Time dependent strain rate response on applied stress reductions in creep of a Cu-16Al solid solution alloy

Abstract

In some alloys, an isothermal transition from Alloy Class to Metal Class creep behavior in the course of primary creep is observed. This holds not only for some solid alloys, but also for some precipitation strengthened, particularly some commercial heat resistant nickel base alloys. Typical model examples of solid solution alloys exhibiting the isothermal transition from Alloy Class to Metal Class creep behavior known as sigmoidal creep, are represented by alpha Cu-Al and alpha Cu-Zn alloys. Until now, the initial, maximum and minimum creep strain rates as well as operational internal stress in a Cu-16Al solid solution alloy exhibiting sigmoidal creep behavior were determined and analyzed. Also, the effect of thermal history on creep behavior of the alloy under consideration was described in some detail. In the present paper, some results of an investigation of the effects of instant applied stress reductions from {sigma} to {sigma}-{Delta}{sigma} in creep just before the minimum creep strain rate is attained at the stress {sigma} are reported. It is shown that after a stress reduction, the (positive) creep strain rate is represented by a sum of contributions resulting from Metal Class creep behavior and Alloy Class creep behavior acting in parallel. Under proper conditionsmore » of {Delta}{sigma}/{sigma}, this is manifested by sigmoidal creep.« less