Performance assessments of porous FeCoNiCrAlx high-entropy alloys in high-temperature oxidation, carbonization and sulfidation atmospheres

Sulfidation behavior of an AlCoCrNiSi high‐entropy alloy

“…The layer built of CrAl 2 S 4 acts as a barrier controlling the diffusion rate of other components in the scale improving its protective properties. [13,16] Aluminum sulfide (Al 2 S 3 ) plays the same role when located in the scale. Unfortunately, XRD analysis provided no evidence that this sulfide was present, although the characteristic H 2 S odor, which is related to the presence of Al 2 S 3 and SiS 2 , was noticeable.…”

“…The current state of knowledge concerning HEA resistance against sulfidation is limited to three papers which present the results of selective corrosion tests on only three systems (CoCrCuFeNiAl 0.5 B x , FeCoNiCrAl x , and CrMnFeCoNi). [12][13][14] These experiments were carried out in an atmosphere containing either H 2 S or SO 2 . The results obtained from these studies indicate that the resistance of HEA against sulfur largely depends on the chemical composition of a given alloy, and the presence of elements, such as Cu and Mn, has a negative impact on this resistance.…”

“…[13] This can be attributed to the formation of Al 2 S 3 or Al-containing sulfide spinel phases on samples with significant Al concentration. [13] It is also known that aluminum, as an alloying additive, has a positive effect on the heat resistance of traditional alloys in such environments. [16,17] Moreover, increased resistance against this type of high-temperature corrosion is observed in the case of the β-NiAl intermetallic compound.…”

“…On the other hand, Al addition noticeably improves the corrosion resistance of a HEA system in a sulfidizing environment. [ 13 ] It should be emphasized, however, that in all of the above‐mentioned cases, the corrosion tests were not performed in pure sulfur vapors, but in atmospheres also containing hydrogen or oxygen, which can significantly affect both the rate of the corrosion process, as well as its mechanism.…”

“…This is in accordance with the results obtained from previously‐mentioned sulfidation studies on the similar FeCoNiCrAl x system, where it was demonstrated that the sulfidation rate decreases as aluminum content in the aforementioned HEA system increases. [ 13 ] This can be attributed to the formation of Al 2 S 3 or Al‐containing sulfide spinel phases on samples with significant Al concentration. [ 13 ] It is also known that aluminum, as an alloying additive, has a positive effect on the heat resistance of traditional alloys in such environments.…”