High Temperature Oxidation of the Haynes 282© Nickel-Based Superalloy

Nickel-based superalloys are used in applications where corrosion and oxidation resistance at high temperatures are required together with microstructural stability. Superalloys with different metallurgical characteristics are therefore currently being developed; the high temperature behaviour of these systems must be evaluated. In this investigation, the isothermal oxidation resistance of a Haynes 282^© nickel-based superalloy was studied by gravimetric means in the temperature range 800–1,000 °C for relatively short exposure times up to 150 h. The results from the tests suggest that the parabolic rate law describes the oxidation kinetics of the alloy. The chemical composition of the oxides present in the scale comprised an outer TiO₂ layer and an inner Cr₂O₃ layer, with the latter located at the metal/oxide interface_. In addition, the formation of an internal oxidation zone of Al₂O₃ and TiO₂ was also observed at all temperatures. The role of oxide formation on microstructural changes experienced by the alloy is discussed.     

Temperature dependence of the flow stress of Fe–18Mn–0.6C–xAl twinning-induced plasticity steel

The tensile properties of Fe–18Mn–0.6C with Al-alloying additions of 0, 1.5 and 2.5 wt.% were investigated in the temperature range from 213 K (?60 °C) to 413 K (140 °C). The addition of Al resulted in an increase of the yield strength due to solid solution hardening and a decrease of the work hardening due to the suppression of deformation twinning. Both the decrease of the deformation temperature and the addition of Al suppressed the dynamic strain aging, clearly indicating an interaction between the stacking fault region of the mobile dislocation and Mn–C point defect complexes. A constitutive model for the temperature dependence of the flow stress, taking into account the thermally activated dislocation glide, Al solid solution hardening and the dynamic Hall–Petch effect caused by deformation twinning, was developed.     

Influence of Titanium on the High Temperature Oxidation and Chromia Volatilization of Ternary Ni–Cr–C Alloys

Two ternary alloys, Ni–25Cr–0.25C and Ni–25Cr–0.50C (wt%) and three versions containing also titanium (1 and 2 wt%) were cast and submitted to oxidation in dry synthetic air at 1200 °C to observe the effects of titanium on the behaviors of the nickel-based alloys belonging to this category. The mass gains are wholly parabolic in all cases and the values of the parabolic and chromia volatilization constants are typical of a chromia-forming behavior. The mass gains of the Ti-containing alloys are faster than for the Ni–Cr–C alloys, and these kinetic differences are consistent with the differences in chromia thickness and in Cr-impoverishment of the subsurface. In addition, the presence of Ti led to the development of thin a TiO₂ outer scale isolating chromia from hot air, but without benefit for the protection of Cr₂O₃ against volatilization. The obtained results also suggest that Ti may perturb the Cr diffusion in volume but also delay the oxide spallation during cooling.     

Iron Oxidation at Low Temperature (260–500 °C) in Air and the Effect of Water Vapor

The oxidation of iron has been studied at low temperatures (between 260 and 500 °C) in dry air or air with 2 vol% H₂O, in the framework of research on dry corrosion of nuclear waste containers during long-term interim storage. Pure iron is regarded as a model material for low-alloyed steel. Oxidation tests were performed in a thermobalance (up to 250 h) or in a laboratory furnace (up to 1000 h). The oxide scales formed were characterized using SEM-EDX, TEM, XRD, SIMS and EBSD techniques. The parabolic rate constants deduced from microbalance experiments were found to be in good agreement with the few existing values of the literature. The presence of water vapor in air was found to strongly influence the transitory stages of the kinetics. The entire structure of the oxide scale was composed of an internal duplex magnetite scale made of columnar grains and an external hematite scale made of equiaxed grains. ¹⁸O tracer experiments performed at 400 °C allowed to propose a growth mechanism of the scale.     

