1. Introduction 2. The physical metallurgy of nickel and its alloys 3. Single crystal superalloys for blade applications 4. Superalloys for turbine disc applications 5. Environmental degradation: the role of coatings 6. Summary and future trends.

The Superalloys: Fundamentals and Applications

Simple rules for the understanding of Heusler compounds

It is suggested that in many ferromagnetic materials there may occur particles distinct in magnetic character from the general matrix, and below the critical size, depending on shape, for which domain boundary formation is energetically possible. For such single-domain particles, change of magnetization can take place only by rotation of the magnetization vector. As the field changes continuously, the resolved magnetization may change discontinuously at critical values of the field. The character of the magnetization curves depends on the degree of magnetic anisotropy of the particle and on the orientation of easy axes with respect to the field. The magnetic anisotropy may arise from the shape of the particle, from magnetocrystalline effects, and from strain. A detailed quantitative treatment is given of the effect of shape anisotropy when the particles have the form of ellipsoids of revolution, along with a less detailed treatment for the general ellipsoidal form.

A mechanism of magnetic hysteresis in heterogeneous alloys

Publisher Summary This chapter describes the essence of the catalytic chemistry of heteropoly compounds in solution and in the solid state. The catalytic properties of heteropoly compounds have drawn wide attention, owing to the versatility of these compounds as catalysts, which has been demonstrated both by successhl large-scale applications and by promising laboratory results. Heteropolyanions are polymeric oxoanions formed by condensation of more than two different mononuclear oxoanions. Heteropolyanions formed from one kind of polyanion are called isopolyanions. Acidic elements such as Mo, W, V, Nb and Ta, which are present as oxoanions in aqueous solution, tend to polymerize by dehydration at low pH, forming polyanions and water.Heteropoly catalysts can be applied in various ways. They are used as acid as well as oxidation catalysts. They are used in various phases, as homogeneous liquids, in two-phase liquids (in phase-transfer catalysis), and in liquid-solid and in gas-solid combinations, etc.

Catalytic Chemistry of Heteropoly Compounds

Spintronics is a multidisciplinary field involving physics, chemistry, and engineering, and is a new research area for solid-state scientists. A variety of new materials must be found to satisfy different demands. The search for ferromagnetic semiconductors and stable half-metallic ferromagnets with Curie temperatures higher than room temperature remains a priority for solid-state chemistry. A general understanding of structure-property relationships is a necessary prerequisite for the design of new materials. In this Review, the most important developments in the field of spintronics are described from the point of view of materials science.

Spintronics: a challenge for materials science and solid-state chemistry.

An X-ray analysis of the nickel-aluminium system has been made. A comprehensive series of powder photographs were taken of slowly cooled alloys, and in addition some quenching experiments were made on the nickel-rich alloys. In several important particulars the results differ from the phase-equilibrium diagram published by Gwyer (1908) (fig. 1 a ). This diagram has therefore been modified in the direction indicated by our work (fig. 1 b ). The solid solution of aluminium in nickel shown by Gwyer has been found to contain a miscibility gap at room temperatures. The α -phase, which is a face-centred cubic solid solution of aluminium in nickel, extends to 89 atomic % of nickel at room temperatures. The α' -phase, which is a facecentred cubic solid solution closely corresponding to the composition Ni3Al, has a superlattice (Westgren and Ekman 1930), nickel atoms occupying centres of cube faces and aluminium atoms cube corners. Quenching extends the range of the α -phase until in alloys quenched from 1100° there is no break between the α and α' structures.

An X-Ray Analysis of the Nickel-Aluminium System

Beginning in the year 1898 Heusler discovered as a series of ferromagnetic alloys, the most important containing copper, manganese, and aluminium. They are characterized by remarkable magnetic properties, because although composed only of paramagnetic or diamagnetic elements, they become ferro-magnetic after suitable heat treatment. Various explanations of this property have been advanced, but it was usually considered to be due to the formation of a series of solid solutions of the type (CuMn)3Al, in which the proportions of copper and manganese may be varied within fairly wide limits. The Heusler alloys have been repeatedly investigated by means of X-rays. Young, using molybdenum radiation examined alloys of two different compositions. He found that one was face-centred cubic, while the other was a mixture of face-centred and body-centred cubic structures. The mixed alloy was the more magnetic.

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The Crystal Structure of the Heusler Alloys

Stimulated by the special interest of iron-nickel-aluminium alloys for the permanent magnet industry, we have made an X-ray investigation of this system. The information obtained has led to a new view of the nature of the permanent magnets of iron, nickel and aluminium, which has been briefly described elsewhere (Bradley and Taylor 1937 a, b, c ). In the present paper we confine ourselves to a description of the X-ray results, which have enabled us to draw a complete ternary diagram representing the phases formed by these metals. The iron-nickel-aluminium alloys are closely related to the systems FeAl, NiAl, CoAl. Every phase which occurs in the ternary system has an analogy in one or another of these binary systems. This makes it possible to interpret the present results in the light of our previous knowledge of those systems.

An X-Ray Study of the Iron-Nickel-Aluminium Ternary Equilibrium Diagram

The special interest of this structure lies in the peculiar manner in which the anions (PW12O40)-3 are linked together by the water molecules. The remarkable number (29) of water molecules associated with each anion is accounted for by symmetry considerations. Alternating with the anions on a body-centred cubic lattice, seventeen molecules of water are linked together in tetrahedral symmetry. These comprise a central molecule in contact with four molecules at the corners of a tetrahedron, and twelve molecules strung out in pairs along fourfold cube axes, to link together six anions. Midway between two blocks of seventeen waters and independent of them, six water molecules form a puckered hexagonal ring, which links together six anions, lying symmetrically about a threefold axis. For each anion there are two hexagonal rings and one block of seventeen molecules. This accounts for the total of 29 molecules per anion. The environment of the water molecules is in striking contrast with that of the oxygen atoms in the anions. The latter are close-packed, being held together by the phosphorus and tungsten atoms. The water molecules are more open, and only six of the 29 have more than four nearest neighbours. The interatomic distances of the water molecules are very consistent, all lying between 2·8 A and 2·9 A.

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Albert James Bradley

Papers

An X-Ray Analysis of the Nickel-Aluminium System

The Crystal Structure of the Heusler Alloys

An X-Ray Study of the Iron-Nickel-Aluminium Ternary Equilibrium Diagram

The Crystal Structure of HFormulaPWFormulaOFormula. 29HFormulaO