Dissolution–precipitation–substitution mechanism of self-propagating high-temperature synthesis of β-NiAl(Cu)/α(Cu,Ni) composite

A mechanism of self-propagating combustion synthesis of β-NiAl(Cu)/α(Cu,Ni) composite from Ni–Al–Cu powder mixture was investigated by observing of the microstructural evolution in a quenched sample prepared using a combustion front quenching method. The results showed that the combustion reaction was initiated by melting of the Al particle and it proceeded in a dissolution–precipitation–substitution mechanism. After melting of the Al particle, the Ni, especially Cu particles dissolved into the Al droplet, as a result, Al2Cu(Ni) grains precipitated out off the saturated liquid solution and then transformed into AlCu(Ni) grains with immersing of the Cu and Ni particles into the Al liquid. After melting of the Cu particle, the dissolving of the Ni particle sped, then the AlCu(Ni) grains were substituted by NiAl(Cu) grains and the Ni content of the NiAl(Cu) grains increased with melting of the Ni particle. The reasons why the melting of the Al particle started at a temperature lower than the melting point of Al and the dissolving of the Cu particle was faster than that of the Ni particle, were analyzed, the intermediate action of the Cu particle in the combustion reaction was discussed, and a model corresponding to the dissolution–precipitation–substitution mechanism was drawn schematically.