Effects of solidification rate and temperature gradient on microstructure and crystal orientation of Co32Ni40Al28 alloys

Abstract

By means of zone melting liquid metal cooling directional solidification, the effects of solidification rate and temperature gradient on the Co32Ni40Al28 polycrystal microstructure and crystal orientation were studied. Results show that when the solidification rate is 15μm/s, the microstructure in the steady growth zone of the unidirectional rod exhibits coarse columnar crystal with worm-like γ′ phase; when the solidification rate increases to 150μm/s with the temperature gradient remaining constant, the microstructure changes into equiaxed grain or cellular crystal. The higher temperature gradient of 1200K/cm is more advantageous to the achievement of columnar crystal than 250K/cm. Oriented polycrystals are relatively easy to get with a higher temperature gradient and a lower solidification rate; an <111> martensitic preferred orientation can be obtained at 1200K/cm and 15μm/s.