Structure and properties of injection-moulded nylon-6

The microstructure and morphology of injection-moulded nylon-6 has been studied using wide-angle and small-angle X-ray diffraction, optical microscopy and a density measurement technique. A non-spherulitic surface layer consisting of a metastable pseudohexagonal phase surrounds the moulding and the thickness of the layer is sensitive to mould temperature. This outer structure gives way to a monoclinic phase containing spherulites between 3 and 6 m diameter. The central core of the moulding consists almost entirely of the phase with spherulites 6 m diameter, approximately. Exposure of nylon-6 to boiling water had no significant effect on the morphology of the moulding but the phase in the surface layer was transformed to the monoclinic phase.     

The optical properties and a.c. conductivity of magnesium phosphate glasses

Magnesium phosphate [X MgO-(100–X) P₂O₅] glasses in the composition range [X=20, 25, 30, 40, 45, 50 mol %] have been made. The optical properties and a.c. conductivities were measured and their amorphous nature confirmed by X-ray diffraction technique. The variation of relative density with x was anomalous. In the ultraviolet/visible regions it was found that the fundamental absorption edge is a function of glass compositions and lower absorption coefficients, () follow the so-called Urbach edge. At lower absorption levels (1<<10⁴cm^–1), the width of the tail of localized states in the band gap, E _g, did not vary significantly with glass composition and lay in the range (0.26–0.343) eV. In the high absorption region (()>10⁴ cm^–1), the behaviour of () suggests that there are two different transition energies for electrons in k-space, namely direct allowed transitions and non-direct transitions. In the infrared region at wavelengths =2.5–30 m, the transmission spectrum has four absorption bands. Using the Kramers-Kronig theory, the optical constants (refractive index n and extinction coefficient k) have been determined from the transmission spectrum. The a.c. conductivity, (), real and imaginary dielectric constants, ₁, ₂, and loss factor, tan , have been determined at room temperature in the frequency region, = 2×10⁴–10⁶ Hz. It has previously been established theoretically that () ^s and s was found to be in the range 0.64–0.73, depending on glass composition.     

Lamellar thickening growth of an extended chain single crystal of polyethylene (II) : ΔT dependence of lamellar thickening growth rate and comparison with lamellar thickening

The degree of supercooling (T ⁰) dependence of lamellar thickening growth rate (U) of an isolated extended chain single crystal (ECSC) of polyethylene is studied. The experimental formula,U = C exp(–D/T ⁰), where C = 130 nm/s and D = 20.0 K is obtained for the first time. The formula is the same as that of lateral growth rate (V). The reason why U and V obey the same formula is well explained by a model named sliding diffusion model of the lamellar thickening growth. The model proposed that the lamellar thickening growth is controlled by both chain sliding diffusion within the ECSC and the nucleation on the side surface. The observed fact that the U increases with increase of T ⁰ is opposite to the well known fact that lamellar thickening rate W decreases with increase of T ⁰. This siginificant difference was well explained by the difference between the primary crystallization and the secondary crystallization, which is a kind of Ostwald's ripening process. The origin of the tapered shape is well explained by coupling of lamellar thickening and lateral growths.     

Electron microscopy studies of α- andβ-form spherulites in weld lines of injection moulded polypropylene parts

The crystal morphology of the weld lines in injection moulded polypropylene parts has been investigated by X-ray scattering and transmission electron microscopy. Wide angle X-ray scattering curves reveal two crystal modifications in the samples: the monoclinic -modification and the hexagonal -modification. The fraction of the crystallinity which is due to the -modification is lower in the vicinity of the weld line and increases with the distance from the weld line.Transmission electron micrographs reveal that in the weld line no crystallization of -spherulites occurs.     

Morphology and phase transition of high melt temperature crystallized poly(vinylidene fluoride)

When PVDF is crystallized at temperatures above 155°C it presents a multiform morphology composed of ringed, non ringed and mixed spherulites. Infrared spectroscopy showed that the ringed spherulites are formed exclusively by the phase when crystallization takes place at temperatures below 155°C. Higher temperatures induce a solid-state phase transformation in these structures, increasing the amount of phase with crystallization time. The rate at which this transformation takes place increases with crystallization temperature. The non ringed spherulites, only formed at crystallization temperatures above 155°C, consist predominantly of the phase, crystallized from the melt, with small phase inclusions. The melt process of the different spherulites, observed by optical microscopy and calorimetric measurements (DSC) showed that the melt temperature of the phase, originated from the phase transition, is 8°C higher than that crystallized directly from the melt. Optical micrographs of samples heated up to 186°C and quickly cooled allowed visualization of the ringed spherulite regions which underwent the phase transformation at different crystallization times and temperatures.     

