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1 – 10 of 52The purpose of this paper is to obtain a single setting (optimal setting) of various input parameters of pack cementation process, i.e. halide salt activator, powder of master…
Abstract
Purpose
The purpose of this paper is to obtain a single setting (optimal setting) of various input parameters of pack cementation process, i.e. halide salt activator, powder of master alloy and wt% of Y2O3 to obtain a single output characteristic as a whole namely resistance of hot corrosion for T91 steel.
Design/methodology/approach
The multi-criterion methodology based on Taguchi approach and utility concept has been used for optimization of the multiple performance characteristics namely hot corrosion rate KP1, KP2 and KP3 for pack cementation coated T91 steel in chlorine and vanadium environment.
Findings
All the three pack cementation parameters, namely, halide salt activator, powder of master alloy and wt% of Y2O3 had a significant effect on the utility function based on analysis of variance for multiple performances. The percentage contribution of halide activator (1.54 percent), master alloy powder (4.66 percent) and wt% Y2O3 (93.79 percent). The results indicated the beneficial influence of yttrium on the chemical stability of the protective layer in presence of chlorine and vanadium environments. The optimal parameter settings obtained in this study is A2B2C1, i.e. halide salt activator (NaCl), powder of master alloy (92Cr-8Al) and 1wt% of Y2O3.
Research limitations/implications
The outcome of this study shall be useful to explore the possible use of the developed coating for high temperature components. Unfortunately, the pack cementation was normally limited by the diffusion and reaction kinetics involved, which has a detrimental effect on the mechanical properties of work pieces. Therefore, reducing pack cementation temperature is required for widespread application of the pack coatings.
Social implications
Pack coating at optimum conditions can be used for surface coating technologies to economically improve high temperature oxidation, corrosion resistance of components.
Originality/value
The multi-criterion methodology based on Taguchi approach and utility concept has been used for first time for parametric optimization of wt% Y2O3 modified chromium- aluminide coatings for T91 steel.
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Somrerk Chandra-Ambhorn, Neramit Krasaelom, Tummaporn Thublaor and Sirichai Leelachao
This study aims to apply the pack cementation to develop the Fe-Al layers on the surface of FC 25 cast iron in order to increase the high-temperature corrosion resistance of the…
Abstract
Purpose
This study aims to apply the pack cementation to develop the Fe-Al layers on the surface of FC 25 cast iron in order to increase the high-temperature corrosion resistance of the alloy.
Design/methodology/approach
Pack cementation was applied on the surface of FC 25 cast iron at 1,050°C. The bare and aluminised alloys were subjected to the oxidation test in 20 per cent O2-N2 at 850 °C. Scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy and X-ray diffraction (XRD) were used for characterisation.
Findings
The layers of pack cementation consisted of Fe2Al5, FeAl2 and FeAl, and solid solution alloyed with Al. The oxidation kinetics of the bare cast iron was parabolic. Mass gain of the aluminised cast iron was significantly decreased compared with that of the bare cast iron. This was because of the protective alumina formation on the aluminised alloy surface. Al in the Fe–Al layer also tended to be homogenised during oxidation.
Originality/value
Even though the aluminising of alloys was extensively studied, the application of that process to the FC 25 cast iron grade was originally developed in this work. The significantly reduced mass gain of the aluminised FC 25 cast iron makes the studied alloy be promising for the use as a valve seat insert in an agricultural single-cylinder four-stroke engine, which might be run by using a relatively cheaper fuel, i.e. LPG, but as a consequence requires the higher oxidation resistance of the engine parts.
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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 evaluate the…
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.
C. Aravindakshan, P. Prabhakaram, A. Sen Gupta, A.N. Mukherji, P.C. Srivastava, T.L. Sharma and P.K. Roy
Aluminium diffusion treated steel by pack process using ferroaluminium was studied for its heat exchanger tube applications properties. The laboratory and inplant corrosion…
Abstract
Aluminium diffusion treated steel by pack process using ferroaluminium was studied for its heat exchanger tube applications properties. The laboratory and inplant corrosion studies reveal that the diffusion treated low carbon steel is extremely resistant to hot corrosion due to sulphurous gases encountered in heat exchanger tubes of sulphuric acid plants at the operating temperatures. The diffusion treated tubes have shown adequate physical properties for heat exchanger tube bundle fabrication.
