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Article

M. Aliofkhazraei, R. Fartash and A. Sabour Rouhaghdam

The purpose of this paper is to investigate improving high‐temperature oxidation resistance of titanium by developing new coatings based on aluminum and its combination…

Abstract

Purpose

The purpose of this paper is to investigate improving high‐temperature oxidation resistance of titanium by developing new coatings based on aluminum and its combination with the substrate. Nanocrystalline plasma electrolytic saturations were applied on the surface of commercially pure titanium in an aqueous bath. The aim was to obtain good corrosion and oxidation resistances of the differently treated samples by investigation of their nanostructures. The advantages of developed new coatings and the necessity of their use in modern gas turbine engines allow the metals to be used safely at high temperatures, which in turn can enhance the efficiency of gas‐turbine engine‐compressor sections.

Design/methodology/approach

The electrolytic saturation process was done in an aqueous bath with different effective parameters such as frequency, peak of applied pulsed voltage, etc. to obtain the desired nanostructures. Systematic characterization was carried out on as‐prepared as well as oxidized coatings and these results are presented. The performance of new coatings was evaluated by generating weight‐gain data as a function of time, followed by detailed characterization in order to confirm the ability of the coatings to prevent oxidation and alpha‐case formation. Potentiodynamic polarization and SEM nanograph analysis were undertaken to study corrosion resistance and the nanostructure of obtained layers.

Findings

The results showed that the corrosion and oxidation resistance of the obtained layers depended strongly to the average size of nanocrystallites and their nanomorphology. All coated samples had better electrochemical and oxidation behavior compared to the untreated substrate.

Practical implications

The results obtained in this research into nanocrystalline plasma electrolytic saturation can be used wherever good corrosion and oxidation resistances with high efficiency are required.

Originality/value

The speed of treatment by this technique makes this method very suitable for industrial surface treatment of different components.

Details

Anti-Corrosion Methods and Materials, vol. 56 no. 2
Type: Research Article
ISSN: 0003-5599

Keywords

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Article

H. Singh, D. Puri, S. Prakash and M. Srinivas

To characterise the high temperature oxide scales for some plasma sprayed NiCrAlY coated Ni‐ and Fe‐based superalloys.

Abstract

Purpose

To characterise the high temperature oxide scales for some plasma sprayed NiCrAlY coated Ni‐ and Fe‐based superalloys.

Design/methodology/approach

Ni‐22Cr‐10Al‐1Y metallic coatings were deposited on two Ni‐based superalloys; Superni 601 and Superni 718 and one Fe‐based superalloy; Superfer 800H by the shrouded plasma spray process. Oxidation studies were conducted on uncoated as well as plasma spray coated superalloys in air at 900°C under cyclic conditions for 50 cycles. Each cycle consisted of 1 h heating followed by 20 min of cooling in air. The thermogravimetric technique was used to approximate the kinetics of oxidation. X‐ray diffraction, SEM/EDAX and EPMA techniques were used to analyse the oxide scales.

Findings

All of the coated, as well as the uncoated, superalloys followed an alnost‐parabolic rate of oxidation. The NiCrAlY coating was found to be successful in maintaining its continuous contact with the superalloy substrates in all the cases. The oxide scales formed on the exposed NiCrAlY coated superalloys were found to be intact and spallation‐free. The main phases analysed for the coated superalloys were oxides of nickel, chromium and aluminium and spinel of nickel and chromium, which are expected to be useful for developing oxidation resistance at high temperatures.

Practical implications

The coated superalloys showed remarkable cyclic oxidation resistance under simulated laboratory conditions. However, it is suggested that these coated superalloys also should be tested in actual industrial environments of boilers and gas turbines, etc. so as to obtain more practical and reliable oxidation data.

Originality/value

The knowledge of the reaction kinetics and the nature of the surface oxide scales formed during oxidation is important for evaluating the alloys for their use and degradation characteristics in high temperature applications such as steam boilers, furnace equipment, heat exchangers and piping in chemical industry, reformer, baffle plates/tubes in fertilizer plants, jet engines, pump bodies and parts.

Details

Anti-Corrosion Methods and Materials, vol. 53 no. 5
Type: Research Article
ISSN: 0003-5599

Keywords

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Article

Rakesh Goyal, Buta Singh Sidhu and Vikas Chawla

This paper aims to discuss that a conventional Al2O3, 1.5 Wt.% carbon nanotubes (CNTs)-Al2O3, 2 Wt.% CNTs-Al2O3 and 4 Wt.% CNTs-Al2O3 composite coatings were deposited…

Abstract

Purpose

This paper aims to discuss that a conventional Al2O3, 1.5 Wt.% carbon nanotubes (CNTs)-Al2O3, 2 Wt.% CNTs-Al2O3 and 4 Wt.% CNTs-Al2O3 composite coatings were deposited with the help of Plasma spray process.

