Influence of carbon nanotubes addition on the mechanical properties of nickel aluminide-NiAl

Nickel aluminides are light-weight intermetallic compounds which combine remarkable properties like high thermal conductivity and outstanding oxidation resistance with mechanical stability especially at higher temperatures. Nevertheless, poor ductility and low fracture toughness at ambient temperatures of these materials have significantly hindered their application especially in the aerospace and automotive industries. Carbon nanotubes (CNTs) are being proposed as excellent reinforcements for intermetallic matrices due to their excellent mechanical properties. However, some crucial factors such as the uniform dispersion of these nanotubes without damage, good interfacial bonding and matrix, and optimum weight fraction of the reinforcement must be paid full attention, if the full potentials of CNTs will be maximized within the intermetallic matrix. In this study, a two-stage milling regime was used to uniformly disperse varying contents of CNTs into NiAl matrix powders while minimizing damage to the nanotubes. Spark plasma sintering technique was employed to consolidate the milled powders into dense, bulk composites. Microhardness values of the bulk composites were obtained and their resulting fracture morphologies studied. The results obtained indicate that the microhardness of the nickel aluminides progressively declined with increase in CNTs content while the fracture morphologies revealed more dimples with increasing CNT content.