Dispersion strengthened aluminum made by mechanical alloying
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have been reviewed in detail by Bloch, z The tensile strength of SAP materials increases with increasing Al2Oa content up to about 12 wt pct to 15 wt pct A1203. SAP with high AlzO3 contents naturally has a low electrical conductivity due to the high amount of nonconducting phase present, The A1203 in SAP acts as an inefficient dispersion as it is in a form of flakes aligned parallel to the extrusion direction, s These flakes are not dispersed evenly through the matrix but a r e segregated in stringers. Other dispersion strengthened metals and alloys such as thoriated nickel and INCONEL* alloy MA 754 *Regtstered trademark of The IntemaUonal Nickel Company, Inc.
achieve comparable strength gains on a homologous femperature basis with a much smaller dispersoid content (2 to 3 vol pct). In these alloys the dispersoid is of a more equiaxed shape, is finer than the A1203 in SAP and is more evenly distributed through the matrix. The mechanical alloying process 4 is a high-energy, dry milling technique producing composite metal particles with submicron homogeneity. This paper describes the production of an efficient A12Oa dispersion in aluminum by the application of the mechanical alloying process. EXPERIMENTAL
powders is introduced into a Szegvari Attritor Grinding Mill* 5 a high energy grinding mill in which the *Registered trademark of Union Process, Inc.
ball and powder charges are held in a stationary, vertical, water cooled tank and agitated by impellers radiating from a rotating central shaft. Mechanical alloying involves a dynamic balance between welding and fracturing of the composite powder particles. Mechanical alloying of aluminum requires the use of a deliberately added process control agent to prevent excessive welding of aluminum to itself, the ball charge, the attritor tank, and impellers. The amount of process control agent added during mechanical alloying of aluminum must be: a) enough to prevent excessive welding of the aluminum, but b) not so much as to completely prohibit that welding. 6 The process control agents used in this study, stearic acid and methanol, were charged into the attritor with the aluminum powder prior to processing. Mechanical alloying of the aluminum was accomplished in a 1 gal (3.8 liters) capacity attritor under a sealed air atmosphere with approximately 50 lbs (22.7 Kg) of 5/16 in. (0.8 cm) diam hardened steel balls. The processed powder was drained from the attritor at the end of the run and sealed in aluminum alloy cans. While some powders were successfully extruded directly to bar, most bars showed cracking around the prior powder particle boundaries if no preliminary hot compaction step was used. For this reason hot compaction to solid was performed at 950 to 1000~ (510 to 538~ prior to extrusion to round bar at 850 to 900~ (454 to 482~ Extruded bars were swaged and/or drawn to rod and wire. Tensile tests in air at room temperature and
PROCEDURE
The preparation of dispersion strengthened nickelbase superalloy powders by mechanical alloying has been described in detail.
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