High temperature surface protection

Alloys of the MCrAlX type are the basis for high temperature surface protection systems in gas turbines. M can be one or more of Ni, Co, or Fe and X denotes a reactive metal added to enhance oxide scale adherence. The selection and formation as well as the oxidation, hot corrosion and thermal fatigue performance of MCrAlX coatings are discussed. Coatings covered range from simple aluminides formed by pack cementation to the more advanced physical vapor deposition overlay coatings and developmental plasma spray deposited thermal barrier coatings

Auger electron spectroscopy study of oxidation of a PdCr alloy used for high-temperature sensors

A Pd-13 wt. percent Cr solid solution is a promising high-temperature strain gage alloy. In bulk form it has a number of properties that are desirable in a resistance strain gage material, such as a linear electrical resistance versus temperature curve to 1000 C and stable electrical resistance in air at 1000 C. However, unprotected fine wire gages fabricated from this alloy perform well only to 600 C. At higher temperatures severe oxidation degrades their electrical performance. In this work Auger electron spectroscopy was used to study the oxidation chemistry of the alloy wires and ribbons. Results indicate that the oxidation is caused by a complex mechanism that is not yet fully understood. As expected, during oxidation, a layer of chromium oxide is formed. This layer, however, forms beneath a layer of metallic palladium. The results of this study have increased the understanding of the oxidation mechanism of Pd-13 wt. percent Cr

Sulfidation of 310 stainless steel at sulfur potentials encountered in coal conversion systems

The sulfidation of SAE 310 stainless steel was carried out in gas mixtures of hydrogen and hydrogen sulfide over a range of sulfur potentials anticipated in advanced coal gasification processes. The kinetics, composition, and morphology of sulfide scale formation were studied at a fixed temperature of 1,065 K over a range of sulfur potentials from .00015 Nm to the -2nd power to 900 Nm to the -2nd power. At all sulfur potentials investigated, the sulfide scales were found to be multilayered. The relative thickness of the individual layers as well as the composition was found to depend on the sulfur potential. The reaction was found to obey the parabolic rate law after an initial transient period. Considerably longer transient periods were found to be due to unsteady state conditions resulting from compositional variations in the spinel layer. The sulfur pressure dependence on the parabolic rate constant was found to best fit the equation K sub p equals const. (P sub S2) to the 1/nth power, where n equals 3.7. The growth of the outer layers was found to be primarily due to the diffusion of metal ions, iron being the predominant species. The inner layer growth was due to the dissociation of the primary product at the alloy scale interface and depended on the activity of chromium

<interdisciplinary materials research including fundamental physics and chemistry of materials, environmental effects and related problems< semi-annual progress report, mar. 1 - aug. 31, 1964

Mechanical properties of polymers, phase particles in dispersion strengthened alloys, molecular structure relation in polymer flow and dispersions, and ceramics researc

Conséquences de l'oxydation haute température sur l'injection de défauts et le comportement mécanique des matériaux métalliques

L'objet de ce travail est de rendre compte de l'effet de l'oxydation haute température de matériaux métalliques à la fois sur leur évolution microstructurale ainsi que sur leur comportement mécanique. Des matériaux modèles comme le nickel, le fer et l'alliage Ni-20Cr sont étudiés. L'analyse de la microstructure d'échantillons de nickel minces oxydés à 1000°C montre que les lacunes métalliques injectées au cours de la croissance cationique de l'oxyde (NiO) peuvent diffuser sur de grandes distances via les joints de grains du métal. Quand une oxydation symétrique du nickel est pratiquée, de nombreuses cavités intergranulaires sont en effet observées, résultat de la condensation de lacunes. La germination de ces cavités n'est cependant possible qu'en présence d'une teneur minimale en carbone dans le métal. Dans le cas où une des surfaces du métal est protégée de l'oxydation (oxydation non symétrique), les lacunes sont annihilées à l'interface métal/atmosphère réductrice qui constitue un puits parfait de lacunes. L'annihilation se manifeste alors par un creusement important des sillons formés par l'émergence des joints de grains à la surface du métal. La géométrie de la pièce métallique joue un rôle primordial sur la quantité de défauts diffusant dans le métal. Cette diffusion est accompagnée par celle d'oxygène si bien qu'un mécanisme de transport de l'oxygène par les lacunes est proposé. Les essais de traction menés à la température ambiante sur du nickel de structure bambou montrent que la couche d'oxyde, très adhérente, constitue une barrière à l'émergence des dislocations, conduisant à un durcissement du métal. L'alliage Ni-20Cr est quant à lui testé en traction et en fluage entre 25 et 825°C sous atmosphère contrôlée. ABSTRACT : The aim of this work is to account for the effects of the high temperature oxidation of metals on their microstructure and their mechanical properties. "Model" materials like pure nickel, pure iron and the Ni-20Cr alloy are studied. Nickel foils have been oxidised at 1000°C on one side only in laboratory air, the other side being protected from oxidation by a reducing atmosphere. After the oxidation treatment, the unoxidised face was carefully examined by using an Atomic Force Microscope (AFM). Grain boundaries grooves were characterised and their depth were compared to the ones obtained on the same sample heat treated in the reducing atmosphere during the same time. They are found to be much deeper in the case of the single side oxidised samples. It is shown that this additional grooving is directly linked to the growth of the oxide scale on the opposite side and that it can be explained by the diffusion of the vacancies produced at the oxide scale - metal interface, across the entire sample through grain boundaries. Moreover, the comparison between single side oxidised samples and samples oxidised on both sides points out that voids in grain boundaries are only observed in this latter case proving the vacancies condensation in the metal when the two faces are oxidised. The role of the carbon content and the sample's geometry on this phenomemon is examined in detail. The diffusion of vacancies is coupled with the transport of oxygen so that a mechanism of oxygen transport by vacancies is suggested. The tensile tests realised at room temperature on nickel foils (bamboo microstructure) show that the oxide scale can constitute a barrier to the emergence of dislocations at the metal surface. Finally, the Ni-20Cr alloy is tested in tensile and creep tests between 25 and 825°C in oxidising or reducing atmospheres

