MICROSTRUCTURE OF TIB2-NIAL

The addition of 20 vol.% titanium diboride in particulate form (1-3 μm) to nickel aluminide (TiB2NiAl) results in a twofold increase in the high temperature strength of NiAl. There are at least two theories that have been proposed to account for the high temperature strength of discontinuous reinforced metal matrix composites. However, they cannot be adequately used as a basis to explain the observed strengthening. An investigation was undertaken of NiAl, 10vol.%TiB2NiAl and 20vol.%TiB2NiAl in the annealed condition and after deformation, allowed to cool slowly. There is a low dislocation density in the annealed samples and the dislocation density did increase slightly as a result of deformation. However, deformation did produce some intriguing dislocation arrangements; for example, it was found that there was a high dislocation density within the TiB2 in the deformed higher volume fraction composites and the dislocation density within the NiAl matrix was not uniform. © 1990.