Oxidation behavior of Nb–24Ti–18Si–2Al–2Hf–4Cr and Nb–24Ti–18Si–2Al–2Hf–8Cr hypereutectic alloys at 1250 °C

Abstract

Abstract Nb–24Ti–18Si–2Al–2Hf–4Cr and Nb–24Ti–18Si–2Al–2Hf–8Cr alloys were prepared by arc melting in a water‐cooled crucible under argon atmosphere. Microstructural characteristics and oxidation resistance of the alloys at 1250 °C were investigated. The results show that, when the Cr content is 4 at%, the microstructures consist of (Nb,Ti) SS and Nb 5 Si 3 ; as Cr content increases to 8 at%, C14 Laves phase Cr 2 Nb is formed. The isothermal oxidation tests show that the oxidation kinetics of the two alloys follow similar features. The weight gains of the two alloys after oxidation at 1250 °C for 100 h are 235.61 and 198.50 mg·cm −2 , respectively. During oxidation, SiO 2 , TiO 2 , Nb 2 O 5 and CrNbO 4 are formed at first. Then, Ti 2 Nb 10 O 29 is formed after oxidation for 20 min and begins to change into TiNb 2 O 7 as the oxidation proceeds. SiO 2 is formed as solid state at first but later evolves into glassy state to improve the cohesion of the scale. After oxidation for 100 h, oxidation products consist of SiO 2 , TiNb 2 O 7 , Nb 2 O 5 and CrNbO 4 .