Hypermonotectic Alloys Research Articles

The influence of interfacial energies and gravitational levels on the directionally solidified structures in hypermonotectic alloys

Several Cu-Pb-Al alloys were directionally solidified under one-g conditions and alternating high-g/low-g conditions in order to determine the influence of interfacial energies and gravitational levels on the resulting microstructures. The low-g conditions were obtained through use of NASA's KC-135 aircraft. In the Cu-Pb-Al system, changes in the Al content are known to result in variations in the interfacial energy relationships between the phases. Theory predicts that this should lead to a transition from an irregular to a regular, aligned microstructure in monotectic composition alloys. Four different hypermonotectic alloy compositions were used in this study in order to vary systematically the interfacial energies between the phases. Preliminary results indicate microstructural variations between control and flight samples and samples processed at different rates under both one-g and high-g/low-g conditions. In addition, directional solidification of low Al content alloys resulted in samples with coarse, irregular microstructures, as compared to finer, more aligned microstructures in alloys with high Al contents. This was seen in samples processed under both one-g and high-g/low-g conditions. The resulting structures have been related to interfacial energies, growth rates, and gravitational levels.

A Study of the Coalescence Process Inside the Miscibility Gap in Zn-Bi Alloys

ABSTRACTThe coalescence process has been studied in four different hyper-monotectic Zn-Bi alloys with 4–10wt % Bi . The alloys have been studied by isothermal treatments at a temperature just above the monotectic temperature and at different holding times. The alloys have been studied both at microgravity and at normal gravity. The change of the particle distribution as a function of composition and holding time has been investigated. The changing of the particle distribution has been compared with the theory of particle collision. The validity of the collision theory is investigated with respect to the theory of liquid phase sintering.

Solidification of Hypermonotectic Al-In Alloys Under Microgravity Conditions

ABSTRACTFour samples of the Al-In system having monotectic and hypermonotectic compositions were solidified under microgravity during the NASA-SPAR IX flight of January 20th,1981. The experimental thermal and physico-chemical conditions actually achieved have been analysed. Radiographic and metallographic observations of the samples show a non-regular dispersed primary phase inside the monotectic matrix. These observations are commented on the basis of capillarity and solidification aspects.

銅-鉛合金の偏晶反応凝固

Principles of monotectic solidification of the binary copper-lead alloy are introduced from the observation of crystallizing courses of direction-free and unidirectional solidification in the monotectic and hyper-monotectic alloys. In the direction-free solidification the α-solid of a monotectic product grows in volume spherically unlike dendritic growth in the hypo-monotectic alloy. The released L2 liquid accompanied by generation of the α-solid lies in the α-solid sphere radiately, while the initial L2 does in the boundaries. Columnar growth of the α-solid of a monotectic product occurs in an opposite direction of heat flow during unidirectional solidification. The monotectic cell is produced in which the α-solid of a monotectic product grows in an opposite direction of heat flow surrounding the released rod-like L2 liquid. In the unidirectional solidification at temperature gradient 50°C/cm and freezing rate 60 mm/min abnormal condensation of the L2 in the liquid in advance of the monotectic cell results in the bell-shape aggregation in the hyper-monotectic copper-50% lead alloy. At temperature gradient 10° to 30°C/cm and freezing rate 0.5 to 4.0 mm/min widening the (L1+L2) layer causes arrangement of coarse and rod-like L2 liquid within the monotectic cell. The inter-rod spacing is in inverse proportion to the square root of freezing rate and is reduced with temperature gradient in the liquid. Both copper and lead in the monotectic cell grow preferentially in the 〈110〉 direction at high rate of freezing and in 〈111〉 at slow rate.