Showing papers in "Journal of Materials Science in 1967"
TL;DR: Vitreous carbon as mentioned in this paper is a nongraphitising carbon which has high lustre and conchoidal fracture, and it has a high strength, hardness and resistance to corrosion, with low porosity and permeability.
Abstract: The carbonisation of certain cross-linked polymers under carefully controlled conditions yields a non-graphitising carbon which, on account of its high lustre and conchoidal fracture, has been called “vitreous carbon”. Other properties distinguishing vitreous carbon from the more common forms of the element include high strength, hardness, and resistance to corrosion, with low porosity and permeability. It has advantages over other materials of construction in a wide range of laboratory, metallurgical, mechanical, and electrical applications.
240 citations
TL;DR: In this article, a detailed experimental study of the behavior of grain boundaries between surface grains has been carried out on a magnesium alloy, Magnox AL 80, and different methods of assessing the strain due to grainboundary sliding were compared; the general agreement obtained confirmed the view that, under conditions of low stress and high temperature, sliding can play a very important role in the overall deformation.
Abstract: A detailed experimental study of the behaviour of grain boundaries between surface grains has been carried out on a magnesium alloy, Magnox AL 80. Different methods of assessing the strain due to grain-boundary sliding were compared; the general agreement obtained confirmed the view that, under conditions of low stress and high temperature, sliding can play a very important role in the overall deformation.
114 citations
103 citations
TL;DR: In this article, the authors studied the properties of Fe2O3 and Fe3+ on hydrogen at temperatures > 1000°C and found that the Fe hardness is relatively about four times less than that in alkali halides containing divalent metallic impurities, where all the impurities are associated with charge compensating vacancies.
Abstract: MgO containing ⩽5000 wt ppm Fe was heat-treated in various ways, so that the Fe was present in solution as Fe2+ or Fe3+, as precipitates of MgO.Fe2O3, or as metallic bcc Fe. Crystals were studied by optical absorption spectroscopy and microscopy. Heating in air at 1400‡ C converts most of the Fe to Fe3+ and some of this is associated with vacancies, particularly at high impurity levels. In crystals containing Fe3+, the magnitude of the hardening is relatively about four times less than that in alkali halides containing divalent metallic impurities, where all the impurities are associated with charge-compensating vacancies. Greater hardening is obtained when precipitates of MgO.Fe2O3 are present. Precipitates of metallic bcc Fe are formed on heating in hydrogen at temperatures >1000‡ C; these have the orientation relationships (001)MgO ∥ (001)Fe and [110]MgO ∥ [100]Fe.
82 citations
TL;DR: In this paper, a metastable phase was discovered which readily nucleated, and, at low concentrations (e.g. 0.045 mol % MgF2), it formed even on slow cooling.
Abstract: X-ray, and optical and electron microscopy studies have been made of precipitation in single crystals of LiF doped with MgF2. MgF2 was found to nucleate only with difficulty, which probably accounts for the large MgF2 precipitates that were observed. However, a metastable phase was discovered which readily nucleated, and, at low concentrations (e.g. 0.045 mol % MgF2), it formed even on slow cooling. Its structure appears to be similar to that proposed by Suzuki for the NaCl/CdCl2 system. The morphology of the metastable phase was seen by electron microscopy to be intersecting {100} platelets. On holding crystals containing the metastable phase at temperatures of about 300° C, particles of MgF2 nucleated at, and grew at, the expense of the metastable phase. The observation of precipitation of the metastable phase at low Mg++ ion concentrations is notable, for precipitation has almost certainly occurred during other studies of ionic conductivity, dielectric loss, and colour centres, etc., where crystals have been held at temperatures below 250° C. Solid-solubility measurements have been made to establish the MgF2 solvus line at concentrations up to 6.5 mol % MgF2 and the metastable phase solvus line up to 0.225 mol % MgF2. Kinetic measurements indicate that the growth of the metastable phase is controlled by bulk diffusion of Mg++ ions, whereas the growth of MgF2 appears to be controlled by the motion of vacancy pairs.
76 citations
TL;DR: In this paper, two techniques are described by which single crystals of sapphire may be grown, one is a development of the vertical-pulling technique for the production of scatter-free, low-dislocation-density material, whilst the other is an extension of a floating-zone, recrystallisation technique previously used for calcium tungstate.
