Pergamon NanaStmctured Materials, Vol. 7. No. 5. pp. 565-512 1996 Elsevier Science Ltd Copyright 0 1996 zyxwvutsrqponmlkjihgfed Acts Metallurgica Inc. Rinled in the USA. All lights rt?sawd 0965-9773196 $15.00 + .OO PlI SO9659773(96)00020-7 THERMAL STABILITY OF NANOCRYSTALLINE Fe-10 wt.% Al PRODUCED BY CRYOGENIC MECHANICAL ALLOYING R.J. Perez, B. Huang and EJ. Lavernia Department of Chemical Engineering and Materials Science University of California-Irvine, Irvine,CA 927 17-2575 zyxwvutsrqponmlkjihgfedcb (Accepted December 1995) Abstract - Nanocrystalline Fe-10 wt.% Al material is synthesized using cryogenic high energy ball milling (cryomilling). The zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA resultant powders are compacted in a rigid die at 350 M Pa and 823 K in an argon atmosphere. The grain size of the powder compacts, determined using transmission electron microscopy, isfound to be II-+5 nm. Subsequent heat treatmentfor I hour at temperatures of 1073 K and 1223 K reveals thatfine grain sizes of I3 f 6 nm and 16 f 7 nm, respectively, are maintained. Only when the heat treatment temperature is increased to 1373 K. or over 75% of the zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA melting zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCB p o int ofFe, do relatively large grainsform, approaching 100 nm. This level of thermal stability is shown to exceed that of pure Fe processed under identical conditions, by a significant margin. The present results indicate that the increase in thermal stability may originate from the pinning effect of fine dispersoids formed during cryomilling and subsequent heat treatment. 1. INTRODUCTION High energy ball milling has evolved into a reliable means by which metallic alloys with grain sizes on the nanometer scale may be synthesized from their elemental constituents (1). Consolidation of these powders to form dense nanocrystalline solids, however, has been found to be difficult, primarily due to the extreme hardness of the powder particles. This, in turn, originates from the superimposed effects of grain boundary strengthening, solid solution strengthening, and strain hardening (2,3). In addition, the metastable nature of the nanocrystalline microstructure dictates that the use of high temperature densification techniques be limited. For this reason, improvement of the thermal stability of milled powders against grain growth is of paramount importance in the development of an economical methodology for the production of bulk nanocrystalline material. One promising technique by which remarkable improvements in the thermal stability of nanocrystalline Al alloys have been achieved is through the in-situ formation of fine dispersoids during cryogenic high energy milling (4). In this work, Luton et al. (4) milled Al powder in an attritor under a liquid nitrogen slurry. Fine particles 2- 10 nm in diameter spaced 50- 100 nm apart formed as a result of this “cryomilling” process were found to impede grain growth at high