Good High Temperature Oxidation Resistance Research Articles

Effect of Nb additions on microstructure and properties of γ-TiAl based alloys fabricated by selective laser melting

Abstract The γ-TiAl based Ti–Al–Mn–Nb alloys with different Nb additions were fabricated by selective laser melting (SLM) on the TC4 substrate. The effects of Nb content on microstructure and properties of the alloys were investigated. The results reveal that the alloys consist of γ-TiAl phase with tetragonal lattice structure and α2-Ti3Al phase with hcp lattice structure, and show a sequential structure change from near full dendrite to near lamellar structure with the increase of Nb addition. Owing to the higher Nb content in γ-TiAl phase and the formation of near lamellar structure, the alloy with 7.0 at.% Nb addition has the best combination of properties among the studied alloys, namely, not only a high hardness of HV 2000, a high strength of 1390 MPa and a plastic deformation of about 24.5%, but also good tribological properties and high-temperature oxidation resistance.

Structure of Al-based composite coatings prepared by thermal diffusion of the arc-ion plating Al coatings

In order to improve the high-temperature oxidation resistance of the hydrogen-resistant steel, Al coatings were firstly deposited on the hydrogen-resistant steel by arc-ion plating and then the thermal diffusion treatment was used to produce the Al-based composite coatings on the hydrogen-resistant steel. The effect of thermal diffusion parameters on the structure of Al-based composite coatings was studied. The crystal structure, composition and morphology of Al-based composite coatings were analyzed by using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The results showed that the double inner diffusion layer was formed on Al coatings treated at 700[Formula: see text]C. And the single inner diffusion layer with uniform composition distribution could be formed on Al coatings treated at 950[Formula: see text]C. The Al-based composite coating prepared by thermal diffusion treatment at 950[Formula: see text]C had a dense and thick [Formula: see text]-Al2O3 surface layer, and it exhibited good high-temperature oxidation resistance.

Permodur 4742

Abstract Permodur 4742 is an alloy with good high temperature strength and oxidation resistance and has an aluminum addition. The alloy is also called Ferrotherm 4742 at Edelstahlwerke Südwestfalen GmbH. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on forming, heat treating, machining, and joining. Filing Code: SS-1284. Producer or source: Deutsche Edelstahlwerke.

Microstructure and high-temperature oxidation resistance of Ti-Al-Nb coatings on a Ti-6Al-4V alloy fabricated by laser surface alloying

In this study, Ti-Al-xNb coatings were deposited on a Ti-6Al-4V alloy by laser surface alloying in order to investigate their oxidation resistance. A Ti-Al coating was fabricated for comparison. It was found that the Ti-Al and Ti-Al-xNb coatings were composed of TiAl and Ti3Al phases. Nb addition reduced the cracking tendency of the Ti-Al-xNb coatings. The Ti-Al and Ti-Al-xNb coatings exhibited good high-temperature oxidation resistance at 800 °C. In comparison, Ti-Al-xNb (x = 10, 20, 30 and 40) coatings had better high-temperature oxidation resistance and Ti-Al-40Nb coating had the best high-temperature oxidation resistance. The mechanism of Nb that improves the high-temperature oxidation resistance of Ti-Al-xNb coatings includes preventing the internal diffusion of oxygen, inhibiting the formation of TiO2, promoting the formation of Al2O3 and increasing the adhesion of the oxide scales.

High temperature oxidation resistance of Ti3SiC2 in air and low oxygen atmosphere

AbstractThe oxidation resistance of high‐purity and dense Ti3SiC2 bulk ceramic which was prepared by hot‐pressing was investigated at 700‐1200°C for 5‐40 hours in air and low oxygen atmosphere, respectively. After oxidation, the mass gain curves of Ti3SiC2 were obtained, and the oxide layer was analyzed qualitatively and quantitatively. The results showed that the oxide layer was mainly TiO2 and SiO2 mixture below 1100°C in air. When the oxidation temperature reached 1100°C and above, the oxidation proceeded rapidly, and the mass gain curves followed the parabolic law. The oxide layer changed from single‐layer to double‐layer structure, which comprised of an inner layer of TiO2 with SiO2 solid solution and an outer layer of TiO2. In low oxygen atmosphere, the oxidation was fainter than that in air. But the double‐layer structure would also occur. These two oxide layers could protect the substrate to be further oxidized. In summary, Ti3SiC2 bulk materials possess good high temperature oxidation resistance both in air and low oxygen atmosphere below 1100°C.

