Experimental Investigation of the Phase Relations in the Fe-Zr-Y Ternary System

The phase relations of the Fe-Zr-Y system at 973 K and 1073 K were experimentally investigated by using the equilibrated alloys. New ternary compounds τ3-Fe₃ZrY and τ4-Fe₁₀Zr₅Y₂ were found in this ternary system. The solubility of Y in Fe₂Zr was measured to be 3.5 at.% and the third component can hardly dissolve in the other binary intermetallic phases. Experiments have verified that Fe_2.9Zr_0.5Y_0.5 has a solid solubility ranging from Fe73Zr12Y14 to Fe77Zr9Y13.

Higher Temperatures Yield Smaller Grains in a Thermally Stable Phase-Transforming Nanocrystalline Alloy

Grains in crystalline materials usually grow with increased thermal exposure. Classical phenomena such as recrystallization may lead to a purely temporary decrease in the grain size, while recent advances in alloy design can yield thermally stable nanocrystalline materials in which grain growth stagnates. But grains never shrink, since there is a lack of interface-generating mechanisms at high temperatures, which are required to decrease the grain size if such was the system's thermodynamic tendency. Here we sidestep this paradigm by designing a nanocrystalline alloy having an allotropic phase transformation-an interface-generating mechanism-such that only the high-temperature phase is stabilized against grain growth. We demonstrate that for an Fe-Au alloy cycled through the α↔γ transformation, the high-temperature phase (γ-Fe) has a stable fine grain size, smaller than its low-temperature counterpart (α-Fe). The result is an unusual material in which an increase in temperature leads to finer grains that are stable in size.

Oxidation mechanism of porous Zr₂Fe used as a hydrogen getter

We determined the oxidation mechanism of porous ST-198, which mainly comprises Zr2Fe. Oxidation kinetics depended on temperature, oxygen partial pressure, and oxidation extent. The passivation role of oxidation in hydrogen scavenging is probably due to the development of a surface oxide, independent of oxygen concentration. Zr2Fe would be a superior hydrogen getter in oxygen-contaminated environments at high temperatures, as most oxygen will be consumed at the outer shell by mass transfer limitations, protecting the bulk of the getter for hydrogen scavenging.