The development of techniques for the detection of inhomogeneities of deformation in nickel and the study of the effect of temperature

The processes by means of which, features present in a deformed metal or alloy may be revealed by etching are reviewed. Etchants have been developed which make possible a comparison of the deformation behaviour of nickel with that of copper and copper alloys, previously investigated by other workers. At room temperature the etchant develops periodic markings parallel to and associated with slip bands, but of wider spacing. Such markings are much better defined in nickel specimens deformed at elevated temperatures. Specimens deformed at room temperature, ultimately exhibit very extensive coarse scaled imhomogeneity of deformation but there is very little evidence of deformation banding. After deformation at elevated temperatures the coarse scaled inhomogeneity is not exhibited in significant amount. Deformation bands are present, but there are fewer the greater the temperature of deformation. Markings found by Samuels and other workers in copper and brass were not observed in nickel deformed at room and elevated temperatures, but were readily found in copper nickel alloys deformed at -183 degrees celsius. Possible reasons for the above observations are discussed and it is suggested that the markings found at -183 degrees celsium are most probably arrays of stacking faults on closely spaced planes or are heavily faulted twins. Only a loose correlation has been found, between the fraction of the the grains containing these markings and the stacking fault energy. Possible reasons for this are considered.