Grain refining mechanism in pure aluminum with nanosized TiN/Ti composite refiner addition

A composite TiN/Ti grain refiner for aluminum and its alloys was prepared through a mixture of micro sized metal powder Ti and nanosized ceramic particles TiN by high energy ball milling. Refinement performance of the TiN/Ti refiner in pure aluminum has been examined in detail by OM, FSEM, EBSD, DSC and TEM methods. Experimental findings indicate that, after adding 0.5 wt% TiN/Ti, the solidification structure of pure aluminum can be refined and the preponderant grain size is reduced to 79.8 mu m from more than 1000 mu m. TiN/Ti significantly refines the aluminum grain size through not only that it makes undercooling be not measured and increase the nucleation temperature from 671 degrees C to 681 degrees C, but also the introduction of potent nuclei. Furthermore, nano TiN particles can act as the nucleus of heterogeneous nucleation of alpha(Al), the alpha(Al) grows along the {111} crystal plane from {200} surface of TiN, Ti-rich transition region surrounding TiN particles and the heat of reaction between Al and Ti enhances the wettability of TiN in the melt. (C) 2016 Elsevier B.V. All rights reserved.