摘要:

AbstractThe past 15 years have seen major advances in the development of ceramic tool materials to give high cutting speeds and long tool lifetimes. These developments require rigid machine tools and high-power motors, and a change in the way the tool tips are used. The main areas of application of these new tool materials are in the aerospace industries and, to a somewhat lesser extent, in cast iron production. There is an ever increasing number of grades (and tradenames) available, and in this paper the background and development of the materials are described. Briefly, the materials may be classified as alumina or silicon nitride based; these base compositions, with alloying additions, form two main families of materials. The manufacturing routes are discussed as these influence both the grain size and the porosity of the finished material, and both these properties affect the behaviour of the materials in use. Finally, the wear of these tools is examined in the light of present understanding of the microstructures.MST/713

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.11.881

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractTheβ-phase of the Au–Cd alloy system exhibits two types of martensitic phase transformation at temperatures of 300±50 K. In the present investigation, the crystallographic, thermodynamic, and resistivity parameters of all phases accompanying the phase transformations have been directly determined. The resistivity and thermodynamic studies have been carried out over a wide range of temperatures. The entropy of mixing term has been interpreted as resulting from positional and vibrational contributions at lower temperatures. At higher temperatures, a high degree of order persists. An attempt has been made to correlate qualitatively the experimental results from the independent studies reported in the present paper.MST/486

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.11.888

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractMicrostructural analysis and mechanical testing have been carried out on medium-carbon steels to which additions of vanadium in the range 0·075–0·6 wt-% were made. The steels were either continuously cooled or isothermally heat treated after austenitization. Vanadium carbide precipitation in the proeutectoid ferrite regions of the microstructure and, more unusually, also in the pearlitic ferrite lamellae, were identified by transmission electron microscopy. Moreover, in both ferrite phases the precipitates are aligned in rows, indicative of interphase precipitation at the austenite/ferrite transformation interface. These observations are discussed in terms of the various mechanisms that have been proposed for the interphase precipitation reaction. In the alloys studied the vanadium additions were found to increase the strength of the steels by up to 100%, but to reduce the ductility and notched impact resistance. The most useful combination of increased strength with reasonable ductility and impact toughness was achieved with an addition of 0·15 wt-% V. The vanadium additions contributed to a number of variations in microstructure and therefore in strengthening mechanisms, but the largest effect was the interphase precipitation strengthening of the ferritic phases. The highest strength levels were achieved in fully pearlitic microstructures with the pearlitic ferrite lamellae strengthened by interphase precipitation of the vanadium carbide.MST/536

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.11.894

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe influence of tempering temperature, stress ratio, and prior strain on fatigue crack propagation in a low-alloy chain steel has been investigated. At small stress ratios (R=0·1) tempering above 400°C is beneficial, resulting in higher threshold levels and slower growth rates in the initial growth regime. Thereafter, crack growth is independent of tempering temperature, as it is over the entire growth period under a high mean stress (R=0·5). Prior strain produces a slower growth and higher thresholds at R= 0·1. Intergranular fracture is common and is a function of stress intensity range and tempering temperature. It is concluded that residual stress effects, rather than microstructural effects, account for the experimental observations. In particular, the existence of a tensile residual stress during initial growth and a crack closure stress greater than the minimum applied stress level are proposed.MST/672

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.11.905

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe influence of strength, precipitate microstructure, temper embrittlement, and environment on fatigue crack growth in 2·25Cr–1 Mo steel has been investigated. Particular attention was paid to the interaction between hydrogen embrittlement and temper embrittlement in fatigue. A range of tempered and aged conditions was examined in air, vacuum, and gaseous hydrogen environments at growth rates between 10−10and 10−5m/cycle. In this paper, discussion focuses on effects observed in hydrogen. Gaseous hydrogen was found to encourage crack growth by promoting intergranular fracture, which peaked at intermediate growth rates, and by reducing the general plasticity associated with transgranular fracture at high growth rates. Mechanisms underlying these effects, which involve stress-driven hydrogen segregation and the facilitation of crack-tip dislocation emission, are considered in detail. Reversible temper embrittlement encouraged crack growth at near-threshold and intermediate rates in hydrogen by increasing susceptibility to intergranular fracture. The magnitude of this effect was directly related to the degree of intergranular phosphorus enrichment, thus clearly demonstrating synergy between hydrogen embrittlement and temper embrittlement in fatigue. In contrast, one-step temper embrittlement encouraged transgranular crack growth in hydrogen only at high growth rates. This is considered to result from a concentration of slip on glide planes intersecting the crack tip under the combined influences of hydrogen and an increasingly dense precipitate microstructure.MST/583

