Multi-layer structure of the diffusion zone of the AL-NI system

Abstract

The diffusion zone of Al-Ni system has been studied using the contact melting method. The microstructure and element composition in cross section of samples have been studied by means of scanning electron microscopy and electron probe microanalysis (SEM-EPMA). The multilayer structure of intermetallics of Al- Ni system has been formed after isothermal treatment in range of 1000-1300 °С. Due to interaction between Al and Ni the width of diffusion zone is growing along with duration of isothermal treatment. Few layers having different phase compositions and widths are formed in contact zone depending on established concentration of metals. Each of the observed layers has its own clear boundaries and structure pattern. Four compounds with the variable compositions Al51Ni49, Al36Ni64, Al30Ni70 and Al32Ni68 have been revealed at 1000-1300°С due to comparison of element distribution in the depth of diffusion zone with its microstructure. The layers are seemed as homogenous and having more smooth boundaries from Ni side. Meanwhile from Al side the layer structure acquires the island-type form, and boundaries become more irregular with dendrite appearance. The intermetallic compounds have been obtained at various temperatures; they correspond pre-established phases with registered compositions (daltonides): Al3Ni, Аl3Ni2, ΑΙNi(β), ΑlNi3(α’), Аl3Ni5. The agglomerates of pores and cracks could be caused by stresses between the layers are detected. The formation of pores in case of the developed layer microstructure is related to Frenkel effect.