Lanthanum Effect on the Isothermal High Temperature Oxidation Behavior at 1,000 °C of a Phosphoric Acid-Treated AISI 304 Stainless Steel

Many studies have shown that a phosphoric-acid treatment improves the high temperature oxidation resistance in air of some alloys. Interestingly, though, the phosphoric-acid treatment generates a structural modification of the steel surface which is catastrophic for the high-temperature oxidation behavior at 1,000 °C. The aim of our work was to test the effect of a reactive element sol–gel coating on high-temperature oxidation resistance of phosphoric acid-treated AISI 304 steel. The oxide scale growth mechanisms were studied by exposing La-coated and uncoated phosphoric acid-treated 304 steel samples to high-temperature conditions in air. A phosphoric-acid treatment modified the structural composition and the surface morphology of the AISI 304 steel by the formation of a FeH₂P₃O₁₀ structure, leading to hematite formation and to a breakaway phenomenon. Lanthanum coating, after initial phosphoric-acid treatment, led to the formation of LaCrO₃ which limited through-scale cracking and reduced the growth of iron oxides.     

Effect of Sulphur on the Oxidation Behaviour of Possible Construction Materials for Heat Exchangers in Oxyfuel Plants in the Temperature Range 550–700 °C

During oxyfuel combustion metallic heat exchangers are subjected to service environments which substantially differ from those prevailing during the conventional air firing process. In the present study the behaviour of three selected construction materials (P92, super S304HCu and alloy 617) during exposure in simulated oxyfuel gas with and without addition of SO₂ at temperatures between 550 and 700 °C has been investigated. The alloy microstructure and the corrosion products formed during exposures up to 1000 h were studied by SEM/EDX and correlated with gravimetric data collected during the discontinuous exposures. It was found that the behaviour of the martensitic steel was hardly affected by the presence of SO₂; however, in the case of the austenitic steel S304HCu the SO₂ suppressed internal oxidation occurring at 650 °C in the SO₂-free gas, thus promoting formation of a protective chromium-rich oxide. In the case of the nickel base alloy 617 the SO₂ addition increased the corrosion rates at 550 and 650 °C due to replacement of the external chromia scale by a multiphase scale with sulphur-containing surface nodules. At 700 °C the alloy formed a chromia base surface scale and SO₂ addition suppressed the formation of volatile Cr species. The results are explained using classical oxidation theory related to conditions for external scale formation in combination with thermodynamic considerations of phase stability as well as relative rates of adsorption of various gas species.     

The Room Temperature Section of the Phase Diagram of Co-Ge-Sn Ternary System

The room temperature section of the phase diagram of Co-Ge-Sn ternary system has been determined by means of X-raypowder diffraction method.The section determined consists of 12 single-phases,22 two-phase regions,and 11 three-phase re-gions.Two new phases,called δ and η respectively in this paper,have been found.The former is a binary phase with invariablecomposition(80.46at%Sn)corresponding to formula CoSn_4,and the latter is a ternary phase occuping a homogenous range.Theexperimental data also show that Co_2Ge phase has a smaller region than that in Ref.1,2,while β-Sn,Ge,CoSn,CoSn_2 andCo_2Ge_3 are phases with invariable compositions.     

Impact of Deposits and Their Morphology on the Active Corrosion of Iron in Chlorine- and Sulfur-Containing Atmospheres in the Temperature Range of 350–500 °C

Iron-based alloys have shown high corrosion rates under ash deposits typical for waste-to-energy plants. The ashes on superheater tubes in waste incineration are multicomponent systems including alkali and alkali–earth chlorides and sulfates. Under and within such salts, the corrosive effect on the alloy is induced by a complicated interplay of such ash products. On the one hand, in chlorine-containing atmospheres iron-based alloys are believed to be attacked by the so-called active corrosion, including the formation of volatile corrosion products and their transformation into stable iron oxides. At the same time, they form complex scales, involving among other compounds iron sulfides, chlorides, and oxides. Thus, in order to directly investigate the influence of a deposit on the corrosion in waste-to-energy plants and to reproduce the scales observed on field tested superheaters, this work compares the scale formation and metal wastage under different chemically inert alumina deposits with different grain sizes to a synthetic salt as well as to an actual deposit taken from a superheater tube in a plant.     

