Effect of environment on the mechanical behavior of Ni–20Cr thin strip

The tensile and creep behavior of a Ni–20Cr thin strip was investigated in air and vacuum in order to determine the constitutive equations of the material and to study the effect of environment. Tensile tests were performed in air in isothermal conditions between room temperature and 900°C. A dramatic loss in ductility was observed around 800°C. Incremental loading tests were performed in air and secondary vacuum at 500–900°C. While the alloy tends to be more creep resistant in vacuum than in air at 500°C, there is no difference at higher temperatures. The effect of environment on the mechanical behavior was attributed to two competing mechanisms, a softening mechanism related to a vacancy flux toward the bulk of the alloy, as a consequence of the NiO cationic growth and a strengthening effect due to the formation of Cr2O3 as internal particles or as a continuous layer, acting as vacancy sinks.