Forming mechanism of gaseous defect in Ti-48Al-2Cr-2Nb exhaust valves formed with permanent mold centrifugal casting method

A method of combining theoretical analysis with experiment is adopted and the flowing process of Ti-48Al-2Cr-2Nb alloy melt poured in a permanent mould during the centrifugal casting process has been analyzed. A mathematical model of the filling process is established and the forming mechanism of internal gaseous defects is summarized. The results of calculation show that the melt fills the mould with varying cross-section area and inclined angle. The filling speed of the cross-section is a function of the filling time. The cross-section area is directly proportional to the filling speed and the inclined angle is inversely proportional to the filling speed at a given rotating speed of the platform. Both of them changes more obvious near the mould entrance. The gaseous defect can be formed in several ways and the centrifugal field has an important influence on the formation of the defect. In addition, the filling process in the centrifugal field has been verified by wax experiments, and theoretical analyses are consistent with experimental results.