Design/methodology/approach

To better understand the effect of CNT reinforcement on oxidation resistance, high-temperature oxidation behaviour of conventional Al2O3, 1.5 Wt.% CNTs-Al2O3, 2 Wt.% CNTs-Al2O3 and 4 Wt.% CNTs-Al2O3 composite coatings at 900°C was compared with the performance of the uncoated ASME-SA213-T11 boiler tube steel substrate.

Findings

The results showed that the CNT-reinforced alumina coatings exhibited better oxidation resistance and thermal stability than uncoated ASME-SA213-T11 boiler tube steel. The coated steel substrates had a lower mass gain rate than the substrate after different oxidation times.

Originality/value

Limited literature is available where the CNT have been reinforced into the composite alloy powders and has been thermally spray-deposited for various surface engineering applications. This research showed that with the increase in the percentage of CNTs into the alloy powder mixture, there is a significant reduction in weight gain and hence higher resistance to oxidation.

Details

Anti-Corrosion Methods and Materials, vol. 65 no. 2
Type: Research Article
ISSN: 0003-5599

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Article

C.A. Smith

Introduction The basic importance of chromium in relation to passivity in the resistance of steels to aqueous corrosion is paralleled by its role as the most important…

Abstract

Introduction The basic importance of chromium in relation to passivity in the resistance of steels to aqueous corrosion is paralleled by its role as the most important alloying element in practice in securing the high‐temperature oxidation resistance of heat‐resisting steels. It is not surprising, therefore, that these two aspects of corrosion resistance developed together, and that early investigators of the chromium‐iron alloys showed interest in the potential usefulness of these materials for high‐temperature oxidation resistance.

Details

Anti-Corrosion Methods and Materials, vol. 27 no. 8
Type: Research Article
ISSN: 0003-5599

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Article

Deng Shu‐hao, Yi Dan‐qing, Gong Zhu‐qing and Su Yu‐chang

To obtain an optimized microarc oxidation (MAO) coating on magnesium alloy from an environmentally‐friendly electrolyte free of Cr6 +  and PO43− and to investigate the…

Abstract

Purpose

To obtain an optimized microarc oxidation (MAO) coating on magnesium alloy from an environmentally‐friendly electrolyte free of Cr6 +  and PO43− and to investigate the influence of oxidation potential on the morphology, composition, structure, and other properties such as micro‐hardness and corrosion resistance.

Design/methodology/approach

A constant potential regime was applied to produce the coatings and scanning electron microscopy, energy dispersive spectroscope, X‐ray diffraction, hardness testing and electrochemical methods were used to study coating properties.

Findings

The results clearly show that oxidation potential plays an important role in the formation of coating structure and properties. The MAO coating is smooth and white and consists of two layers. The external layer is loose and porous and enriched in Al and Si. Moreover, the content of Al and Si increase with operated potential. The inner layer is compact and the content of Al and Si are lower than are those of the external layer. The coating is composed of several phases: the main phase is MgAl2O4/MgO, and the minor phase is Al2O3/SiO2 when the potential is higher. The micro‐hardness of the coating obtained a maximum at a potential of 45 V, as does the corrosion resistance.

Originality/value

This paper provides information relating to MAO technology and the morphology, structure and properties of MAO coatings.

Details

Anti-Corrosion Methods and Materials, vol. 55 no. 5
Type: Research Article
ISSN: 0003-5599

Keywords

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Article

A.N. Mukherji and P. Prabhakaram

In the present work, the authors carried out siliconizing, chromizing, aluminizing and chrome‐aluminizing of mild steel in a pack cementation process with a view to…

Abstract

In the present work, the authors carried out siliconizing, chromizing, aluminizing and chrome‐aluminizing of mild steel in a pack cementation process with a view to evaluate the optimum experimental conditions to obtain satisfactory coatings which possess high resistance to oxidation. It is visualised to adopt some of the experimental conditions in later experiments where diffusion coating treatments are carried out using pastes containing the various diffusion elements. Some of the findings of the authors in siliconizing, chromizing, aluminizing and chrome‐aluminizing of mild steel in pack process are reported. It was observed that there is excess grain growth during siliconizing by the pack process and the coatings are porous and lack good oxidation resistance compared to coatings in the gas phase carried out by other workers. Chromized, aluminized and chrome‐aluminized samples are superior to 18/8 stainless steel and even Inconel in their oxidation resistance. Chromizing followed by aluminizing makes the coating layer less brittle as observed by the micro hardness measurements across the layer and hence chrome‐aluminizing will improve the spoiling resistance of the coatings.

