Melt-Processed Ni 3 Al matrix composites reinforced with TiC particles
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I.
INTRODUCTION
AT the present time, over 300 different intermetallic systems have been identified as potential hightemperature materials. Of these, Ni3A1 is considered to have two major advantages over the others. First, its room-temperature ductility has been significantly improved to 35 to 50 pct elongation by micro- and macroalloying, m Second, it has the distinct advantage of increased strength with temperature up to almost 850 ~ tz'3] However, its higher density compared to that of titanium aluminides and disilicides has been a cause for skepticism as far as commercial applications are concerned. It can be envisioned that introduction of ceramic reinforcements in a Ni3A1 matrix would produce a composite with lower density, improved tensile strength, and stiffness. Not surprisingly, intermetallic matrix .strengthening with either fibrous or particulate reinforcements has recently been an area of considerable research. The majority of the intermetallic matrix composite systems that have been investigated to date have been fabricated by conventional powder metallurgy techniques, t41 Apart from the inability to produce complex near-net-shape parts, the major drawbacks of the powder metallurgy route are the poor bonding between the matrix and the reinforcement [5~ and extensive interfacial reactions due to higher processing temperatures or longer processing times. [6~ Consequently, efforts have been directed toward producing such composites by the S. SEN, Postdoctoral Fellow, and D.M. STEFANESCU, University Research Professor, are with the Department of Metallurgical Engineering, University of Alabama, Tuscaloosa, AL 35487. B.K. DHINDAW, Visiting Scholar, Solidification Laboratory, University of Alabama, is Professor, Department of Metallurgical Engineering, liT Kharagpur, Kharagpur, India. Manuscript submitted October 5, 1993. METALLURGICALAND MATERIALS TRANSACTIONS A
liquid metal processing route. Pressure infiltration of A1203 fibers with molten Ni3AI resulted in inferior interfacial bonding, tTJ Although rapidly solidified NiAI reinforced with TiC and HfC has yielded superior mechanical properties up to 1027 ~ 181the inability of the process to produce net shape parts has been a disadvantage. The most promising liquid metal technique so far has been the XD,* process which uses thoroughly mixed *XD is a trademark of Martin Marietta Corporation, Bethesda, MD.
powders of elemental components of a ceramic phase and the intermetallic phase, t91 This mixture is then enclosed in a vessel and heated to just over the melting point of the intermetallic where an exothermic reaction precipitates the desired ceramic phase. Several different intermetallic matrix composites have been fabricated using this method. For example, the NiA1 matrix has been loaded with 10 to 40 vol pct of 1 to 3 /xm TiB2 precipitates.[l~ These composites show a significant improvement in 0.2 pct compressive flow stress from room temperature to 1027 ~ Similarly, TiA1 has been reinforced with up to 7 vol pct TiB2. m] Although this process is capa
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