Showing papers by "National Physical Laboratory published in 1988"

Metastable lattice stabilities for the elements

Abstract: Lattice stabilities for the metastable FCC (Al), BCC (A2) and CPH (A3) allotropes of 43 elements have been evaluated. The results are based on (1) Assessed stable phase data; (2) Phase boundary extrapolations from binary alloy, and elemental pressure-temperature, phase diagrams; (3) A relationship between the entropy of fusion, crystal structure and melting point; (4) Stacking fault energies; (5) Periodic and group trends and (6) First principle electronic energy calculations. Qualitative trends proposed by previous thermochemical evaluations for the transition metals are to a large extent confirmed. However, the evaluated energy differences between the different crystal allotropes are substantially higher and can be closer in magnitude to those predicted by ab-initio electron energy calculations, although particular discrepancies, for example concerning Cr(FCC), still remain. Many of the changes proposed here arise from the reassessment of stable phase data, particularly with respect to recently measured heats of fusion of the high melting point elements.

Identification of optimum binder phase compositions for improved WC hard metals

Abstract: The possibility has been investigated of using measurements of the mechanical properties of alloys with binder phase compositions to identify binder phases that will provide high hardness and toughness in WC hard metals based on cobalt, nickel, CoNi, NiAl, NiCrMo and NiCrMoAl. The results showed that, in WCCo and WC(CoNi) hard metals with constant grain size and binder phase content, an optimum grain size and binder phase content, an optimum combination of fracture toughness and compressive strain could be obtained at particular tungsten and carbon contents which could be determined from measurements of magnetic saturation and lattice parameters. As predicted from tests on NiWC alloys, it was found that WCNi hard metals had lower toughness and strength than WCCo hard metals do. Additions of aluminium to nickel binder phases to form γ′ precipitates raised the strength and conferred creep resistance but decreased the fracture toughness. Solid solution strengthening by chromium and molybdenum raised the hardness without reducing toughness as measured by Palmqvist tests and gave properties which matched those of WCCo hard metals. By combining γ′ hardening and solid solution hardening by chromium and molybdenum in nickel-based binder phases, better values of hardness and toughness were obtained than those of WCCo hard metals. The new compositions also offered the possibilities of enhanced resistance to creep and corrosion, and properties that could be varied by heat treatments to meet specific requirements.

The structure and composition of TiZrN, TiAlZrN and TiAlVN coatings☆

Abstract: In this paper, we deal with physically vapour-deposited hard coatings in the ternary system TiZrN and in the quaterrnary systems TiAlZrN and TiAlVN on various substrate materials such as cold-worked steels, high speed steels and cemented carbides. The reactive gas high performance sputtering technique has specific advantages in the deposition of these innovative complex coating materials with extremely different melting points because there is no intermediate liquid phase in the coating process. All the compound coatings investigated crystallize in a cubic face-centred TiN lattice with reduced or enlarged lattice parameters depending on the amount and type of the “foreign” atoms present. There was no real correlation found between wear properties, foreign metal type and content, and lattice distortion.

Creep and fracture of metals : mechanisms and mechanics

Abstract: Modern methodologies that aim to reduce conservatism in the design of components operating at high temperatures rely on accurate predictions of materials’ behaviour in conditions relevant to those experienced in service. This requirement has focussed the attention of materials engineers on developing a quantitative understanding of damage-accumulation in engineering alloys. The microstructure of metallic materials can degrade by several mechanisms at rates that depend; (i) on temperature; (ii) often on stress level or state; and (iii) sometimes on the chemistry of the surrounding fluid environment. In this paper, some recent developments in the modelling of damage processes have been reviewed; in particular, the single state variable approach has been assessed and the potential benefits of using two state variables outlined. Also, a two-bar mechanical analogue has been used to quantify certain features of creep deformation associated with grain boundary cavitation and the close agreement between theory and experiment is demonstrated. A model for the creep damage associated with the evolution of the dislocation substructure in nickel-base superalloys has been developed further and experimental support for an unusual feature of the model has been demonstrated. Revue Phys. Appl. 23 (1988) 605-613 AVRIL 1988, : Classification Physics Abstracts 62.20

