Different oxidation protection mechanisms of HAPC silicide coating on niobium alloy over a large temperature range

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...

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Bibliographic Details
Published in:Journal of alloys and compounds 2019-06, Vol.790, p.1014-1022
Main Authors: Sun, Jia, Li, Tao, Zhang, Guang-Peng, Fu, Qian-Gang
Format: Article
Language:English
Subjects:
Adsorptivity
Aluminum oxide
Catastrophic failure analysis
Depletion
Halide activation pack cementation
Healing
Intermetallic compounds
Niobium alloy
Niobium base alloys
Niobium oxides
Oxidation
Pack cementation
Protective coatings
Silicide coating
Silicides
Silicon dioxide
Structural integrity
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Summary: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. •Oxidation behaviors of silicide coating on Nb alloy were comparatively investigated.•Adsorptive particles block the oxidation at the so-called pest temperature.•Nb2O5 was restricted by the seal-healing SiO2 at 700–1200 °C.•Seal-healing effect was weakened near eutectic point of the Nb2O5-SiO2 system.•Surface scale was overwhelmingly destroyed at temperatures above the eutectic point.
ISSN:0925-8388
1873-4669
DOI:10.1016/j.jallcom.2019.03.229