Figure 1. Elongation as a function of strain rate in 4% hydrogen/ nitrogen.

Mechanical properties of eutectic Fe30Ni20Mn35Al15 Ian Baker, Dartmouth College,DMR 0905229

The objective of this project is to understand and model the microstructure and deformation mechanisms controlling the strength and ductility as a function of temperature and strain rate for different lamellar spacings in a recently-discovered, high-strength, ductile, two-phase, FeNiMnAl eutectic alloy, Fe30Ni20Mn35Al15.

Tensile tests of the alloy performed at strain rates from 3 x 10 -6 s-1 to 3 x 10-1 s-1 in 4% hydrogen/nitrogen showed that the material is sensitive to hydrogen, i.e. the elongation was ～ 4% when the strain rate was 3 x 10-3 s-1 or lower, and increased gradually with increasing strain rate. The elongation at 3 x 10 -1 s-1 was ～ 11%, which is similar to the value from tests performed in oxygen and in air at high strain rates. Testing in air at low strain rates also produced reduced elongations.

Figure 1. Elongation as a function of strain rate in 4% hydrogen/nitrogen.

We also performed wear tests on as-cast Fe30Ni20Mn35Al15 using pin-on-disk tribo-testing in four different environments: air, dry oxygen, dry argon and a 5% hydrogen/nitrogen mixture. It was found that the wear rate was about 40% lower for tests in argon compared to tests in either air or oxygen. However, the wear rate was about 1000% higher when the tests were conducted in a hydrogen-containing environment. Fig. 2 shows the worn surfaces of the pins tested in the four environments. In the oxygen-containing environment, two-body and three-body abrasive wear-controlled mechanisms were observed, while under argon plastic flow mechanisms dominated. The dramatic increase of wear in 5% hydrogen/nitrogen was due to hydrogen embrittlement. Figure 3. shows FIBbed pits produced from the tips of the wear pins, from which TEM specimens were taken.

Fanling Meng, a Ph.D. student, performed the mechanical testing, wear testing and microstructural analysis of the alloy, while Christopher Bustard, an undergraduate, helped with casting the alloy and prepared specimens for wear testing. The work involves co-operation with Dr. Paul R. Munroe from University of New South Wales, who provided elemental X-ray maps of the wear pin cross-sections using a Philips CM 200 TEM.

Figure 2: SEM images of the surfaces of the pins worn in different environments: (a) air (b) oxygen (c) argon (d) hydrogen. Parallel grooves and pits in (a), (b) and (d) show abrasive wear, while smearing of the wear tracks in (c) shows plastic flow.

Mechanical properties of eutectic Fe30Ni20Mn35Al15 Ian Baker, Dartmouth College,DMR 0905229

Figure 3. SE images from pits produced from worn pin tip using a FIB: (a) tested in argon, and (b) tested in air, showing the eutectic alloy with a crack running above it and zirconia on top.

(a)

Air Oxygen

Argon Hydrogen