VAMAS Surface chemical analysis standard data transfer format with skeleton decoding programs

Abstract: In surface analysis today many commercial instruments are operated through a computer. This computer is also used for processing the captured data, using routines from a built-in set of options for peak synthesis, peak deconvolution, background subtraction, peak area measurement, quantification in various levels of sophistication, mapping, depth profile presentation, smoothing, differentiation and a host of other functions. However, many analysts wish to process their data on another computer in their own particular way using programs written to their specification and under their full control. They need to encode the data in the data-capture computer into a form suitable for transmission then decode it into the form required in the receiving computer. A standard format for the transferred data would clearly lead to economies in the number of programs required to effect the encoding and decoding. To meet the above requirement, as a result of a series of iterative discussions over the last three years, first within the UKESCA Users Group and then with the VAMAS National Representatives and users and manufacturers within the VAMAS Community as well as the ASTM Committee E-42.11, we have produced a Surface Chemical Analysis Standard Data Transfer Format defined in a standard metalanguage. This Format is intended to be used by those wishing to transfer data from computer to computer via parallel interfaces or via serial interfaces over direct wire, telephone line, local area network or other communications link. It is suitable for AES, EDX, FABMS, ISS, SIMS, SNMS, UPS, XPS, XRF and similar analytical methods. It covers elemental maps, depth profiles and sequences of data resulting from a variety of experiments. Thus the application of the Format is very general.

Concept of an imaging XPS system

Abstract: The concept of an imaging XPS system is analysed and the various approaches discussed. For instrument and design flexibility it is shown that a standard XPS system with an efficient input lens can be used to form a virtual image of the spectrometer input aperture on the sample surface. This defined area of analysis may be rastered across the sample surface using a pre-lens scanning deflector system. In this way good XPS images of 256 × 256 pixels and of 250 μm resolution over an area of diameter 10 mm may be formed in ten minutes. Examples are provided from components for the electronics assembly industry demonstrating that insulators cause no problems. Design considerations are then detailed for optimizing imaging XPS systems at 25 μm and 10 μm spatial resolution involving pre-lens scanning systems and position-sensitive detectors.

Multichannel phase-stepped holographic interferometry

Abstract: A modified holographic interferometer is described which enables automatic fringe pattern analysis to be achieved when recording transient events. The introduction of a phase grating enables the method of phase-stepping fringe analysis to be applied to a wide range of measurement problems. The theory is developed, and an analysis of the sources of error is presented with the aid of computer simulations. Initial experimental results confirm the utility of the method and its potential application in pulsed laser holography. The method can in principle be applied to electronic speckle pattern interferometry.

An intercomparison of absolute measurements of the oxygen and tantalum thickness of tantalum pentoxide reference materials, BCR 261, by six laboratories

Abstract: Samples of the NPL/BCR reference material of 30 nm and 100 nm of tantalum pentoxide on tantalum foil have been analysed by six independent laboratories. Four laboratories used nuclear reaction analysis involving the 16O(d, p1)17o∗ reaction, traceable to weighing and charge transfer standards, three used Rutherford backscattering analysis traceable to calculated cross sections and stopping powers, and one used elastic recoil detection analysis, again traceable through calculated parameters. Although the assessed mean result is beyond one standard deviation of the estimated error from some of the individual results, the mean results for oxygen contents and the thickness ratio agree very well with the results from a previous paper (ref. [1]: M.P. Seah et al. Nucl. Instr. and Meth. B30 (1988) 128). Individual results of the Ta and O contents of the films confirm the Ta2O5 stoichiometry within 2.5% and the thickness ratio of 0.332 to better than 2%. The average thicknesses and standard deviations of the measurements of the two films, in oxygen atoms m 2 from this study, are (1.77 ± 0.05) × 1021 and (5.38 ± 0.21) × 1021, respectively, in close agreement wi values of (1.80 ± 0.04) × 1021 and (5.42 ± 0.10) × 1021 of the previous paper. An overall analysis gives final values as (1.79 ± 0.04 and (5.40 ± 0.10) × 1021 atoms of oxygen m 2 , respectively, where the uncertainties are the 95% confidence limits.

