The effect of prolonged heat treatments on the microstructural evolution of Al/Ni intermetallic compounds in multi layered composites

• Study of the prolonged annealing on Al/Ni system.
• The presence of AlNi3 phase, not detected in similar researches, has been observed.
• Three different sequences of phases were detected.
• From EBSD analysis the intermetallic compounds have no preferred orientation.

In this work the effects of prolonged heat treatments on the microstructural and crystallographic evolution of Al–Ni intermetallic compounds were studied in Al/Ni multilayer samples, produced by accumulative roll bonding (ARB) process. Starting from aluminium and nickel sheets, the stacks were composed alternating three aluminium with two nickel sheets. After six rolling passes, the roll-bonded material was heat treated in a tubular furnace at 500, 550 and 600 °C for different times (1–20 h). The ARB process followed by the diffusion heat treatments allowed the formation of four Al–Ni intermetallic phases (Al3Ni, Al3Ni2, AlNi and AlNi3). Microstructural analyses of the obtained samples were carried out by scanning electron microscopy (SEM). The electron backscattered diffraction (EBSD) technique was used for the crystallographic analysis of the samples. After the prolonged annealing, three different sequences of phases, starting from Al, were observed: Al3Ni2–AlNi–AlNi3, Al3Ni and AlNi–Al3Ni. The EBSD analysis showed that the intermetallic phases grew with a mean grain size between 0.5 μm and 3 μm and without a preferential crystallographic orientation.