Effects of hydrostatic extrusion on the mechanical and thermal properties of polypropylene

The structure change in spherulites for hydrostatically extruded polypropylene (PP) was studied by the use of internal friction measurements and thermophotometry tests. The onset temperature of the -loss peak of the PP sample decreases with increasing reduction in area, R. For the extrudates below R=50%, the peak temperature of -loss shifts to lower temperature. The and absorptions for the extrudates up to R=50% become broad and overlap with each other. The intensity of the -loss peak, _max, is maximum for the extrudate with R=50%. The results of tan , damping, and the intensity of the -loss peak indicate that the mechanism of molecular chain deformation is divided into two stages, below and above R=50%. The results are due to spherulitic changes, i.e. the shape of spherulites changed from spherical to elliptical in the extrudates above R=50% and the spherulite with R=50% changed from coarse structure to a finer one by the imposition of hydrostatic pressure.     

An asymptotic theory of guided waves

Summary A procedure is developed for finding asymptotic expansions at high frequencies of the solutions of Helmholtz's equation subject to boundary conditions on certain guiding surfaces. This includes surface waves along surfaces of rather general shapes, and wave-guide modes in a class of non-uniform waveguides. Guided waves have some features of both eigenvalue (mode) and radiation problems. The method of this paper combines the two techniques, finding modes that propagate along rays in the general waveguide region and whose amplitudes vary along the paths of propagation. The phases of these modes are found from two coupled equations, one analogous to the eiconal equation of geometrical optics, and the other analogous to the eigenvalue or transverse resonance equation of waveguides. The amplitudes are asymptotic series in inverse powers of the wavenumber, and the coefficients satisfy a set of ordinary differential equations that can be solved recursively. It is found that the ray paths are not only functions of the refractive index (as in pure radiation problems), but depend also on the local geometrical properties of the guiding surface.     

Phase transformations in permanent-mould-cast aluminium bronze

The phases obtained in aluminium bronze (Cu-10Al-4Fe) cast into a permanent mould were investigated. The parameters examined were the pre-heating temperature of the mould and the graphite coating thickness. The phases and ₂ were detected as well as the metastable phases and . The intermetallics of the system Fe-Al were obtained in various stoichiometric compositions. The different cooling rates of the casting resulted in two mechanisms of transformation to grains out of the unstable phase, one being nucleation and growth producing needle-shaped grains, the other exhibiting a massive transformation to spherical grains. These two mechanisms determine the changes in the size of the a grains as result of changes in the cooling rate in its various ranges.     

Swelling parameter of polypropylene used in household appliances

Samples of unfilled copolymer polypropylene were immersed in various solvents and the equilibrium swelling was recorded. Two-dimensional solubility maps of the Hildebrand parameter, , versus hydrogen bonding parameter, _c, and _h versus _v for polypropylene were plotted. Using the calculated percentage swell values and the solubility maps, the and _h values for detergent were postulated. No changes in the polypropylene backbone were revealed by mid- or far-infrared spectra, showing that the polypropylene polymer, when subjected to a number of different solvents, had not altered substantially.     

The mechanism of continuous dissolution of the lamellar structure in aged Al 22 at% Zn alloy

The mechanism of continuous dissolution was studied using transmission electron microscopy, X-ray diffraction and hardness measurements. The metastable phase was identified in the first stage of dissolution nucleating at the - boundaries. Interface dislocations at the - boundaries forming a perpendicular net in the 110 directions were identified as of screw character and of Burgers vector b=1/2a 110. During dissolution a change of shape of precipitates occurs leading to their fragmentation and to a change of the direction of boundaries into 110 directions.     

