Dislocation mobility in copper and zinc at 44°K

Abstract

The torsion technique for dislocation mobility studies in close-packed metallic crystals developed by Pope, et al. (1) was first extended to low temperatures by Gorman, et al. (Z). With this method, dislocation displacements are observed by x-ray diffraction on a crystal surface which was previously bonded directly to the torsion machine. Therefore a bonding agent must be utilized which is sufficiently strong to transmit the torsional stress pulse but pliable enough to prevent damage to the very soft test crystal. Various mixtures of organic solvents were found to have suitable properties when cooled to their glass-transition temperatures, and with these bonding agents mobility experiments were extended down to 66°K (2, 3, 4, 5).The torsion tests were carried out in an apparatus in which the test crystal could be cooled to any temperature down to the freezing point ·of nitrogen.Recently the apparatus was modified to increase the range of measurements to 0 4. Z K. A schematic diagram of the equipment is shown in Fig. 1. A long rod of steel or titanium, of 1. 27 cm diameter, extends from the torsion machine into a moveable liquid helium cryostat. The rod is fitted with semiconductor strain gages to record the loading and unloading torsion waves. The rod is also fitted with a test section by means of aligning bearings. The test section is supported externally by support bearings and compression springs, and may move vertically along the torsion rod. Its position is fixed by the setting on the micrometer. The test crystal sits on the aligning plate which is screwed into the bottom of the test section.Helium gas acts as the heat transfer mediurn between the cryostat and test crystal. The rate of cooling of the test crystal and the minimum temperature reached (below 77°K) are controlled by the flow rate of the transfer gas and the "~This work was supported by the U. S. Atomic Energy Commission.

The mechanics and physics of high-speed dislocations: a critical review

“…Further selective etch experiments in the next decades replicated these results in a vast number of materials, under different temperature ranges and under irradiation conditions [50]. Materials tested in this way include the metals W [51], Fe [44,52], Fe-C [53], Fe-Si [16,54,55], Al [56], Cu [57,58,59,60], irradiated Cu [61], Al-Cu alloys [17,21,57,62], Ni [63], Pb [64], Mg [65], Zn [66,67,68,59,69,70,71,72], Nb [73,74,75], α-Ti [76], In [77], K [52], Mo [65,78,79], Ag [80], and a number of ceramics and semiconductors, including pure Ge [81] and Si [82,83], LiF [48,84,85,86], BeO [87], KCl [88], Na...…”

“…Further selective etch experiments in the next decades replicated these results in a vast number of materials, under different temperature ranges and under irradiation conditions [50]. Materials tested in this way include the metals W [51], Fe [44,52], Fe-C [53], Fe-Si [16,54,55], Al [56], Cu [57–60], irradiated Cu [61], Al–Cu alloys [17,21,57,62], Ni [63], Pb [64], Mg [65], Zn [59,66–72], Nb [73–75], α -Ti [76], In [77], K [52], Mo [65,78,79], Ag [80], and a number of ceramics and semiconductors, including pure Ge [81] and Si [82,83], LiF [48,84–86], BeO [87], KCl [88], NaCl [89], KBr [90,91], InSb [82,92], GaAs [93], GaSb [82], InP [94], GeSi [95,96]. In Si, particular focus was placed on studying the mobility of dislocations under various temperatures and doping conditions, often with seemingly contradictory results [82,…”

Coarse-grained elastodynamics of fast moving dislocations

“…Extensive experiments [15][16][17] have successfully captured the motion of dislocations in materials under external loading, however, current experimental investigation of dynamic behavior of an individual dislocation in metallic solids is a daunting challenge due to the angstrom-scale core structure and the characteristic THz-level frequencies of the localized lattice vibrations associated with the fast moving dislocations. Direct experimental observation of sonic dislocations in solids were not possible until an alternative material, a plasma crystal, was recently developed [18][19][20].…”

High Velocity Behavior of Dislocations in Copper

“…to measure dislocation mobility in copper by Greenman,et al,and Jassby and Vreeland.3,4,5 Dislocation velocities up to about 90 m/sec were observed in these measurements, and the velocity increased linearly with resolved shear stress (up to about 1.7 M Pa). The velocity increased with decreasing temperature at constant stress, and it was concluded that phonon drag was the primary source of resistance to dislocation motion at resolved stresses areater than about 0.1 M Pa.…”