Creep as a Surface Dependent Phenomenon.

Comparative creep tests have been described for single crystal and polycrystalline zinc, with and without the presence of a surface layer containing electrodeposited copper. For polycrystalline zinc, neither the creep rate at constant temperature and load, nor the temperature dependence of the creep rate at constant load was affected by the presence of copper in the surface layer. The single crystals, on the other hand, showed a marked increase in the resistance to creep as a result of the electrodeposited copper layer. The copper also caused an increase in the temperature dependence of the creep rate, suggesting that a higher activation energy is required to generate dislocations when copper is present in the surface layer. A study was made of the steady state creep behavior of A nickel in different environments and surface conditions. It was found that resistance to high temperature creep was much greater in air than in either purified hydrogen or nitrogen. The presence of tungsten in the surface layer did not affect the resistance to creep. In regard to the temperature dependence of steady state creep, A nickel was found to be insensitive to conditions at the surface. An important conclusion resulting from this work is the fact that under certain conditions, creep is a surface dependent phenomenon.