Interdiffusion in a dilute solid solution of Al-Li alloy measured by electrical resistance
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decays so that after aging at 300 ~ the hardness has already begun to decrease. At this stage we can only speculate that perhaps some intermediate stage of precipitation akin to the formation of GP zones may be occurring. In conclusion three points can be made: metastable A14Gd has been observed and identified as the intercellular phase in the as-cast rapidly solidified ribbon. Rapid coarsening of the microstructure is seen at 500 ~ and after 1 hour the microstructure is completely spheroidized, with second phase particles of 1 /xm or greater in size distributed at the grain boundaries. A 40 pct increase in hardness (compared to the as-cast ribbon) to about 95 k g / m m 2 is observed on aging at 150 ~ for 1 hour.
The authors acknowledge the assistance of E. Minkovitz, Ben Gurion University of the Negev, Beer Sheva, Israel, in assisting with the transmission electron microscopy. S. J. S. acknowledges the sponsorship of a Visiting Scientist program by the United States Air Force Materials Laboratory. Acknowledgment is made to the United States National Research Council for provision of a Resident Research Associateship (D. E.). Helpful and stimulating discussions with many colleagues are gratefully acknowledged, particularly Drs. Jackson and Mahajan.
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