Showing papers on "Alloy published in 1979"

Pressure derivatives of the elastic moduli of BCC Ti-V-Cr, Nb-Mo and Ta-W alloys

Abstract: The single-crystal elastic moduli Cij and their pressure derivatives dCij/dP have been measured ultrasonically at 25 degrees C for six Ti-V-Cr, eight Nb-Mo and seven Ta-W solid solutions. The rigid-band model for the alloy electronic structure is known to work fairly well for these BCC metals in predicting the density of states at the Fermi energy and related properties. The results of this study show that changes in the composition dependence of the Cij and dCij/dP appear to be related to specific topological changes in the Fermi surface which occur as the electron population varies in the rigid-band model. The relationship between the bandstructure and the Cij is discussed and a qualitative explanation is given for the correlations between the moduli and the Fermi surface and for some of the differences between the three alloy series.

Macrosegregation in a multicomponent low alloy steel

Abstract: Macrosegregation theory is extended to predict the formation of channel-type segregation for multicomponent systems. Specifically, calculations are carried out for 0.7 pct C steel, by considering heat, mass and momentum transport in the mushy zone. In the model used for calculations the momentum transport equation and the energy equation were solved simultaneously. It is confirmed, by comparing calculated results with experimental results, that this model successfully predicts the occurrence of channel-type segregation. This analysis is also more rigorous than previous works on macrosegregation because previous analyses were done by solving for convection in the mushy zone with an “uncoupled” temperature field. Using the model, the effects of adjusting the compositions of silicon and molybdenum in steel were quantitatively evaluated in order to show how channel-type segregates can be avoided by adjusting alloy composition. A method of optimizing composition to minimize segregation is presented. It is recommended that this methodology be applied to alloy design so that ingots of alloys amenable to commercial practice can be obtained readily with a minimum amount of “trial-and-error” development work and expense.

Formation and magnetic properties of Fe-B-Si amorphous alloys

Abstract: The magnetic properties and crystallization temperatures of alloys in the ternary Fe-B-Si system are reported. The Curie temperature increases slightly on replacement of boron by silicon. This results in a sharp ridge of relatively constant room-temperature saturation magnetization extending from Fe 80 B 20 to Fe 82 B 12 Si 6 . The coercivity exhibits a broad minimum, both before and after stress relief annealing, in the region around Fe 81 B 15 Si 4 and extending at least to Fe 77 B 13 Si 10 . The crystallization temperature increases with increasing silicon and with decreasing iron and boron. The alloys with silicon are generally easier to prepare in the amorphous state than the binary Fe-B alloys. Thus for the highest saturation magnetization alloy combined with ease of preparation, stability, and lowest losses, the alloys between Fe 81 B 17 Si 2 and Fe 82 B 12 Si 6 are preferred.

X‐Ray Photoelectron Studies of the Aqueous Oxidation of Inconel‐600 Alloy

Abstract: Aqueous oxidation of the nickel‐based alloy Inconel‐600 has been studied using x‐ray photoelectron spectroscopy as the primary means of determining the elemental composition and chemistry of the surface films produced. Composition profiles of the entire film thickness back to the metal‐oxide interface were determined using ion bombardment for controlled removal of successive surface layers. Samples of the alloy were exposed to aqueous attack in static and continuous autoclaves at 285°C for periods of 1–168 hr. The pH range 7–14 was studied and the dissolved oxygen concentration was varied from using hydrogen, argon, and oxygen overpressures. In hydrogen‐saturated water of pH 10, a thin (<10 nm) film, rich in chromium oxide forms. This is shown to result from a solid‐state growth process. A similar film, rich in chromium oxide, grows on Inconel‐600 in pH 10 water containing higher concentrations of dissolved oxygen, but it is rapidly overgrown by a nonpassivating layer of metal hydroxides whose composition and rate of growth vary with the oxygen concentration of the solution. The chemical stability of the alloy surface is likely determined by the magnitude of the solubility of the chromium oxide layer which is formed on initial oxidation.

Solution treatment behavior of Co-Cr-Mo alloy

Abstract: Current practice in the manufacture of Co-Cr-Mo alloy total hip prostheses is the use of a solution treatment to increase the ductility of the as-cast alloy. This study is concerned with the reactions encountered during solution treatment at temperatures between 1165-1270 degrees C. These reactions, including incipient melting, a carbide transformation from M23C6 to M6C and sigma-phase formation, have been examined using both qualitative and quantitative metallographic techniques, and are shown to influence the production of a single phase microstructure. As a result, an optimum temperature for solution treatment of 1220 degrees C has been determined. It is further proposed that a reduction in the carbon content of this alloy would improve its solution treatment behavior.

Effect of low-temperature annealing and deformation on the structure of metallic glasses by X-ray diffraction

Abstract: The changes in the atomic structure of amorphous Pd-Si and Ni-P alloys due to low-temperature annealing, cold-rolling and isothermal creep have been studied by the conventional X-ray diffraction. The present results on the effect of low-temperature annealing were consistent with those of amorphous Fe40Ni40P14B6 alloy studied by the energy dispersive X-ray diffraction method. In addition, the present results have indicated that the effect of cold-rolling causes small changes in the structure of amorphous Pd80Si20 alloy which are qualitatively different from the structural relaxation, and the effect of annealing plays a significant contribution in the structural change during an isothermal creep test.

