Microstructures and high temperature oxidation resistance of alloys from Nb–Cr–Si system

Effect of Cr Addition on the Phase Equilibria and Oxidation Behavior of NbSi₂

“…It has been pointed out that formation of NbCrO 4 instead of Nb 2 O 5 is beneficial for suppressing the pest-like behavior and thereby enhancing the oxidation resistance of Nb silicides. 17,21) Therefore, the significant improvement in the oxidation 7 alloys, formation of crystalline SiO 2 (¡-cristobalite) during oxidation at 1200°C for 50 h was indicated in this study. It is well known that, for many silicides, amorphous SiO 2 usually forms at the early stage of its formation, and crystallization of SiO 2 gradually proceeds during exposure at temperatures higher than 1100°C.…”

“…This is consistent with the previous reports, where the formation of Nb 2 O 5 is responsible for pest-like behavior due to its porous and non-protective character. 7,17) Although the binary NbSi 2 compound did not show any protective oxidation behavior, Cr addition to NbSi 2 was found to improve the oxidation resistance drastically. At 1000°C, all the Cr-containing alloys exhibited no spalling or disintegration after oxidation up to 500 h. The surfaces of the samples have tarnished into a greenish color, implying that Cr 2 O 3 could have formed on the surface.…”

High-temperature oxidation behavior of Nb–Si–Cr alloys with Hf additions

“…Below 1000 • C orthorhombic form of Nb 2 O 5 was present, while the formation of monoclinic Nb 2 O 5 initiated above 1100 • C for 5Hf and 1200 • C for 10Hf alloy. Experiments indicate that the intermediate temperature range where bulky oxide formed might be associated by the formation of base-centered monoclinic Nb 2 O 5 since the lattice of Nb 2 O 5 expands twice when it undergoes polymorphic changes from low temperature form (␣-Nb 2 O 5 ) to ␤-Nb 2 O 5 [18]. The SiO 2 formation has been limited to temperatures above 1300 • C.…”

Elevated-temperature wear behaviors of NiMo/Mo2Ni3Si intermetallic “in situ” composites

“…A great deal of works on improvement of ductility and toughness has been carried out for binary refractory metal-based metal silicides in Mo-Si, W-Si, and Nb-Si systems, and so on. [13][14][15] It is reported that ternary metal silicides exhibit better mechanical properties, compared to the binary metal silicides, because of their relatively weaker atomic bonding which provides good toughness at high hardness so as to become a promising reinforcement phase for wear resistant composites. 16,17 Molybdenum nickel silicide Mo 2 Ni 3 Si, with a topologically closed packed (TCP) having the hP12 MgZn 2 -type Laves phase crystal lattice, has been proved to be a novel and potential high-temperature wear resistant material.…”