Synthesis of Novel Aluminide-Based Materials

Abstract

18 INTRODUCTIONAluminide intermetallics have the desirable property combination of low density, high strength and general oxidation resistance. However, these materials are limited in their application since they typically exhibit poor ductility and fracture toughness. To improve the mechanical properties of aluminide intermetallics, it is necessary to determine how alloy chemistry and processing conditions can influence crystal structure and deformation behavior. In addition, innovative processing methods are required to produce these new materials. In experiments at the McDonnell Douglas Research Laboratories and the Center for Explosives Technology Research at the New Mexico Institute of Mining and Technology, novel methods are being used to produce aluminide-based alloys in experimental quantities.The use of explosively generated shock waves in the synthesis of new materials is a relatively recent concept. DeCarli and Jamieson 1,2 were the first to synthesize diamond from graphite by using dynamic pressure, and today this is a successful industrial process. 3 Shock-induced chemical reactions were first used by Sawaoka and Akashi to aid in shock consolidation of hard boron nitride powders. 4 Additions of elemental titanium, aluminum and carbon powders to boron nitride were found to enhance interparticle bonding and to allow full densification of the compact. There has been little investigation, however, of the potential of using shock synthesis to produce novel intermetallic compounds with improved properties. In our experiments, an explosively generated shock wave is used to simultaneously synthesize niobium-, nickel-and titanium-aluminide phases and to consolidate titanium aluminide powders. The goals ofthis work are to apply shock synthesis to as-yet-unexplored alloy systems, and to establish the underlying mechanisms of the synthesis-assisted consolidation process.Another method of synthesizing an aluminide phase involves the use of a solidi liquid reaction to form the alloy. This synthesis approach makes use ofthe fact that refractory metals such as niobium rapidly react with molten aluminum to form refractory metal aluminide phases. These reactions are highly exothermic and proceed rapidly until one or all of the reactants are completely consumed. The use of a solid/liquid reaction to produce an intermetallic compound is not a new concept, especially when one considers the large number of intermetallic compounds formed naturally by peritectic reactions. In addition, processes such as transient liquid-phase sintering have been used to produce a variety of materials from blended elemental powders. The distinctions to be made between these processes and reaction synthesis are that the solid/liquid reaction used here is applied to a congruently melting system rather than to a peritectic system, and that the resultant product is a single-phase material, rather than the typically multiphase product of liquid-phase sintering. EXPERIMENTAL PROCEDURESIn the shock-wave synthesis-assisted consolidation process, Ti...

Síntese por combustão do NbAl3 e de ligas do sistema Nb-Ni-Al

“…A aplicação de pressão simultânea à reação, seja por prensagem isostática a quente [76], seja por compactação dinâmica [75].…”