Al₂O₃scale development on iron aluminides

Abstract

The structure and phase of the Al 2 O 3 scale that forms on an Fe 3 Al-based alloy found between the bands. Extended oxidation produced a double-layered scale structure, with a continuous layer at the scale/alloy interface, and a / layer at the gas surface. The mechanism for the formation of Al 2 O 3 scales on iron aluminide alloys is discussed and compared to that for nickel aluminide alloys.

Acceleration of Metastable to Alpha Transformation of Al2O3 Scale on Fe–Al Alloy by Pure-Metal Coatings at 900 °C

“…interface, and the a-Al 2 O 3 /metastable interface moved toward to the scale/metal interface. As mentioned in the introduction, metastable to a-Al 2 O 3 transformation was reported to occur at the scale/alloy interface [2,3,10,12,13]. In the present study, it was also confirmed that transformed a-Al 2 O 3 with relatively large grains was formed at the scale/alloy interface as shown in Fig.…”

“…Not only Cr, but also Fe and Ti should have this same effect on the transformation to a-Al 2 O 3 , since those elements also form corundum structure oxides, Fe 2 O 3 and Ti 2 O 3 , respectively. In fact, Fe was also frequently recognized to accelerate this Al 2 O 3 scale transformation [9][10][11].…”

“…In general, nucleation of transformed a-Al 2 O 3 was reported to occur at the metastable Al 2 O 3 scale/alloy interface [2,3,10,12,13], except an earlier TEM study reported it occurred at gas/scale interface [14]. According to above mentioned acceleration mechanism of the transformation by Cr or Fe, the nucleation of a-Al 2 O 3 may occur at the outer part of metastable Al 2 O 3 , since Cr 2 O 3 and Fe 2 O 3 are thermodynamically less stable than Al 2 O 3 , and therefore, found at the outer part of Al 2 O 3 .…”

Phase Transformation Behavior of Al2O3 Scale Formed on Pt-Modified γ′-Ni3Al-Based Alloys With and Without Hf Addition

“…The stable -Al 2 O 3 has a corundum crystal structure. Thus, other corundum-structured oxides, such as Cr 2 O 3 and Fe 2 O 3 , can serve to facilitate -Al 2 O 3 nucleation, as has been reported for Fe-and Cr-containing alloys [4,25,26]. In those studies, cross-sectional TEM analysis strongly indicated that the -Al 2 O 3 nucleated initially at the scale/alloy interface.…”

Metastable-Stable Phase Transformation Behavior of Al2O3 Scale Formed on Fe–Ni–Al Alloys

“…The phase transformation behavior of thermally grown Al 2 O 3 scale formed on Fe-and Ni-based alloys has been widely investigated [6][7][8][9][10][11][12][13]. In these studies, different factors, such as atmospheres and alloy compositions affecting the phase transformation, were reported that, for example, reactive elements, such as Y, Hf, and Zr, slow the transformation [12,13], and Fe and/or Cr accelerate the transformation [6,11].…”