SEM/EDS elemental mapping of cross-sections of the samples are shown in this figure. At 650 °C, oxygen concentrates in the oxide scale of CP Ti, while nitrogen distributes uniformly (Fig. a). However, not only Si and Nb are found in the oxide scale of the alloy, but also a nitrogen-rich scale is revealed beneath the outer oxygen-rich scale (Fig. b), in-dicating the formation of Ti2N scale. Similarly, at higher temperatures, nitrogen distributes uniformly in the oxide scale of CP Ti (Fig. c and e), while it concentrates between the Ti matrix and the outer oxygenrich scale of the alloy (Fig. d and f). In Fig. d, two Si rich regions are detected in the Ti matrix, which correspond to Ti5Si3 particles that are common in Si-containing Ti alloys .

SEM/EDS elemental mapping of cross-sections of the samples are shown in this figure. At 650 °C, oxygen concentrates in the oxide scale of CP Ti, while nitrogen distributes uniformly (Fig. a). However, not only Si and Nb are found in the oxide scale of the alloy, but also a nitrogen-rich scale is revealed beneath the outer oxygen-rich scale (Fig. b), in-dicating the formation of Ti2N scale. Similarly, at higher temperatures, nitrogen distributes uniformly in the oxide scale of CP Ti (Fig. c and e), while it concentrates between the Ti matrix and the outer oxygenrich scale of the alloy (Fig. d and f). In Fig. d, two Si rich regions are detected in the Ti matrix, which correspond to Ti5Si3 particles that are common in Si-containing Ti alloys .