Reaction synthesis and microstructures of NiAl/Ni micro-laminated composites

Abstract

The effects of process parameters on reaction synthesis of NiAl/Ni micro-laminated composite from micro-foils of Ni and Al have been investigated. NiAl/Ni micro-laminated composites were fabricated through diffusion bonding, reaction synthesis and post-heat treatment of alternatively stacked Ni/Al multilayers. DTA analysis showed that the reaction between Ni and Al foils started from the nucleation and growth of NiAl3 at Ni/Al interfaces followed by a diffusional growth of NiAl3 at Ni/NiAb interfaces. The volume fraction of un-reacted Al after reaction was thermodynamically calculated from the initial thickness ratio of Ni:Al and diffusion bonding time before the reaction. As the thickness ratio of Ni:Al increased, the adiabatic temperature and the volume fraction of pure liquid Al decreased. Experimentally measured adiabatic temperature, T-a, was lower than the thermodynamically calculated value, decreased with increasing the thickness ratio of Ni:Al. As the diffusion bonding time increased, the volume fraction of pure liquid Al decreased gradually due to the consumption of Al forming intermetallic at interface of Ni-Al. When initial thickness ratio of Ni:Al during post-heat treatment increased, Al-rich nickel aluminide (Ni0.9Al1.1) was transformed to Ni-rich nickel aluminide (NiAl) so that the final microstructures resulted in a formation of compositionally gradient series of intermetallic phases which consisted of NiAl and Ni3Al. (c) 2005 Elsevier B.V. All rights reserved.