Effect of Long-Term Aging on the Evolution of γ' and TCP Phases of a Ni<sub>3</sub>Al Based Single Crystal Superalloy

The coarsening behavior of γ' phase and precipitation behavior of TCP phase in a Ni3Al based single crystal superalloy were investigated by experimental and calculation. The Re-containing and Mo-rich single crystal superalloy used in this study exhibit good high-temperature strength and oxidation resistance. After fully heat-treated, the experimental superalloys were aged at 1050°C and 1150°C for different time periods from 50h to 1000h. The microstructure after thermal exposure was examined by field emission-scanning electron microscopy (FE-SEM). The results indicated that the coarsening behavior of γ' phase agrees well with the typical Lifshitz-Slyozov-Wagner (LSW) theory. After thermal exposure, both the size and the volume fraction of the TCP phase changed perceptibly.

Oxidation Performance Coating for Future Supercritical Power Plants

For improved efficiency and reduced emissions, the future power plants need to operate at high temperatures and pressures, which however are limited by the durability of conventional materials such as ferritic steels. Steam oxidation of a number of coatings (Al slurries, thermal spraying, chemical vapor deposition siliconizing, and nickel plating) has demonstrated the feasibility of coatings to improve oxidation resistance. Al slurry coatings combine good high-temperature oxidation resistance through the growth of an Al2O3 layer and the possibility to apply the coating on an industrial scale at moderate cost. This work aimed to test the oxidation performance of coatings and reference alloys in ultra-supercritical (USC) water. The tested materials included Al slurry coating on ferritic 9%Cr steel and nickel-based A263 substrates, and bulk P92, MARBN, and A263 alloys as reference specimens. Oxidation resistance was tested by exposure to flowing supercritical water (SCW) with 125 ppb dissolved oxygen at 650°C (1202°F)/25 MPa (3625 psi) up to 1000 hr.

Oxidation behaviour of glass–quartz and glass–quartz–aluminium composite coatings on Ti–6Al–4V alloy

Glass–quartz and glass–quartz–aluminium composite coatings were successfully produced on Ti–6Al–4V alloy by slurry method. The oxidation behaviour of the specimens at 800°C for 100 h was studied. Both composite coatings exhibited good high temperature oxidation resistance. After oxidation for 100 h, quartz and diopside were main crystalline phases in the glass–quartz composite coating. Some open pores appeared on the surface of the glass–quartz composite coating, which might be related to the intensive crystallisation of diopside in the composite coating. While in the glass–quartz–aluminium composite coating, no open pores could be seen, and some new phases such as silicon and alumina were observed. The silicon and alumina phases might be originated from the reaction between glass and molten aluminium. Because of this, incorporation of aluminium particles into the composite coating slows the nucleation and growth rate of diopside.

Effect of electrospark deposited surface layers on bond strength of titanium–porcelain

Casting of titanium can be successfully used in prosthodontic applications, but it demands special machines and protection gas to avoid oxidation of the metal. The aims of this study are to investigate the bond compatibility between porcelain and titanium using three-point bending, oxide adherence and thermal expansion tests, and to compare the results with those of a conventional titanium–porcelain system. Titanium alloy surfaces were modified with Nb, YG8 and silicon electrode by electrospark surface modification process. The effect of electrospark surface depositing (ESD) layers on bond strength of titanium to porcelain was evaluated comparatively. Some reasons about bond strength of titanium to porcelain were discussed. Results indicate that ESD modified layer prepared in atmosphere using Si electrode can obtain the strongest bonding to porcelain. The ESD modified layer show metallurgical bond to Ti substrate. In addition, the facts that rough surface can help to improve physic bond, similar nature can also help to chemical link and compact ESD layer represent good high temperature oxidation resistance are the reasons that enhance good bond strength of titanium to porcelain.

