Showing papers on "Alloy published in 1976"

On the heat of formation of solid alloys. II

Abstract: In Part I of this paper [1] it has been shown that a relatively simple atomic model does account for the sign of the heat of formation, ΔH, in a wide variety of alloy systems. Here we consider numerical values of ΔH for solid alloys; a quite satisfactory agreement is obtained for the heat of formation of intermetallic compounds of transition metals, including their borides, carbides and nitrides. Transition metal suicides, germanides, carbides, and nitrides, can be treated in the same way as the other compounds if one allows for an additional positive energy contribution required to convert elementary Si, Ge, C or N2 into a metal (8, 6, 24 and 57 kcal per gram-atom of these four elements, respectively). As an example, predictions for heats of formation of binary intermetallic compounds containing a rare-earth element have been tabulated.

The influence of yttrium additions on the oxide-scale adhesion to an iron-chromium-aluminum alloy

Abstract: The oxidation behavior of an Fe-27%Cr-4%Al alloy and similar alloys containing 0.023% and 0.82% Y in 1 atm oxygen at 1200°C has been examined. The oxide formed on the yttrium-free alloy develops a highly convoluted configuration, apparently resulting from lateral growth of the oxide. The latter leads to oxide detachment from the alloy at temperature and extensive spalling during cooling. It is postulated that lateral growth results from the formation of oxide within the existing oxide layer by reaction between oxygen diffusing inward down the oxide grain boundaries and aluminum diffusing outward through the bulk oxide. Additions of yttrium to the alloy apparently prevent the formation of oxide within the oxide layer, the oxide-forming reaction occurring as the alloy-oxide interface. Thus lateral growth is prevented and spalling during cooling does not occur. Secondary advantages conferred by the addition of 0.82% Y to the alloy are the prevention of void formation at the alloy-oxide interface, the avoidance of alloy grain growth during oxidation, and the creation of an oxide “keying” or “pegging” effect.

Transformation from austenite in alloy steels

Abstract: This paper is concerned with the direct transformation of austenite at high temperatures to form ferrite and alloy carbide dispersions. The ferrite/austenite interfaces vary from high energy random boundaries to low energy planar boundaries which grow by step propagation, while the alloy carbide morphologies include a pearlitic form, fine fibers and fine banded arrays of particles. It is shown that these morphologies are closely related to the mode of growth of the ferritic matrix. The role of various alloying elements on the carbide dispersion is examined, and the effects of other metallurgical variables on the banded dispersions are discussed, including factors which influence the dispersion stability. The mechanical properties of directly transformed alloy steels are shown to depend largely on the ferrite grain size and the state of the carbide dispersion. Micro-alloyed steels subjected to controlled rolling provide an excellent example of the achievement of high strength and toughness levels by control of these variables. The paper finally attempts to show how such benefits can be achieved in low and medium alloy steels, and in particular where resistance to creep failure at elevated temperatures is an important property.

Alloy scattering in ternary III-V compounds

Abstract: The mean time between scattering due to a random alloy potential is considered. The development makes use of the Warren-Cowley order parameters and uses a pseudobinary alloy model for describing the arrangement of alloy concentrations on the allowed lattice sites. The resulting mean time between scattering is found to depend inversely on the square root of temperature and energy.

Aluminum matrix composites: Fabrication and properties

Abstract: Aluminum alloy matrix composites containing 1 to 30 wt pct of fibrous and particulate nonmetals varying in size from 0.06 μm to 840 μm were fabricated. The composites were cast into cylindrical molds for friction and wear tests, hot extrusion and tensile tests. The distribution of the nonmetals in the cast ingots was homogeneous. Friction and wear tests were done on a pin (52100 bearing steel) and dish type machine without lubrication. It was found that composites containing ∼10 wt pct or more of SiC, TiC, Si3N4, Al2O3, glass, solid waste slag, and silica sand wear less than the pure matrix alloy, but have slightly higher average coefficients of friction. Wear in composites containing soft particles, especially MgO and boron nitride was higher than the pure matrix alloy. The average coefficient of friction of all the composites was in the range of 0.35 to 0.58. Increasing the sliding velocity reduced this range to ∼ 0.4 to 0.45. The longitudinal tensile properties of the extruded composites (with the exception of loss of ductility in some cases) are comparable to that of the matrix alloys. Improvements in strength or ductility were noted. For example, addition of 15 wt pct of 3 μm size Al2O3 particles raised the yield and ultimate strength of the Al-4 pct Cu-0.75 pct Mg alloy matrix from 227 to 302 MPa, and 356 to 403 MPa, respectively. The corresponding percent elongation decreased from 25.8 to 12.5. The fact that the various composites can be readily cast and hot formed suggests a variety of engineering applications.