Details

Anti-Corrosion Methods and Materials, vol. 25 no. 1
Type: Research Article
ISSN: 0003-5599

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Article

Yan Jun Xi, Yong Jun Liu, Zhi Xin Wang and Jin Bin Liu

The purpose of this paper is to investigate the oxidation behavior of Ti‐48Al‐8Cr‐2Ag (at.%) at 900°C and 1000°C for various different times.

Abstract

Purpose

The purpose of this paper is to investigate the oxidation behavior of Ti‐48Al‐8Cr‐2Ag (at.%) at 900°C and 1000°C for various different times.

Design/methodology/approach

Laboratory tests were performed to determine growth process of the oxide scale at 900°C and 1000°C for various different times with SEM/EDX, XRD and TEM.

Findings

Merely Al2O3 occurred on the Laves phase at the initial stage at 900°C, while a mixture of Al2O3+TiO2 formed at the initial stage at 1000°C. Oxidation rate of the alloy at 900°C after long‐term oxidation was higher than that at 1000°C because a dense Al2O3 scale formed on the surface at 1000°C.

Originality/value

The paper shows that the oxidation behavior of TiAl alloy at initial stage is the basis of the revealing mechanism of oxidation. It is necessary to further investigate the oxidation of Ti‐Al‐Cr‐Ag alloy in more detail to clearly understand its oxidation process and growth process of the oxide scale.

Details

Anti-Corrosion Methods and Materials, vol. 59 no. 4
Type: Research Article
ISSN: 0003-5599

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Article

Tomasz Pawel Dudziak, Hailiang Du and Prasanta Datta

The purpose of this study is to investigate the high-temperature behavior of newly developed high-impulse power magnetron sputtering system (HIPIMS) coatings and compare…

Abstract

Purpose

The purpose of this study is to investigate the high-temperature behavior of newly developed high-impulse power magnetron sputtering system (HIPIMS) coatings and compare them to the standard TiAlCr system deposited on to a Ti–Al intermetallic alloy. The corrosion test was performed in air for 4,000 hours at 850°C.

Design/methodology/approach

In this study, air oxidation test was performed at high temperature. Design and methodology is described in detail in the methodology section in the submitted manuscript. The test was carried out by discontinuous exposure of the three different systems produced by different deposition technique. The exposed samples were investigated using scanning electron microscope coupled with energy dispersive X-ray spectroscopy. The exposed samples were investigated from the surface and cross-sections.

Findings

The performed study shows that HIPIMS coatings had a much better oxidation resistance at a high temperature than that offered by the standard physical vapor deposition (PVD) system. HIPIMS costing developed Al–Cr oxide on the surface; however, cracks and detachments were found at the interface between the coating and the substrate. TiAlCr coating spalled off from the material due to the critical thickness reached; moreover, high brittleness and lack of adherence were found. Due to poor oxidation resistance, TiAlCr coating was discarded from the test after 3,000 hours of exposure.

Originality/value

The work performed in this study was designed for 4,000 hours oxidation at 850°C. The long-term exposures are not commonly met in the research work due to the cost and time. The work clearly shows differences between new type of coatings and standard PVD system applied on TiAl lightweight alloy.

Details

Anti-Corrosion Methods and Materials, vol. 62 no. 6
Type: Research Article
ISSN: 0003-5599

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Article

C.A. Smith

Introduction The behaviour of metals at elevated temperatures in an oxygen atmosphere depends upon the protection afforded to the metal by the oxide film. Highly reactive…

Abstract

Introduction The behaviour of metals at elevated temperatures in an oxygen atmosphere depends upon the protection afforded to the metal by the oxide film. Highly reactive metals such as sodium and potassium form discontinuous oxide films that provide no protection, and consequently oxidation proceeds according to a linear law—the reactive aluminium forms a protective film, but its application is limited by its low melting point. Metals like gold and platinum are inert in oxygen, but their high cost precludes their use for most high temperature engineering applications. Thus, the major part of this branch of industry is dependent on iron and iron‐base alloys for its material requirements.

Details

Anti-Corrosion Methods and Materials, vol. 28 no. 12
Type: Research Article
ISSN: 0003-5599

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Article

R. Drewett

This article is primarily concerned with those metallic diffusion coatings that are applied for the protection of iron and steel. It will be presented in three parts: 1…

Abstract

This article is primarily concerned with those metallic diffusion coatings that are applied for the protection of iron and steel. It will be presented in three parts: 1. Aluminium coatings. 2. Chromium coatings. 3. Zinc coatings. Special reference is made in each part to the available methods of application, the coatings' composition and structure, their physical properties, and their corrosion and oxidation resistance.

Details

Anti-Corrosion Methods and Materials, vol. 16 no. 4
Type: Research Article
ISSN: 0003-5599

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