Phase-Structural State of τ-MnAl(Ga) Alloys Prepared at Different Cooling Rates

An alloy with a nominal composition of Mn₅₅Al₃₆Ga₉ is prepared by four different methods which ensure different cooling rates. Two bulk samples are prepared by induction melting followed by water quenching from a homogenizing temperature of 1100ºС; one of the samples was sealed in a quartz ampoule and subjected to water quenching, whereas the other sample directly was subjected to water quenching. Two samples are prepared in the form of ribbons by quenching from the melt on a rotating copper wheel at linear speeds of 10 and 40 m/s. Thus, samples quenched at different rates are prepared. For these samples, regularities of phase transitions occurred during heating are determined, and difference in the regularities for the bulk and rapidly quenched samples are found. Based on the data obtained, we make an assumption that the γ₂ → τ phase transition has features of a bulk transition. Magnetic hysteretic properties of the rapidly quenched ribbons are measured. The high thermal stability of the rapidly quenched ribbons alloyed with gallium is shown.