Further Measurements of Thermodynamic Temperature Using a Total Radiation Thermometer: the Range - 130°C to +60°C

Abstract: Brief descriptions are given of the design and operating principles of the NPL total radiation thermometer. Further measurements of T-T68 are reported for the temperature range - 130 to +60°C and tabulated with previous measurements made in the range -40 to +100°C. A graph is presented of all the published measurements of T-T68 from various independent primary thermometers in the range 50 to 400 K, and their relevance to the construction of a reference function for the proposed ITS-90 is discussed.

Limits of topographic measurement by the scanning tunnelling and atomic force microscopes

Abstract: SUMMARY Parameters describing the topographic character of a surface (height, surface wavelength, slope and curvature) can be derived from equivalent sinusoidal profiles. The response of a surface-measuring instrument may be modelled in terms of instrument parameters such as stylus radius, and scanning range and resolution. The performance of the instrument may then be mapped as a zone in amplitude-wavelength (AW) space to show the sinusoidal profiles it is capable of measuring. In a first-order analysis the STM and AFM are considered as equivalent to contact-stylus instruments with a notional stylus radius equal to the tip radius plus the gap. Comparisons between different instruments and types of instrument are readily made by mapping in AW space. The error arising from convolution of the sinusoidal profile with that of the finite tip may be quantified and plotted as contours in AW space.

Electron spin resonance and optical spectra of VO2+ and Cu2+ in ZnOB2O3 and PbOB2O3 glasses

Abstract: Electron spin resonance and optical spectra of 2RO-3B2O3 (where R = Zn and Pb glasses containing V2O5 and CuO in different proportions have been studied. Spin hamiltonian parameters of TM ions have been calculated. It is found that for VO2+g‖, g‖, A‖, K and Δg‖/Δg‖ increase while A‖, P, A‖′, A‖′ decrease when V2O4 is replaced by CuO. For Cu2+, g‖ and A‖ decrease and g‖ increases when V2O5 is added to CuO containing glasses. The bonding coefficient and normalised covalency of Cu2+ have also been calculated.

Predicting the kinetics of hydrogen generation at the tips of corrosion fatigue cracks

Abstract: A model has been developed to predict the rate of generation of hydrogen atoms at the tips of fatigue cracks for steel cathodically protected in marine environments. The model incorporates crack-tip chemistry, scraping electrode measurements, and crack-tip deformation. The current density for generation of hydrogen atoms by reduction of water at the crack tip has been calculated for a range of electrochemical and mechanical variables (electrode potential, cyclic frequency, waveform, ΔK, and R value). The crack-tip current density is always greater than on adjacent crack walls and tends to increase with decreasing (more negative) potential. However, at potentials more negative than about-900 mV (SCE), at a cyclic frequency of 0.1 Hz, cathodic reduction of water on the external surface of the steel is predicted to be the dominant source of hydrogen atoms. Decreasing the frequency reduces the crack-tip current density and further emphasizes the dominance of bulk charging. There is little difference in hydrogen charging current densities at the crack tip for sinusoidal, triangular, or positive sawtooth waveforms, but square-wave loading provides a greater charging current. Increasing ΔK and R value have only a small effect on crack-tip current density but increase the area of the active surface and thus lead to more significant charging. Hydrogen-atom concentration profiles in fracture mechanics specimens and in tubular sections have been calculated for conditions in which bulk charging of the steel with hydrogen is dominant. To ensure that crack growth rates are “steady-state” values, test times have to be long enough to establish steady conditions of hydrogen charging. Crack growth data from fracture mechanics specimens may not be directly relevant to cracking in tubular sections because of hydrogen concentration gradients in the latter.