Effect of Substrate Type and Temperature on the Tribological Properties of MoS_x Coatings

SPUTTERING deposited MoSx coatings are often usedas a solid lubricant in space applications,where a lowcoefficient of friction and long lifetime of coating areneeded.But the lubricating properties and endurancelives of sputtered MoSx coatings are strongly dependenton the sputtering parameters and the substrateconditions.Spalvin[1]showed that three groups can be dividedabout the effect of temperature on the nucleation ofMoSx coatings:(1)amorphous(-195°C);(2)crystalline-amorphous(-195°C …     

Calculation of the thermodynamic interaction parameter ρ C C,Ni , in the austenite of the Fe-C-Ni system

In the study, the interaction model has been considered, which assumes that the radius of interaction between carbon and nickel atoms in austenite corresponds to the nearest neighborhood of an octahedral interstice by lattice sites, and the interaction radius between two carbon atoms corresponds to two nearest coordination shells formed by octahedral interstices in the lattice. The three-particle potential of approach of C-Ni-C atoms is taken equal to zero. The pair potential of interaction between carbon atoms in austenite is taken to be equal to that obtained from the data of Mössbauer spectroscopy. In this model, the magnitude of the secondorder thermodynamic cross-interaction parameter ρ _C ^{C, Ni} in the austenite at a temperature of 1273 K has been calculated. The results of the calculation (ρ _C ^{C, Ni} = 11.4) satisfactorily agree with the experimental value (ρ _C ^{C, Ni} = 11.1).     

Effect of Bonding Temperature on the Microstructures and Strengths of C/C Composite/GH3044 Alloy Joints by Partial Transient Liquid-Phase（PTLP） Bonding with Multiple Interlayers

With the use of Ti/Ni/Cu/Ni multiple foils as interlayer,carbon/carbon(C/C) composite was bonded to Nibased superalloy GH3044 by partial transient liquid-phase bonding technique.The effect of bonding temperature on the microstructures and strengths of the joints was investigated.The results showed that gradient structural multiple interlayers composed of ‘‘C–Ti reaction layer/Ti–Ni intermetallic compound layer/Ni–Cu sosoloid/residual Cu layer/Ni-GH3044 diffusion layer' were formed between C/C composite and GH3044.The shear strength of the C/C composite/GH3044 joint reached the highest value of 26.1 MPa when the bonding temperature was 1,030 °C.In addition,the fracture morphology showed that the fracture mode changed with the increase of bonding temperature.     

Details on the Formation of Ti<Subscript>2</Subscript>Cu<Subscript>3</Subscript> in the Ag-Cu-Ti System in the Temperature Range 790 to 860 °C

Silver-copper-titanium (Ag-Cu-Ti) ternary alloys are often used as active braze alloys for joining ceramics to metals at temperatures ranging from 780 °C (the melting point of the Ag-Cu eutectic) up to 900 °C. When Ti/Ag-Cu joints are brazed at low temperature (near 800 °C), the intermetallic compound Ti₂Cu₃ (tetragonal, P4/nmm, a = 0.313 nm, c = 1.395 nm) is systematically missing from the interface reaction layer sequence. An experimental investigation based on isothermal diffusion experiments in the Ag-Cu-Ti ternary system has then been undertaken to clarify the issues of thermal stability and formation kinetics of this compound. Evidence has been found for the stability of Ti₂Cu₃ at temperatures ranging from 790 to at least 860 °C. By heat treating Ag-Cu-Ti powder mixtures at 790 °C for increasing times, it has moreover been shown that Ti₂Cu₃ forms at a much slower rate than the two adjacent Ti-Cu compounds: TiCu₄, the first phase to form, and Ti₃Cu₄. This explains why although thermodynamically stable, Ti₂Cu₃ is not obtained when temperature is too low or reaction time too short.     

Note on the Temperature Stability of Wüstite in Surface Oxide Films on iron

Abstract

Davies et al. have shown that, when iron is oxidised at temperatures above 700°, the oxide film present on flat specimens contains mainly wüstite (FeO), in fact the three oxides FeO, Fe₂O₄ and Fe₂O₄ are all present, approximately in the ratio 95 : 4 : 1. Below 570°, FeO is not stable, as shown by the iron–oxygen equilibrium diagram₂ and Collongues & Chaudron₃ have shown that in vacuo wüstite decomposes to give iron and magnetite at temperatures below 570°. Wüstite formed as an oxide layer on iron oxidised at temperatures above 570° should also become unstable on cooling to room temperature. The following results show how the degree of wüstite breakdown can be easily estimated.     

