Effect of Heat Treatment on Formation of Al-Al₃Ni Hypereutectic Alloys

Abstract

The paper deals with the mechanism of eutectic formation in a nickel coated aluminium system after heat treatment. The initial coating was produced from a nickel powder by means of high velocity oxyfuel (HVOF) spraying onto an aluminium sheet substrate. Specimens for investigations were manufactured immediately after the spraying. The specimens were heat-treated using a differential thermal analysis (DTA) apparatus up to the temperature of 700 or 900 °C and then cooled down to room temperature in argon atmosphere with a constant heating and cooling rate of 5 °C / min, under which Al-Al3Ni + Al3Ni hypereutectic alloys were formed within the initial substrate. Two different alloy microstructures consisting of intermetallic layers and coarse eutectic or an ultrafine well-dispersed eutectic were formed. Formation processes and resulting microstructures were studied by means of DTA, metallography, scanning electron microscopy, focused ion beam, energy dispersive microanalysis and image analysis techniques.