Photoluminescence in ZnSe grown by liquid‐phase epitaxy from Zn‐Ga solution

Abstract: Photoluminescence has been studied of epitaxial ZnSe layers grown from a pure Zn or a Zn‐Ga alloy solution on ZnSxSe1−x (0⩽x⩽1) single‐crystalline substrates. Intense blue emission bands at room temperature have been observed in the layers grown from a Zn‐Ga alloy solution. The spectrum of the layer at 4.2 K generally consists of a strong emission line due to radiative recombination of excitons bound to the neutral donor, I2, an associated donor‐acceptor pair emission band with LO‐phonon replicas, and a deep‐level emission, i.e., the so‐called SA emission band. The effect of Ga on the emission spectrum is to greatly increase the intensity of the blue part of the spectrum. On the basis of the comparison between the experimental results and theoretical calculations, it is tentatively proposed that the blue emisison bands at room temperature originate from the radiative recombination due to band‐to‐band transition.

Improvements in oxidation resistance by dispersed oxide addition: Al2O3-forming alloys

Abstract: The improvement in oxidation resistance produced by small additions of active elements to Al 2O3-forming CoCrAl alloys is primarily dependent on the formation of oxide pegs which grow into the alloy around the internal oxide particles of the active element; void formation at the alloy-scale interface is also suppressed. The distribution of these pegs is critical and this paper demonstrates that an internal oxidation pretreatment can be used to convert the active element to its oxide in a controlled manner, thereby optimizing the peg distribution. Al2O3-forming CoCrAl containing 1% Hf or Ce is internally oxidized in a sealed quartz capsule containing a 50/50 powder mixture of CoAl-Al2O3; it was not possible to oxidize internally Y-containing alloys. The isothermal and cyclic oxidation resistance of these alloys is superior to that of alloys not given a prior treatment. Detailed metallographic examination indicates that the prior internal oxidation treatment produces a finer, more uniform distribution of oxide pegs penetrating into the alloy which is more efficient in combatting scale spallation. Furthermore, the lower residual hafnium content in the alloy minimizes large HfO2 precipitates and the formation of gross Al2O3 intrusions, which can initiate scale failure. Thus, by internally oxidizing the alloy first, the advantages of a high alloy Hf content (1%) in producing sufficient oxide pegs, but of the right size, coupled with minimal thickening of the surface scale, can be achieved.

Method for welding hard metal

Abstract: Disclosed is a method for welding wear-resisting hard metals directly to iron base members which are slide or wear members of machinery. Hard metals comprising a tungsten carbide and a binder consisting of 15 to 30% by weight of Ni and/or Co is employed as said hard metals. A Ni alloy metal containing no Cr is used as a filler metal.

AN INVESTIGATION OF THE CREEP‐FATIGUE‐ENVIRONMENT INTERACTION IN A Ni‐BASE SUPERALLOY

Abstract: — This work was conducted to study the significant increases in fatigue crack growth rates at low frequencies commonly observed at high temperature. Creep tests and fatigue tests at 0·01, 0·1 and 1·0 Hz were conducted at 650°C in air and in helium on samples of INCONEL alloy 718 in two different heat treatments. Creep crack growth rates were 50–100 times greater in air than in helium. Fatigue tests in helium showed little sensitivity to frequency, but tests in air showed considerable increases in crack growth rates at lower frequencies. The results indicate the air environment played a predominant role in both the creep and the fatigue tests. Oxygen diffusion into grain boundaries appeared responsible for the accelerated crack growth in air. An overaging heat treatment reduced the crack growth rates.

Control of ordered structure and ductility of (Fe, Co, Ni)3V alloys

Abstract: This study is directed toward improvement of the ductility of long-range ordered alloys through control of their ordered crystal structure. A series of ordered alloys was prepared with a base composition of Co3V, where Co was partially replaced with Fe and Ni. The stability and structure of the ordered phases in these (Fe,Co,Ni)3V alloys were characterized by various metallurgical methods. The results indicate that the ordered structure in this alloy system can be controlled by adjusting the electron density, and that the L12 type cubic ordered structure (α′) is stable in the alloys with electron density less than 7.888. The phase relation in the cubic ordered alloys depends on the Fe concentration. For the alloys containing 20 pct Fe, the α′ is formed through a peritectoid reaction, namely, α+σ→α′. Tensile tests indicate that the alloys with multilayered hexagonal ordered structure are very brittle, while the alloys with the cubic ordered structure are ductile at room temperature. The ductility of the cubic ordered alloys increases with decreasing Co content. The alloys with <55 pct Co showed dimple type ductile rupture with elongation over 40 pct at room temperature. The correlation of ductility with ordered structure is discussed.

