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

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 15 mu m/s, the microstructure in the steady growth zone of the unidirectional rod exhibits coarse columnar crystal with worm-like gamma' phase; when the solidification rate increases to 150 mu m/s with the temperature gradient remaining constant, the microstructure changes into equiaxed grain or cellular crystal. The higher temperature gradient of 1200 K/cm is more advantageous to the achievement of columnar crystal than 250 K/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 1200 K/cm and 15 mu m/s. (C) 2011 Elsevier B.V. All rights reserved.