Competing effects of Mo addition and boronizing on oxide scale stability in Al0.25CoCr1.5FeMoₓNi high-entropy alloys
Surface and Coatings Technology, cilt.541, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 541
- Basım Tarihi: 2026
- Doi Numarası: 10.1016/j.surfcoat.2026.134073
- Dergi Adı: Surface and Coatings Technology
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Chemical Abstracts Core, Chimica, Compendex, INSPEC, Academic Search Ultimate (EBSCO), Engineering Source (EBSCO)
- Anahtar Kelimeler: Boronizing, Cr2O3, High-entropy alloys (HEAs), High-temperature oxidation, Spinel
- Ondokuz Mayıs Üniversitesi Adresli: Evet
Özet
This study systematically investigates the influence of molybdenum addition and boronizing treatment on the microstructure and high-temperature oxidation behavior of Al0.25CoCr1.5FeMoxNi (x = 0, 0.5, 1) high-entropy alloys (HEAs). The alloys were produced via vacuum arc melting and subsequently boronized at 875 °C using the powder-pack method. Cyclic oxidation tests were conducted at 900 °C for up to 30 h. Microstructural results revealed that the Mo-free alloy exhibited a homogeneous single-phase FCC structure, whereas the addition of Mo led to the formation of σ-phase and increased chemical segregation, resulting in a dual-phase (FCC + σ) microstructure. Furthermore, boronizing produced a distinct layer consisting of FeB, (Cr,Fe)B, and Mo-containing borides. A reduced boride-layer thickness was observed in the Mo-containing alloys and was associated with the chemically heterogeneous FCC + σ microstructure and the formation of mixed Mo-containing borides. High-temperature cyclic oxidation tests conducted at 900 °C demonstrated that the Mo-free alloy formed a dense and relatively compact Cr2O3 layer, providing superior oxidation resistance. In contrast, Mo addition promoted the formation of spinel-type oxides and Mo-containing phases such as NiMoO4, while the possible formation and volatilization of Mo-containing oxides such as MoO3 may have contributed to oxide-layer disruption and spallation. After boronizing, the oxidation behavior changed significantly due to the possible B2O3 formation and borate phases, which suppressed the formation of a continuous Cr2O3 layer and facilitated the development of complex and unstable oxide structures. The presence of viscous B2O3 further may have facilitated oxygen transport and contributed to oxide layer degradation.