Highly dense sintered YBa2Cu4O8 has been produced by hot isostatic pressing (HIP). The electrical resistivity ρ of this material has been measured as a function of temperature T and pressure p in the range 40-650 K and 0-0.7 GPa. Both the temperature dependence and the pressure dependence of ρ are found to be well described by a model based on the standard Bloch-Grueneisen theory. It is pointed out that ρ is liner in T only under isobaric conditions, while ρ is strongly nonlinear in all high-Tc superconductors under isochoric (constant volume) conditions. The critical current density of the material is 900 A/cm2 at 4 K, while the resistivity is 630 μΩ cm at 294 K.

The construction of mechanism maps for hot-isostatic pressing is described. Maps are constructed for a number of materials of commercial and scientific interest: a tool steel, a superalloy, Al₂O₃, and ice. They allow the processes involved in hot-isostatic pressing to be examined, and suggest ways of picking optimum combinations of pressure, temperature, and time to give maximum density.

Data for carbide dissolution, grain growth and martensite formation in the heat-affected zone of a weld can be assembled into a diagram showing the extent of each, for different weld cycles, and at different points in the zone. The diagrams are based on elementary kinetic models for grain growth and carbide dissolution, integrated over the weld cycle; and on experimental data. The sets of poorly-known kinetic constants which appear in such a treatment are determined by fitting the equations to data from real or simulated welds, at certain fixed points. Diagrams are presented for six steels. As well as summarising much data they allow the effect of change in weld procedure, or of preheat, to be predicted.

Crack propagation in various woods has been examined by scanning electron microscopy, and the observations related to measurements of fracture toughness. It is found that the toughness is related in a simple way to the density of the wood, which is explained by a straightforward model. The apparent fracture toughness of wood for cracks that lie normal to the grain is larger, by a factor of about 10, than that for cracks which propagate parallel to the grain. This difference can be explained in terms of the fracture mechanics of very anisotropic solids

Data for carbide dissolution and grain growth in the heat affected zone of a weld can be assembled into a diagram showing the extent of each, for different weld cycles, and at different points in the zone. The diagrams are based on elementary kinetic models for grain growth and carbide dissolution, integrated over the weld cycle. The sets of kinetic constants which appear in such a treatment are determined by fitting the equations to data from real or simulated welds, at certain fixed points. Diagrams are presented for six steels. As well as summarizing much data they allow the effect of change in weld procedure, or of preheat, to be predicted.

Surfaces can be treated with a scanning laser beam to modify their properties. The beam subjects the near-surface to a thermal cycle with an amplitude and shape which depends on the process variables: the beam size, energy, scan rate and on whether the laser is pulse or continuous, and the chemistry and metallurgy of the steel. Approximate solutions to the equations of heat flow are combined with kinetic models to predict the near-surface structure and hardness of plain carbon steels after laser treatment. The results are assembled into diagrams which show immediately the combination of process variables for a desired surface structure and the associated hardness profile

Experimental steels similar in composition to structural grades were prepared from weld metal deposits to study the formation of acicular ferrite under conditions experienced in the heat affected zone for a range of welding processes. The formation of acicular ferrite under these conditions is found to be dependent on the presence of a suitable distribution of oxide inclusions > 0·4 μm in size. The characteristics and proportion of acicular ferrite in the microstructure also depend on the prior austenite grain size and cooling rate. The relationship between these factors is presented in a simplified quantitative model, which is supported by data from limited welding trials. Metallographic observations suggest that acicular ferrite forms in two stages. The first involves the formation of relatively large primary acicular ferrite plates by multiple nucleation at intragranular inclusion sites, and the second involves the formation of many smaller acicular ferrite grains that grow sympathetically from the primary plates.

