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Electron Microscope Observation of the Substructure Developed during Creep Deformation of Copper Single Crystals

1969; Japan Institute of Metals and Materials; Volume: 33; Issue: 11 Linguagem: Inglês

10.2320/jinstmet1952.33.11_1239

1880-6880

Tadashi Hasegawa, Hiroshi Sato, Seiichi Karashima,

Aluminum Alloy Microstructure Properties

Dislocation arrangements in copper single crystals crept at high temperatures were investigated by means of transmission electron microscopy. Creep tests were performed in argon atmosphere at 0.65Tm=610°C and 0.75Tm=745°C (Tm: the melting temperature in Kelvin). Thin foil specimens with the primary slip plane (111) parallel to the plane of the foils were prepared from the deformed crystals and examined by a 500 kV electron microscope.The main results obtained are as follows: (1) The deformation substructure at 610°C was similar to that at 745°C, except that spacings between the sub-boundaries at 610°C were smaller than those at 745°C. (2) From the results obtained by the Berg-Barrett method, etch-pit observation and transmission electron microscopy, the mobile dislocation densities in the steady-state creep were estimated to be ∼5×106/cm2 and ∼3×106/cm2 at 610°C and 745°C, respectively. (3) Dislocations bowing out from the sub-boundaries and dislocations having dipoles were observed in the vicinity of the sub-boundaries. They may be the dislocations emitted from and absorbed into the sub-boundaries, respectively. (4) In the tensile test inside the electron microscope of the thin foil specimens prepared from the deformed crystals, it was found that the dislocations bowing out from the sub-boundaries formed during creep were emitted from the sub-boundaries, and also that the glide motion of the dislocations was stopped by the sub-boundaries. It was concluded from these observations that the sub-boundaries act as sources and sinks of the mobile dislocations during high-temperature creep deformation. The mean free path of the mobile dislocations is thus limited by the sub-boundaries, that is, a few μ∼10μ and 10μ∼ a few 10μ for the primary edge and screw dislocations, respectively. (5) The fact that the dislocation density in the sub-boundaries increases and the mobile dislocation density remains constant during steady-state creep, shows that some kinds of dislocation multiplication should occur in high-temperature creep deformation.