Scripta METALLURGICA Vol. 26, pp. 1727-1732, 1992 Pergamon Press Ltd. et MATERIALIA Printed in the U.S.A. All rights reserved MILLING MAPS FOR PHASE IDENTIFICATION DURING MECHANICAL ALLOYING C. Suryanarayana, Guo-Hao Chen and F.H. (Sam) Froes Institute for Materials and Advanced Processes University of Idaho Moscow, ID 83843-4195, USA (Received March 31, 1992) Introduction Mechanical alloying (MA), a high-energy ball milling technique, has been employed to produce oxide- dispersion-strengthened nickel and iron-base superalloys since the 1960's [1,2]. In recent years, use of this solid-state powder processing technique has been extended to the synthesis of a variety of stable and metastable phases (supersaturated solid solutions, crystalline and quasicrystalline intermediate phases and metallic glasses) starting from either blended elemental or pre-alloyed powders [3-5]. Since the MA process involves repeated welding, fracturing and rewelding operations leading to microstructural refinement [6], the amount of mechanical energy input is a critical parameter in determining the constitution of the final product [7]. There are several variables in the MA process which have a profound bearing on the final constitution of the powder. Even though the nature of the phases to be formed is intrinsically dependent on the alloy chemistry, external parameters such as (a) type of mill, (b) intensity of milling, (c) type of milling media, (d) milling atmosphere, (e) ball-to-powder ratio, (f) milling time, (g) milling temperature and (h) nature and amount of the process control agent have also been shown to affect the product of the MA process. For example, it has been shown that the glass-formation range can be expanded in alloy systems, or the time required for amorphization reduced by increasing the milling intensity [8-10], It has also been shown that transformations occur about 5-6 times faster in a SPEX shaker mill than in an attritor mill [11]. Similar results on the effects of other variables are also being reported. For example smaller diameter balls tend to produce an amorphous phase while larger diameter balls result in the formation of crystalline phases [12]. Lee et al. [13] showed that the higher the milling temperature, the faster the amorphization proceeded. Further, the times to obtain a 100% amorphous phase were shorter when the powders were loaded in air rather than in an argon or helium atmosphere [14,15] and oxygen contamination was reported to crystallize an amorphous phase in Ni-Ti alloys [16]. Variations in the parameters mentioned lead to differences in results in the same system regarding the sequence and time of formation of phases, and the final phase(s) produced, leading to considerable difficulty in comparing the results of different investigators. The aim of the present communication is to report on the construction of milling maps to represent the boundaries of phase formation in mechanically alloyed powders as a function of ball-to-powder weight ratio (BPR) and milling times. It will be shown that these diagrams can be used as "road maps" to predict the phase(s) formed at any given BPR or milling time. 1727 0036-9748/92 $5.00 + .00 Copyright (c) 1992 Pergamon Press Ltd.