Showing papers on "Alloy published in 1986"

Precipitation processes in near-equiatomic TiNi shape memory alloys

Abstract: Metallographic studies have been made of precipitation processes in Ti-50 pct Ni and Ti-52 pct Ni (at. pct) shape memory alloys. The eutectoid and peritectoid reactions previously reported for near-equiatomic and Ni-rich TiNi alloys were not observed for either composition. In the Ti-52Ni alloy, diffusional transformations take place, similar to those in supersaturated alloys. The precipitation sequence can be written asβ 0 → Ti11Ni14 → Ti2Ni3 → TiNi3. The solidus line of the TiNi phase in the Ti-52Ni alloy lies at 812 ± 22 °C. Morphological characteristics of the various precipitate phases are described in detail.

Strain Hardening of Hadfield Manganese Steel

Abstract: The plastic flow behavior of Hadfield manganese steel in uniaxial tension and compression is shown to be greatly influenced by transformation plasticity phenomena. Changes in the stress-strain (σ−e) curves with temperature correlate with the observed extent of deformation twinning, consistent with a softening effect of twinning as a deformation mechanism and a hardening effect of the twinned microstructure. The combined effects give upward curvature to the σ−e curve over extensive ranges of plastic strain. A higher strain hardening in compression compared with tension appears to be consistent with the observed texture development. The composition dependence of stacking fault energy computed using a thermodynamic model suggests that the Hadfield composition is optimum for a maximum rate of deformation twinning. Comparisons of the Hadfield steel with a Co-33Ni alloy exhibiting similar twinning kinetics, and an Fe-21Ni-lC alloy deforming by slip indicate no unusual strain hardening at low strains where deformation is controlled by slip, but an unusual amount of structural hardening associated with the twin formation in the Hadfield steel. A possible mechanism of anomalous twin hardening is discussed in terms of modified twinning behavior (pseudotwinning) in nonrandom solid solutions.

Formation of ultra-fine amorphous alloy particles by reduction in aqueous solution

Abstract: Amorphous alloys are normally prepared as thin ribbons or films by the liquid quench technique or by vapour deposition. Recently we have shown1 that ultra-fine amorphous Fe–C alloy particles can be prepared by thermal decomposition of Fe(CO)5 in an organic liquid; that is, by a chemical reaction. Here we report the preparation of small alloy particles by reduction of metal ions by KBH4 in aqueous solutions. Mossbauer and X-ray diffraction studies show that the particles are amorphous. The amorphous phase is formed because the chemical reaction takes place below the glass transition temperature and because boron atoms are present in the particles. The method may be used for the large-scale production of ultra-fine amorphous alloy particles, which may have applications in ferrofluids, magnetic memory systems and catalysis.

The welding metallurgy of HASTELLOY alloys C-4, C-22, and C-276

Abstract: The welding metallurgy (solidification and solid state transformations) of HASTELLOY* Alloys C-4, C-22, and C-276 has been determined. Varestraint hot-cracking tests performed on commercial alloys revealed a weldability ranking as follows: C-4 > C-22 > C-276. All alloys would be expected to have good weldability, with Alloy C-4 having a very low hot-cracking tendency, comparable to 304L stainless steel. Microstructures of gas-tungsten-arc welds of these alloys have been characterized by scanning electron microscopy and analytical electron microscopy. Intermetallic secondary solidification constituents have been found associated with weld metal hot cracks in Alloys C-276 and C-22. In Alloy C-276, this constituent is a combination ofP and ώ phases, and in Alloy C-22, this constituent is composed of σ,P, and ώ phases. With phase composition data obtained by AEM techniques and available ternary (Ni-Cr-Mo) phase diagrams, an equivalent chemistry model is proposed to account for the microstructures observed in each alloy's weld metal.

Microstructural dependence of Fe-high Mn tensile behavior

Abstract: The tensile properties of Fe-high Mn (16 to 36 wt pct Mn) binary alloys were examined in detail at temperatures from 77 to 553 K. The Mn content dependence of the deformation and fracture behavior in this alloy system has been clarified by placing special emphasis on the starting microstructure and its change during deformation. In general, the intrusion of hcp epsilon martensite (e) into austenite (γ) significantly increases the work hardening rate in these alloys by creating strong barriers to further plastic flow. Due to the resulting high work hardening rates, large amounts of e lead to high flow stresses and low ductility. Alloys of 16 to 20 wt pct Mn are of particular interest. While these alloys are thermally stable with respect to bcc α’ martensite formation, 16 to 20 wt pct Mn alloys undergo a deformation induced e →α’ transformation. The martensitic transformation plays two contrasting roles. The stress-induced e→ α’ transformation decreases the initial work hardening rate by reducing locally high internal stress. However, the work hardening rate increases as the accumulated α’ laths become obstacles against succeeding plastic flow. These rather complicated microstructural effects result in a stress-strain curve of anomolous shape. Since both the Ms and Md temperatures for both the e and α’-martensite transformations are strongly dependent on the Mn content, characteristic relationships between the tensile behavior and the Mn content of each alloy are observed.

