Grain-boundary displacement, occurring in bicrystals during creep at elevated temperature {350°C},has been measured as a function of the copper content (0.1 to 8 percent) in a series of aluminum-rich aluminum-copper solid-solution alloys. The minimums in stress and temperature, below which grain-boundary motion does not occur, increase regularly with the copper content as would be expected if recovery is necessary for movement. Otherwise, the effects, if any, of the copper solute upon grain-boundary displacement and its rate are too small for identification by the experimental technique employed. It was shown, additionally, that grain-boundary displacement appears regular and proceeds at a constant rate if observed parallel to the stress axis, whereas the motion is seen to occur in a sequence of surges and the rate, to diminish with time if the observations are made perpendicular to the stress axis. This is interpreted as further evidence that grain-boundary shearing occurs, within a layer of metal of finite thickness and not by sliding upon a single interface.
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