Oxidation Behavior of Fe–Al, Fe–Si and Fe–Al–Si Intermetallics

Abstract

Iron aluminides are still deeply investigated materials for their use in power plants, automotive and chemical industry, and other sectors. This paper shows that it is possible to strongly improve their oxidation behavior by the addition of silicon. The description of the synergic effect of aluminum and silicon on the oxidation behavior of Fe–Al–Si alloys at 800 °C in air is presented. The oxidation rate, microstructure, phase, and chemical composition of these ternary alloys are compared with the binary Fe–Al and Fe–Si alloys. Results showed that the oxidation of Fe–Al–Si ternary alloys provides an oxide layer based on aluminum oxide with a low concentration of iron and silicon. Below this oxide layer, there is a layer of silicides formed as a result of depletion by aluminum, which forms a secondary oxidation protection.

Effect of Nickel and Titanium on Properties of Fe-Al-Si Alloy Prepared by Mechanical Alloying and Spark Plasma Sintering

“…The effect of silicon on the oxidation behavior was thoroughly discussed in our previous works [15,17]. The effect of alloying elements (Ni and Ti) on the oxidation behavior was examined in this work.…”

“…However, it was possible to recognize them by optical microscopy. On the optical micrographs, the silicides appear as the white particles, Fe 2 Al 5 forms the dark grey regions, and the FeAl phase is the matrix (Figure 2a) due to different etching sensitivity of the phases [17]. These phases, especially the aluminum-rich Fe 2 Al 5 phase, are visible on the EDS map ( Figure 3).…”

“…Powder metallurgy methods, including our high-energy mechanical alloying [18] and spark plasma sintering, allowed for an increase in the fracture toughness, but the values at room temperature still reached the parameters of brittle ceramics, i.e., approximately 3.5 MPa.m 1/2 [16]. Due to these parameters, the alloy could be applicable as a protective coating rather than as a bulk material.In recent research, we studied the high-temperature oxidation resistance of Fe-Al-Si alloys and its dependence on the Al:Si ratio, and we found that the 35:5 provided almost the same oxidation performance [17]. Since silicon is listed as a critical raw material in the EU [19], the minimization of its amount is reasonable.…”

“…In recent research, we studied the high-temperature oxidation resistance of Fe-Al-Si alloys and its dependence on the Al:Si ratio, and we found that the 35:5 provided almost the same oxidation performance [17]. Since silicon is listed as a critical raw material in the EU [19], the minimization of its amount is reasonable.…”

“…plasma sintering [16]. The alloys exhibited a very good oxidation resistance at high temperatures-much better than binary Fe-Al and Fe-Si alloys [17]. The improvement of oxidation resistance does not lie in the incorporation of silicon to the oxide layer in a significant amount; rather, it lies in the formation of large volume fraction of silicides under the oxide layer, when aluminum diffuse to the surface in order to form Al 2 O 3 .…”