Oxidation and Sulfidation Resistance of Hot-Pressed AlCrMoTaTi and AlCrNbTaTi Alloys at High Temperatures

A metallic material resistant to the attack of both oxygen and sulfur at high temperatures has been desired for years. Unfortunately, commonly used commercial oxidation-resistant materials degrade rapidly in the presence of sulfur. Conversely, sulfidation-resistant metals oxidize at a rate that eliminates their practical use in oxygen-containing atmospheres. However, the latest studies in this area strongly suggest that some refractory high-entropy alloys produced by arc melting can be resistant to oxidation and sulfidation to a degree comparable to that of several traditional materials currently used in individual gas environments. Nevertheless, melting refractory metals require high temperatures and expensive equipment. To eliminate these difficulties, this work used hot pressing to fabricate the AlCrMoTaTi and AlCrNbTaTi refractory multi-component alloys, the resistance of which was tested thermogravimetrically in atmospheres containing oxygen and sulfur vapors at temperatures ranging from 800 to 1000 °C. The achieved results clearly indicate that although these alloys are not homogeneous, they exhibit high resistance. In general, both alloys react in accordance with the parabolic law, with the AlCrMoTaTi alloy exhibiting greater resistance than the AlCrNbTaTi counterpart. Consequently, these alloys can potentially be used not only as solid materials but also in coatings produced, for example, by plasma spraying.