FeNiMnAl alloys show a wide range of microstructures and mechanical properties, but have been little explored. Studies on four different types of microstructures in this alloy system will beoutlined: 1) ultrafine microstructures (5-50 nm), present in Fe
30Ni
20Mn
20Al
30,Fe
25Ni
25Mn
20Al
30 and Fe
35Ni
15Mn
25Al
25,which consist of (Fe, Mn)-rich B2-ordered (ordered b.c.c.) and (Ni, Al)-rich L2
1-ordered (Heusler) phases, and in Fe
30Ni
20Mn
25Al
25,which consist of (Ni, Al)-rich B2 and (Fe, Mn)-rich b.c.c. phases, with the phases aligned along <100>; 2) fine microstructures (50-70 nm), present in Fe
30Ni
20Mn
30Al
20, Fe
25Ni
25Mn
30Al
20, and Fe
28Ni
18Mn
33Al
21, which consist of alternating (Fe,Mn)-rich f.c.c and (Ni, Al)-rich B2-ordered plates with an orientation relationship close to f.c.c.(002)//B2(002); f.c.c.(011)//B2(001); 3) coarser (0.5-1.5µm) lamellar microstructures observed in alloys with a lower aluminum content, such as Fe
30Ni
20Mn
35Al
15, that consistof alternating (Fe,Mn)-rich f.c.c and (Ni, Al)-rich B2-ordered phases with a Kurdjumov-Sachs orientation relationship between the phases; and 4) high-entropy Fe
40.4Ni
11.3Mn
34.8Al
7.5Cr
6alloys. The microstructures and mechanical properties in these alloys have been determined as a function of annealing time, testing temperature and strainrate. Some of the unusual mechanical behavior that has been observed will be emphasized. This research was supported by the US Department of Energy (DOE), Office of Basic Energy Sciences (grant DE-FG02-07ER46392).
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