Morphology and properties of sputtered (Ti,Al)N layers on high speed steel substrates as a function of deposition temperature and sputtering atmosphere

Abstract: (Ti,Al)N layers were prepared by reactive dc and radio‐frequency (rf) magnetron sputtering onto polished flat high speed steel (HSS) surfaces. The rectangular samples were mounted on a special sample holder providing a temperature gradient in the range of 500 °C to room temperature along the length of the sample. The (Ti,Al)N layers were deposited at various N2 and Ar pressures. The target was a Ti–50 at. % Al alloy. The film morphology and composition was observed by scanning electron microscopy (SEM) and Auger electron spectroscopy (AES), respectively, and correlated to mechanical properties like hardness and critical load (scratch test). The results are discussed with the respect of the sputtering conditions.

Development of Al-Ti-C grain refiners containing TiC

Abstract: Cast Al-Ti-C grain refiners were synthesized by reacting up to 2 pct graphite particles of 20 micron average size with stirred Al-(5 to 10) pct Ti alloy melts, which generated submicron-sized TiC particles within the melts, and their solidified structures showed preferential segregation of the carbide phase in the grain or cell boundary regions and occasional presence of free carbon whose amount exceeded equilibrium values. At the usual melt temperatures of below 1273 K, though, TiC formed first, but was subsequently found to react with the melt forming a sheathing of A14C3 and Ti3AlC which resulted into poisoning of the TiC particles. However, it was possible to reverse these reactions in order to regain the virgin TiC particles by superheating the melts in the temperature region where TiC particles are thermodynamically stable. Grain refining tests using the TiC master alloys produced fine equiaxed grains of cast aluminum whose sizes were comparable to that obtainable with the standard TiB2 commercial grain refiner. TiC particles introducedvia the master alloys were found to occur in the grain centers, thereby confirming that they nucleated aluminum crystals.

Inclusion Phases and the Nucleation of Acicular Ferrite in Submerged Arc Welds in High Strength Low Alloy Steels

Abstract: Series of submerged arc welds of HSLA steel made with three different fluxes and metallic additions of Ti, Mo, and Cr have been examined to study the inclusions and their role in the nucleation of acicular ferrite. Inclusion phases and compositions have been analyzed by electron diffraction and X-ray microanalysis. These analyses have shown that the inclusions contained many different compounds, the proportions of each depending upon both the flux and metallic additions. Six inclusion phases have been identified: galaxite (Al2O3 ⋅ MnO), a titanium-rich compound (probably TiO), a copper sulfide, a manganese sulfide, a silica, and an aluminum-rich phase. No correlation was found between the amount of acicular ferrite in the weld metal and either average inclusion composition or individual inclusion phases. No epitaxial relationships between inclusions and adjacent ferrite grains could be identified. It has been concluded that inclusions nucleate acicular ferrite by acting as inert substrates according to the classical theory of heterogeneous nucleation. Because most inclusions are multi-phase and are touched by several ferrite grains, it has also been concluded that each inclusion can nucleate several ferrite grains, due to local regions of high surface energy on the inclusion.

On the influence of silicon on the growth of the alloy layer during hot dip aluminizing

Abstract: The reactions between a low alloyed steel and a pure as well as a 2% silicon containing aluminium melt where studied at 780 and 792‡ C, respectively. The velocity of the iron enrichment was the same for both cases, whereas the alloy layer growth was much faster in the case of the pure aluminium melt. After hot dip aluminizing in the 2% silicon containing aluminium melt silicon was found to be incorporated in the alloy layer. From that it is clear that silicon acts on the solid state side, when reducing the alloy layer thickness during hot dip aluminizing.

