungen to Solitons and Kinks

“…Note the two different energy scales for Wand the other four metals. Schultz et al 1985 B Werner 1987Bauretal.1989D'Anna -Benoit 1993Mizubayashi et al 1985 §] Brunner-Diehl 1991Weller-Diehl 1982Schultz et al 1985 Brunner 2000 Suzuki -Seeger 1992Hollang et al 1997Hollang et al 2001 MQhlbach 1982 Delima - Benoit 1981Seeger et al 1982Ackermann et al 1983 Funk -Schultz 1985Holzwarth -Seeger 1991 A qualitative affirmative answer can be given for valence crystals such as Si and Ge, where both U rnax and the barrier for kink migration have been deduced to be rather high (see Fig.2). At low temperatures, these materials are indeed brittle.…”

“…For the identity of the the 13-and the 111*-relaxation see Seeger (2003). References: Mizubayashi et al (1985); Brunner-Diehl (1991); Weller-Diehl (1982); Delima-Benoit (1981); Seeger et al (1982); Ackermann et al (1983);Funk-Schultz (1985); Holzwarth-Seeger (1991); D'Anna- Benoit (1993a,b); Conrad (1963); Schultz et al (1985); Werner (1987), Werner & Seeger, (1998); Baur et al (1989); Suzuki-Seeger (1992); Hollang et al (1997;2001);MOhlbach (1982);Brunner (2000). Note the two different energy scales for Wand the other four metals.…”