Spatially Resolved Velocity Mapping of the Melt Plume During High-Pressure Gas Atomization of Liquid Metals

We present details of an image analysis algorithm designed specifically to determine the velocity of material in the melt plume during high-pressure, close-coupled gas atomization. Following high-speed filming (16,000 fps) pairs of images are used to identify and track dominant features within the plume. Due to the complexity of the atomization plume, relatively few features are tracked between any given pair of images, but by averaging over the many thousands of frames obtained during high-speed filming a spatially resolved map of the average velocity of material in the plume can be built up. Velocities in the plume are typically very low compared to that of the supersonic gas, being around 30 m s−1 on the margins of the plume where the melt interacts strongly with the gas and dropping to < 10 m s−1 in the center of the melt plume. Consequently, the efficiency of the atomizer in transferring kinetic energy from the gas to the melt is correspondingly very low, with this being estimated as being no more than 0.1 pct

Tempering stability of retained austenite in nanostructured dual-phase steels

The tempering resistance and stability of retained austenite in super-bainitic and quenching-partitioning martensitic steels were investigated over the temperature range of 400 to 700 °C. The X-ray diffraction analysis and hardness tests showed that the quenching-partitioning-martensitic steel contained a considerable amount of retained austenite (26.6 vol%) and had a relatively high hardness up to 556 HV1 after tempering at about 600 °C. In contrast, the fraction of retained austenite and hardness of super-bainitic steel were considerably lower (24.5 vol% and 385 HV1) after the same tempering cycle. The work also showed that the quenching-partitioning steel had a higher tempering stability, probably, due to the higher fraction of carbon-rich retained austenite

Control of Jupiter's radio emission and aurorae by the solar wind

Radio emissions from Jupiter provided the first evidence that this giant planet has a strong magnetic field(1,2) and a large magnetosphere(3). Jupiter also has polar aurorae(4), which are similar in many respects to Earth's aurorae(5). The radio emissions are believed to be generated along the high-latitude magnetic field lines by the same electrons that produce the aurorae, and both the radio emission in the hectometric frequency range and the aurorae vary considerably(6,7). The origin of the variability, however, has been poorly understood. Here we report simultaneous observations using the Cassini and Galileo spacecraft of hectometric radio emissions and extreme ultraviolet auroral emissions from Jupiter. Our results show that both of these emissions are triggered by interplanetary shocks propagating outward from the Sun. When such a shock arrives at Jupiter, it seems to cause a major compression and reconfiguration of the magnetosphere, which produces strong electric fields and therefore electron acceleration along the auroral field lines, similar to the processes that occur during geomagnetic storms at the Earth.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62740/1/415985a.pd

A Microstructural Investigation of Gas Atomized Raney Type Al-27.5 at.%Ni Catalyst Precursor Alloys

Quantitative image analysis has been used to investigate the phase composition of gas atomized powders of a Raney type Ni catalyst precursor alloys of composition Al-27.5 at.% Ni in the powder size range 150-212 μm. We find that there are considerable variations in phase composition both between powders from the same batch and as a function distance from the particle surface within individual particles. Such variations may have significant implications for the future production and uptake of such catalysts, including the necessity for post-production crushing of gas atomized powders. Models are proposed to account for both variations

Microstructure evolution and mechanical properties of drop-tube processed, rapidly solidified grey cast iron

The microstructure, phase composition and microhardness of rapidly solidified grey cast iron BS1452 Grade 250 are compared against the conventionally solidified alloy. Powder samples were prepared using containerless processing via the drop-tube technique. The rapidly cooled droplets were collected and sieved into size range from ≥850μm to ≤53μm diameters corresponding to estimated rates of 200-23,000Ks-1. Microstructure evaluations were made by optical and scanning electron microscopy, while XRD was used for identification and analysis of evolved phases. The control sample showed extensive graphite flake formation which was absent in virtually all the droplets samples. With decreasing particle size (increasing cooling rate) we observed an increase in the proportion of Fe3C present and the retention of γ-Fe in preference to α-Fe, with the proportion of retained austenite increasing with increasing cooling rate. At the highest cooling rates utilised a Martensitic or acicular ferrite structure was observed. Cooling rates of 200Ks-1 resulted in a doubling of the measured microhardness relative to the as-received (slowly cooled) material. Cooling at the highest rates achieved resulted in a further doubling of the measured microhardness