A wide range of microalloyed steels containing various combinations of Al, Ti, V, Nb, and submerged-arc welded using wires of either high or low Mo additions, were studied in both the as-welded and stress-relieved conditions, with particular reference to impact toughness and microstructure. It was found that, irrespective of thermal treatment, the heat-affected base metal always has a much lower impact transition temperature than the weld metal. In the as-welded condition, the most important constituent with respect to toughness is the amount of pro-eutectoid ferrite present

The effects of hot isostatic pressing (HIPing) on densification and the superconducting properties of the Bi-Pb-Sr-Ca-O system were investigated. A relative density up to 95% and a critical current density greater than 1100 A/cm2 at 77 K were achieved through HIPing at 650°C for 2 h under 200 MPa argon. Under these conditions, the product gave a value of Jc four times that without HIPing. To was unaffected by HIPing for samples encapsulated with a combination of glass and silver tubes. However, To was suppressed from 103 K to 86 K for samples encapsulated with stainless steel and silver tubes while Jc increased from 260 A/ cm2 to 1086 A/cm2 during HIPing, indicating that the weak links were significantly improved. A new minor phase, having a composition of Bi/Pb/Sr/Ca/Cu=0.58/2.8/3.0/2.1/1.1, was observed in HIPed samples but its effect on Jc is not clear

The critical current density (Jc) of Ag-clad Bi-Pb-Sr-Ca-Cu-O wire has been measured to be 1.2×104 A/cm2 at 77 K in zero field. The high Jc is attributed to a combination of elimination of the poisoning effect of Ag on superconductivity, grain alignment, and enhancement of flux pinning. Jc-H dependence was significantly improved in the Ag-clad tape, which has a Jc of 1.0×103 A /cm2 at 77 K and 4000 Oe, while the Jc of the sintered pellet drops two orders of magnitude at only 100 Oe. A pronounced anisotropy in Jc under high magnetic field is attributed to the grain alignment. Planar defects, such as heavy stacking faults parallel to the a-b plane in the rolled tape, are considered to be effective pinning centres.

Recent developments across the whole field of electron microscopy and associated equipment and techniques are reviewed with particular emphasis on quantitative measurements and analysis. The review is intended to cover a wide field embracing transmission, scanning, and scanning transmission microscopy as well as X-ray spectroscopy, on-line image analysis, and in situ experimentation, with the object of seeing how and to what effect quantitative electron microscopy is serving materials technology.

The course described attempts to help engineering students adapt themselves to solving problems typically encountered in the metals industries

It is shown that scanning transmission microscopy (STEM) has followed two main lines of development, the pure STEM based upon a field emission electron source in which the emphasis is given to high resolution, and a combined system in which STEM is an attachment to a conventional transmission microscope (TEM+STEM). When used in combination with an energy dispersive X-ray spectrometer, the combined TEM+STEM system is shown to be extremely versatile and possibly the more useful for the applied metallurgist. The high vacuum requirements of pure STEM, however, make this system suitable to be used in conjunction with an Auger spectrometer. Examples of the various microanalysis facilities of STEM are given in the article, including micro-diffraction, rocking-beam channelling patterns, qualitative and quantitative X-ray spectroscopy analysis, particle analysis, and in situ experimentation. The controversial subject of whether thicker specimens can be studied in STEM compared with conventional TEM is also discussed

The structure of balsa wood has been characterized by scanning microscopy. The moduli and crushing strengths of the wood, in three orthogonal directions, have been related to the structure and its reponse to load: during deformation the cell walls bend elastically and collapse plastically or by fracture. It is found that the moduli, crushing strengths and anisotropy of balsa and of other wood are determined, in part, by the properties of the cell-wall material, and, in part, by the dimensions and shape of the cells themselves.

The authors concentrate on some recent scientific and technological developments in the two main areas of activity in Sweden, i.e. cemented carbides and steel powder metallurgy. They also give a few details of some interesting preliminary work on the hot isostatic pressing of silicon nitride and the development of sintered oxide containers for storing nuclear waste materials

There has been considerable progress in producing and characterizing high Tc superconductors, but a number of materials science-related problems still exist, before their mechanical and electrical properties meet the requirements of many of the proposed applications. These materials are brittle, ceramic compounds with long unit cells that can be thought of as formed from layers of various oxides are an important common feature. The long unit cell structure leads to anisotropy in their electrical and mechanical properties, including the current carrying capacity or current density Jc. The crystallography and microstructure of the three major families of high Tc superconductors are reviewed and possible solutions to some of the materials problems are presented

