Oxidation Behavior of an Al-Modified Silicide Coating on an Nb-Silicide-Based Ultrahigh-Temperature Alloy

CORROSION ◽  
2010 ◽  
Vol 66 (2) ◽  
pp. 025003-025003-6 ◽  
Author(s):  
X. Tian ◽  
X. Guo
Keyword(s):  
Outer Layer ◽  
Oxidation Behavior ◽  
Al2o3 Scale ◽  
Oxidation Rate Constant ◽  
Silicide Coating ◽  
Parabolic Oxidation ◽  
Ultrahigh Temperature ◽  
Parabolic Oxidation Rate ◽  
Α Al2o3 ◽  
Pack Cementation Process

Abstract The oxidation behavior of an Al-modified silicide coating prepared through a siliconization and then an aluminization pack cementation process on an Nb-silicide-based ultrahigh-temperature alloy was investigated in air at 1,250°C. The coating consisted of a 50-μm-thick (Nb,X)Si2 (X represents Ti, Cr, and Hf elements) outer layer with (Nb,Ti)3Si5Al2 distributed discontinuously in its superficial part and a 90-μm-thick (Nb,Ti)Al3 inner layer containing Si-rich precipitates. The oxidation of this coating was controlled primarily by the preferential oxidation of Al with the formation of α-Al2O3 scale. The (Nb,Ti)Al3 inner layer could act as an Al reservoir for forming scale and maintaining the existence of (Nb,Ti)3Si5Al2 phase in the zone just beneath the scale. The parabolic oxidation rate constant of this coating was about 1.72 μm2/h, lower than that of the bare alloy by about 4 orders of magnitude.

Oxidation of Single-Crystal γ′-Ni3A1 at Low Oxygen Partial Pressure

1990 ◽  
Vol 213 ◽  
Author(s):  
E. Schumann ◽  
G. Schnotz ◽  
U. Salzberger ◽  
M. Rühle
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Oxide Scale ◽  
Special Technique ◽  
Microstructural Development ◽  
Low Oxygen ◽  
Oxidation Rate Constant ◽  
Fine Grained ◽  
Parabolic Oxidation ◽  
Parabolic Oxidation Rate

ABSTRACTSingle crystals of γ′-Ni3Al((001)-oriented) were oxidized at 1223 K under an oxygen partial pressure of ∼4 ×10−19 atm for times ranging from 0.1 to 50 hours. Microstructural development of the oxide scale and subscale metal was studied by electron microscopy. A special technique permitted the reproducible and efficient preparation of TEM cross section specimens. Initially, a fine-grained γ-Al2O3 scale formed with a preferred orientation. Depletion of Al from the γ′-Ni3Al resultedin a Ni-Al solid solution zone between the oxide scale and the intermetallic. After 20 hours oxidation, a discontinuous α-A12O3 layer between the γ-A12O3 and the metal was observed. The α-A12O3 layer exhibited a much larger grain size than that of the γ-A12O3 and was continuous after 50 hours oxidation. Formation of the α-A12O3 layer correlated with a decreasing parabolic oxidation rate constant kp, as measured by thermogravimetric analysis (TGA).

Oxidation Behavior and Pack Siliconized Oxidation-Resistant Coatings of an Nb-Based Ultrahigh Temperature Alloy

2007 ◽  
Vol 561-565 ◽  
pp. 371-374 ◽  
Author(s):  
X.P. Guo ◽  
L.X. Zhao ◽  
Ping Guan ◽  
K. Kusabiraki
Keyword(s):  
Oxidation Resistance ◽  
Double Layer ◽  
Outer Layer ◽  
Oxidation Behavior ◽  
Layer Structure ◽  
Transitional Layer ◽  
Double Layer Structure ◽  
Oxidation Resistant ◽  
Ultrahigh Temperature ◽  
Two Phases

