Abstract
In this paper, we report a significant improvement in Microstructure and oxidation roperties of near eutectic NbSi alloys by the addition of aluminum (Al) and control of microstructural length scale. A comparative study of two alloys Nb-18.79at%Si and Nb-12.3at%Si-9at%Al were carried out. The processing for microstructure refinements were carried out by vacuum suction casting in water cooled thick copper mould. It is shown that addition of Al suppresses Nb3Si phase and promotes βNb5Si3phase under nonequilibrium solidification condition. The microstructural length scale and in particular eutectic spacing reduces significantly to 50100 nm in suction cast ternary alloy. The indentation fracture toughness of Al containing suction cast alloy shows a value of 20.2±0.5 MPam which represents a major improvement over bulk NbSi eutectic alloy. The detailed thermal studies confirm a multifold improvement in oxidation resistance up to 1000°C.
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