Quaternary and quinary modifications of eutectic superalloys strengthened by delta Ni3Cb lamellae and gamma prime Ni3Al precipitates

By means of a compositional and heat treatment optimization program based on the quaternary gamma/gamma prime-delta, a tantalum modified gamma/gamma prime-delta alloy with improved shear and creep strength combined with better cyclic oxidation resistance was identified. Quinary additions, quaternary adjustments, and heat treatment were investigated. The tantalum modified gamma/gamma prime-delta alloy possessed a slightly higher liquidus temperature and exhibited rupture strength exceeding NASA VIA by approximately three and one-half Larson-Miller parameters (C = 20) above 1000 C. Although improvements in longitudinal mechanical properties were achieved, the shear and transverse strength property goals of the program were not met and present a continuing challenge to the alloy metallurgist

Combustion system processes leading to corrosive deposits

Degradation of turbine engine hot gas path components by high temperature corrosion can usually be associated with deposits even though other factors may also play a significant role. The origins of the corrosive deposits are traceable to chemical reactions which take place during the combustion process. In the case of hot corrosion/sulfidation, sodium sulfate was established as the deposited corrosive agent even when none of this salt enters the engine directly. The sodium sulfate is formed during the combustion and deposition processes from compounds of sulfur contained in the fuel as low level impurities and sodium compounds, such as sodium chloride, ingested with intake air. In other turbine and power generation situations, corrosive and/or fouling deposits can result from such metals as potassium, iron, calcium, vanadium, magnesium, and silicon

Life prediction of materials exposed to monotonic and cyclic loading: A new technology survey

Reviewed and evaluated technical abstracts for about 100 significant documents are reported relating primarily to life prediction for structural materials exposed to monotonic and cyclic loading, particularly in elevated temperature environments. The abstracts in the report are mostly for publications in the period April 1962 through April 1974. The purpose of this report is to provide, in quick reference form, a dependable source for current informatio

Bioleaching of Lateritic Nickel Ore using Chemolithotrophic Micro Organisms(Acidithiobacillus ferrooxidans)

In this study, the recovery of nickel from a low grade ore was attempted employing a chemolithotrophic micro organism, a bacteria, named Acidithiobacillus ferrooxidans. The factors studies were pulp density of the ore for leaching and the effect of residence time on leaching of nickel from the ore at a constant total iron. The entire experiment was carried out at room temperature. The objective of the study was thus to calculate the amount of nickel leached or extracted from a low grade ore by bio leaching methods at different pulp densities of the ore as well as at different residence times. The first step in the procedure was the collection and activation of the bacterial strains of Acidithiobacillus ferrooxidans. The bacteria were raised in a culture of 9K+ media supplied with adequate calculated amount of nutrients and were shaken continuously in a shaker cum incubator to fully activate them. The activity and fully active conditions were determined by Ferrous Iron and Total Iron estimations. Pulp densities of 2%, 5%, 10% and 20% were prepared. For each residence time, 5 conical flasks were allocated for testing samples at 0 hour, 5 days, 10 days and 15 day and a control flask were prepared. Then the samples were analyzed by an Atomic Absorption Spectrophotometer at Regional Research Laboratory, Bhubaneswar for the percentage of nickel extracted from each sample of residence time and different pulp densities. The pH was maintained at around 1.5-2 for each sample for the optimum activity of the bacteria. The data obtained was tabulated and the required graphs were drawn to get the final result. The graphs were plotted between percentage of nickel extracted vs. residence time at various pulp densities and nickel extracted vs. pulp densities at various residence times. From the graphs, it was observed that the maximum nickel extraction was observed for a pulp density of 2% at 15 days. The percentage of nickel extraction decreases with increase in pulp densities for a particular residence time. The percentage of nickel extracted increases with the increase in residence time for a particular pulp density. The percentage of nickel extracted also depends a lot on the type of ore used, modifications made on the ore as well as on the activity of the bacteria. Higher is the activity of the bacteria, more is the extraction of nickel