Size effects on strength and plasticity of ferrite and austenite pillars in a duplex stainless steel

Abstract

The mechanical properties of the austenite and ferrite phases in a high Cr content 2205 duplex stainless steel (DSS) have been investigated using single crystal micropillars of size 200–2000 nm. Austenite pillars with axial orientation [123] show a strong size effect with strength increasing as pillar size decreases, following a power-law relation, with exponent -0.62. Pillars of diameter d = 300 nm show a strength >2.4 GPa. The strength of ferrite pillars with axial orientation [001] also shows a power-law with exponent -0.56 and strength > 1.5 GPa at d = 260 nm. However, [123]-orientated ferrite showed no size effect and a mean strength of 760 MPa. Both phases show localised multiple slip on non-parallel slip planes with high Schmid factors, with the ferrite showing a wider spacing of the slipped regions. On comparison with previous work, the strength of both phases in this alloy are shown to have greater strength than lower Cr content steels. Combining our data with results in the literature for larger diameter micropillar specimens supports the hypothesis that the high Cr content of the DSS leads to a larger bulk stress and a reduction in the magnitude of the apparent size effect exponent with larger pillar diameters.