Potentiodynamic and Galvanostatic Stripping Methods for Characterization of Alloy Electrodeposition Process and Product

Abstract: Potentiodynamic and galvanostatic stripping techniques have been applied towards the characterization of zinc‐nickel alloy deposition process and product. The current‐potential relations required to recover the equilibrium and kinetic properties of alloys have been obtained for the eutectic, solid solution, and intermediate phase types of alloys. The galvanostatic stripping response shows a series of plateau regions, and the potentiodynamic response reveals a peak structure. These stripping responses have been employed to determine the chemical and phase compositions of electro‐deposited zinc‐nickel alloys, evaluate their corrosion resistance, and estimate the equilibrium potentials of various zinc‐nickel phases (α, γ, and η‐phases). The zinc‐nickel deposition process has been characterized through evaluation of partial currents due to alloy components and the current efficiency of alloy deposition. The design of multiple layered zinc‐nickel alloy films for the protection of steel is discussed on the basis of the accelerated corrosion behavior of the γ‐phase and the equilibrium potentials of the phases.

Calorimetric study of amorphization in planar, binary, multilayer, thin-film diffusion couples of Ni and Zr.

Abstract: We have utilized differential scanning calorimetry to monitor the solid-state reaction of crystalline metals to form an amorphous alloy in multilayered thin-film diffusion couples of elemental Ni and Zr. The heat of formation of amorphous Ni68Zr32 alloy from the elemental metals is measured directly and found to be 35 ± 5 kJ/mole. The kinetics of these reactions has been examined. The activation energy for interdiffusion in the amorphous phase is determined to be E=1.05±0.05 eV.

Effect of microstructure on strength and toughness of heat-treated low alloy structural steels

Abstract: Several low alloy structural steels with different levels of Ni, Cr, and Mo and carbon contents ranging from 0.12 to 0.42 wt pct have been studied to determine the effect of transformation structures on strength and toughness. The strength and toughness were, respectively, evaluated with the yield stress (0.2 pct proof stress) in tensile tests under ambient temperature and ductile-brittle transition temperature (DBTT) in Charpy impact tests. The significant conclusions are as follows: well-defined packets are observed in martensitic and lower bainitic structures, and in this case the packet diameter is the primary microstructural parameter controlling the yield stress and DBTT. The mechanical properties are also improved to a lesser degree with decreasing width of the lath present within the packet. If the steel has an upper bainitic structure, the packet is composed of well-defined blocks, and the block size controls the yield stress and DBTT.

Transmission electron microscopic observations of amorphous NiZr alloy formation by solid‐state reaction

Abstract: The interdiffusion of nickel and zirconium by a solid‐state reaction to form an amorphous NiZr alloy has been followed by transmission electron microscopy. Cross‐sectional examination of NiZr bilayers annealed at 300 °C has shown the formation of amorphous NiZr and the development of large voids in the nickel neighboring the Ni/NiZr interface. Our results indicate that nickel is the dominant diffusing species in the amorphous alloy and that the diffusion requires a defect mechanism. Prolonged annealing at 300 °C results in the formation of a crystalline NiZr phase, which co‐exists with the amorphous alloy.

Method for diffusion bonding of alloys having low solubility oxides

Abstract: Diffusion bonding of surface layers of an alloy, such as an aluminum alloy, having surface oxides of low solubility in the alloy includes treating the surface layers to be bonded to remove existing surface oxide coatings, and diffusion bonding the surface layers to one another by placing the alloy to be bonded under sufficient pressure to cause disruption of the oxide coatings by localized surface deformation of the alloy, enhanced by a superplastic microstructure, without substantial deformation of the alloy, i.e., macroscopic deformation approaching zero percent, while heating the alloy in a non-oxidizing atmosphere for a time sufficient for diffusion bonding to occur. The alloy may be treated so that at least the surface layers thereof have a fine grain structure of the type associated with superplastic forming properties. Components may be formed by diffusion bonding and superplastic forming.

Fibre-reinforced metal matrix composites

Abstract: A metal matrix composite comprises randomly-­oriented inorganic oxide fibres of density below 3 g/ml embedded in a metal matrix material such as a light metal, for example aluminium or magnesium or an alloy thereof. In a particular embodiment the fibres are of density l.8 to 2.5 g/ml and preferably are of mean diameter from 2 to l0 microns. The composite can be made by liquid infiltration of a fibre preform comprising the fibres bound together with an inorganic or an organic binder or by extrusion of a mixture of the fibres and a powdered metal matrix material.

