Effect of particle size and volume fraction on hot extrusion reaction synthesis of SiC particle reinforced NiAl
- PDF / 1,321,384 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 13 Downloads / 217 Views
INTRODUCTION
THE high-temperature properties of intermetallic compounds make them candidate materials for high-temperature structural applications. The addition of ceramics to the intermetallic system can improve the mechanical properties of the final composite. An important issue when considering composite materials is the chemical as well as the mechanical compatibility between the matrix and the reinforcement material. The chemical and mechanical compatibility of reinforcements with the nickel aluminide matrix have been previously investigated for a number of reinforcements. Titanium diboride (TiB2) and alumina (Al2O3) appear to be the materials currently favored.[1] The addition of SiC to the nickel aluminide system was reported to be chemically incompatible with the Ni3Al compound when SiC fibers were used.[2] Chemical incompatibility problems can arise either during processing or in service. Most of these studies were reported for either SiC fibers or whiskers.[2,3,4] In the current work, SiC particulates are used as reinforcements. In the past, intermetallic matrix composites have been formed by conventional reaction synthesis (RS) and reaction synthesis under applied pressure.[5,6,7] TiAl/SiC, TiAl/Al2O3, and NiAl/TiB2 are among numerous composites formed by RS/self-propagating high-temperature synthesis (SHS) from elemental powders.[8,9,10] Reaction synthesis of nickel aluminide composites involves mixing powders of aluminum (Al), nickel (Ni), and reinforcement in the correct composition to arrive at the intermetallic of choice, followed by cold compaction into a pellet. The pellet is then heated in a furnace under atmosphere or vacuum to the reaction temperature, typically greater than 640 8C. At this temperature, a reaction occurs converting the elemental powders to the intermetallic of choice, e.g., Ni 1 Al → NiAl. The heat of formation (DHf) of NiAl (DHf , 298 K 5 2118.4 KJ ? K. MORSI, Assistant Professor, is with the Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO 65211, USA. H.B. McSHANE, Senior Lecturer, and M. McLEAN, Head of Department, are with the Department of Materials, Imperial College, London SW7 BP, United Kingdom. Manuscript submitted May 26, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
mol21[11]) is released and heats the NiAl product to the adiabatic temperature, Tad (assuming no heat loss to the surroundings). In the case of unreinforced NiAl, the adiabatic temperature exceeds the melting point, Tm (Tm 5 1638 8C) of the NiAl, resulting in a molten product. It was reported that the heat produced in forming the NiAl was not just sufficient to melt the NiAl product, but also destroyed the alumina sintering crucibles in which they were placed.[12] The addition of ceramics and preformed NiAl powder[6] to the original nickel and aluminum elemental powder mixture and recently a prereaction synthesis heat treatment[13] have provided means of buffering the NiAl reaction and hence preventing the melting of NiAl. The resulting microstructures of interm
Data Loading...
