Study of the Influence of High Pressures on the Solidification of the Al<sub>86</sub>Ni<sub>6</sub>Co<sub>4</sub>Gd<sub>2</sub>Tb<sub>2</sub> Liquid Alloy
The purpose of the present paper is to study the possibility of the formation of new phases in the Al<sub>86</sub>Ni<sub>6</sub>Co<sub>4</sub>Gd<sub>2</sub>Tb<sub>2</sub> alloy upon rapid solidification of its high-temperature melt under high pressure. Samples for research were obtained under high pressure of 3, 5 and 7 GPa in a high-pressure chamber of the "toroid" type. The heating and melting of the sample were carried out by passing an alternating current through the sample placed in a hexagonal boron nitride crucible. High pressure punches served as current leads. The melts were cooled at a rate of 1000 deg/sec, the temperature of the melt before quenching was 1500 °C. The experimental scheme is as follows: pressure setting → pulse heating → holding at a set pressure and temperature → cooling without depressurization to room temperature → reduction of high pressure to atmospheric. The microstructure of the samples of the alloy of the eutectic composition Al<sub>86</sub>Ni<sub>6</sub>Co<sub>4</sub>Gd<sub>2</sub>Tb<sub>2</sub>, obtained depending on the quenching temperature (1500 °C) and high pressure (3, 5 and 7 GPa), was investigated by the methods of X-ray diffraction analysis, optical and electron microscopy. The cooling rate was 1000 deg/sec. Due to the combination of a high solidification rate and mechanical compaction under high pressure, samples of the alloy of the composition Al<sub>86</sub>Ni<sub>6</sub>Co<sub>4</sub>Gd<sub>2</sub>Tb<sub>2</sub> with a fine structure and high density were obtained. At pressures of 5-7 GPa, the formation of new phases was observed in the alloy. The studies show that the average microhardness of a sample obtained, in particular, under pressure of 7 GPa, is high (~1700 MPa) due to the solid solution and precipitation hardening. It is almost twice as high as the average microhardness in the original sample. The results obtained show the fundamental possibility of using the method of solidification of the melt under high pressure to change the level of properties of aluminum alloys used in industry without changing their chemical composition by modifying the structure and changing the composition of the structural components of a sample.