No abstract

A numerical modeling of dissolution and isothermal solidification during the transient liquid-phase (TLP) diffusion bonding process of Al using pure Cu filler metal based on a diffusion-controlled model was carried out. In the modeling, both the changes in volume accompanying interdiffusion between the base metal (Al) and the filler metal (Cu) and the solid-liquid transformation were taken into account by using variable grids. The effect of a load applied to the base metal was also examined by considering simple force balance among the surface and interface energies of the base metal and liquid formed in the bonding region. The early dissolution process simulated by the developed model agreed with the experimental results, and the predicted isothermal solidification time of a sample with an applied load also agreed with the experimental results.

Phase-field simulation of the dendrite growth of an Fe-0.15 mass%C binary alloy with fluid flow was carried out, and the mechanism of deflection of dendrites in the alloy system was examined. In the simulation, the primary arms growing in a flowing melt inclined toward the upstream direction, and the deflection angle increased with increase in flow velocity. Decrease in deflection angle with increase in growth velocity of the dendrite tip and accelerated growth of side branches were also observed in the simulation. These results of simulation were in good agreement with experimental results. The simulation showed that the change in the thermal field has little effect on the deflection and that the change in the solutal field is the main factor responsible for the deflection of a dendrite in an alloy system. The maximum deflection angle of a single dendrite in the simulation was less than 15 • . The large deflection angles of grains (more than 20 • -30 • ) in the experiments were thought to have been caused by nucleation in front of the dendrites and the subsequent competitive growth.

No abstract

In-situ observation of unidirectional solidification using transparent substance has been performed to investigate the growth direction of solid phase. Cell and/or dendrite, the preferred growth directions of which are not parallel to the heat flow direction, were observed with various solidification conditions. Dimensionless growth direction (π = (angle between heat flow direction and growth direction)/(angle between heat flow direction and preferred growth direction)) changes from zero to unity with increasing growth velocity at a constant temperature gradient. Introducing the normalized growth velocity (V /V c , where V c is the critical growth velocity for breaking down a planar interface), the relation between π and growth condition could be correlated and π could be expressed by a unique line with respect to the normalized growth velocity. Furthermore, the growth directions of cells or dendrites under the condition of unidirectional solidification have been analyzed by the phasefield model. The calculated results agree with the experimental results and the functional relationship between growth velocity and growth direction is qualitatively explained.