Influences of solution cooling rate on microstructural evolution of a multiphase Ni3Al-based intermetallic alloy

摘要

In present work, a multiphase Ni3Al-based intermetallic alloy with complex components of gamma'+gamma dendrite comprising extremely high volume fraction (81 vol %) of gamma' phase and interdendritic beta phase is investigated, the microstructure evolution and phase transformation behavior tailored by different solution cooling rates are studied by applying different cooling methods of water cooling (WC, 138 degrees C/s), air cooling (AC, 72 degrees C/s), and furnace cooling (FC, 0.05 degrees C/s) after solution treatment at 1200 degrees C for 10 h. Results show that the cubic degree, size and volume fraction of cuboidal primary gamma' as well as size of spherical secondary y' particles in the gamma' + gamma dendrite are improved by decreasing cooling rates, and the average sizes of the primary and secondary gamma' particles are found to meet logarithmic relationships with cooling rates. There are three kinds of precipitates in the interdendritic beta phase resulted from different cooling methods, i.e., the rod-like Cr3C2 carbides, the semi spherical alpha-Cr particles, and the long acicular gamma' precipitates. The lower cooling rate decreases the number of rod-like Cr3C2 carbides, increases the number and size of the semi-spherical alpha-Cr particles, and promotes the formation of long acicular gamma' precipitates in the interdendritic beta-matrix. The semi-spherical alpha-Cr particles play the role of pinning dislocations in the 13-matrix and have the orientation relationship of [(_)101](alpha-Cr)//[(_)101](beta). (matrix). In addition, the precipitation of semi-spherical alpha-Cr particles in beta-matrix is observed to accomplish in two sequential stages and grow in an onion-like ordered way. Stacking faults existed in partial of alpha-Cr particles due to the nanotwins in beta-matrix. Microtwins are observed in the interdendritic beta-matrix after water cooling, which have a bimodal configuration of nanotwins at the microtwinning boundaries and interior stacking faults. Besides, gamma'-envelope formed between the gamma' + gamma dendrite and interdendritic beta phase dependent on the solution cooling processes.