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SEMI-SOLID PROCESSING OF METAL-OXIDE COMPOSITE
Jirková, H. ; Aišman, D. ; Mašek, B. ; Svoboda, Jiří
One of the available routes to developing a new material resistant to high-temperature creep is to create a microstructure consisting of a metal matrix and dispersed stable particles. For making intricately shaped components from such materials, new processes must be found to allow near net shape products to be manufactured in a simple and rapid manner. A semi-solid processing chain relying on mini-thixoforming could become one such process. For this purpose, an unconventional technology chain was designed in the present experiment. The chain comprises mechanical alloying, powder metallurgy techniques and thermomechanical treatment with transition through the semi-solid state. In this chain, thanks to the intensive deformation at the thixo-forming stage, the desired shape is achieved effectively. The second requirement was the good creep resistance of the material. To this purpose, two different powder materials consisting of metals and oxides were proposed. In both cases, the metal constituent contained iron and aluminium. The primary difference between the materials denoted as A and B was the nature of the oxides acting as strengthening particles. The powder mixture was prepared by mechanical alloying and compacted using various techniques. The powder mixture for the A material was compacted using high-pressure torsion (HPT). The B material was compacted by heating the mechanically alloyed powder enclosed in a steel container in a furnace and by subsequent intensive compressive deformation in a press. From the resulting products, cylindrical specimens for semi-solid processing were cut. The rate of heating to the semi-solid processing region was high. In the first stage, appropriate temperatures and heating rates were sought and optimized. These are crucial in obtaining the desired fine and adequately uniform dispersion of particles providing the strengthening effect.
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