Calculations of the total energy for transforming austenite to martensite in the form of thin ellipsoidal plates, fully coherent with the austenite, show that the process may be spontaneous in the presence of pre-existing dislocations. It is found that dislocations, or groups of dislocations, in the austenite are suitable sites for martensite nucleation in that their strain fields may interact favourably with the strain field associated with the Bain deformation thereby eliminating the energy barrier to nucleation. The driving force for twinning to occur virtually simultaneously with nucleation is large and when this happens energy is released for thickening and growth of the nucleus. It is also found that the strain energy of coherent plates of martensite, whether twinned or untwinned, is a function of their orientation in the austenite, although the lowest strain energy case occur nevertheless over a relatively wide range of orientations

Criteria based on minimum energy and maximum stress considerations have been developed for the first stages of growth of martensite in steel. It is shown that the critical size of nucleus at which dislocation-assisted growth can occur is about 25 nm diameter. The mode of growth governing low carbon lath martensite forming on {111} austenite habit planes is found to be fundamentally different from that of plate martensite which forms on irrational habit planes. A mechanism for lath thickening and growth is advanced in which dislocations nucleate at the thickest section of the lath and then follow after the coherent leading edge of the lath to generate ledges. Plate growth on the other hand can occur by the formation of twins which nucleate and thicken laterally behind the coherent leading edge of the plate.

Swedish materials engineering, with its emphasis on the high tech end of engineering products such as electronics and fibre optics, automobiles, aircraft and submarines, high performance machine tools and high grade steels, etc is backed by a comprehensive network of Institutes of Technology and state-supported research laboratories, all of which ensure the continued high calibre and reputation of Swedish products. The future is likely to see more amalgamation between Swedish and European concerns following the government's recent decision to seek full EEC membership. This article looks at the various constituent parts making up materials engineering in Sweden, including its main industries and products, its educational system, its research institutes and its methods of funding.

The process of hot isostatic pressing is modelled in terms of the various mechanisms of densification and sample shrinkage. Using input data of material type, mean powder size, sample size and shape, and the hot isostatic pressing parameters of pressure, temperature, time, etc. a computer program provides output data on time to complete densification, sample shrinkage and mode of densification. It is shown that the program can be used to help optimise the HIP cycle and provide information of sample (tool steel) shrinkage and potential residual stress problems.

The process of hot isostatic pressing is modelled in terms of the various mechanisms of densification and sample shrinkage. Using input data of material type, mean powder size, sample size and shape, as well as the hot isostatic pressing parameters of pressure, temperature, time, etc., a computer program provides output data on time to complete densification, sample shrinkage and mode of densification. It is shown that the program can be used to help optimise the HIP cycle and provide information of sample shrinkage and potential residual stress problems

review is made of the main areas of current research interest in modelling and predicting the microstructural/property changes occurring in the heat affected zone in fusion welding. The main subject areas considered are single run welds, multi-run welds, and pulsed welding. The key to modelling in all these cases is the establishment of good equations for the weld thermal cycle. Modelling of other phenomena such as precipitate dissolution, grain growth, phase transformation, property changes, etc. are then tractable. Heat flow equations are well established for single run welds, but there are difficulties in defining the complete thermal cycle in multi-run welding. Pulsed welding, on the other hand, offers good possibilities for accurate modelling and, hence, a better degree of microstructural prediction may be possible in this case. Data are shown for T10 steel

The microstructure developed during weld solidification and the effect of the various welding and materials parameters is discussed. It is shown that weld solidification is in several ways fundamentally different from solidification in conventional casting in that it is a dynamic (moving heat source) process in which the `mould' material (the base metal) has approximately the same composition as that of the solidifying metal. The moving arc also has the effect of continuously varying the solidification conditions, e.g. the temperature gradient and degree of convection, in the melt. The additional modifications to microstructure during cooling of the weld metal are also briefly discussed

Examples of new materials dealt with in this book include aluminium--lithium alloys and fibre polymer composites for aircraft and sports equipment, rolled structural beams made of toughened concrete, new engineering polymers that may soon displace metals, advanced ceramics that promise to revolutionise the machine tool, electrical and automobile engine industries, fibre optical materials, new generations of transistors, and a "warm" superconducting ceramic with applications in computing, medical scanners and levitating trains. The book begins with an introduction to the fundamentals of materials science and continues with a wide range of current and potential applications for structural and lightweight materials, wear and heat resisting materials, optical materials, electronic and magnetic materials, and sporting materials, and winds up with a section on the environmental issue and the role of advanced materials in tomorrow's world

