A. G. Jackson

Relationship of the second order nonlinear optical coefficient to energy gap in inorganic non-centrosymmetric crystals

Abstract Second order nonlinear optical coefficient and energy gap data collected from the literature have been classified and are organized by plotting their respective values. The two-dimensional plots indicate that both large energy gap and small ζ(2) and small energy gap and large ζ(2) are highly correlated. It was found that a single law expression cannot represent the data well for energy gaps over the entire range from 0 to 10 eV. Therefore a fit for narrow energy gap (0 1 eV) materials are provided. A corresponding trend and fitting strategy is also demonstrated for the figure of merit (FOM) which is used to rank materials for wavelength conversion efficiency. Results of the analysis are used to estimate the second order nonlinear optical properties and conversion efficiencies of several less-well-known materials. Trend analysis suggests that ordered GaInP2 would be exceptional as an E-O waveguide material and that the FOM of AgGaTe2 is 3.3 times that of AgGaSe2 and that crystals of HgGa2Se4 and TexSe(1 − x) alloys should be of distinct interest as wavelength conversion materials for infrared applications. The maximum attainable ζ(2) is in the range of 3500–4000 pm/V for bound electrons. For energy gaps less than one eV, the increase in ζ(2) with decreasing energy gap slows considerably.

The effect of cooling conditions on the microstructure of rapidly solidified Ti-6Al-4V

The effect of cooling conditions, giving estimated cooling rates in the range 104 °C per second to 107 °C per second, on the microstructure of Ti-6Al-4V has been evaluated. The microstructures of as-solidified particulates were martensitic, with the martensite lath length decreasing with beta grain size,L, which in turn decreased with increasing cooling rate. For material alpha + beta heat-treated or vacuum hot pressed, the alpha morphology was dependent on the prior cooling rate. For materials cooled at <5 × 105 °C per second martensite transformed to lenticular alpha, while material cooled at >5 × 105 °C per second developed an equiaxed alpha morphology. This change in morphology was explained in terms of high dislocation density or grain size refinement, both of which result from the high cooling rate. When the beta grain size (L) was plottedvs section thickness (z), and estimated cooling rate (T), power law relationships analogous to those reported for secondary dendrite arm spacing were found:L = 1.3 ± 0.4z089±006 (thin, chill-substrate quenched),L = 0.17 ± 0.05z0.86±0.01(thick, convection-cooled material), andL = 3.1 × 106 T−0.93±0.12 (all material), whereL and z are in μm andT is in K/s. The last relationship is in agreement with the 0.9 exponent predicted using a model developed for the effect of grain size on cooling rate assuming classical homogeneous nucleation and isotropic linear growth during solidification. The first two relationships were rationalized by assuming that the two materials cooled under near-Newtonian conditions.

Study of the formation of the amorphous phase in metallic systems by mechanical alloying

Abstract At present, there is considerable interest in the formation of amorphous phases in alloy systems, because of the property and processing advantages possible. The advantages of mechanical alloying (MA) for the formation of amorphous phases are a more homogeneous product and good reproducibility. Hence amorphous phase formation through MA in titanium systems was examined and compared with rapid quenching. Because TiNiCu possesses a deep eutectic, favorable diffusivity and heat of mixing, it is prone of the formation of amorphous phases during rapid quenching. The response to similar MA in the systems TiAl, TiMg and commercial purity titanium was also studied since these are not prone to amorphous phase formation in rapid quenching. The results of calorimetry, X-ray and electron diffraction are reported and the mechanism of amorphous phase formation in MA as opposed to that in rapid solidification is discussed.

Rough sets applied to materials data

Abstract Rough sets is a mathematically well-grounded approach to discovering patterns in data. Examples related to materials science illustrate the application of rough sets methodology to identifying related objects, determining the degree of dependency of subsets of attributes on other attributes, and testing subsets of objects for patterns. Classification of objects into classes that exhibit specific behavior is important in understanding material behavior and in predicting material properties. The lower approximation identifies those objects that belong with certainty to a pattern; the upper approximation identifies those objects that have some probability of belonging to some pattern. Results of the application of the rough sets method to the chalcopyrite family of crystal structures are presented.

Synchroshear of Laves Phases

The three Laves phases consist of alternating single layers and triple layers of atoms. Shear of the structure within the triple layers may be achieved by moving synchrodislocations. The dislocation with the smallest Burgers vector is the synchroshockley a/6 which has a core split over two planes. If a synchroshockley sweeps every triple layer of the cubic C15 it is twinned, if it sweeps every other triple layer, C15 is transformed into hexagonal C14. If the synchroshockley sweeps two triple layers, leaves out two, sweeps two etc. C15 is transformed into C36. Synchroshockleys travelling in pairs in any of the structures form dissociated perfect dislocations capable of giving slip.