The influence of thermal exposure on the microstructure of a Ni3Al-based single crystal superalloy

The effect of thermal exposure on the microstructure of an Ni3Al-based single crystal superalloy was investigated. The Ni3Al-based single crystal superalloy used in this experiment contained a high content of molybdenum (Mo) and a low content of chromium (Cr), which had good high-temperature strength and oxidation resistance. The alloy was exposed at 1020–1200°C for different time periods. The microstructure after thermal exposure was examined by scanning electron microscope (SEM) and field emission microscope (FEM). The results indicated that precipitation of needle-like topologically close-packed (TCP) phases was only observed at certain intermediate temperature intervals (1020–1080°C). Moreover, once the TCP phases precipitated, they would not dissolve back even after thermal exposed for 1000 h. No precipitation phases were observed after high-temperature thermal exposure at 1100–1200°C for 25 h.

Synthesis and Characterization of Fluorinated Alkyl Substituted Disiloxane

Alkyl substituted disiloxanes demonstrated promising applications as high performance hydraulic oil, diffusion pump oil, etc. In this study, fluorinated alkyl substituted disiloxane was synthesized via Grignard reaction followed by condensation reaction. Its chemical structure was verified by FTIR and NMR. Measurement results showed that this silicon oil exhibited good high temperature performance, oxidation resistance and rust resistance.

Microstructure Evolution of Fe-Al-Si and Ti-Al-Si Alloys during High-Temperature Oxidation

Alloys based on TiAl and FeAl aluminides are modern materials for high-temperature applications in automotive or aerospace industry due to low density combined with good high-temperature mechanical properties and oxidation resistance. Previous works proved that the addition of silicon to these alloys improves the oxidation resistance as well as the thermal stability. In this work, the mechanism of the silicon effect was investigated by observing the microstructure of the oxide layer and the near-surface area of the Ti-Al-Si and Fe-Al-Si alloys prepared by reactive sintering powder metallurgy. It was found that silicon improves the compactness of the oxide layers. The oxide layers on Fe-Al-Si alloys are formed by Al2O3 and small amount of iron oxide (Fe2O3) while Ti-Al-Si alloys cover by TiO2 and Al2O3 during the oxidation. Due to aluminium depletion of the alloy, a layer of silicides is formed under the oxide layer, thus acting as the additional protection against high-temperature oxidation.

High temperature oxidation resistance of cluster model designed alloys Cu-Cu12-[Mx/(12+x)Ni12/(12+x)]5 (M=Si, Cr, Cr+Fe)

Based on the stable solid solution cluster model, cupronickel is microalloylized in this paper. Alloys with different Ni-M (M=Si, Cr, Cr+Fe) ratios are designed at constant atomic ration of Cu (72.22 at.%). The high temperature oxidation resistance and mechanism of alloy are also investigated. In the Cu-Ni-Si system, the addition of Ni-Si can enhance the oxidation resistance of the alloy from two aspects: firstly, the Ni-Si is in solid solution state when being added as a cluster, it can inhibit the chemical reactivity of Cu-Ni-Si alloy; secondly, anti-oxidation precipitation can be obtained with the increase of Si/Ni ratio. Therefore, the oxidation resistance of the alloy is not because of the formation of the compact silicon oxide film. In the Cu-Ni-Cr system, the oxidation is obviously inhibited at medium temperatures (lower than 800 ℃). But at higher temperatures, the oxidation resistance is relevant to the integrality of chrome oxide layer. The high temperature oxidation resistance is closely related to Cr/Ni ratio, hence an appropriate Cr/Ni ratio is necessary for the good high temperature oxidation resistance. Compared with the third element Cr, the forth element Fe cannot be oxidized first. Therefore, combined addition of Cr and Fe can only inhibit the medium temperature oxidation, but not high temperature oxidation.

Mechanical Properties and Oxidation Resistance of CrN Coatings Deposited by Closed Field Unbalanced Magnetron Sputter Ion Plating

CrN coatings were prepared by Closed Filed Unbalanced Magnetron Sputter Ion Plating (CFUMSIP). The microstructure and morphologies of CrN coatings before and after oxidation were analyzed by XRD and SEM. At the same time, the mechanical properties and oxidation resistance of CrN coating were also studied. The results indicate that the phase in the dense CrN coatings with a hardness of 1979 HV and a adhension of 54 N was the coexistence of Cr, Cr2N and CrN. Besides, The CrN coatings showed good high-temperature oxidation resistance at 700°C while the coating failed at 800°C.

