Full homogenisation response of Ni 3 Al based alloy containing Cr,Mo,Zr and B

Full homogenisation behaviour of a Ni₃Al based alloy containing Cr, Mo, Zr and B was investigated. At the as cast condition, the microstructure of this alloy consists of a γ solid solution γ′(Ni₃Al) and a low melting point structure. At first, the low melting point structure, which is detrimental for full homogenisation process, was eliminated by annealing the specimens at 1100°C. After this prerequisite process, based on differential thermal analysis results, 1260°C was determined for the full homogenisation annealing temperature. The results showed that this alloy cannot be fully homogenised without the formation of locally melted regions. In order to explain the mechanism of this local melting phenomenon during full homogenisation treatment, some heating cycles were performed at 1200 and 1240°C. A scanning electron microscope equipped with energy dispersive spectroscopy and differential thermal analysis was used for introducing the local melting (incipient melting) mechanism. It was found that the difference in zirconium solubility limit in the γ and γ′ phases is the main reason for the negative response to full homogenisation treatment.