Effect of plastic deformation on the coarsening of
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I.
INTRODUCTION
ALUMINUM alloys produced by rapid solidification processing (RSP) have great potential for elevated temperature applications. These alloys contain a high volume fraction of dispersed phases which provide higher room temperature strength and elastic modulus than are obtainable by conventional ingot metallurgy. In addition, certain RSP alloys retain their desirable properties up to higher temperatures than do the ingot metallurgy alloys. One such RSP alloy, the A1-8 wt pct Fe-4 wt pct Ce alloy prepared at Alcoa, exhibits promising mechanical properties at temperatures up to 316 ~ Exposure to higher temperatures leads to significant coarsening, transformation of metastable phases, and subsequent loss of strength. Plastic deformation may affect the stability of the dispersed phases by increasing diffusion rates and assisting in the nucleation of more stable phases. Diffusion rates may be increased by the generation of excess vacancies or by short circuiting along dislocations and grain or subgrain boundaries. While the subject of strain enhanced diffusion has received much discussion in past y e a r s , 2'3'4 little attention has been paid to the influence of plastic deformation on particle coarsening rates. Therefore, the effect of static and cyclic deformation at 425 ~ on microstructural stability in an A1-8.8 wt pct Fe-3.7 wt pct Ce alloy was examined. Coarsening rates in these specimens have been compared to the coarsening rates in specimens isothermally annealed at the same temperature.
L. ANGERS is Staff Scientist, Alcoa Technical Center, Alloy Technology Division, Alcoa Center, PA 15069. M.E. FINE, W.P. Murphy Professor of Materials Science and Engineering, and J. R. WEERTMAN, Professor, Department of Materials Science and Engineering, are with Northwestern University, Evanston, IL 60201. Manuscript submitted January 13, 1986.
METALLURGICALTRANSACTIONS A
II.
EXPERIMENTAL PROCEDURE
An A1-8.8 wt pct Fe-3.7 wt pct Ce alloy, developed at Alcoa under AFML Grant No. F33615-77-C-5086, was obtained from Wright-Patterson Air Force Base in plate form prepared by gas atomization, cold isostatic pressing, hot vacuum pressing, and finally extrusion. To study the effect of deformation on the coarsening kinetics in this system, isothermal annealing and both creep and load control fatigue tests were done. Creep specimens were flat with gage section dimensions of 6 mm length x 2.8 x 2 mm 2 cross section. Round threaded fatigue specimens had both a gage diameter and gage length of 4.77 mm. Prior to testing, all specimens were polished to a 0.3/xm finish. Preliminary creep tests were run at 316, 375, and 425 ~ to determine whether any effect of deformation on the coarsening rate could be detected. To obtain a quantitative measure of the extent of the enhancement, a series of specimens were either isothermally aged at 425 ~ crept at 425 ~ under an initial stress of 17.2 MPa, or fatigued in load control at 425 ~ and stress amplitudes of 34.4 or 68.8 MPa and frequencies of 0.1 Hz. Creep elongation was monitored
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