Add time:07/29/2019         Source:sciencedirect.com

Oxidation behaviors of halide activated pack cementation (HAPC) silicide coatings on niobium alloy were elaborately studied by experimental and theoretical analysis. The HAPC process was performed with a commonly applied powder pack of Si, NH4F, and Al2O3 filler. Adsorptive Al2O3 particles from the pack from HAPC process played a positive role against oxidation at 700 °C (the so-called pest temperature). Above this temperature, the passion behavior rather than pulverization gradually appeared by the occurrence of seal-healing SiO2. However, the seal-healing effect was meanwhile weakened by the generation of the volatilized Si-O (g) species when the temperature rose up to the eutectic point of Nb2O5-SiO2 system. Continuously temperature-elevated (1500–1700 °C) oxidation overwhelmingly destroyed the surface protective scale by the depletion of melting Nb2O5 and the volatilization of SiO2 (g), leading to a catastrophic failure of structural integrity for the coated samples.

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