The Tensile Behavior of a Ni 3 Al-Based Composite with TiC Reinforcement
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THE TENSILE BEHAVIOR OF A NiaAl-BASED COMPOSITE WITH TiC REINFORCEMENT Gerhard E.Fuchs* The Aerospace Corporation, P.O. Box 92957, Los Angeles, CA 90009-2957. *Currently at General Electric Co., P.O. Box 1072, Schenectady, NY 12301. ABSTRACT The tensile properties of a powder processed intermetallic matrix composite (IMC) and a similarly processed matrix alloy were investigated in the temperature range 298-1273K. The matrix alloy utilized in the study was the advanced nickel-aluminide IC-221 (Ni-16A1-8Cr-lZr-0.05B). The composites contained 25 vol% TiC particulate reinforcement. The specific modulus of the composites was 20-30% higher than that of typical Ni-base superalloys. The yield strength of the composites were 10-20% greater than that of the matrix at all test temperatures. However, the composites exhibited lower ductility than the matrix. SEM fractography revealed that tensile failure occurred at the matrix/particulate interface. However, remnants of the matrix was observed on TiC particles on the fracture surface, suggesting good matrix/particle bonding. The strengths of the composites were very competitive with Ni-base superalloys. INTRODUCTION Recent advances in ductilizing several intermetallic alloys has generated a great deal of interest in these materials for elevated temperature applications (1,2]. For example, the aluminides of Ni, Ti, and Fe have been investigated due to their low density, inherent oxidation resistance and their high specific strengths. The boron-doped nickel aluminides have, in particular, been extensively evaluated as alternative materials to replace nickel-base superalloys for high temperature applications[3,4]. Alloy development programs have yielded high strength advanced nickel-aluminides (with Cr additions for oxidation resistance and Zr or Hf additions for solid solution strengthening) [3]. However, a clear cut advantage over the Ni-base superalloys has not yet been realized. In order to become more competitive with conventional superalloys, the strength of Nialuminides must be increased still farther. The high strength, high ductility nickel-aluminides are excellent candidates for matrix materials for high temperature composites. Although Ni-aluminides posses a density approximately 7% less than Ni-base superalloys, selection of the appropriate reinforcement could further reduce the density of the intermetallic matrix composite (IMC) while increasing the strength. In addition, the slowed diffusion of the ordered lattice should reduce the formation and growth of any reaction product at the matrix/reinforcement interface. Since the useful life of metal matrix composites is limited by this interfacial reaction, the slowed diffusion and interaction of the intermetallic matrix should increase the life and/or operating temperature of the IMC. Previous investigations have reported that Ni-aluminides react extensively with SiC[6], B4C[71 and TiBz[8], but very little reaction is observed with AlzO3 or TiC(9,10]. However, AlzO3 does not adequately bond to the Ni-aluminide matrix, r
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