Effect of testing atmosphere (air/in vacuo) on low cycle fatigue characteristics of a duplex stainless steel

The effect of testing atmosphere on low cycle fatigue characteristics of a duplex stainless steel has been studied at room temperature. Fatigue tests have been conducted under fully reversed plastic strain control and constant plastic strain rate in two different environments: air and in vacuo. The material has been investigated under two distinct conditions: as annealed or unaged and as thermally aged, corresponding to different dominant cyclic deformation mechanisms at the plastic strain amplitudes chosen for the study. In vacuo testing resulted in longer fatigue lives, and consequently, higher cumulative plastic strain than in air experiences for both material conditions. Although prominent fatigue micromechanisms for a given plastic strain amplitude did not seem to be affected by testing atmosphere, for both unaged and aged conditions, strain localization and cracking phenomena were enhanced in air as compared to vacuum. The experimental results were finally discussed in terms of fatigue micromechanisms-environment interactions. (C) 1999 Elsevier Science Ltd. All rights reserved.