Effect of withdrawal rates on temperature field and grain competitive growth of directionally solidified DZ4125 alloy

In order to investigate the distribution of temperature field in directionally solidified DZ4125 columnar superalloy, and to study the effects of different withdrawl rates on the changes of temperature gradient and mushy zone, the directional solidification processes with withdrawal rates of 3, 5 and 7 mm/min were simulated by ProCAST software. The results show that when the test rod is located in the heating zone, the isotherm is inclined distribution with low outside and high inside. And when the test rod is located in the cooling zone, the isotherm is inclined distribution with high outside and low inside. With the increase of withdrawal rate, the temperature gradient decreases gradually. The shape of the mushy zone depends on the withdrawal rate and the distance from the water-cooled plate. When the withdrawl rate is 5 mm/min, the horizontal state of the solidification front is maintained for a longest time. On this basis, the precision casting experiment of directional solidification test rod is carried out, and the relationship between the shape of liquidus and grain structure is found for castings withdrawn at 3 and 7 mm/min. It is found that when the liquidus is concave and convex, the grain grows towards the center and the surface of the test rod, and the horizontal liquidus can promote the grain growth along the axis of the test rod.