• PDF / 6,093,660 Bytes
• 7 Pages / 612 x 792 pts (letter) Page_size
• 108 Downloads / 245 Views

DOWNLOAD

REPORT

---

NTRODUCTION

REACTION synthesis refers to a processing technique whereby the thermal activation energy for the formation of certain compounds is provided in a self-sustaining fashion from the evolution of their exothermic heats of formation. The process is a derivative of the broad technology area known as self-propagating high-temperature synthesis (SHS) and shares a common mechanistic base with numerous other processes which seek to exploit the exothermicity of a participating chemical reaction to provide kinetic advantage. Notable examples of the latter include pressureless and pressure-assisted reactive sintering, reactive hot pressing, combustion milling, and reactive casting.[1,2,3] A useful variation of the principles of reactive processing has been in its application for the synthesis of in-situ–derived metal or intermetallic matrix composites.[4,5] In this regard, the evolution of a ceramic particulate reinforcement occurs directly within a metallic solvent, the latter eventually representing the metallic or intermetallic matrix of a resulting discontinuously reinforced (DR) composite. The technique differs from the conventional SHS-based methodologies in that the metallic matrix often serves as a nonstoichiometric liquidous solvent (e.g., a diluent), which acts to kinetically facilitate the particulate-forming exothermic (i.e., thermodynamically favored) reaction. Used in this way, the technique offers several practical and theoretical advantages which influence both the processability and ultimate performance R. MARTIN, Program Quality Manager, is with The French Procurement Agency, Ministry of Defense, Paris 00303, France. S.L. KAMPE, Associate Professor, is with the Department of Materials Science and Engineering, Virginia Tech, Blacksburg, VA 24061-0237. Contact e-mail: [email protected] J.S. MARTE, Materials Scientist, is with the Ceramic and Metallurgy Technologies Group, GE Global Research Center, Schenectady, NY 12301. T.P. PETE, Senior Scientist, is with the Research and Development Division, Sasol Technology (Pty) Ltd., Sasolburg, South Africa. Manuscript submitted September 11, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS A

of the composite, largely as a consequence of the clean and thermodynamically stable matrix/reinforcement interfaces that will form during the process.[6] While clean interfaces and thermodynamic stability are most frequently cited as support for in-situ processing strategies, the ultimate performance will also rely heavily on the details of the size, shape, and microstructural stability of the evolved reinforcement. For example, the strengthening potency of DR composites tends to scale inversely with interparticle spacing, according to traditional Orowan or enhanced work-hardening models.[7,8] As an independent variable of composite behavior, interparticle spacing incorporates both the reinforcements’ size and volume fraction. Thus, any methodology that can successfully relate processing details to reinforcement spacing can provide a direct link between processing and performan