First-Principles Study on the Thermodynamic Properties of Nb, Cr<sub>2</sub>Nb and Nb<sub>5</sub>Si<sub>3</sub> Alloys

Nb-Si-Cr alloys have shown great potential as the aviation materials because of their good mechanical properties and high temperature oxidation resistance. The thermodynamic properties of Nb, Cr2Nb, α-Nb5Si3, β-Nb5Si3, as the main constituent phases of Nb-Si-Cr alloys, were calculated by first-principles methods combined with quasi-harmonic Debye model. The calculated results are in agreement with available experimental data. Compared the thermo-dynamic properties of different phases, it is found that the thermal expansions of these phases are similar and have the same trend with change of temperature. Thermal expansion coefficient of these phases are dependent with increases with temperature and decreases with pressure, respectively, while the bulk moduli decreases with increasing temperature. At last, the micro stress created by the differences in coefficients of thermal expansion between Nb and Cr2Nb upon cooling was evaluated. The result showed that the stress is too small to cause cracking at the interface between Nb and Cr2Nb.

Laser gas assisted nitriding of Hastelloy G Alloy: thermal stress analysis and characterization

Hastelloy G alloy has good high temperature strength and oxidation resistance. The hardness and tribological properties of the alloy surface can be improved through the laser nitriding process under a controlled environment. Laser gas assisted surface nitriding of Hastelloy G alloy is carried out using a CO2 laser. Temperature and stress fields in the nitrided layer are modeled using the finite element model. Metallurgical and morphological changes in the nitrided region are examined using SEM, energy dispersive spectroscopy, and X‐ray diffraction. It is found that a uniform nitride layer is formed in the surface region of the workpiece and the depth of the nitride layer extends over 40 µm below the surface. The nitride layer is free from cracks and surface abnormalities such as cavity and pores. Copyright © 2011 John Wiley & Sons, Ltd.

Oxidation resistance of SHS Fe–Al–Si alloys at 800 °C in air

Alloys formed by Fe–Al intermediary phases have lower density than common metallic high-temperature alloys and good high-temperature oxidation resistance. Previously it was proved that silicon additions to these alloys enable to produce them efficiently by reactive sintering and improves the wear resistance. In this work, the oxidation resistance of the novel Fe–Al–Si alloys containing 10–30 wt. % of aluminium and 5–30 wt. % of silicon produced by the reactive sintering technology was tested. Cyclic and isothermal oxidation tests were carried out at 800 °C in air. Tested alloys exhibit excellent oxidation resistance, which increases with silicon content up to 20 wt. %. The reasons are discussed in terms of the phase composition of the oxide layer and the changes in chemical composition under the oxide layer during oxidation.

The Effect of DCF on Codeposition of Al and Si by Pack Cementation

An energy-saving and high-efficient powder Al and Si codeposition process was employed on 1045 steel, the new technology was mainly based on applying direct current field (DCF) with proper parameters between the treated samples and the powder. The microstructure, thickness and the phase constituents of the coating were analyzed by OM and XRD. The high temperature oxidation resistance for a total duration of 120h and the corrosion resistance in 10% H2SO4 for 8h were investigated. The results showed that DCF could lower heating temperature and accelerate the diffusion rate. The phase of the coatings with DCF was composed of Al0.7Fe3Si0.3 and AlFe3. The treated samples had good high temperature oxidation resistance and corrosion resistance in 10% H2SO4 solution.

High-temperature behaviour of Ti–Al–Si alloys produced by reactive sintering

Alloys formed by Ti–Al intermediary phases have low density and very good high-temperature oxidation resistance. Further improvement of high-temperature behaviour can be achieved by a suitable addition of silicon. In this work, Ti–Al–Si alloys containing 20 wt.% of aluminium and 10–20 wt.% of silicon produced by a reactive sintering technology were tested. Isothermal oxidation tests were carried out at 1000 °C in air. The oxidation rate was determined from weight gains caused by oxide formation. Microstructure and phase composition of the oxide layers were studied. Microstructure and hardness changes after various annealing durations were described.

AK STEEL 441

Abstract AK Steel 441 has good high-temperature strength, an equiaxed microstructure, and good high-temperature oxidation resistance. The alloy is a niobium-bearing ferritic stainless steel. This datasheet provides information on composition, hardness, and tensile properties as well as deformation. It also includes information on high temperature performance and corrosion resistance as well as forming and joining. Filing Code: SS-965. Producer or source: AK Steel.