30 research outputs found
Distortion in a 7xxx aluminum alloy during liquid phase sintering
The distortion in a sintered 7xxx aluminum alloy, Al-7Zn-2.5Mg-1Cu (wt. pct), has been investigated by sintering three rectangular bars in each batch at 893 K (620 °C) for 0 to 40 minutes in nitrogen, followed by air or furnace cooling. They were placed parallel to each other, equally spaced apart at 2 mm, with their long axes being perpendicular to the incoming nitrogen flow. Pore evolution in each sample during isothermal sintering was examined metallographically. The compositional changes across sample mid-cross section and surface layers were analyzed using energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy depth profiling, respectively. The two outer samples bent toward the middle one, while the middle sample was essentially distortion free after sintering. The distortion in the outer samples was a result of differential shrinkage between their outer and inner surfaces during isothermal sintering. The porous outer surface showed an enrichment of oxygen around the large pores as well as lower magnesium and zinc contents than the interior and inner surface of the same sample, while the inner surface was distinguished by the presence of AlN. The differential shrinkage was caused by different oxygen contents in local sintering atmosphere and unbalanced loss of magnesium and zinc between the outer and inner surfaces
Sinterização de uma mistura de cavaco de aço inoxidável com pó do mesmo material: uma nova tecnologia para a reciclagem de metais?
Pore shrinkage and Ostwald ripening in metallic systems. Progress report, July 1, 1978-June 30, 1979
The new theory of Ostwald ripening phenomena is gradually unfolding. Based on the principle of minimum rate of entropy production, the general method including the mathematical formalisms of variational calculus, is now understood and has been applied to the case of annealing of void structures, a situation somewhat simpler to model than is particle coarsening. The resultant void distribution function is compared with that expected from the LSW theory and with experiments. Developments in three areas are described: generation and annealing of voids in HVEM, distribution of Ni/sub 3/Al in Ni-Al alloys, and production of reproducible pore structures in nickel powder compacts
Coalescence of Two Equal Cylinders: Exact Results for Creeping Viscous Plane Flow Driven by Capillarity
Testing the robustness of daily associations of affect with alcohol and cannabis use
Etiological models of alcohol and cannabis use disorders hypothesize that people are more likely to use and consume more of these substances when they experience heightened negative affect, yet recent EMA studies found no evidence for the daily association between negative affect and substance use. However, the theory underlying affect regulation of substance use is vague and has been translated into many different statistical tests across the literature, with inconsistent results. We aim to test the affect regulation hypothesis in a large sample of participants and across hundreds of statistical models to provide a robust understanding of whether and when affect regulation is supported in everyday life. This will enable us to update theoretical models and inform future clinical interventions aimed at the affect-substance use association