The halide-activated pack cementation method was utilized to deposit silicide coatings on a multicomponent Nb-Ti-Si based alloy. The siliconized temperature was 1150 °C and the holding time was 10h. Both the specimens with siliconized coatings and without coatings were oxidized at 1250°C for 5, 10, 20, 50 and 100h respectively. The coating possessed a double layer structure with the composition of (Nb,X)Si2 (X represents Ti, Cr and Hf), and the outer layer was denser. The major structure in the outer layer was composed of columnar crystals perpendicular to the interface between the coating and the substrate, and that in the inner layer was mainly composed of equiaxed crystals. A transitional layer about 5μm thick was found between the coating and the substrate. After oxidation at 1250°C, the major constituents in the scale were SiO2 and TiO2 and the mole ratio of these two phases was about 2:1. The thickness of the (Nb,X)Si2 layer decreased and that of transitional layer increased as the oxidation time prolonged. The siliconized coating exhibited excellent oxidation-resistance at 1250°C within 50 hours.

Influences of Duty Ratio on Structure and Corrosion Resistance of Ceramic Coatings on Ti-6Al-4V by Micro-Plasma Oxidation

2007 ◽  
Vol 336-338 ◽  
pp. 2454-2457
Author(s):  
Hong Qi Ben ◽  
Zhong Ping Yao ◽  
Zhao Hua Jiang
Keyword(s):  
Corrosion Resistance ◽  
Outer Layer ◽  
Oxidation Process ◽  
Ceramic Coatings ◽  
Duty Ratio ◽  
Plasma Oxidation ◽  
Rutile Tio2 ◽  
Key Factor ◽  
Α Al2o3 ◽  
Better Than

Duty ratio is a key factor during micro-plasma oxidation process. Its influences on structure and corrosion resistance of ceramic coatings on Ti–6Al–4V by pulsed bi-polar MPO in NaAlO2 solution were investigated. The ceramic coatings were composed of Al2TiO5, α-Al2O3 and rutile TiO2, of which Al2TiO5 was the main crystalline. The coating can be divided into a porous outer layer and a dense inner layer. Compared with the condition of the same duty ratio for both pulses, the rise of anode duty ratio (D1) led to an increase in the amount of Al2TiO5 and α-Al2O3 and increased the thickness of the coating; whereas the rise of cathode duty ratio (D2) led to a decrease in the amount of α-Al2O3 and decreased the thickness of the coating. Besides, the corrosion resistance of the coated samples was better than that of Ti-6Al-4V substrate. When D1 / D2 = 60 / 30, the produced coating’s corrosion resistance was best.

scholarly journals Oxidation Behavior of Ferritic Steel T22 Exposed to Supercritical Water

2019 ◽  
Vol 38 (2019) ◽  
pp. 476-484 ◽  
Author(s):  
Zhongliang Zhu ◽  
Hasan Izhar Khan ◽  
Qi Cao ◽  
Naiqiang Zhang
Keyword(s):  
Iron Oxide ◽  
Supercritical Water ◽  
Layered Structure ◽  
Outer Layer ◽  
Ferritic Steel ◽  
Oxidation Behavior ◽  
Spinel Oxide ◽  
Initial Oxidation ◽  
Exposure Temperature ◽  
Oxidation Stage

AbstractThe oxidation tests of Ferritic Steel T22 exposed to supercritical water (SCW) at 540–620°C and 25 MPa was performed for up to 1000 h. The oxidation rate increased with increasing exposure temperature and time. Oxide films formed on T22 have a double-layered structure with an outer layer consisting of iron oxide and an inner layer consisting of spinel oxide. Numerous pores on the surface can be observed at the initial oxidation stage while they seemed to heal with increasing exposure time at 620°C. Cracks occurred along grain boundaries in the oxide scale when T22 exposed for 200 h at 620°C. The influence of time and temperature on the oxidation of Ferritic Steel T22 was discussed.

scholarly journals Investigation on Oxidation Behavior of Super304H and HR3C Steel in High Temperature Steam from a 1000 MW Ultra-Supercritical Coal-Fired Boiler

