Influence of the Processing Route in the Microstructure and Mechanical Properties of NiAl/TiB 2 Composites Produced by C
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HE combustion synthesis process, also known as self-propagating high-temperature synthesis (SHS) has been widely used to produce a variety of materials.[1–3] Single compounds such as NiAl,[4] TiC, TiB2, and MoSi2 have currently been produced, as well as composites such as TiB2/NiAl,[5] TiC/NiAl,[6] and TiB2/SiC.[7] These materials are used in applications that involve high temperature or require high wear resistance; they may be used as cutting tools or as a route to produce targets for the physical vapor deposition process.[8] In the case of NiAl/TiB2, a typical application would be in a hightemperature crucible or reactor. These crucibles or reactors would be made applying a functionally graded materials concept, where the internal wall would be pure TiB2, the external wall pure NiAl, and in between a continuous composition variation. In this application, TiB2 would be exposed to high temperature and oxidative environment, while NiAl would offer the possibility of yielding, avoiding catastrophic failure. RICARDO D. TORRES, Professor, is with the Mechanical Engineering Department, Pontifı´ cia Universidade Cato´lica do Parana´ – PUCPR, Curitiba, CEP 80215 901, Brazil. Contact e-mail: ricardo. [email protected] CARLOS M. LEPIENSKI, Professor, is with the Physics Department, Universidade Federal do Parana´, Centro Polite´cnico, Curitiba 81531-990, Brazil. JOHN J. MOORE, Professor and Department Head, and IVAR E. REIMANIS, Professor, are with the Metallurgical and Materials Engineering Department, Colorado School of Mines, Golden, CO 80401. Manuscript submitted August 12, 2008. Article published online March 19, 2009. METALLURGICAL AND MATERIALS TRANSACTIONS B
An alternative route to produce such composite materials is the combustion synthesis route. The main advantage of the combustion synthesis process over other processing routes, such as powder metallurgy, infiltration, and other conventional routes, relies on the fact that part of the energy required to achieve the desired product phases and the plastic state necessary for densification is generated by an exothermic chemical reaction. The main disadvantage with respect to the fabrication of dense composites is that the inherently high energy of the reaction typically results in a porous microstructure; however, full densification may be achieved by simultaneously coupling the combustion synthesis reaction and hot pressing of the initial powder mixture at the ignition temperature. The combustion synthesis process can be conducted using either high heating rates or more moderate heating rates. High heating rates are usually applied when the exothermic reaction is conducted in a glass chamber with a tungsten coil, producing heating rates as high as 500 °C/min. The resulting synthesized products are generally porous. An alternative processing route is to conduct the exothermic reaction simultaneously while applying a consolidating pressure via a hot press, in which the heating rates are typically around 50 °C/min, facilitating the densification of the combustion synthesized
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