Abstract: Two techniques are described by which single crystals of sapphire may be grown. One is a development of the vertical-pulling technique for the production of scatter-free, lowdislocation-density material, whilst the other is an extension of a floating-zone, recrystallisation technique previously used for calcium tungstate. The origin and control of defects in crystals grown by these techniques are discussed.
74 citations
TL;DR: In this article, it is suggested that the retardation of nucleation, observed by other workers, in more closely spaced dispersions, occurs because nucleation at particle/matrix interfaces becomes difficult when the interparticle spacing becomes of the same order as the diameter of the sub-structure of the deformed matrix.
Abstract: The recrystallisation of aluminium alloys in the composition range 0.002 to 1.08 wt% iron has been followed metallographically and by hardness measurements. The recrystallisation of solid-solution alloys was retarded as the iron content increased, whereas that of the two-phase alloys was accelerated. This latter effect was associated with a marked increase in nucleation rate, with no significant change of growth rate, as the Al3Fe particle spacing decreased from 15 to 4μm. Decreasing the grain size of the two-phase alloys, at constant composition, also caused an acceleration of recrystallisation, the magnitude of which decreased as the Al3Fe content increased. These effects have been shown to be independent of the size of the Al3Fe particles, within the range studied (diameters 0.6 to 2.2μm). The results are discussed in terms of a model (which is based on metallographic observations) of nucleation at matrix grain boundaries and at particle/ matrix interfaces. It is suggested that the retardation of nucleation, observed by other workers, in more closely spaced dispersions, occurs because nucleation at particle/ matrix interfaces becomes difficult when the inter-particle spacing becomes of the same order as the diameter of the sub-structure of the deformed matrix.
70 citations
TL;DR: In this paper, it was shown that temperature oscillations have been detected in oxide and fluoride melts which can be directly correlated to the movement of convection patterns visible on the melt surface.
Abstract: Temperature oscillations have been detected in oxide and fluoride melts which can be directly correlated to the movement of convection patterns visible on the melt surface. It is shown that such oscillations cause growth striations in single crystals grown from these melts. Additional experiments are reported in which the effect of changes in growth parameters upon the oscillations and melt temperatures have been investigated.
69 citations
TL;DR: For some time now, the bombardment of solids by heavy ions has been an active field of research It has been carried out for a variety of reasons, for example with a view to increasing knowledge of atomic collision processes and how they relate to such phenomena as secondary electron emission and sputtering as discussed by the authors.
Abstract: For some time now, the bombardment of solids by heavy ions has been an active field of research It has been carried out for a variety of reasons, for example with a view to increasing knowledge of atomic collision processes and how they relate to such phenomena as secondary electron emission and sputtering In addition, the implantation of inert-gas ions followed by thermal treatment of the bombarded solid has been undertaken with a view to studying diffusion processes and thereby providing information on the damage induced by the bombardment More recently, ion implantation has become important as a means of changing the electrical and chemical properties of the bombarded material Of particular interest is the doping of semiconductors in order to produce changes in the conductivity of the material in a highly controlled manner In this field, the technique is not merely a diagnostic tool but may well become an important addition to the present-day industrial technology of production of solid-state circuits and devices
65 citations
TL;DR: In this paper, single crystals of CuAu were used to examine the changes in hardness, flow stress, and microstructure resulting from heat treatment at 150 to 340°C, which produces the tetragonal superlattice.
Abstract: Single crystals of CuAu were used to examine the changes in hardness, flow stress, and microstructure resulting from heat treatment at 150 to 340° C, which produces the tetragonal superlattice. The crystals, quenched from a high temperature, were in the disordered cubic form to begin with; some were also cold-rolled, to permit comparison of the ageing characteristics of as-quenched and of cold-worked specimens. The asquenched crystal hardened much more than the cold-rolled ones; a peak hardness was attained and followed by a fall in hardness. At 150° C, no microstructural changes were seen; at 240° C, spontaneous recrystallisation took place at grain boundaries; while at 340° C, there was twinning and spontaneous grain-boundary fracture. The observations are rationalised in terms of the various mechanisms for relief of the large microstrains that accompany ordering in this alloy.
61 citations
TL;DR: In this paper, the effects of internal stress and elastic properties of the crystalline inclusion on composite mechanical properties were studied, and the results indicated that the fracture path rarely traversed the inclusions, except when internal stresses were of sufficient magnitude to cause cracking of the glassy matrix.