Flow Characteristics of Metal with Phase Transformation and Prediction of Its Microstructure

We propose a flow-stress characteristic of SUS430F steel that takes in account the effects of temperature, strain rate and their deformation history. In the framework of this characteristic, the history effects of strain rate and temperature are estimated through the plastic strain energy stored. The formulated characteristic () may be shown as a function of temperature (), strain rate ((), and the stored energy W or the reference stress (_st). The energy is stored through plastic deformation and released during annealing process. The energy is also referred by the yield flow stress (_st), which is measured under the reference condition. The discussion on the characteristic is extended to the material at high temperature (1073–1473 K) with the + gamma phase of a given phase ratio. The equilibrium ratio of ()- or ()-phase at a given temperature can be estimated on the basis of an equilibrium phase diagram. In order to introduce the flow-stress characteristic with phase transformation using the proposed formulation, we also analyze the phase transformation rate from () to + with temperature elevation, and from () to > + in the cooling process on the basis of the time–temperature–transformation diagram that includes the quenching process as well. The flow stress characteristic and phase ratio are estimated simultaneously for a hot forging process.     

Localization of vibrations of shrouded turbomachine rotor blading

We study the influence of the nature of the circumferential distribution of the blade frequencies on the localization of the vibrations of shrouded blade rings. It is shown that the most favorable configuration (with regard to both the level of the vibratory stresses and the scatter of the resonant amplitudes of the vibrations) for the shrouded blade rings with mistuning of the blade frequencies is the sawtooth arrangement of the frequencies around the circumference of the disk, while the most unfavorable configuration is the arrangement with two or three neighboring blades with the same or similar frequencies. We propose a technique for studying the localized vibrations of the subject systems, making it possible to significantly simplify the solution of the problem.This work was performed under the State Research Program Improving the Reliability and Service Life and Eliminating Catastrophic Failures of Gas Turbine Transport Engines,Translated from Problemy Prochnosti, No. 7, pp. 53–61, July, 1994.     

TEM study of metastable β-phase decomposition in rapidly solidified Ti-6Al-4V alloy

A new rationale is presented for various decomposition products obtained from the metastable -phase found in Ti-6A1-4V alloy produced by hot isostatic pressing comminuted melt-spun fibres and cooled to room temperature by furnace cooling. This alloy has an -matrix with about 8 vol% retained -phase, which is supersaturated with -stabilizers to such an extent that the martensitic transformation has been suppressed. The metastable -phase decomposes by different modes during continuous cooling, depending on the actual composition of individual -grains. Less enrichment of vanadium and iron favours the direct formation of the equilibrium -phase from the -matrix, while greater enrichment of vanadium and iron leads to a spinodal decomposition of the metastable -phase, resulting in a + two-phase structure. During further continuous cooling, the -phase which is lean in -stabilizers will transform into isothermal -phase. In addition, an unknown phase has also been observed in the -phase, which is typified by the appearance of 1/2{112} reflections in the SAD patterns.     

Thermodynamic Properties of Intermediate Ni–P Phases (26–32.5 at. % P) between 971 and 1440 K

The vapor composition over and thermodynamic properties of crystalline nickel–phosphorus alloys (26–32.5 at. % P) are studied by Knudsen cell mass spectrometry between 971 and 1440 K. Mass spectra of the saturated vapor in the Ni–P system indicate the presence of the Ni⁺, P⁺ ₂, and P⁺ ions. The P concentration in the vapor phase does not exceed 1% of the ₂ concentration. The experimental data are used to evaluate the complete set of thermodynamic functions of nickel phosphides. Based on the data for the low-temperature (, ) and high-temperature (, ) forms of Ni₅P₂ and Ni₁₂P₅, the thermodynamic characteristics of the corresponding polymorphic transformations are evaluated. The results obtained for a large number of compositions under different experimental conditions (different effusion-cell and coating materials and effusion-orifice diameters) coincide to within the experimental error and are in good agreement with earlier reported phase-equilibrium data and enthalpies of formation, attesting to the high accuracy and reliability of the calculated thermodynamic functions.     

Etching of MgO crystals in acids: surface micromorphology

Several etchants based on simple acids are proposed for revealing dislocations on {100}, {110} and {111} faces of MgO single crystals. Some acids under different etching conditions are shown to produce etch pyramids at decorated dislocations, while etch hillocks, spherulites and dendrites are formed under different conditions. With increasing concentration of H₂SO₄, 110 pits, circular pits, 100 pits, 110 pyramids as well as 100 pits, dendrites and spherulites, and hillocks are formed in that order. Etching characteristics of other acids also showed a more or less identical trend. The observations are interpreted with the assumption that with increasing concentration of acid, an effective undersaturation and later supersaturation is developed very close to the dissolving crystal face. The chemistry of the dissolution process is also discussed.     