The influence of strain path on subsequent mechanical properties—Orthogonal tensile paths

Abstract: Several aluminum alloys have been subjected to two stage tensile straining, an initial prestrain followed by a subsequent tensile strain at 90 deg to the initial direction. In AA1100-0 and AA3003-0 the prestrain produces dislocation tangling and diffuse cell walls resulting in an enhanced flow stress and decrease in ductility when the material, is subsequently strained in the orthogonal direction. In a fine grained experimental Al−Fe−Ni alloy the prestrain is accompanied by a very low accumulation of dislocations and in this case the flow stress is reduced and ductility enhanced in subsequent orthogonal straining. The commercial alloys AA2036-T4 and AA5182-0 are unaffected by the two stage tensile strain path. The results are considered in terms of the forming limit curve and it is also shown that the behavior is consistent with the concept of an “alien” dislocation distribution being generated during the prestrain.

Alloying aluminum with magnesium for ductility at warm temperatures (25 to 250°C)

Abstract: Solute additions generally increase flow stress and decrease ductility. However, in an earlier study which compared the tensile behavior of a commercial Al-4 pct Mg alloy (5182-0) relative to pure aluminum, the commercial alloy exhibited increases in both strength and ductility at elevated temperatures (<250°C). To more fully understand this unexpected behavior, a series of high purity Al-Mg alloys (0 to 6 wt pct) were tested over the same range of temperatures (25 to 250°C) and initial strain rates (10-4 to 10-1 s-1) as in the earlier study. At ambient temperature the Mg solutes decreased elongation while increasing flow stress, but as the temperature was increased to 250°C the elongation increased with Mg content. This increase in ductility accompanied the linear increases in strain-rate sensitivity which occurred with increasing amounts of Mg. Stress relaxation tests indicated that Mg solutes increase the amount of dynamic recovery occurring at elevated temperatures. These results are explained on the basis of an increased amount of vacancies in the Al-Mg alloys relative to pure aluminum.

Hydride Phases in Austenitic Stainless Steels

Abstract: Electrolytic charging of austenitic stainless steels with hydrogen induces formation of two distinct alloy hydride phases, both being unstable under normal atmospheric conditions. One of the new phases denoted Hγ, has the same Bravais lattice as austenite (fcc), whereas another, denoted Hϵ, exhibits an hcp structure. Compared with hydrogen-free austenite and ϵ-martensite, respectively, the lattice constants of hydride phases are larger by about 5%. During charging of austenitic stainless steels with hydrogen evolved electrolytically from promoter containing acid solutions, these hydrides form a hard and brittle surface layer, several μm thick with numerous microcracks, and it is probable that these hydride phases play an important role during stress corrosion cracking (SCC) of austenitic stainless steels.

Corrosion Behaviour of Cast Nickel Aluminium Bronze in Sea Water

Abstract: Corrosion trials have been carried out using cast nickel aluminium bronze alloy in the as cast, heat treated and welded states, and the specimens examined using optical and electron optical techniques. It has been shown that selective phase corrosion can occur near the heat affected zone of welded cast nickel aluminium bronze which is due to the attack of the a phase adjacent to the continuous lamellar K phase. Heat treatment of this alloy considerably reduces its susceptibility to corrosion due to both stress relief and structural changes caused by the thermal treatment.

Influence of Silicon and Phosphorous on the Mechanical Properties of Both Ferrite and Dual-Phase Steels

Abstract: A study has been made of the influence of up to 2 pct Si and 0.42 pct P upon the strength and ductility of ferrites over a wide grain size range; the grain size was varied fromd −1/2 mm−1/2 = 4 to 14. Although the ductility decreased with increasing strength for all the alloys, the 2 pct Si alloy had the best combination of strength and ductility. The ferrites containing 2 pct Si and 0.2 pct P had greater uniform elongations than conventional HSLA steels at the same tensile strength; it is thought that the ductility of the ferrites is enhanced by the presence of Si while the ductility of conventional HSLA steels is reduced by the presence of carbide precipitates. With the theory for a composite of two ductile phases and the results for the fine-grained alloyed ferrites, the change in uniform elongation as a function of tensile strength was predicted for dual-phase (martensite plus ferrite) steels. Good agreement was found between the prediction and experimental results for dual-phase steels containing up to 0.2 pct P or 2 pct Si; the 2 pct Si alloy had the best combination of strength and ductility of all dual-phase steels so far reported. This study again emphasizes the importance of the high strength, high ductility ferrite in controlling the properties of dual-phase steels.

Enhanced oxide whisker growth on peeled Al-containing stainless steel foil

Abstract: In the preferred embodiment, a method is disclosed for preparing a metal foil composed of a ferritic stainless steel alloy and having a surface that is substantially covered by high aspect alumina whiskers. The preferred foil alloy comprises 15 to 25 weight percent Cr, 3 to 6 weight percent Al, 0.3 to 1.0 weight percent Y and the balance Fe. The method comprises forming the foil by a metal peeling process and treating the foil by heating in air at a temperature between about 870° C. and about 930° C. for a time sufficient to grow the alumina whiskers. In a particularly useful embodiment, the whisker-covered foil is coated with a noble metal-impregnated alumina layer and wound into a suitable cylindrical structure for use as a monolith-type catalytic converter for automotive exhaust gas treatment.