Energies ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 521
Author(s):  
Jingjing Li ◽  
Haidong Ma ◽  
Yungang Wang ◽  
Min Xue ◽  
Qinxin Zhao
Keyword(s):  
High Temperature ◽  
Oxide Scale ◽  
Outer Layer ◽  
Oxidation Product ◽  
Oxidation Behavior ◽  
Product Layer ◽  
Two Samples ◽  
High Temperature Steam

Oxidation behavior of Super304H and HR3C steel in high temperature steam from an ultra-supercritical coal-fired boiler was investigated in this paper. The results showed that the steam oxidized surface of Super304H ware composed of Fe2O3, Cr2O3 and FeCr2O4, the oxide scale had a thickness of 50–70 μm. In addition, the steam oxidized surface of HR3C ware composed of Fe2O3, the oxide scale was about 20μm in thickness and contained few pitting. The oxidation product layer of the two samples could be divided into two layers, including outer layer enriched O element and Fe element, and inner layer enriched O element and Cr element. Furthermore, oxide scale spalling was observed on the surface of Super304H sample.

Effects of an α-Al2O3 thin film on the oxidation behavior of a single-crystal Ni-based superalloy

2004 ◽  
Vol 35 (3) ◽  
pp. 1055-1065 ◽  
Author(s):  
Y. -F. Su ◽  
W. Y. Lee ◽  
L. F. Allard ◽  
D. W. Coffey
Keyword(s):  
Thin Film ◽  
Single Crystal ◽  
Oxidation Behavior ◽  
Α Al2o3 ◽  
Al2o3 Thin Film

Oxidation behavior of silicide coating on Ti3SiC2-based ceramic

2002 ◽  
Vol 6 (5-6) ◽  
pp. 226-231 ◽  
Author(s):  
G. M. Liu ◽  
M. S. Li ◽  
Y. C. Zhou ◽  
Y. M. Zhang
Keyword(s):  
Oxidation Behavior ◽  
Silicide Coating

The Oxidation off Iron, Nickel and Cobalt-Base Alloys Containing Aluminum

CORROSION ◽  
1965 ◽  
Vol 21 (10) ◽  
pp. 316-326 ◽  
Author(s):  
W. C. HAGEL
Keyword(s):  
Weight Gain ◽  
Internal Oxidation ◽  
Outer Layer ◽  
Al Alloys ◽  
Reaction Products ◽  
Parabolic Growth ◽  
Iron Nickel ◽  
Α Al2o3 ◽  
Cobalt Base ◽  
Continuous Weight

Abstract By conducting continuous weight-gain measurements from 500 to 1300 C on a variety of Fe-Al, Fe-Cr-Al, Ni-Al and Co-Al alloys in oxygen at 100 torr and examining the reaction products which form, reasons for the enexpected ineffectiveness of preferential aluminum oxidation have been explored. With Fe-4.4 percent Al and Fe-12 percent Al, there are two different regions of parabolic growth- these are associated with the appearance of γ-A12O3 below 900 C and α-Al2O3 above. The latter is normally more protective but possesses a greater tendency for cracking and spalling; adding 24.6 percent chromium promotes its formation at lower temperatures. With Ni-5.0 percent Al, two displaced regions are also found; here, nickel penetrates alumina to provide intermediate NiO · Al2O3 and an outer layer of NiO. With Co-4 percent Al, somewhat less cobalt penetrates γ-Al2O3 to provide CoQ · Al2O3 and an outer layer of Co3O4. When both CoO and α-Al2O3 are stable phases, the latter grows mainly by internal oxidation and offers little protection.

Microstructure and cyclic oxidation behavior of silicide coating and Si–Al coating on Cr–50Nb alloy

2014 ◽  
Vol 89 ◽  
pp. 326-330 ◽  
Author(s):  
Haizhong Zheng ◽  
Lingling Xiong ◽  
Qinhao Luo ◽  
Shiqiang Lu
Keyword(s):  
Cyclic Oxidation ◽  
Oxidation Behavior ◽  
Silicide Coating ◽  
Al Coating
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