FORMATION AND COARSENING OF A NANODISPERSED MICROSTRUCTURE IN MELT-SPUN AL-NI-ZR ALLOY

The paper reports a detailed investigation on the microstructure evolu tion during rapid solidification and subsequent heat treatment of an A l89Ni10Zr1 alloy and evaluates the role of Zr in the phase selection a nd the stability of the microstructure. It is shown that the as solidi fied alloy consists of grains of aluminium solid solution containing f ine nickel rich clusters having an Al3Ni crystal structure. Low temper ature heat treatments lead to further development of these Al3Ni parti cles yielding a uniform nanodispersed microstructure. The dispersed ph ase does not have any orientation relationship with the matrix. The co mposite displays very high hardness values (similar to 5 GPa). At high er temperatures, the super saturated solid solution precipitated a met astable Al3Zr phase, less than 5 nm in size, which was found to be ver y stable to coarsening even up to 425 degrees C. The Al3Zr also precip itated inside the Al3Ni phase indicating the partition of Zr in both t he phases. However, it coarsened at a higher rate inside this phase. T he presence of Al3Zr was also found to be effective in resisting coars ening of the matrix grains (Al), due to the similarities in structure and lattice constants between Al and Al3Zr. To bring out the effect pr oduced by the added Zr, a binary counterpart was studied. Zr was found to have an effect equivalent to that produced due to a higher quench. (C) 1998 Elsevier Science S.A. All rights reserved.