Dynamics of phase transitions in the SHS of a 3Cu–Al powder mixture in the regime of thermal explosion

The paper reports results of dynamic x-ray photography of self-propagating high-temperature synthesis of a 3Cu–Al powder mixture in the regime of thermal explosion. The stages of formation of the final product are considered, beginning with the heating of the starting mixture and interaction of its components and ending with phase transitions during cooling of the product – intermetallides Cu$_9$Al$_4$ and Cu$_3$Al, which are the main components of Cu based tribotechnical materials. It is shown that upon heating in the temperature range of 550 – 590$^\circ$C, the intensity of diffraction lines of Al drops to the background level. The exothermicreaction of synthesis of the intermetallide is initiated at a temperature of 610 – 630$^\circ$C. In the period of sharp increase in temperature to 1040$^\circ$C, the presence of the starting copper and the newly formed high-temperature $\beta'$ phase with the Cu$_9$Al$_4$ tructure are detected simultaneously in the combustion wave. When cooled to 300$^\circ$C, the material contains two cubic phases – Cu$_9$Al$_4$ and an $\alpha$-solid solution of Al in Cu. Further cooling is accompanied by formation and increase of peaks of the Cu$_3$Al phase with an orthorhombic lattice. The phase composition of aluminum bronze produced by SHS with combustion in the regime of thermal explosion is not in equilibrium.