The effects of chromium on the microstructure and tensile behavior of Fe30Ni20Mn35Al15

The effects of different additions of chromium (≤8 at. %) on both the microstructure and room-temperature flow and fracture behavior of as-cast Fe30Ni20Mn35Al15 have been investigated. For ≤6 at. % Cr, the microstructure was lamellar consisting of (Ni, Al)-rich B2 and (Fe, Mn)-rich f.c.c. phases with most of the Cr residing in the f.c.c. phase, whilst the addition of 8 at. % Cr produced a more complex microstructure. The room-temperature elongation to failure at a strain rate of 5×10−4 s-1 increased with increasing Cr from 6.5% for the Cr-free material to ~18% at 6 at. % Cr, and then decreased dramatically for 8 at. % Cr to 6.3 %. Concomitantly, the yield stress decreased slightly from 820 to 679 MPa as the Cr content increased to 6 at. %, and then increased to 819 MPa for 8 at. % Cr. The addition of 6 at. % Cr also resulted in the complete suppression of the environmental embrittlement that is observed at slow strain rate at room temperature in the Cr-free alloy [1], i.e. at a strain rate of 3×10−6 s−1 unalloyed Fe30Ni20Mn35Al15 showed only 0.7% elongation, whereas the alloy with 6 at. % Cr exhibited 18% elongation. The 6 at. % Cr modified alloy showed a similar temperature dependence of the yield strength as the Cr-free alloy [2], with the yield strength decreasing steadily to 150 MPa at 1000 K. Interestingly, the elongation to failure was largely independent of temperature for this alloy.