Creep deformation behavior of metals under repeated stress reversals

Reversed creep tests on chemical lead, 1100-F aluminum and OFHC copper were conducted and creep deformation behavior under repeated stress reversals was studied. Metallographic observations were also made to determine the nature of the structural alteration accompanying reversed creep deformation. It is shown that the creep deformation resistance of a variety of metals is reduced by repeated reversed deformation at temperatures above 0.4Tm, where Tm is the absolute melting temperature of each metal. The reduction of creep deformation resistance due to stress reversals is most prominent at approximately 0.5Tm, and it is of a persistent nature. Metallographic studies show that the observed acceleration of creep at high temperatures is in part due to the enhancement of grain boundary sliding as a result of gradual grain boundary migration toward planes of maximum shear stress during reversed creep deformation.National Aeronautics and Space Administration, Lewis Research Center, Research Grant NGR-14-005-025, 71/0