ESCA Study of the Passive Film on an Extremely Corrosion-Resistant Amorphous Iron Alloy

Abstract: X-ray photoelectron spectroscopy was applied to study the composition of the passive film formed on an extremely corrosion resistant amorphous Fe-10at.%Cr-13at.%P-7at.%C alloy in 1 N HCl. The passive film consists mainly of hydrated chromium oxyhydroxide which is a common major constituent of passive films on crystalline stainless steels. The extremely high corrosion resistance of the amorphous alloy can only in part be attributed to the formation of a protective hydrated chromium oxyhydroxide film.

The growth of intermetallic compounds on common basis materials coated with tin and tin-lead alloys

Abstract: This paper is the second in a series which reports the results of experiments to determine the rate of compound growth at temperatures below the melting point of tin and tin alloy coatings on vario...

Processing materials with lasers

Abstract: How can we make an alloy to fit a specific materials requirement? The oldest method of alloy fabrication, casting, has two inherent limitations: Phases with high melting points are difficult to melt; and the cooling of the alloys from the melt is slow, so that alloy segregation and phase separation have time to occur. The other traditional method, powder metallurgy, has helped with the second of these problems: Allowing the homogeneous melt to be cooled in tiny droplets makes it possible at least to limit segregation to the scale of the resulting powder particles.

Electrochemical properties of aluminium alloys containing indium, gallium and thallium

Abstract: The electrochemical behaviour of aluminium alloyed with small amounts (up to 0.2%) of indium, gallium and thallium has been investigated. It has been found that these additions result in: (a) A considerable shift of the rest potential in the negative direction (to 1.4–1.7 V versus SCE), (b) A significant increase of the passivating current density (up to 0.1–1 Acm−2) and (c) A considerable decrease in the negative difference effect (increase of the faradaic efficiency to 99.5%) compared to the behaviour of pure aluminium. Except for the gallium alloy, the rate of corrosion of the alloys in neutral salt solutions is also decreased compared to that of pure aluminium. A ternary alloy, Al-0.01 In-0.01 Ga, exhibited a more negative rest potential than the Al-In alloy and a corrosion stability superior to that of the Al-Ga alloy. The negative difference effect was found to depend on the cation of the neutral salt in solution. The lowest effect was obtained in ammonium chloride solutions.

Surface plasmons in small Au-Ag alloy particles

Abstract: The optical absorption spectra in 2-butanol have been studied. The position of the absorption peak which is attributed to surface plasmons of small alloy particles depends on the composition of the alloy. The spectra obtained are qualitatively in agreement with those calculated by Mie's equation.

The relationship of microstructure to monotonic and cyclic straining of two age hardening aluminum alloys

Abstract: The effect of microstructure on the monotonic and low cycle fatigue properties of a high purity, large grain, ternary aluminum-zinc, magnesium (Al-Zn-Mg) alloy and a high strength 7050 aluminum alloy was investigated. The best combination of fatigue life, strength, and ductility for the ternary alloy resulted when aged to produce a microstructure containing predominately η′ having a Guinier radius of approximately 65a and a small amount of incoherent η (MgZn2). Superior fatigue life, strength, and ductility were found when the 7050 alloy was aged to produce the maximum number of partially coherent η′ precipitates having a Guinier radius of approximately 35a. Aging the 7050 alloy to produce particles larger than 50a gave a microstructure that had lower fatigue properties at the low plastic strain amplitudes, δep/2 <1.0 pct. The empirical CoffinManson relationship was found to hold for a given deformation process, however changes in deformation character resulted in changes in the Coffin-Manson parameters.

Surface alloying and heat treating processes

Abstract: A method is disclosed for increasing physical properties of a non-allotropic metal article along a beam affected zone. A preferred method comprises passing a high energy beam (of at least 10,000 watts/cm2 measured at the interface of the beam with the article across a predetermined surface area at a rate to cooperate with the proportioning of the total article mass with respect to the beam affected zone mass to produce a rapid self-quenching rate and thus assure a desired precipitate and/or intermetallic compound in the resolidification zone. The high energy beam is preferably a laser generated by a device having a power level of at least 500 watts. The method requires and facilitates alloying which may be varied in several respects: (a) alloying ingredients may be previously deposited over the beam affected zone so as to be turbulently mixed with melting of the base material in said zone, (b) alloying ingredients may be constituted as a wire and fed into the high energy beam to be contemporaneously melted with the base material, (c) the alloying ingredients are selected as those having an affinity to form intermetallic compounds with the non-alloptropic metal base, such as copper, manganese, chromium, zinc, cobalt, magnesium, molybdenum, titanium, vanadian, tungsten, zirconium, iron and nickel for an aluminum base and silicon as an independent wear resistance particle, and (d) the alloying ingredients are proportioned with respect to the thickness of the melted zone to render a desired alloy concentration after melting to facilitate greater hardness, greater corrosion resistance, or greater fatigue life of the affected surface region of the article.

