Effect of Al and Si contents on the microstructure and oxidation behavior of Nb74-(x+y)SixTi22.5AlyHf3.5 alloys

Journal article, 2026

This study investigates the oxidation behavior at 1300 °C of Nb74-(x+y)SixTi22.5AlyHf3.5 alloys (x + y = 30–62) with varying Al + Si contents. The results indicate that the oxidation resistance depends on both the total content of Al + Si and their relative ratio. When the total Al + Si content is ≥60 at.%, a continuous α-Al2O3 protective layer forms. Among these alloys, the 27Si33Al composition (x + y = 60) exhibits the best oxidation resistance, with the lowest mass gain of 8.23 mg/cm2 after 100 h. Excessive content of either Al or Si alone leads to a decline in oxidation performance. When the total Al + Si content decreases to 50 at.% or below, depletion of the Al-rich phase causes the oxide layer to transform into a porous mixture of oxides, resulting in a sharp deterioration of oxidation resistance and the occurrence of “Pesting”. Furthermore, the 27Si33Al alloy shows favorable thermal expansion compatibility with typical Nb-Si-based alloys and the α-Al2O3 layer. This study provides a systematic bulk oxidation screening; The identified compositional window is intended to serve as a reference for future bond coat design.