Alloy Microstructures in Cast Metal Matrix Composites

Abstract: This article provides some insight into an area that has here-to-fore been ignored, namely, the matrix microstructure of cast metal matrix composites (MMC). Using the Al-4.5% Cu alloy as a model matrix alloy, the factors influencing the cast microstructure are explored on samples reinforced with several types of fibers. The nature of the fibers, their diameter and distribution along with conventional solidification parameters have a profound influence on the matrix microstructure. A full exploration of the relationships between properties, microstructures and processing parameters is required for the optimization of this class of materials.

Platinum-titanium alloy formation from high-temperature reduction of a titania-impregnated platinum catalyst: implications for strong metal-support interaction

Abstract: Highly dispersed Pt supported on carbon black was impregnated with titania and heated in an inert atmosphere. The amount of titania used was twice the stoichiometric amount required for the formation of the ordered alloy phase Pt/sub 3/Ti. The chemical state of Ti at various stages of heating was determined by X-ray photoelectron spectroscopy and by extended X-ray absorption fine structure (EXAFS) analysis. The formation of alloy phases could also be determined by conventional X-ray diffraction methods. The characterizations showed unambiguously the conversion of separate Pt and TiO/sub 2/ dispersed phases into Pt-Ti alloy phases at progressively higher heat treatment temperatures, eventually resulting in the formation of crystallites of the ordered (intermetallic) phase Pt/sub 3/Ti. On the basis of this observation and other related work in the literature, they present a model for the chemistry occurring during the formation of the SMSI state of Pt/TiO/sub 2/ catalysts.

Method to produce metal matrix composite articles from lean metastable beta titanium alloys

Abstract: A method for fabricating an improved titanium alloy composite consisting of at least one high strength/high stiffness filament or fiber embedded in an alpha-beta titanium alloy matrix which comprises the steps of providing a rapidly-solidified foil made of a rich metastable beta titanium alloy, fabricating a preform consisting of alternating layers of the rapidly-solidified foil and the filamentary material, and applying heat and pressure to consolidate the preform, wherein consolidation is carried out at a temperature below the beta-transus temperature of the alloy.

The use of new PHACOMP in understanding the solidification microstructure of nickel base alloy weld metal

Abstract: The weld metal microstructures of five commercial nickel base alloys (HASTELLOYS* C-4, C-22, and C-276, and INCONELS* 625 and 718) have been examined by electron probe microanalysis and analytical electron microscopy. It has been found that solidification terminates in many of these alloys with the formation of a constituent containing a topologically-close-packed (TCP) intermetallic phase(i.e., σ, P, Laves). Electron microprobe examination of gas-tungsten-arc welds revealed a solidification segregation pattern of Ni depletion and solute enrichment in interdendritic volumes. New PHACOMP calculations performed on these segregation profiles revealed a pattern of increasingM d (metal-d levels) in traversing from a dendrite core to an adjacent interdendritic volume. In alloys forming a terminal solidification TCP constituent, the calculatedM d values in interdendritic regions were greater than the criticalM d values for formation ofσ as stated by Morinagaet al. Implications of the correlation between TCP phase formation andM d in the prediction of weld metal solidification microstructure, prediction of potential hot-cracking behavior, and applications in future alloy design endeavors are discussed.

Platinum alloy electrocatalyst and acid-electrolyte fuel cell electrode using the same

Abstract: A platinum alloy electrocatalyst, composed of a platinum-copper alloy containing 15 to 50 atomic percent of copper (the balance being platinum) and supported on a suitable carrier, shows high activity over long periods because of the enhanced specific activity of supported metal and improved maintainability of its specific surface area. Thus acid-electrolyte fuel cells using the electrode comprising such an electrocatalyst feature better output performances and longer service life than fuel cells using conventional electrodes.

An18O tracer study on the growth mechanism of alumina scales on NiAl and NiAlY alloys

Abstract: The effect of Y additions on the oxidation mechanism of NiAl at 1270 K has been investigated. Mass transport in the alumina scale was examined with18O tracers. Proton activation analysis (18O(p, α)15N) and SIMS were used to measure the18O distribution in the scale. On pure NiAl and low-doped (0.07% Y) NiAl mainly outward scale growth was observed. Addition of 0.5% Y induces oxide formation at both interfaces of the scale. Larger quantities of Y added to the alloy (>0.5%) do not dissolve completely in the NiAl, but form Y-rich segregates. Internal oxidation of these intergranular segregates was observed. The relation between the modification of the scale-growth mechanism and the improved adherence of the scale to the alloy due to the addition of Y is discussed.