This study showed pronounced changes in the Raman scattering of silicon powder during
high-energy ball milling. The powders were milled for 1–18 h in a steel ball mill in argon.
The approximate pressure imposed on particles was 2 GPa. The spectra of the as-milled
powders were compared with the initial silicon. It was found from the Raman peak position
shifts that milling generated strains in the silicon lattice, bringing about a transformation
of cubic silicon to tetragonal silicon and amorphization. The relative amount of
new phases was determined from the area under the measured Raman peaks.
Direct monitoring of temperature, chemistry and microstructure is required to understand microwave heating in more detail, in order to fully exploit the unique features this non-equilibrium processing method can offer. In this paper, we show first that microwave radiometry can be used to follow volumetrically the thermal trajectory of microwave-heated aluminium powder. In-situ Raman spectroscopy is then shown to evidence thermal gradients between diamond and silicon grains in a binary powder mixture. Finally, perspectives and preliminary results of microstructural analysis obtained from X-ray microtomography are presented. r
a b s t r a c tIngots of an oxide dispersion strengthened reduced activation ferritic steel with the Fe-14Cr-2W-0.3Ti-0.3Y 2 O 3 chemical composition (in wt.%) were synthesized by mechanical alloying of elemental powders with 0.3 wt.% Y 2 O 3 particles in a planetary ball mill, in a hydrogen atmosphere, and compacted by either hot extrusion or hot isostatic pressing. The microstructures of the obtained materials were characterized by means of light microscopy, transmission electron microscopy and chemical analyses. The mechanical properties were evaluated by means of Vickers microhardness measurements and tensile tests. It was found that the microstructure of both materials is composed of ferritic grains having a submicron size and containing nanometric Y-Ti-O oxide particles with a mean size of about 10 nm, uniformly distributed in the matrix. The oxide particles in the hot extruded steel were identified as YTiO 3 phase. In larger (>10 nm) oxide particles Cr was found next to Ti, Y and O. The steel produced by hot extrusion exhibits much higher tensile strength and hardness at low to moderate temperatures, as compared to the steel fabricated by hot isostatic pressing, which was mainly attributed to smaller pores but also to more severe work hardening in the case of the hot extruded steel.
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