Relationship between eta phase formation and solidification rate in directionally solidified IN1792 plus Hf alloy

The effect of solidification rate on the formation of eta phase in a direct ionally solidified IN792 + Hf super alloy was studied. A Cr rich 'precipita te free zone' adjacent to the eutectic (gamma + gamma') was noticed in the quenched directionally solidified microstructure of the alloy. The formatio n of the precipitate free zone Mras due to the solidification of eutectic ( gamma + gamma') which consumed a large amount of the gamma' forming element s and increased the ratio of (Ti + Hf + Ta + W)/Al in the residual liquid. The high ratio of(Ti + Hf + Ta + W)/Al in the final residual liquid induced the formation of eta phase and hence eta phase always appeared at the boun dary between the eutectic regions and the dendrite core regions. The ratio of (Ti + Hf + Ta + W)/Al was decreased by the diffusion of elements between the residual liquid and the surrounding ai ea. A lower solidification rate favoured the back diffusion and decreased the ratio of (Ti + Hf + Ta + W)/ Al in the residual liquid and hence reduced the formation of eta phase. MST /4279.