| To identify the important mechanisms contributing to the creep strengthening of the eutectic composites, the creep behavior of two NiAl based directionally solidified eutectics has been studied. In both eutectics, the NiAl based matrix was reinforced with semi-coherent Cr fibers or plates. The anisotropy in the creep behavior has been investigated as a function of the orientation of the reinforcement with respect to the loading axis. The details of the deformation behavior were characterized using transmission electron microscopy, finite element methods and compressive creep tests. The studies were conducted in the power law creep regime.;The behavior of both fibrous NiAl-Cr and lamellar NiAl-Cr(Mo) composites differed significantly from that of binary NiAl. At comparable stresses, the minimum creep rates were reduced by several orders of magnitude in both eutectics compared to binary NiAl. When the secondary creep rates were comparable, the eutectics exhibited more pronounced primary transients compared to the binary NiAl. An experimental study on NiAl(2%Cr), a single phase intermetallic whose composition corresponded to that of the matrix of the eutectic, established that a significant portion of the strengthening in the eutectics was due to the Cr in solution in NiAl. (Abstract shortened by UMI.). |
