The production of electron transparent areas by splat-quenching

(See also following abstract). Maximizing the quench rate gives rise to metastable, nonequilibrium structures. Certain areas can be thin enough for direct EM observation at 100 kV. Vitek has proposed these areas are not simply due to spreading of individual droplets. From combined scanning transmission and scanning EM, two alternative mechanisms were suggested: interaction on the substrate between a solidifying droplet and a subsequently impacting droplet that had undergone in-flight solidification; and interaction of a solidifying droplet with a flaw, or solid droplet, on the substrate. For comparative microstructural studies, regions observed must have cooled under similar conditions. Manipulation of variables allows production of thin areas arising mainly from simple impact spreading, having had a relatively reproducible quench. Micrographs for Al-17.3 at. per cent Cu are shown. The thickness distribution obtained would arise through the spreading of a viscous solidifying droplet down an inclined surface. Specimens of 100 mg and a nozzle diameter about 0.85 mm are recommended.--EPAA/AF.