SOLIDIFICATION MICROSTRUCTURE MAPS IN NI-AL ALLOYS

Laser surface resolidification experiments have been performed on Ni-A l alloys with 70-89 at.% Ni in the velocity range of 5.10(-4)-5.10(-1) m/s. Microstructures have been studied by optical and transmission el ectron microscopy. Growth of primary gamma-Ni, beta-NiAl and metastabl e beta-gamma eutectic occurred whereas no primary gamma'-Ni3Al was obs erved. A solidification microstructure selection map has been drawn, s howing the coupled zone of metastable eutectic and the limit of plane front growth of gamma-Ni. The microstructure map has also been calcula ted on the basis of plane front, cellular/dendritic and eutectic growt h models. There was a good agreement between experimental and calculat ed results, showing the potential of this approach for prediction of s olidification microstructure. (C) 1997 Acta Metallurgica Inc.