Abstract: Desirable physical properties not provided by single-phase materials are often conveniently attained by multiphase composites. This paper is concerned with the variation of the mechanical properties of bulk glass through the incorporation of a crystalline oxide phase. Glass-Al2O3 and glass-ZrO2 composites containing 20 and 40 vol % spherical, crystalline inclusions, 125 to 150 μrn in diameter, were prepared by hot pressing. The effects of internal stress and elastic properties of the crystalline inclusion on composite mechanical properties were studied. Experimental elastic-property values agreed well with theoretical values calculated from Hashin's equations. Flexural strength tests of all composite compositions revealed that the fracture path rarely traversed the crystalline oxide inclusions. The Al2O3 and ZrO2 additions strengthened the glass considerably, except when internal stresses were of sufficient magnitude to cause cracking of the glassy matrix upon cooling and before flexural testing. Glass-Al2O3 composites were consistently stronger than the glass-ZrO2 counterparts. This strength difference is attributed to the higher elastic moduli of the Al2O3 composites. Hypotheses which postulate strengthening as a result of restricted flaw size are apparently not applicable to these materials.
TL;DR: The contribution of dipole orientation to dielectric constant is markedly affected by rolling as discussed by the authors, and the observed effects can be explained by a substantial orientation of chains in the roll plane, which is perpendicular to the applied electric field.
Abstract: The contribution of dipole orientation to dielectric constant is markedly affected by rolling. The intensity of the γ peak is increased and the maximum shifted slightly to higher temperatures and frequencies. The shift is much larger with the β peak. Its intensity, however, is reduced by rolling. Long before the maximum of the β peak is reached, annealing effects irreversibly change the sample. With annealing, the values of the dielectric constant gradually approach those of the unrolled material. The observed effects can be explained by a substantial orientation of chains in the roll plane, which is perpendicular to the applied electric field. Such an orientation increases the average contribution of dipoles in crystal defects to polarisation as observed in the γ peak. Stronger interaction between partially aligned chains in the amorphous matrix hampers the rotation of chain segments in the electric field, and hence reduces the β peak and shifts it to higher temperatures.
TL;DR: In this paper, a system of photochromic glasses is described and the mechanism of photolytic reactions is postulated, and compared with the theory of the photographic process for silver halides.
Abstract: Photochromic materials are those which react reversibly to light. Photochromism is therefore distinguished from the familiar photographic processes, which, because of the chemical development of the image, are essentially irreversible. Many organic materials, and a few inorganic ones, show this phenomenon. Their general properties are described, with particular emphasis on those of a system of photochromic glasses. The behaviour of these glasses results from reaction of light with silver halide crystals deliberately formed in the glass during its manufacture. The mechanism of the photolytic reactions is postulated, and compared with the theory of the photographic process for silver halides. Reversibility of photochromism in these glasses is explained by prevention of diffusion of the products of photolysis from the original crystal site within the glass structure, and their subsequent recombination when the activating light is removed. These glasses show large ranges in all their photochromic properties resulting from ranges in composition, and in size and number of the included crystals. The behaviour of typical glasses, in both sunlight and under artificial sources, is reported in this paper, and some applications for these glasses are suggested.
TL;DR: In this article, the mechanical properties of NiO scales produced by the complete oxidation of high-purity (grade-1) Ni and commercial purity (Grade-A) Ni have been investigated at 700 to 1000 ǫ C.
Abstract: The mechanical properties of NiO scales produced by the complete oxidation of high-purity (grade-1) Ni and commercial-purity (grade-A) Ni have been investigated at 700 to 1000‡ C. The modulus of elasticity of both grades of oxide decreased with increasing temperature, whereas the modulus of rupture for grade-A oxide exhibited a maximum at 850‡ C and that for grade-1 oxide decreased with increasing temperature. At 700‡ C, elastic deformation to fracture occurred with both oxides, whereas, at temperatures ≥850‡ C, plasticity was also observed. The plasticity of grade-1 oxide was ∼3 times greater than that of grade-A oxide.
TL;DR: A comprehensive list of references on semiconductor heterojunctions can be found in this article, where several methods of producing such structures are given, together with a table of materials between which heterjunctions have been formed.
Abstract: The article serves as an introduction to a comprehensive list of references on semiconductor heterojunctions. Several methods of producing such structures are given, together with a table of materials between which heterojunctions have been formed. The more important measurements which are made on semiconductor heterojunctions are discussed and typical results quoted. A brief description of band models proposed for various heterojunctions is given. The references are arranged by year and in alphabetical order for convenience. Several articles are included which are not referred to in the text: these articles are included since they discuss certain theoretical aspects and possible practical applications of semiconductor heterojunctions.