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.11.912

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractA model was developed almost 20 years ago which described how precipitation during the quench affected the development of properties of aluminium alloys during subsequent aging treatment. This model was the basis for an analytical process, known as quench factor analysis, that was used to predict the effects of quench path on corrosion characteristics and strength. The purpose of this paper is to provide a theoretical basis for the model and to review how quench factor analysis has been used in solving industrial problems. Several investigators have confirmed that quench factor analysis is an effective predictive method for all quenching conditions save one. The exception is when material has been quenched below the knee of the C-curve and subsequently reheated above the knee before the quench is complete. Applications include the design of quench systems, the development of quench practices which optimize combinations of high strength and low residual stress and distortion, and predictions of the magnitude of loss in strength as a result of unsuitable quenching conditions. By combining quench factor analysis with homogeneous nucleation theory, interactions between quenching and aging conditions have been clarified, and aging treatments have been developed which minimize the low and variable strengths caused by less than ideal quenching conditions. Quench factor analysis also adequately describes the rate of loss in toughness of an AA 6000 series extrusion alloy for those cooling conditions which produced commercially significant loss in strength. The latest use of quench factor analysis is in a specification for quenchants for aluminium alloys.MST/573

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.11.923

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractDuring the development of new processing routes for Nb3Sn superconductor, factors influencing the workability of two-phase metallic composites have been investigated. The ease with which such composites can be fabricated depends strongly on the relative hardnesses of the phases. Production of a regular, uniform filamentary structure is promoted by low hardness ratios in the initial composite.MST/547

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.11.936

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractModelling of diffusion bonding has been carried out to quantify the kinetics of the bonding processes and to predict the time for achieving a sound bond. An alternative geometric assumption for the shape of the interfacial cavities to those considered previously was employed. Three subprocesses of bonding were introduced to simplify the modelling. These involved volume and interfacial diffusion coupled with creep, rigid collapse, and surface diffusion. The effects of grain size and phase ratio on diffusion bonding have also been considered. The predictions are compared with existing experimental data for copper and Ti–6Al–4V alloy and in general show good agreement.MST/588

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.11.945

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractMethods of surface preparation of steel for adhesive bonding are reviewed. With advanced adhesives, joints of unprepared oily steel can prove very strong, but for durability in adverse environments one must remove all contamination and provide a new, chemically active surface of high surface energy. Degreasing, organic or inorganic, can improve the characteristics of the bond, but even better results can be achieved by mechanical removal of the outer, inactive contaminated layer. Specially formulated chemical etching (with a nitric-phosphoric acid solution) can produce a receptive and active substrate surface for the adhesive that results in both high initial strength and good durability. On the basis of the available information, mechanisms of bond formation and deterioration in humid atmospheres are clarified and suggestions for the improvement of durability are discussed.MST/685

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.11.954

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe high-voltage electron microscope has been used to study the structure and morphology of electroless Ni–P deposits of varying phosphorus contents. Except for low (<3 wt-%) phosphorus contents the deposits are amorphous. The crystallization processes depend on a number of variables, including thickness and phosphorus content of the deposit and presence or otherwise of an iron substrate. These processes include epitaxial crystallization of Ni2.55P, spherulitic (or dendritic) crystallization of Ni2.55P and Ni3P, precipitation of nickel particles, and structures arising from interdiffusion between nickel, phosphorus, and the substrate.MST/660

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.11.963

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor