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Introducing high temperature intermetallic eutectic as potential structural materials

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Introducing high temperature intermetallic eutectic as potential structural materials

Intermetallic fascinated high temperature materials community for the last five decades. Starting with gamma TiAl, both Ti based and Ni based single phase intermetallics have been subject of extensive investigation. It took five decades for actual application in latest generation GE engine. However, very little attention has been given to multiphase multicomponent intermetallics. These, in particular eutectics, are abundant in the central regions of phase diagrams of ternary and higher components. With a hypothesis that they represent exciting opportunity, this talk will present the outline of our fairly extensive efforts in developing high temperature intermetallic composites based on a novel design of materials through microstructural engineering of intermetallics at nano scale. We shall concentrate on the Ni-Al-Zr system and show that unique complex multiphase microstructures could be developed containing intermetallics of Ni3Al, Ni5Zr, Ni7Zr2 and NiAl. The microstructures contain single or multiple coupled eutectics that are distributed seamlessly along the entire samples. For example, for an alloy Ni-12At%Al-11at%Zr, two intermetallic phases (Ni3Al and Ni5Zr) are seamlessly distributed along the entire sample with two different length scales and morphologies. Often these microstructures can be visualised by a 3D analysis that shows variations of connectivity among phases. Many of these alloys show strength in excess of 2GPa This architecture exhibits excellent high temperature microstructural stability, exceptional high strength with reasonable tensile ductility at high temperature. We show that this can be derived from an approach designed to exploit eutectic reactions that combine Intermetallics in a microstructural scale that restricts slip lengths to obtain both strength and ductility. Some of these alloys also have exceptional oxidation resistance that is retained up to a temperature of 973K. Finally we shall present some results of creep strength of these alloy that hints at the stress induced transformation. [more]

 
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