Goro Ohira

Stability of a planar solid-liquid interface during unidirectional solidification of A1-0.1wt%Cu alloy

Abstract Samples of A1-0.1wt%Cu were solidified unidirectionally. Metallographic observations of the samples quenched during solidification showed that the stability-instability transition of the planar solid-liquid interface occured at the condition predicted by the perturbation theory, where the effect of interfacial energy on it was small. But the interfacial wave of the solid-liquid interface did not have the frequency predicted by the perturbation theory and was discussed.

The solute distributions in dilute Al-Ti alloys during unidirectional solidification

Abstract A non-steady state solidification was observed where the solute concentration in the liquid in and out of the solute boundary layer decreased with the progress of solidification, when a dilute Al-Ti alloy was unidirectionally solidified vertically upwards with a planar or cellular solid-liquid interface. This was caused by an unusual quick transfer of solute atoms from the higher temperature to the lower temperature region in the liquid. Some discussions were presented on the observed abnormality. As a result, the convection due to the density inversion of the liquid seems to be the most possible cause for it.

Eutectic growth of unidirectionally solidified iron-carbon alloy

Unidirectional solidification experiments were conducted on high purity iron-carbon eutectic alloys containing 0.007-0.449 wt% sulphur to study their solidification behaviour and influence of sulphur on it. Rod specimens of 16 mm diameter X 135 mm long were melted and moved at a constant speed through a vertical furnace. The temperature gradient at the solid-liquid interface was 45°C/cm and the solidification rates were varied from 1 to 250 mm/hr. The inter-graphite spacing, λ, of specimens solidified with a macroscopic planat interface changed in accordance with the relationship λ = Av-12 as found for normal lamellar eutectics, where A is a constant and v is the solidification rate. A small amount of sulphur decreased the intergraphite spacing markedly but more sulphur did not decrease the spacing any more. While, in the solidification condition under which eutectic cells were formed, sulphur increased the intergraphite spacing. The critical value of G/v for the morphological stability of microscopic interface was estimated about 10 X 106 deg sec/cm2 theoretically. When G/v is less than this value, the interface of the austenite becomes unstable and the depth of the austenite groove increases with the proceeding of solidification. The branching and the pinching off of the graphite would occur to cancel the instability of the groove. Colony breakdown of the macroscopic planar interface was accelerated by increasing the sulphur content and/or by decreasing the value of G/v. The stability of the observed macroscopic planar interface is higher than the theoretical expectation.

Interfacial stability of α(Al-rich solid solution)-liquid interface of unidirectionally solidified AlFeAl3 eutectic alloy

Abstract Unidirectional solidification experiments were carried out to observe the interface morphology of a AlFeAl 3 eutectic alloy and to investigate the critical condition for the morphological stability of the α-liquid interface ( α : Al-rich solid solution). The experimental apparatus was based on “the thermal valve technique”. Solidification was carried out under constant growth rate and constant temperature gradient in the liquid. The temperature gradients in the liquid ( G L ) were 45, 70 and 100°C/cm, and growth rates were in the range of 4 × 10 −5 to 10 −3 cm/sec. The various morphologies due to the break down of α-liquid interface were observed to depend on G v , where G is the effective gradient of interfacial temperature due to small deviations from a planar interface. The interfacial stability was compared with theory. The relation between inter-FeAl 3 spacing and growth velocity was also measured. The gradient G was obtained by Coriell and Sekerkas method.

Interfacial wave of maximum growth velocity at the morphological instability of the planar solid-liquid interface in the solidification of alloys: An approximation of the growth function of the interfacial wave ƒ(ω)

Abstract An approximation was obtained to the growth function ƒ(ω) of the perturbation theory on the instability of the planar solid-liquid interface during unidirectional solidification. Using this approximation, the wave frequency of the interface, and a little deviated condition from the critical state was obtained analytically. As a result it was predicted that the wave frequency deviates little in the alloy of large k , but considerably in the alloy of small k , from the value of the critical state in a condition little deviated from the critical state.

Directional cellular solidification of eutectic and hypereutectic mottled cast irons

Abstract Directional solidification experiments were conducted on Fe-C eutectic and hypereutectic alloys to investigate the mechanism of the formation of a mottled structure, the growth pattern and the microstructures. The effects of manganese, silicon and the growth rate on the transition in eutectic growth from the stable Fe-C to the metastable Fe-Fe 3 C type were investigated. The mottled structures formed by the cellular mode of solidification can be classified into three types. The compositional change during solidification in the cast iron due to the segregation of the alloying elements (in this case, Mn and Si) which occured in the melt between the leading eutectic cells result in the change of the eutectic solidification temperature. If the effect of the compositional change on the eutectic solidification temperature is sufficient, the eutectic mode of solidification in the cast iron may be changed from one to the other. The mechanism of the formation of a mottled structure may be explained in terms of this conception.