The structure of the iris leaf resembles that of a sandwich beam with fibre composite faces separated by a low-density foam core. Such structures have a high specific stiffness because the separation of the faces by the lightweight core increases the moment of inertia of the section with little increase in weight. In this paper we examine the structure of the leaf of the bearded iris and show that its flexural stiffness can be explained in terms of the mechanics of sandwich beams

Bi-Sr-Ca-Cu-O single crystals obtained thus far commonly have a very small thickness in the c-axis because of the weak bonding between two adjacent BiO layers and the high vapour pressure of Bi2O3 at high temperature. To overcome these difficulties a presintered SrCaCu4O6 was used to seal the Bi-Sr-Ca-Cu-O melt from which the single crystals grew during slow cooling. In the SrCaCu4O6 sealed cavity the Bi loss through vaporization was prevented and Sr and Ca were enriched in the superconducting crystals. The resulting single crystals have a dimension of up to 3.0×1.5×0.7 mm3, which is two orders of magnitude thicker than those grown from alkali chloride flux. The composition of the crystals is Bi2.2Sr1.8Ca0.75Cu1.8Ox and they possess a zero resistance at temperature above liquid nitrogen

The equation and procedures for constructing hot-isostatic pressing diagrams are simplified and clarified. In earlier work, three classes of mechanism were modelled: plastic yielding, power-law creep and diffusional densification. In this paper two further mechanisms are added: diffusional deformations of particles when the grain size is smaller than the particle size, and separation of pores from boundaries when grain growth occurs. Application of HIP diagrams to tool steels, alumina and copper are discussed

A theoretical model is developed for determining the optimum notch position in an implant test used for predicting the susceptibility to hydrogen cracking during welding. Using a microcomputer for processing the equations for weld-bead geometry and heat flow during welding, a microstructural cross-section, with the notch positioned at the center of the grain-growth zone, and an implant testing diagram, showing the notch position and microstructure as a function of welding parameters, can be generated. A single bead-on-plate weld is used to determine the unknown kinetic and geometrical constants in the equations. It is shown that notch position is very sensitive to the type of welding process employed and that implant diagrams thus can be used to position the notch with greater reliability and hence reduce the scatter in the fracture loads measured in this test.

The paper improves and extends kinetic models to include: precipitate coarsening; the use of semi-empirical equations including carbon-equivalence to predict microstructure and hardness; a comparison between the theory and data obtained from different types of real welds; and an alternative, more easily used diagram.

The martensitic transformation of small, fully coherent, gamma iron precipitates in an epsilon copper matrix, brought about by the bombardment of thin foils with argon ions, has been studied using lattice fringe imaging. It is found, in general, that only partial transformation of individual particles occurs, this corresponding to a simple homogeneous shear (a Bain strain). In addition, the transformation is limited to particles located within about two particle diameters of the foil surface. It is established that the mere presence of a Frank (or Shockley) loop in a particle, due to the bombardment, is insufficient to trigger the transformation. The implications of this result are discussed with reference to bulk martensite. In the present case, it is concluded that transformation may simply initiate at sites of local decohesion or microslip at the matrix/particle boundaries brought about by vacancy condensation following ion bombardment, these sites being most effective in the vicinity of free surfaces

Practically all papers concerned with grain refinement based on pinning by particle dispersions have considered spherical particles. This paper avoids this restriction and develops Zener pinning equations for ellipsoidal particles of any shape, orientation and degree of coherency. Theoretical predictions are verified using soap bubble model experiments. It is found that within well defined conditions of particle orientation, disk or needle-shaped particles may offer greater pinning resistance, or Zener drag to migrating boundaries than spherical ones. However, the pinning resistance of non-spherical particles is sensitive to particle orientation. Their use in alloys is best utilised in systems based on mono-orientation dispersions