Phase transformation of stainless steel during fatigue

Abstract: Transformation of austenite during cyclic loading was studied in AISI 301 and 304 alloys whose stability was adjusted by heat treatment and temperature changes. Fatigue life was determined under controlled strain amplitude tension-compression conditions. The amount of transformation to α’ (bcc) martensite was continuously indicated magnetically during testing, and the α’ and ∈ (hcp) phases were observed metallographically at failure. It was found in room temperature testing that at strain amplitudes in excess of 0.4 pct the formation of α’ (bcc) martensite was detrimental to the fatigue life. At 200°F (366 K) the fatigue life of an unstable alloy was increased, while in a completely stable austenitic alloy (20Cr, 6Ni, 9Mn), the life at 200°F (366 K) was less than that at room temperature for the same cyclic strain amplitude. The differing effect of temperature on life of these two types of alloy is attributed to the alteration of the austenite stacking fault energy and the relative free energies of the α’ (bcc), ∈ (hcp) and γ (fcc) phases in the unstable alloys. It has been observed that within the standard composition ranges of the two 300 series stainless steel grades there can be marked differences in the degree of transformation resulting from cyclic loading. This has the implication that for fatigue applications modifications in the specifications for the different grades of stainless would be advantageous.

Surface segregation in alloys: Equilibrium segregation of Au to the (111) surface of Ni

Abstract: The experimental pitfalls in determining the equilibrium composition of an alloy surface are discussed. Among them are too‐slow bulk diffusion, surface evaporation, and contamination. These problems are illustrated with data on alloys containing less than 1% Au in Ni. We show that in the temperature range 800°–1000 °C, one can with care measure the equilibrium concentration of Au on the surface of the alloy using Auger spectroscopy. The heat of segregation of Au to the (111) surface of Ni has been obtained to be 12±2 kcal/mole.

Electronic Structure of Ni-Mn and Ni-Fe Alloys

Abstract: The electronic structures of ferromagnetic Ni-Mn and Ni-Fe alloys are investigated theoretically. The Hartree-Fock calculation combined with the coherent potential approximation is shown to give two magnetic states for Mn and Fe atoms in Ni-Mn and Ni-Fe alloys, respectively. By introducing the ternary alloy picture in which Mn(Fe) atoms having antiparallel moments to the bulk magnetization are distinguished from Mn(Fe) atoms having parallel moments for a given Ni-Mn(Ni-Fe) alloy, the possibility of the coexistence of the two magnetic states is shown by an energy consideration. On the basis of the results obtained by this calculation, various magnetic properties are discussed.

Analysis of the Air‐Formed Oxide Film on a Series of Iron‐Chromium Alloys by Ion‐Scattering Spectrometry

Abstract: Low energy ion‐scattering spectrometry has been used to obtain the composition‐depth profiles of air‐formed oxide films on a series of iron‐chromium alloys. By using iron, chromium, , , and as standards, the atom composition ratios Cr/Fe and have been obtained quantitatively as a function of sputtering time. The air/oxide interface appears to be oxygen‐rich or metal‐deficient. The Cr/Fe ratio is low at this interface but increases and peaks a few angstroms inside it. This ratio then diminishes continuously to its value in the alloy at the oxide/metal interface. The ratio diminishes continuously from the air/oxide to the oxide/metal interface and appears to be independent of alloy composition. There is no region of constant concentration of any of the components. The average Cr content of the oxide varies linearly with alloy composition but exceeds the Cr content of the alloy. This may be associated with the method of surface preparation. Based on differences in the shape of the composition profiles, it is speculated that the distribution and bonding of cations in the oxide phase, not their concentration, differentiate the stainless from the nonstainless alloys.

Diffusion in copper and copper alloys part IV. Diffusion in systems involving elements of group VIII

Abstract: A survey, comparison, and critical analysis is presented of data compiled from the scientific literature concerning diffusion in copper alloy systems involving elements in Group VII (Co, Fe, Ni, Pd, Pt, Rh, Ru). Here the term ’’copper alloy system’’ is interpreted in the broadest sense. For example, the review of diffusion in the Cu‐M system reports all diffusion situations which involve both copper and element M. including diffusion of Cu in M or in any binary, ternary or multicomponent alloy containing M; diffusion of M in Cu or in any alloy containing Cu; and diffusion of any element in any alloy containing both Cu and M. Topics include volume diffusion, surface diffusion, grain boundary diffusion, tracer diffusion, alloy interdiffusion, electromigration, thermomigration, dislocation‐pipe diffusion, and diffusion in molten metals. An extensive bibliography is presented along with figures, tabular presentation of data and discussion of results.