Temperature Dependence of the Magnetocrystalline Anisotropy in Nd_2Co_(14)B Compound

Easy and hard magnetization curves of Nd_2Co_(14)B compound have been measured withextracting-sample-magnetometer(μ_0H_(max)=6T)at 10～300 K.Magnetic anisotropy constants K_1 and K_2have been determined by fitting the hard magnetization curves,in which only K_1 ,K_2 and misalignment anglehave been taken as fitting parameters.The values of K_1 and K_2 at 4.2 K were derived by extrapolation.Anisotropy coefficients,x_2~° and x_4~°were derived from the anisotropy constants.The anisotropy constant K_2increases rapidly with increasing temperature when TT_(sr).The temperature depen-dence of the magnetic anisotropy coefficient x_2~° was fitted with the formula.The anisotropy coefficients x_2~°can be well described by the tenth-power law from 4.2 K to T_(sr)and by the sixth-power law from T_(sr_ to 300 K.     

What are the,Combined Effects of Temperature and Very High Pressure on Metals?

The inception of high-pressure, high-temperature operations has opened many new avenues of investigation. The author discusses the possible effects of both on electrical resistance, ductility, hardening, and other mechanical and structural properties of metals.     

Temperature effect in thermosonic wire bonding

1 Introduction Currently, thermosonic wire bonding and flip chip bonding are the main electrical packaging types in first level IC chip manufacture domain. Wire bonding is simple and somewhat mature, and nowadays it holds 75% in all electrical packaging …     

Understanding the Formation of Limited Interlamellar Bonding in Plasma Sprayed Ceramic Coatings Based on the Concept of Intrinsic Bonding Temperature

Interlamellar bonding is an important factor controlling the mechanical, thermal and electrical properties of plasma sprayed ceramic coatings. In order to understand the formation of limited interlamellar bonding, a theoretical model is proposed based on the concept of the intrinsic bonding temperature. The numerical simulation of the interface temperature between a molten splat and underlying splats was performed for splats with uniform and non-uniform thickness, in order to reveal the conditions for the interlamellar bonding formation. The interlamellar bonding ratio was theoretically estimated based on the bonding forming conditions. The features of interlamellar bonding revealed by the simulation agree well with the experimental observations. The bonding ratio of plasma sprayed coatings is significantly influenced by the distribution of splat thickness. According to the distribution of Al₂O₃ splat thickness in the coating, the theoretical estimation of bonding ratio yielded a value of 0.41 for the plasma sprayed Al₂O₃ coating at the ambient atmosphere conditions, which is reasonably consistent with the observation value. Therefore, the limited interlamellar bonding can be reasonably explained based on the sufficient condition that the maximum interface temperature between a molten splat and underlying splats is larger than the intrinsic bonding temperature.     

Modeling of Reversibleγ/αTransformations of Low Carbon Steels in the Intercritical Temperature Range

IN THE COURSE OF TRANSFORMATIONPROCESSES in metals and alloys(e.g.decomposition,precipitation)the reaction is often not fully complete,i.ethe transformed fraction after the accomplishment of thereaction is a positive number less than1.A typicalexample is the austenite-ferrite(7<=>cc)transformation inlow carbon hypoeutectoid steels between theequilibrium temperatures Aei and Ae3which is both anincomplete and a reversible reaction.Investigations based on computer simulationdemonstr…     

Modeling of Reversible γ／α Transformations of Low Carbon Steels in the Intercritical Temperature Range

A phenomenological kinetic model has been developed for the prediction of non-isothermal reversible incomplete transformations in low-carbon hypoeutectoid steels. The theoretical basis of the proposed method has its origin in a possible extension of the traditional Austin-Rickett kinetic differential equation. To critically assess the applicability of the model, a number of experiments based on computer simulations have been performed to predict the austenite/ferrite proeutectoid transformation in the temperature range of Ae1 to Ae3 on plain carbon hypoeutectoid steels. A comparison with published experimental data has verified that the model developed is reasonable both quantitatively and with respect to well-established trends. Extension of the method of prediction appears promising when the non-isothermal reactions occurring during heat treatment (such as carbide precipitation and dissolution) can be assumed to proceed in a reversible manner.