Microyielding in tantalum single crystals—I. Microflow parameters

✍ Scribed by M.J. Cowling; D.J. Bacon

• Publisher: Elsevier Science
• Year: 1977
• Weight: 982 KB
• Volume: 25
• Category: Article
• ISSN: 0001-6160
• DOI: 10.1016/0001-6160(77)90006-2

✦ Synopsis

M&ract-The micraflow parameters of ~~~~a~~rn single crystals of three purity ievels have been detrrmined from uniaxiai compression tests at temperatures in the range ?7-295K. The parameters measured were the e&tic limit o,, the microyieid stress o-~*%, the activation volume t.* and the activation energy AH. Specimens were tested in the as-annealed state or after a lo,, prestrain at 77K. which increased the density of dislocatians near the screw orientation. and the data show that the mechanism of dislocation motion in these two states is different. In both cases interstitial impurities increase ee by an athermal process. but at CT,,, dislocations overcome interstitial barriers by thermal activation. The possible mechanisms of dislocation motion are discussed. and it is suggested that screw dislocations can be mobile in the microflow region above about ZOOK. Tests on crystals of different orientation produced results which were ambiguous. It is concluded that further interpretation of the data may be possible if reference is made to the results of internal friction experiments.