A method has been developed whereby the velocity of motion of fresh dislocations introduced into a crystal by scratching the surface may be measured as a function of stress. The velocities of unpinned edge dislocations in 3¼% silicon-iron have been measured as a function of stress over a range of five orders of magnitude in velocity from 10−7 cm/sec to 10−2 cm/sec. The velocity has been found to be very sensitive to the applied stress in this velocity range. Measurements of velocity as a function of stress have been made for four temperatures in the range 78°K to 373°K. It has been found that over this range of temperature the yield stress changes with temperature in the same way as the stress to produce a constant velocity of dislocation motion. From the result it is concluded that the rise in yield stress at low temperatures exhibited by this silicon iron is due primarily to an increase in the lattice resistance to dislocation motion and not to an increase in the Cottrell locking force. Preliminary experiments on pinned dislocations suggest that there may also be an effect of temperature on the strength of pinning by impurities which would be superimposed on the increase in lattice resistance with decreasing temperature.
The basis of intergranular corrosion in austenitic stainless steels is examined by relating the grain boundary composition to the corrosion properties. The technique of Auger electron spectroscopy has been used to obtain the chemistry of intergranular fracture surfaces. It was found that the chromium depleted zones exist and that the depletion theory was valid for tests in weakly oxidizing solutions. In highly oxidizing solutions, however, the impurity segregation and not chromium depletion best explains the deterioration of corrosion properties. Impurity elements such as sulfur, silicon, nitrogen, and phosphorous were observed in the various steels examined. An attempt is made to explain the observed corrosion properties on the basis of chromium depletion and solute segregation theories combined with an electrochemical mechanism.
The adiabatic single−crystalline elastic constant of W−3 at.% Re and W−10 at.% Re were measured in the temperature range 77−298 °K. The elastic anisotropy ratio, C44/C′, was found to follow the behavior predicted by Fisher for transition−metal alloys. Re additions to W decrease the elastic constant C′ which indicates decreasing stability of the bcc structure. This behavior is believed to be related to the d−band structure. The Debye temperature for alloys was calculated and found not to vary appreciably from the value for pure W.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.