Preliminary studies on NiAl/Nb2Be17 reaction and effectiveness of BeO as an interfacial reaction barrier

Abstract

Alloys based on the ordered B2 NiAl phase are being considered as potential high-temperature structural materials. One drawback for this material is its lack of high-temperature strength,[1] which can be overcome by reinforcing the alloy with high-strength fibers. Like any other composite system, a suitable reinforcement material must have a matching coefficient of thermal expansion (CTE) with the matrix in addition to high-temperature strength and be chemically compatible with the matrix. Although there are many high-melting ceramic materials which are thermodynamicalry stable in the NiAl matrix, [2] the high CTE of NiAl,[3] 16 X 10−6 K−1 at 1200 K, makes it difficult to find a suitable ceramic reinforcement material with a matching CTE. Thus, there is a need to develop high CTE fibers for the NiAl matrix. One group of materials with matching CTE[3] to NiAl are the Be-rich intermetallic compounds called beryllides (CTEs in the range of 16 to 18 × 10−6 K−1 at 1200 K) of formula M2Be17, M2Be13, or M2Be12 (where M = Ta, Nb, Ti, Zr, Hf, or Y). Matching CTEs with the NiAl matrix along with their good high-temperature strength[4] and low densities[4] make Be-rich intermetallic compounds attractive as candidate reinforcement materials for the NiAl matrix.