STUDY OF ALLOY PHASE FORMATION USING ION-BEAMS

This paper attempts to present a brief review of recent progress obtained by the author's group in the research area of ion beam metallurgy, namely (i) formation of metal-nitride by nitrogen implantation; (ii) metallic glass formation by ion mixing; and (iii) icosahedral phase formation by ion mixing. Silver- and copper-trinitrides have been formed, for the first time, by RT 80 keV nitrogen ion implantation for doses up to 2×1018 N cm-2. These indicated that deposition of large amounts of energy during implantation could provide the reaction energy of noble-metal-nitride with rather positive heat of formation, and that local nitrogen concentration in the implanted films could be considerably greater than that limited by the sputtering yield involved. Besides, our observation of the reverse sequence of phase transition TiTiNTi2N with increasing nitrogen dose suggested that growth kinetics (or structural compatibility between newly formed phase and the matrix) might be a key factor in determining the nitride formation in some systems. Two parameters were found of importance in influencing the glass forming ability (GFA) of binary metal systems. One is MPAR (maximum possible amorphization range), which equals 100% minus the maximum solid solubilities observed in the equilibrium phase diagram. The other is the heat of formation. A map was constructed by these parameters and some empirical qualifications were found to classify the systems according to GFA into three categories of Hardly (HGF), Possible (PGF) and Readily (RGF) Glass Forming systems. The FeCu system is an immiscible one, in which amorphization induced by ion mixing could only occur within a narrow composition range. The favored composition was figured out experimentally, and an icosahedral phase was also formed by ion mixing without post-annealing at corresponding atomic stoichiometry. Interestingly, a similar phase was also formed in the FeMo system. © 1990.