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

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 Ni2Al3 at Ni/NiAl3 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, Ta, 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.