For pt.I see ibid., vol.32, p.1935 (1984). The properties of surfaces can be modified by heat-treatments using a scanning laser beam. In pt.I it was shown that the hardness and the depth of the laser-hardened layer in hypereutectoid steels could be predicted, with reasonable accuracy, from a model which combined an analysis of heat flow with one of the kinetics of pearlite dissolution, carbon redistribution in austenite, and subsequent transformation to martensite. In the present study the model is extended to include the case of hypereutectoid steels. A new approximate solution for carbide dissolution is developed, which allows both the changes in particle size and volume fraction, and in carbon content of the austenite, to be estimated. Reasonable agreement between measured and predicted hardness for a laser treated 1% C steel are obtained. The results are presented as laser processing diagrams which show how the case depth and hardness depend on the process variables

A physically-based theoretical model is developed for describing the phenomenon of indentation creep over the whole temperature range, from 300 K to melting. In agreement with experimental data collected, the model predicts that most materials, including ceramics, exhibit indentation creep at temperatures down to 300 K. It is established that the principal mechanism causing indentation creep is dislocation glide plasticity. The dominance of this mechanism over the whole temperature range is due to the very high stresses involved in indentation creep. If, however, the grain size is small (typically less than 0.3-0.4 μm) indentation creep may be dominated by grain boundary (Coble) diffusive creep instead. The implications of these results in terms of the design, forming and application of the so-called "hard materials" is discussed.

When the temperature of a powder compact is raised, heat diffuses inwards from the surface. If the compact is under pressure (as it is during HIPing), the surface layers start to densify, increasing the local thermal conductivity. Under certain conditions a densification front then propagates into the powder, and this leads to changes of shape of the compact, which is no longer identical to the preform shape. The conditions which lead to non-uniform densification are analyzed and the consequences are discussed, and compared with experiments

Hot isostatic pressing of metallic or ceramic porous preforms occurs by the densification of a shell at the surface of the preform, which then thickens until the whole sample is fully densified. It is shown that the development of such a dense shell can reduce the pressure acting to densify the remaining porosity. Furthermore, this pressure difference can lead to anisotropic creep of the shell, and this may be a contributory cause of shape change of samples during HIPing. The stresses occurring during cooling of the sample and the residual stresses, are calculated as a function of various input parameters. It is found that the cooling stresses can be particularly large and tensile, and may be the cause of surface cracking observed in certain HIPed ceramic samples.

Hot isostatic pressing (hipping) is an extremely efficient way of densifying ceramic and high alloy metallic powders, or for healing porosity in castings. However, depending on the parameters of pressure, temperature, rate of heating, and sample size, hipping can result in a non-uniform mode of densification. This mainly occurs when a rapidly heated sample, or a sample of large dimensions, densifies quickly at the surface to produce, if effect, a fully dense, hard shell. It is shown that there can be a number of negative factors resulting from this, including reduced rates of densification, sample sample shape change, non-uniform shrinkage, and the development of residual stresses in the sample. Criteria for predicting whether or not non-uniform densification will occur are presented and evaluated. Steel and Cu are discussed.

When the temperature of a powder compact is raised, heat diffuses inwards from the surface. If the compact is under pressure (as it is during HIPing), the surface layers start to densify, increasing the local thermal conductivity. Under certain conditions a densification front then propagates into the powder, and this leads to changes of shape of the compact, which is no longer identical to the preform shape. The conditions which lead to non-uniform densification are analysed and the consequences are discussed, and compared with experiments

A simple analytical solution is developed for calculating the residual stresses which occur as a result of the laser transformation hardening of steel surfaces. The solution is based mainly on taking account of the dilatation resulting from the martensitic transformation and allows the influence of the many and varied parameters involved in laser transformation hardening (beam size and intensity, material properties, composition, etc.) to be readily assessed. Satisfactory agreement between the theoretical predictions and reported experimental measurements of residual stress is obtained

Under many conditions, hot isostatic pressing (HIP) of metallic or ceramic porous preforms occurs by the densification of a shell at the surface of the preform, which then thickens until the whole sample is fully densified. The development of such a dense shell reduces the effective pressure acting to densify the remaining porosity. Furthermore, this pressure difference can lead to anisotropic creep of the shell, and this may be a contributary cause of shape change of samples during HIP. The stresses occurring during cooling of the sample and the residual stresses are calculated as a function of all of the various material and pressing parameters. It is found that, in many cases, the cooling stresses which are tensile at the surface may well be large enough to cause cracking in ceramic samples