Heat transfer and macrostructure formation of Nb containing TiAl alloy directionally solidified by square cold crucible

Abstract

Cold crucible can be designed as a manufacturing tool to directionally solidify TiAl alloys of industrial size and with low contamination. In this process, the shape of solidification interface and the macrostructure formation are determined by the heat transfer and temperature distribution in charge. For the cold crucible directional solidification (CCDS) of Ti-46Al-6Nb (at.%) alloy, a finite element (FE) model without considering the melt convection was established to calculate the temperature field. The effects of power, frequency, lateral heat transfer and charge position on the temperature field were evaluated. Calculated results reveal that a planar interface can be obtained under appropriate process parameters. Further, Ti-46Al-6Nb ingots were directionally solidified by square cold crucible. The interface shape and macrostructure were investigated. An overly-high power and fast withdrawal velocity are not beneficial to the continuous growth of columnar grains. Based on these results, an optimum process window for the CCDS of TiAl alloys was proposed.