TL;DR: In this paper, a technique for observing dislocations by their photoelastic patterns is described, which is successfully applied to the determination of Burgers vectors of dislocation in flux-grown single crystals of yttrium gallium garnet.
Abstract: A brief outline of the technique for observing dislocations by their photoelastic patterns is given. The method is successfully applied to the determination of Burgers vectors of dislocations in flux-grown single crystals of yttrium gallium garnet, and the origin and elimination of dislocations in this material is discussed.
TL;DR: The influence of the oxygen content of copper on its wetting of, and bonding to, tungsten has been investigated in detail using sessile-drop and pull-out strength tests as mentioned in this paper.
Abstract: The influence of the oxygen content of copper on its wetting of, and bonding to, tungsten has been investigated in detail using sessile-drop and pull-out strength tests. As little as 41 ppm of oxygen has been found to inhibit wetting and to result in bond strengths of less than 2 ton/in.2 (3.2 kg/mm2).
TL;DR: A theory predicting the velocity of a TAZ along a solid charge, published previously (D. T. Hurle, J. B. Mullin, and E. R. Pike, the authors, is extended to include the case where one of the solid phases is metastable.
Abstract: The basic principles of a family of crystal-growing techniques in which crystallisation of a substance is achieved via diffusion through a thin alloy zone (TAZ) from a third phase (solid, liquid, or vapour) are described. Crystallisation is achieved by the application of a gradient of a thermodynamic potential across the zone and various methods of establishing such a gradient are considered. A theory predicting the velocity of a TAZ along a solid charge, published previously (D. T. J. Hurle, J. B. Mullin, and E. R. Pike, Phil. Mag.
9 (1964) 423), is extended to include the case where one of the solid phases is metastable. Expressions for the gradient of constitutional supercooling in the zone are derived for conventional and thin alloy zone crystallisation (TAZC) processes. It is shown that the important advantage in the use of a TAZ is the dramatic reduction in the supercooling at a given velocity compared to conventional processes. A rationalisation of various published techniques of crystal growth within the concepts of TAZC is presented and some existing and potential applications of TAZC processes are reviewed.
TL;DR: In this paper, the structure of pyrolytic graphite has been examined on several samples deposited under various conditions at 1340 to 2310° C and 5 to 200 torr by means of an X-ray technique.
Abstract: The structure of pyrolytic graphite has been examined on several samples deposited under various conditions at 1340 to 2310° C and 5 to 200 torr by means of an X-ray technique. The structural features investigated include interlayer spacing, ordering, preferred orientation, intercrystallite porosity, and crystallite size. These features are closely related to the microstructure and density. In particular, the temperature dependence of crystallite size explains three types of formation mechanism, the cause of the occurrence of a minimum density at a certain temperature, and the cause of a preferred orientation in pyrolytic graphite.
TL;DR: A review of studies of fatigue in fibres and plastics is presented in this article, where the authors discuss the importance of imperfect elastic recovery and of time-dependent effects in determining behaviour in a fatigue test.
Abstract: A review is presented of studies of fatigue in fibres and plastics. The nature of fatigue in visco-elastic systems is discussed, and the reasons for the use of cumulative extension testing are given. A model is described showing the importance of imperfect elastic recovery and of time-dependent effects in determining behaviour in a fatigue test. Superimposed on this, there may be some true fatigue effects. Using this model, a more rational explanation of experimental results, which are otherwise confusing, is attempted.
TL;DR: In this article, two distinct recovery stages at annealing temperatures of about 450 and 550° K were found for vanadium containing oxygen and nitrogen, respectively, after deformation at room temperature by rolling.
Abstract: Vanadium containing oxygen and nitrogen shows, after deformation at room temperature by rolling, two distinct recovery stages at annealing temperatures of about 450 and 550° K. Measurements of electrical resistivity and of low frequency damping were made. By variation of the gas content of the samples, it was established that the stage situated at 450° K is caused by the migration of oxygen atoms to dislocations, whereas at 550° K nitrogen atoms migrate to dislocations. Two small steps occurring at 340 and 400° K can be attributed to ordering of oxygen and nitrogen atoms in the dislocation stress fields.
TL;DR: Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) combined with an infrared absorption study have been used to examine the mechanisms involved in the crosslinking or curing of phenol formaldehyde novolac resins with hexamine as discussed by the authors.
