Study on dispersion of Ti2AlC particle and formation of columnar crystal with different solidification rates during CCDS TiAl-based composite

Abstract

Abstract Directional composite microstructures have successfully been prepared with directional columnar crystal forms at the center and equiaxed crystals with Ti2AlC particles at the edge of sample. Microstructure evolution, influenced by different solidification rates, is discussed and forming mechanisms of this composite microstructure have been revealed. Results show that the primary phase of α is observed from 60° of the primary dendritic arms, and β is from 90°. When the drawing velocity increases from 0.2 to 1.1 mm/min, the width of the columnar crystal decreases from 1.95 to 0.61 mm, and the distance between growth sites of Ti2AlC and most edge of the sample decreases from 1.04 to 0 mm. Obviously, the solid-liquid interface forms with low solidification rate. Forming the Ti2AlC phases consumes Ti the in local area, and the α primary phase forms with more than 49.4 at. % Al. The change of solidification rate has no effect on the concave shape of the solid-liquid interface because the influence of the drawing rate cannot change the influence of the heating power on the thermal balance of the molten pool. Ti2AlC particles move to the skin layer with the melt flow during directional solidification. This leads to a decrease in the heterogeneous nucleated particles near the centre of molten pool, to guaranteeing the growth conditions necessary for large columnar crystals.