Jia Jun

Composition control of a TiAl melt during the induction skull melting (ISM) process

Abstract The properties of intermetallic compounds are sensitive to alloying composition determined by the melting process. This article describes research that aims to control the composition of a TiAl melt during the ISM process. Firstly, the vapor pressures of Al and Ti in the TiAl melt were established and the results show that P Al / P Ti is over 300. The ratio points out that Al will evaporate more predominantly than Ti in the TiAl melt during the vacuum melting process. Then, the mass transport coefficient K and the mass evaporation rate N m were calculated. The vacuum pressure has the same influence on K and N m . There are two contraflexure points of the vacuum pressure, namely the critical point and the impeding point. When the vacuum pressure surpasses the impeding point, the evaporation of Al can be neglected. When the vacuum pressure is below the critical point, the evaporation of Al will take on a free evaporation and the Al content will decreases to 40at% from 48at%. The calculated results were compared with the experimental data, which verified the calculation results.

Coarsening mode and microstructure evolution of Al-In hypermonotectic alloy during rapidly cooling process

Abstract A numerical model reflecting the real physical processes well is developed to predict the coarsening mode of the second phase droplets and the microstructural evolution under the common action of nucleation, diffusional growth, collision coagulation during rapid cooling Al–In hypermonotectic alloys.

Numerical simulation of off-centred porosity formation of TiAl-based alloy exhaust valve during vertical centrifugal casting

The vertical centrifugal casting method has been used to cast a TiAl-based alloy exhaust valve. Although mould filling and solidification of TiAl-based alloy melt proceed under pressure generated by the centrifugal force, an unfavourable solidification sequence is formed because of the special mould filling mode and finally results in the formation of off-centred porosity. Numerical simulation is applied to study the vertical centrifugal casting process of the TiAl-based alloy exhaust valve in this paper. On the basis of simulations of the flow field and the temperature field, the law of porosity formation during the vertical centrifugal casting of the TiAl-based alloy exhaust valve is discussed by analysing the mould filling and solidification process. The results of the numerical simulation show that off-centred porosity forms easily near the entrance of the cast product and the tendency for off-centred porosity formation decreases with increasing distance from the entrance to the far end. The experimental results agree well with those of the numerical simulation.