Etching and morphology of poly(vinylidene fluoride)

The lamellar structures within spherulites of melt-crystallized poly(vinylidene fluoride) have been examined following the development of an etching technique which allows the study of representative morphologies in this polymer. The banded -spherulites, which predominate at crystallization temperatures below 165°C, are found to be made up of densely packed lamellae with an intrinsically planar habit, whilst the -spherulites which develop preferentially at higher temperatures, have a curious architecture in which the lamellae adopt a highly curved scroll-like morphology. These observations are discussed in terms of existing models for spherulite banding and non-planar lamellar habits.     

The magnetic and mechanical hardness of the intermetallic compounds SmCo5 and LaCo5

The magnetisation, coercivity, H _C, and remanence coercivity, H _R, have been measured for the intermetallic compounds SmCo₅ and LaCo₅. The coercivities H _C and H _R for SmCo₅ are very much greater than those for LaCo₅. The differences in these parameters are much greater than would be expected from a simple theoretical model, so that they cannot be accounted for in terms of differences in the magnetocrystalline anisotropy constants. Since the specimens used for the magnetic measurements were produced by mechanical comminution, Knoop hardness measurements were made in an attempt to account for the magnetic behaviour in terms of the crystallographic damage and plastic deformation produced during the grinding process. The hardness results show that, within experimental error, the SmCo₅ is very nearly isotropic, whereas the LaCo₅ is very anisotropic on the {10¯10} planes with a Knoop hardness of 138 in the 0001 directions and 511 in the 12¯10. It is concluded that plastic deformation will occur more easily in LaCo₅ and that this could, to some extent, explain the comparatively low coercivities.     

Strain-induced β-α polymorphic transition in iPP as revealed by microhardness

The microhardness (H) technique was used for characterization of the - polymorphic transition in isotactic polypropylene (iPP). For this purpose the microhardness in the damage zone of a tensile loaded deeply edge-notched (DEN-T) -iPP specimen was mapped. Mapping of H was performed, both along the loading direction (central) and close to the shorter fracture edge. Around half-length of the plastic zone a sharp increase of the H values in both cases was observed. The H increase is related to the polymorphic transition. Microvoid formation in the central part results in lower H values. However for the edge zone close to the top of the fracture surface unusually high H values (around 200 MPa) are obtained. The latter are explained in terms of the formation of microfibrils due to crazing during deformation which are characterized by very high molecular orientation as reported from X-ray analysis.     

The influence of molecular weight and mould temperature on the skin-core morphology in injection-moulded polypropylene parts containing weld lines

The sandwich structure of injection-moulded polypropylene parts with and without weld lines has been investigated using optical microscopy. X-ray scattering, and differential scanning calorimetry. It was found that the skin-layer thickness is strongly dependent on whether the mould is injected through one gate or through two gates. Samples containing a weld line show a much lower skin-layer thickness than samples without a weld line. This difference, however, depends strongly on the molecular weight of the polypropylene. The skin-layer thickness also varies along the flow path and decreases with increasing mould temperature. While most of the polypropylene crystallizes in the crystallographic -modification, in the textured skin layer, some -modification occurs. The -crystallinity depends on the molecular weight but disappears in the weld line. X-ray investigations exhibited a bimodal crystal orientation in the skin layer, one with thec-axis oriented parallel to the flow direction, the second one with thea ^*-axis oriented parallel to the flow direction. The core exhibited only a weakc-axis orientation. In the skin, the metastable ₁-modification was found.     

Phase transformations in Ti-Nb-Ta and Ti-Nb-Ta-Zr alloys

Phase transformations in solution treated and quenched Ti-(13-26) Nb-(22-38) Ta (wt.%) and Ti-(13-35.5) Nb-(5-22) Ta-(4-7.2) Zr alloys have been studied. It has been observed that phase transformations in these alloys are sensitive to both composition and cooling rate. In ternary alloys, water and oil quenching resulted in the formation of orthorhombic martensite () in a retained + _athermal matrix, whereas slower cooling showed evidence of fine and _isothermal formation within the matrix. Increase of Nb + Ta content decreases the volume percentage of martensite. Moreover, addition of Zr stabilized the phase, lowered the martensite start temperature and suppressed formation. Finally, dynamic moduli of air cooled quaternary alloys showed that the modulus was sensitive to the composition, a minima at Nb/Ta ratio of 12.0 and 5 at% Zr being observed, this minimum in dynamic modulus being consistent with phase suppression.