Dispersoid Size Research Articles

Influence of an Assumed Size of a Dispersoid on the Calculated Flow Curves of Immiscible Polymer Blends by Concentric Multi-layer Model

The effect of assumed size of dispersoid was investigated by the concentric multi-layer model proposed earlier for simulating the flow of immiscible polymer blend through a tube. The flow curves of PC, SAN and their blends were calculated by changing the diameter (d) of a dispersoid from 0.01 μm to 100 μm. The influence of diameter on calculated results was negligible provided that the diameter was 1 μm (d/2R1=2×10-3, R1; radius of a capillary) or less. The calculated result was not affected by the order of layers, i.e., the matter of which component was in contact with the tube wall, when the assumed particle size was small, and was in good agreement with the observed result.

Determination of dispersoid size distributions in Inconel MA 754 by small-angle X-ray scattering

The dispersoid size frequency distribution and volume fraction of the nickel based oxide dispersion strengthened alloy Inconel MA 754 have been determined using small-angle X-ray scattering (SAXS). Two methods of determining dispersoid size distributions from the SAXS spectra are utilized. One method involves a calculation of log-normal distribution parameters from the integrated intensity, forward scattering and the Porod radius. A second method employs an integral transform of the data to calculate the size distribution. Dispersoid size distributions from the transform method exhibit close agreement with histograms obtained from thin foil transmission electron microscopy. Measurement of dispersoid volume fractions from the integrated intensity, coupled with dispersoid size frequency distributions allow a calculation of the average planar separation distance of the dispersoids. The results for two heats of MA 754 lead to predicted dislocation creep strengths which are in reasonable agreement with short time creep data at 1000 and 1093°C. The effect of the presence of mixed aluminum-yttrium oxides in MA 754 is considered.

Dispersoid size distribution measurements in a SEM equipped with an image analysis system

Dispersoid size distribution measurements in a SEM equipped with an image analysis system

Laser-melting/spin-atomization method for the production of titanium alloy powders

Recent studies of the rapid solidification of titanium alloys have demonstrated that significant microstructural refinement and property improvements can be achieved in titanium alloys solidified at cooling rates >10 3 K per second.~-5 However, methods for producing rapidly solidified titanium powders have received little attention. Most titanium alloy powders have been produced by the hydride-dehydride process or by spin-atomization from rotating electrodes, ingots, or crucibles. 6-~~ Except for the hydride-dehydride process, all the powder-production methods involve various degrees of rapid solidification, which have not yet been quantified. Recently Konitzer et al. ~ used laser melting and spin atomization to produce rapidly solidified Ni-Mo-A1 and Ti-6A1-4V alloy powders. In the present investigation, laser-melting/spin-atomization was used to produce and characterize rapidly solidified powders of a beta titanium alloy Ti-15-3 (Ti-15V-3A1-3Sn3Cr) and a rare-earth-modified Ti (Ti-1.0Y) alloy. The objectives of this study were to quantify the dependence of powder diameter on process variables and the dependence of cooling rate on powder diameter. The as-solidified dendrite structures are revealed in both alloys by simple etching, and the dendrite-arm spacings (DAS) can be used to estimate the cooling rates from a previously established correlation between DAS and cooling rate. t2 Because rapid solidification of the Ti-I.0Y alloy results in homogeneously distributed fine dispersoids in the Ti matrix, ~-5 dispersoid sizes can also be used to quantify the cooling rates produced in the lasermelt/spin-atomization process. A schematic diagram of the experimental arrangement is shown in Figure 1. The apparatus provides an inert gas environment and simple mechanism for controlling the melting and spin-atomization. A 6.2-kW continuous wave CO2 laser beam is directed at a glancing angle of 3 to 5 deg to one end of a rotating titanium alloy rod. High speed video recordings indicated that a thin molten layer forrps on the end surface and spreads radially under the influence of the melt viscosity and the rod rotation. At the circumference of the rod, the molten layer breaks into droplet s as the centrifugal force balances the surface tension according to

Relief etching technique for scanning and transmission electron microscopy characterization of submicron precipitates in aluminum alloys

The size, type, and distribution of insoluble dispersoids and age-hardening precipitates influence the processing and final properties of aluminum alloys, and accurate characterization of these submicron precipitates is often required. A modified version of a relief etching technique introduced by Ryvola and Morris now allows rapid determination of their size, shape, and distribution in the scanning electron microscope in addition to facilitating accurate chemical and microstructural analyses by transmission electron microscope/STEM analytic and diffraction techniques. The etching procedure is applicable to almost all second phases commonly found in aluminum alloys and is simple to use.

Microstructural Studies of Laser-Melted Titanium-Rare-Earth and Titanium-Boron Alloys

The feasibility of producing super-saturated solid solutions with small grain sizes and fine, stable, incoherent dispersoids was determined in laser-surface-melted Ti-rare-earth (RE) (RE = Er, Y, Gd, Nd, or Sc) and Ti-B alloys. Titanium specimens, coated with 0.02 to 1-μm thick electron-beam-evaporated rare-earth metal films or with a 10 to 25-μm thick boron slurry, were surface melted using a 1.5 kW continuous-wave CO2 laser beam at specimen traversing speeds of 0.5 to 40 cm/s. The microstructures of the laser-melted regions, determined by scanning and transmission electron microscopy, were correlated with the laser-processing parameters.Figures 1a-1c are scanning electron micrographs of transverse sections of the laser-melted Ti-Y alloy at traversing speeds of 0.5, 10, and 30 cm/s respectively. The positions of the solid-liquid interfaces match the theoretically predicted melting isotherms for a specimen-beam coupling efficiency of 25%. Constant cooling-rate curves, calculated from the heat-transfer model for a rapidly moving, high-power, Gaussian source, are included in Figures 1a-1c. In the laser-melted Ti-RE alloys with the 0.2-μm thick rare-earth films, the microstructure consists of fine 10-20 nm dispersoids. The dispersoid size decreases with increasing specimen traversing speed as well as with increasing distance from the specimen surface. The volume fraction of the dispersoids increases with increasing film thickness and with melt depth. The equilibrium, coarse, constituent particles, which are generally observed in conventionally cast Ti alloys containing corresponding amounts of rare-earth elements, were completely absent in the laser-melted alloy.

The high-temperature oxidation of Ni-20%Cr alloys containing various oxide dispersions

The oxidation behavior of Ni-20%Cr alloys containing approximately 3 vol.% Y2O3, ThO2, and A12O3 as dispersed particles has been examined in the temperature range 900 to 1200° C in slowly flowing oxygen at 100 Torr. The results show that the oxidation behavior of the Y2O3-, ThO2-, Al2O3-, and Ce02-containing alloys is very similar and that some anomalies in the behavior of the ThO2-containing alloy might be explained by the slower rate of chromium diffusion in this coarse-grained alloy. Two Al2O3-containing alloys were studied. One with a relatively coarse dispersoid size behaved in a manner analogous to a dispersion-free Ni-30% Cr alloy at 1100°C. The other alloy contained a dispersion of fine Al2O3 particles and behaved exactly like the Y2O3-containing alloy at 1000 and 1100°C, but at 1200° C oxidized at a faster rate. It has been shown that the adherent scales on dispersion-containing alloys have a stabilized fine grain size, whereas the nonadherent scales on dispersion-free alloys undergo grain growth.