Abstract: Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) combined with an infrared absorption study have been used to examine the mechanisms involved in the crosslinking or curing of phenol formaldehyde novolac resins with hexamine. It has been shown that the curing reaction is a three-stage process. The first stage is the physical change of melting and subsequent formation of hexamine solutions. The second and third stages were found to be two, distinct, crosslinking reactions occurring in two, successive, temperature regions. The presence of absorbed moisture modifies the melting and curing processes.
TL;DR: In this article, the influence of channelling of incident 80 keV Ne+ ions on the formation of amorphous phases in silicon was investigated and it was found that channeling significantly reduced the rate at which this phase is produced, and in the particular case of the 〈110〉 axial channel this corresponds to a reduction in radiation damage by a factor of about 8.
Abstract: The ion bombardment of silicon results in the formation of an amorphous phase in the vicinity of the bombarded regions. This gives rise to a milky appearance which is easily distinguishable from an adjacent unbombarded region. An experiment is described which was specifically designed to study the influence of channelling of incident 80 keV Ne+ ions on the formation of this amorphous phase. It is found that channelling significantly reduces the rate at which this phase is produced, and in the particular case of the 〈110〉 axial channel this corresponds to a reduction in radiation damage by a factor of about 8. The results are compared with the current theories of channelling and are found to be in reasonable quantitative agreement.
TL;DR: Tensile tests at 20° C have been carried out on seventy-three sapphire whiskers and on seventeen silicon nitride whiskers as mentioned in this paper, and the tensile strength data have been analysed and fitted to empirical equations describing the effect of size on strength for different orientations.
Abstract: Tensile tests at 20° C have been carried out on seventy-three sapphire whiskers and on seventeen silicon nitride whiskers. The sapphire whiskers were of 〈0001〉, 〈1¯120〉, 〈10¯10〉, and 〈10¯11〉 orientations, while the silicon nitride whiskers were 〈0001〉, 〈11¯20〉, and 〈10¯13〉. Tensile strengths were in the range 45 to 1500 kg/mm2, and deformation was found to be purely elastic. The tensile strength data have been analysed and fitted to empirical equations describing the effect of size on strength for different orientations. These empirical equations have been used to deduce possible fracture nucleation mechanisms. It is concluded that, in the case of 〈0001〉 sapphire whiskers, fracture nucleation may be due to dislocation pile-ups or interactions, while in the other cases a Griffith flaw mechanism is probably applicable.
TL;DR: Hardening of fcc metals by incoherent particles is studied in this paper, where it is shown that the presence of the particles indirectly determines the rapid multiplication of dislocations in the matrix.
Abstract: Hardening of fcc metals by incoherent particles is analysed. The presence of the particles indirectly determines the rapid multiplication of dislocations in the matrix. The hardening is related to the dense tangles so formed. Recovery of these tangles occurs by cross-slip, climb, and probably by some other complex, thermally activated mechanisms.
TL;DR: In this paper, the mobility of the inert gases xenon or radon in five anisotropic oxides (hexagonal corundum Al2O3, Cr2O 3, Fe2O4, tetragonal rutile TiO2, and orthorhombic U3O8) was studied.
Abstract: The mobility of the inert gases xenon or radon in five anisotropic oxides (hexagonal corundum Al2O3, Cr2O3, Fe2O3, tetragonal rutile TiO2, and orthorhombic U3O8) was studied. The gases were introduced by ion bombardment. The oxides were in the form of powders, sinters, or single crystals. Normal volume diffusion was found at low gas concentration, the activation energies in kilocalories per mole being ⩾85 for Al2O3, 73±5 for Cr2O3, 68±5 for Fe2O3, 78±5 for TiO2, and 85±8 for U3O8, and the pre-exponential termsD0 falling into the “ideal” range of about 3×10−1±1 cm2/sec. Structural radiation damage, the annealing of which coincided with gas release at low temperatures, and, in some cases, retardation of the gas release were found at higher gas concentrations. Some evidence is presented that grain boundaries, pre-existing vacancy clusters, and dislocation loops may act as trapping sites for gas atoms (or bubbles) and may be stabilised after trapping of the gas.
TL;DR: In this article, single crystals of stoichiometric NiAl, nickel-rich Ni3Al, and Ni3(Al, Ti) have been grown by a modified Bridgman technique.
Abstract: Single crystals of stoichiometric NiAl, nickel-rich Ni3Al, and aluminium-rich Ni3(Al, Ti) have been grown by a modified Bridgman technique; a strain-anneal method has also been used to produce small, single crystals of non-stoichiometric NiAl.