Experimental determination of the electrochemistry in corrosion fatigue cracks in structural steel in artificial seawater

Abstract: An experimental method has been developed for measuring the electrode potential and solution pH at the tip of a growing fatigue crack in BS 4360 5OD steel in seawater The technique involved insertion of separate 1- to 2-mm diameter glass and reference electrodes in holes drilled to intersect the growing crack A compact tension specimen was used with the holes drilled in the transverse direction, ie, perpendicular to the crack front, to minimize perturbation of the local stresses Measurements of the crack tip pH and potential were made for a range of applied potentials, at varying ΔK (range of the stress intensity factor) and R-value (minimum load/maximum load) At cathodic protection potentials, the pH was alkaline but generalizations about the potential drop were not possible, although the potential in the crack was always in a region of “protection” for the conditions investigated At the free corrosion and anodic potentials the pH was neutral to slightly alkaline The potential drop was s

Design and performance of phase reversal traveling wave modulators

Abstract: A new optimization routine for the design of integrated optic phase reversal traveling wave modulators is demonstrated. The positions of the microwave phase reversal are computed to give a flat frequency response over the required frequency range. Experimental results on a three section periodic phase reversal modulator exhibiting a 7.5-GHz bandpass response centered at 12.75 GHz and a peak phase shift of 0.725 rad at 11.5 GHz for 20-dBm microwave power are presented. >

Quantitative AES: The establishment of a standard reference spectrum for the accurate determination of spectrometer transmission functions

Abstract: The precise shape of the whole electron spectrum in AES is defined by (i) the physics of the process, and (ii) the intensity/energy transmission function of the measurement system. In many systems item (ii) is uncharacterized and surveys show variable effects of over an order of magnitude. This gives rise to equivalent errors in quantitative AES where published data banks are used and the spectrometers are uncalibrated. In this study we consider both the process and the measurement system, and show how the parameters of each may be measured and how each affects the final measured spectrum in the direct mode. The factors considered include the orientation of both the incident and emitted electrons, and the energy dependence of the transmissivities of the spectrometer and the detection system. Detailed measurements of high accuracy for a copper reference sample show the extent to which the reference procedures may be followed and equivalent data be recorded from different instruments.

Bibliometric analysis of scientific productivity: a case study of an indian physics laboratory

Abstract: The paper analyses the output of the publication data of an Indian laboratory in the field of physics inSCI and nonSCI covered Indian and foreign journals, processes developed and Indian patents filed during the period 1965–82 to find out the pattern of productivity. Looks at the journals wherein the laboratory scientists publish. Also points out the sub-areas of physics in which the laboratory scientists have published maximum papers and also mentions about the pattern of scientific co-authorship in the research work. Correlation coefficients between input variable (manpower and budget) with output variables (number of papers published, processes developed and Indian patents accepted) have been calculated.

Interlaboratory comparison of hydrophone calibrations

Abstract: The results of an interlaboratory comparison of hydrophone calibration techniques in the frequency range 1-10 MHz are reported. Two membrane hydrophones were calculated to six laboratories, and each laboratory determined the end-of-cable loaded sensitivities using their normal calibration methods; these included optical interferometry, planar scanning, reciprocity combined with time-delay spectrometry, and suspended-sphere radiometry. After converting the results to end-of-cable open-circuit sensitivities, in most cases agreement between the various values was within +or-10% at all frequencies. >

Goniometer with continuously rotating gratings for use as an angle standard

Abstract: The paper describes an angle measuring system for the calibration of reference angle standards used by standardizing laboratories and industry. The machine has a range of 360° with a measurement uncertainty of 0.05 are sec. Measurements of angle gauges and a polygon are tabulated and discussed.