Modelling generation mechanism of defects during permanent mould centrifugal casting process of TiAl alloy exhaust valve

Abstract

In this paper, the TiAl liquid filling process during vertical centrifugal casting into a permanent mould has been described analytically. A model has been established to simulate the forward filling and backward filling process, and two parameters were used to provide a quantitative description of the defect generation that is associated with the forward filling of the mould cavity. One of the parameters used was the forward filling cross-sectional area, and the other was the inclined angle of the free surface of forward filling flow. The cross-sectional area decreases, and the inclined angle increases when the rotational speed increases, the tendency of which becomes more obvious near the mould cavity entrance. The residual volume of the mould cavity after the forward filling is related to the volume of trapped pores. The filling process has also been investigated using numerical simulation. Based on the filling and solidification characteristic of a TiAl valve, the off-centre porosity distribution is also discussed.

Keywords:

• TiAl alloys
• Centrifugal casting
• Mould filling
• Exhaust valve
• Defects

Acknowledgement

The authors would like to acknowledge the financial supported by NSFC (grant no. 50975060) and the Foundation of State Key Lab of Advanced Welding Production Technology of China.