Oxidation behavior of Nb–Si–B alloys with the NbSi2 coating layer formed by a pack cementation technique

• Published in: International journal of refractory metals & hard materials 2013-11, Vol.41, p.103-109
• Main Authors: Cheng, Jingchang, Yi, Seonghoon, Park, Joon Sik
• Format: Article
• Language: English
• Subjects: High temperature alloy; Nb alloy; Oxidation; Pack cementation; T2 phase
• ISSN: 0263-4368; 2213-3917
• DOI: 10.1016/j.ijrmhm.2013.02.010

The oxidation behavior of Nb–Si–B alloys with NbSi2 coating layers was investigated at 1100°C under ambient atmosphere. Continuous NbSi2 layers with a thickness of 40–60μm were coated by depositing Si on the alloy surfaces at 900°C using a pack cementation technique. A sharp interface was observed between the NbSi2 layer and the pure Nb, while a (Nb5Si3+T2) two-phase region formed between the NbSi2 layer and the alloy with the T2 phase composition. During oxidation, a glassy SiO2 layer formed significantly increasing the oxidation resistance of the coated alloys. However, evaporation of B occurred forming a porous SiO2 layer during the oxidation of the alloys with high B content. The oxidation behavior of the coated pure Nb and T2 phase alloys is discussed based on a microstructural analysis of the oxidized samples. •The continuous NbSi2 layers were coated by depositing Si on the surface at 900°C through pack cementation.•A synthesized glassy SiO2 layer increased oxidation resistance of the coated alloys during oxidation.•Boron in the alloy was evaporated and a porous SiO2 layer was produced during the oxidation of alloys.