Scripta METALLURGICA et ~TERIALIA Vot. 24, pp. 1303-1306, 1990 Pergamon Press plc Printed in the U.S.A. All rights reserved PREPARATION OF SOME SPECIFIC GRAIN BOUNDARIES IN ALUMINUM FOR HREM STUDIES BY COLD ROLLING AND ANNEALING M. Shamsuzzoha and P.A. Deymier Department of Materials Science and Engineering University of Arizona, Tucson, AZ 85721 (Received April 2, 1990) (Revised May 3, 1990) Introduction The preparation of bicrystals with an aim to study grain boundary structure by high resolution electron microscopy (HREM) requires a careful approach. Primary attention needs to be directed towards the orientations of the crystals forming a boundary so that atomic resolution images of the bicrystai can be achieved by HREM. Mader, Necker and Bailuffi (1) have reviewed the limitations of present day high resolution microscopes in resolving grain boundary structures. According to these authors, the resolution limit (information resolution limit = 0.14 n.m) of such microscopes now allows most f.c.c metallic crystals to reveal a projected point pattern along any of the < 100 >, < 110 >, < 111 > and < 112 > directions. Resolving a grain boundary structure requires simultaneous imaging of atomic columns in crystals on both sides of the boundary. For a very thin f.c.c. metallic bicrystal, a 1" or less misorientation between neighboring crystals is required to achieve a simultaneous imaging of atomic columns across the interface (2). The {200}, {220} and {111} projected line pattern of a f.c.c. metallic crystal can also be obtained with current microscopes. A misorientation of 1" to 3" between such planes of f.c.c, metallic bicrystal can provide atomic plane resolution across the interface. Bierystals meeting these criteria for HREM studies are usually prepared either by disposition of thin film on a suitable substrate (3) or by solidification of a required orientation seeded bicrystal either by the Bridgeman technique (4) or by the Czochraiski technique (5). These techniques are rather expensive and require sophisticated instrumentations. In the present work we investigated a relatively simple and inexpensive cross- rolling and annealing technique to obtain bicrystals of aluminum for HREM studies of grain boundary structures. In this paper we give a report of such preparation techniques for certain specific aluminum bicrystals, which were found suitable for HREM imaging. Experimental Procedures The starting material consists of polycrystalline aluminum (with 99,999% stated purity) cylindrical bars of 10 mm in diameter by 50 mm in length. The bars were longitudinally strained to 1% reduction and then annealed at 600" C for one hour. The annealed bars typically revealed randomly oriented centimeter size grains. Single crystal slices of 15 mm length were cut from the annealed bars and then subjected to equal step pass cross- rolling to obtain ten different thicknesses with a total reduction ranging from 90 to 99%. The pass steps used were varied between 1.25 to 20% of the initial thickness. Heavily deformed specimens were given either a single cycle or a two cycle annealing. The single cycle annealing was performed at three different temperature ranges: (1) between 125 to 225"C, (2) between 250 to 350"C and (3) between 400 to 600"C. The two cycle annealing was comprised of a primary recrystallization annealing (at temperatures ranging either between 125 to 225" C or between 250 to 350" C) and a respective secondary recrystallization annealing (at temperatures ranging either between 250 to 350" or between 400 to 500" C). For thin foil preparation, 3 mm diameter discs were spark-cut from the annealed samples and then electropolished at a voltage of 50 V at room temperature in a solution of 73% methanol, 25% nitric acid and 2% hydrochloric acid. The thin foil thus prepared was examined with 120 kV Hitachi and 400 kV JEM 4000EX electron microscopes. A minimum of 30 grain boundaries selected at random for each cold rolling and annealing 1303 0036-9748/90 $3.00 ÷ .00 Copyright (c) 1990 Pergamon Press plc