The influence of Nb addition on structure and properties of rapidly solidified intermetallics

Abstract The intermetallic alloys Ti-15wt.%Al-7wt.%Cu, Ti-15wt.%Al-7wt.%Cu-10wt.%Nb and Ti-15wt.% Al-14wt.%Cu were vacuum arc melted followed by rapid solidification by the pendant drop melt extraction technique in vacuum. A detailed characterization of these rapidly solidified materials was conducted using light optical microscopy, scanning electron microscopy-energy dispersive spectroscopy, microhardness, bend ductility tests, scanning transmission electron microscopy, X-ray diffraction and differential thermal analysis. The presence of niobium improved chemical homogeneity of the copper and alluminum and refined the microstructure, resulting in improved ductility at room temperature.

Characterization of the phases present in a Ti-45a/oAl-10a/oNB alloy

In this paper details of the ternary phase equilibria for the Ti-Al-Nb system are studied to identify the phases present in the near gamma region and to determine the phase boundaries. Uncertainties in the location of the boundaries have an important impact on the choice of processing parameters for gamma aluminides. Hence, it is of some practical importance to clearly identify the phases expected. Perepezko et al. reported that the Ti-Al-Nb ternary system possesses an isolated ternary high temperature phase at about 45Al-10Nb (a/o) that is cubic in the temperature range between 1200{degrees} C and the liquidus. This implies that simple extension of the binary Ti-Al phase equilibria and reactions into the ternary field is inappropriate. They used drop quench techniques that utilized a flowing inert-gas furnace and an ice water quench bath. They reported that, in comparison to the {alpha}{sub 2} and {gamma} regions, only small microstructural regions of the T2 cubic phase were produced, suggesting that this high temperature T2 phase decomposes rapidly and is difficult to retain at room temperature. Data presented that support the identification of the cubic structure include electron diffraction patterns (SADP and CBED zolz) from the zone of a body centered cubic lattice.

Beta-Eutectoid Decomposition in Rapidly Solidified Titanium-Nickel Alloys

The eutectoid reaction, β → α + Ti2Ni, has been observed in as-produced rapidly solidified ribbons and flakes of hypoeutectoid and near-eutectoid beta titanium-nickel alloys prepared by chill block melt spinning (CBMS), pendant drop melt extraction (PDME), and electron beam melting/splat quenching (EBSQ) processes. Microstructural characterization of these materials was carried out by scanning electron microscopy, transmission electron microscopy, and X-ray energy dispersive spectroscopy. The occurrence of eutectoid decomposition in the rapidly solidified alloys was attributed to the breakaway of the ribbons or flakes (while still at an elevated temperature) from the quench wheel, resulting subsequently in a lower cooling rate. Fast quenching, as obtained in the hammer-and-anvil process, resulted in a martensitic structure free from products of eutectoid decomposition. The eutectoid morphology was nonlamellar in hypoeutectoid alloy ribbons, while a hitherto unreported lamellar eutectoid was observed in the near-eutectoid ribbons and flakes. The formation of this unusual lamellar eutectoid was rationalized in terms of the predominance of allotriomorphs of alpha phase and consequent availability of sufficiently mobile and maneuverable alpha/beta interphase boundaries in the fine-grained, rapidly solidified titanium-nickel alloys.

Bulk deformation of Ti-6.8Mo-4.5Fe-1.5Al (Timetal LCB) alloy

Recently, a low-cost near-β titanium alloy (Timetal LCB Ti-6.8Mo-4.5Fe-l.5Al wt %) containing iron and molybdenum has been developed. This alloy is cold formable in the β microstructure and can be aged to high strengths by precipitating the a phase. Due to its combination of cold formability and high strength, the alloy is a potential replacement for steel components in the automotive industry. The current study was undertaken to evaluate the cold bulk forming characteristics of Timetal LCB for use in lightweight automotive applications. Room-temperature compression tests conducted over a strain-rate range of 0.01 to 5/s indicate that the bulk cold compression of the alloy is affected by two factors: the microstructure and the length-to-diameter aspect ratio of the specimen. In the aged condition, when the microstructure has a-phase particles distributed along flow lines in the β-phase matrix, the alloy has the propensity for shear failure when deformed in compression in a direction parallel to the flow lines. In the solution-heat-treated condition, the microstructure consists of β grains with athermal ω phase. In this condition, the alloy can be cold compressed to 75 % reduction in height using specimens with aspect ratio of 1.125, but fails by shear for a larger aspect ratio of 1.5. Plastic deformation of the material occurs initially by single slip in most grains, but changes to multiple slip at true plastic strains larger than about 0.15. At a slow strain rate, the deformation is uniform, and the material work hardens continuously. At high strain rates, shear bands develop, and the localized deformation and temperature rise due to deformation heating leads to flow softening during compression. Although there is a considerable rise in temperature (200 to 500 °) during deformation, precipitation of the a phase was not observed.

SENSOR PRINCIPLES AND METHODS FOR MEASURING PHYSICAL PROPERTIES

Because the scientific method is based on and observation, measurement methodologies and techniques are critical advancement of science and technology. Direct measurement of physical properties, inferences from physical properties, are based on models of behavior. To reduce the possibility of erroneous measurement, a clear understanding of how a sensor translates properties into measured values is vital to advancing materials and process design. The linkage between the accepted models, sensor principles, and methods of measurement enables one to optimally choose a sensor technology. Opportunities for innovation and research are abundant in this field, with the trend toward micro- and nano-sized integrated systems being especially notable.