Abstract
The effect of heat treatment on room temperature microhardness, hardness and tensile properties of directionally solidified and heat-treated multiphase intermetallic alloy with chemical composition Ni-10.65Al-6.79Cr-4.90Ta-2.44Mo-0.96Zr-0.078Fe [wt.%] was studied. Except of γ, γ', α and β phases the alloy contained eutectic regions with Zr-rich phase. The chemical composition of Zr-rich phase was determined as Ni-4.9Al-8Cr-5Mo-1.9Ta-19.1Zr [wt.%]. The volume fraction of eutectic regions decreased with increasing time of annealing. The melting temperature of the eutectic was measured to be 1453 K. Annealing at 1493 K and gas fan cooling to room temperature caused a decrease of microhardness of interdendritic region and significant increase of microhardness of dendrites. Consecutive ageing at 1173 K caused a decrease of hardness and microhardness. During the first stages of ageing the ultimate tensile strength rapidly decreased, but after 4800 s of ageing, increased. Generally, heat treatment caused significant embrittlement of the alloy.

Key words
Ni-based intermetallic, mechanical properties, directional solidification

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