Zinc coatings are applied commercially by hot‐dipping, electro‐deposition, metal‐spraying, cementation and vacuum deposition (see Table 5). Galvanizing (zinc hot‐dipping) has been…
Abstract
Zinc coatings are applied commercially by hot‐dipping, electro‐deposition, metal‐spraying, cementation and vacuum deposition (see Table 5). Galvanizing (zinc hot‐dipping) has been done for more than 200 years now and is undoubtedly the most widely‐used form of metal coating. The production and pro‐perties of these coatings have received intensive study over the last 10 years; much of this has been reported at the ‘International Conferences on Hot‐Dip Galvanizing’.
A.U. Malik, Rais Ahmad, Sharif Ahmad and Sultan Ahmad
Nickel aluminide coatings on mild steel have been prepared by pack cementation process. The high temperature oxidation behaviour of the coatings have been studied at 750°, 800…
Abstract
Nickel aluminide coatings on mild steel have been prepared by pack cementation process. The high temperature oxidation behaviour of the coatings have been studied at 750°, 800° and 850° in flowing air. The influence of different rare earth oxide addition on the oxidation rates of nickel aluminide coating on mild steel has also been investigated. The kinetic of the oxidation of nickel aluminide coating on mild steel, with or without addition of RE2O3 proceeds by a diffusion controlled mechanism as revealed by the parabolic nature of weight gain Vs time plots. At higher temperatures the oxidation rates of the nickel aluminide coatings are lowered down markedly irrespective of rare earth oxide concentration. The oxidation rates are significantly affected by the morphology of the oxide scales, in cases where the structure of oxide scales is not seriously disrupted due to decarburization, the oxidation rates are significantly reduced.
M.A. Quraishi and Hariom K. Sharma
Stainless steel 316 was coated with CeO2 and Y2O3 modified aluminide and titanium aluminide coatings. The coatings were prepared by the pack cementation method and the high…
Abstract
Stainless steel 316 was coated with CeO2 and Y2O3 modified aluminide and titanium aluminide coatings. The coatings were prepared by the pack cementation method and the high temperature oxidation behaviour of the coatings was investigated in an atmosphere containing a limited supply of air. The performance of the coatings was studied by measuring oxidation kinetics, and by scanning electron microscopic techniques. The oxidation rates of these coatings were reduced in the presence of CeO2 and Y2O3 due to better adherence of their oxide scales.
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M. Mobin, H.K. Sharma and S.K. Hasan
The aluminide and CeO2 and La2O3 containing aluminide coatings on carbon steel have been prepared by a pack cementation process. The influence of CeO2 and La2O3 additions on the…
Abstract
The aluminide and CeO2 and La2O3 containing aluminide coatings on carbon steel have been prepared by a pack cementation process. The influence of CeO2 and La2O3 additions on the oxidation rates of aluminide coatings has been investigated. The performance of coatings was studied by measuring oxidation kinetics, metallography, SEM and X‐ray diffraction analysis techniques. The oxidation‐resistance of coated carbon steel is discussed on the basis of a decrease in oxidation rates as well as adherence of oxide scales. The oxidation rates of carbon steel and aluminide coatings were markedly reduced in the presence of CeO2 and La2O3 in the temperature range of 700‐900°C. The oxidation rates were significantly affected by the morphology of oxide scales. In the case where the structure of oxides scales was not seriously disrupted due to decarburisation, the oxidation rates were significantly reduced.
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R.G. WING and I.R. McGILL
Turbine blades in gas turbine engines operate at elevated temperatures and in highly oxidising atmospheres that can be contaminated with fuel residues and sea water salts. These…
Abstract
Turbine blades in gas turbine engines operate at elevated temperatures and in highly oxidising atmospheres that can be contaminated with fuel residues and sea water salts. These components, which are expensive to produce, are subjected to high stresses during operation but must be totally reliable during their design life. An economic way to maintain blade properties is to coat the base metal superalloy with a protective layer capable of resisting both high temperature oxidation and hot corrosion. Conventional aluminide coatings are widely used for this purpose but platinum aluminides offer improved corrosion resistance. A collaborative exercise involving Rolls‐Royce and Johnson Matthey has now resulted in the development of a platinum aluminide diffusion coating that offers some advantages over the commercial systems.
THE METHODS available for the application of chromium coatings are listed in Table 2. Until recently most chromium coatings have been applied either by electrodeposition or…
Abstract
THE METHODS available for the application of chromium coatings are listed in Table 2. Until recently most chromium coatings have been applied either by electrodeposition or chemical vapour deposition. Vacuum and powder‐coating techniques are breaking through in strip‐coating, and electrodeposition has also been investigated extensively since steel, having a thin ‘flash‐coating’ of chromium, can compete successfully with tin‐plate.