A Fundamental Study of P/M Processed Elevated Temperature Aluminum Alloys.
Annual technical rept. 1 Oct 84-30 Sep 85,
DREXEL UNIV PHILADELPHIA PA DEPT OF MATERIALS ENGINEERING
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The ambient and elevated temperature strength and microstructural stability of powder processed Al-Fe-Ni alloys are being evaluated with respect to processing mode, microstructure, and microstructural stability. The overall objective is to establish a basic understanding of processing-microstructure relations in this new class of alloys in order to establish design guidelines for limiting stresses and temperatures. In the current program year, rapidly solidified prealloyed powder containing 0.19 volume fraction of FeNiAl9 dispersoid similar to 0.18 micrometer was mechanically alloyed MA and subsequently hot extruded to full density. The MA alloy is stronger than the non MA alloy at temperatures up to about 300 C. In addition, MA enhances microstructural stability at elevated temperature for example there is no significant coarsening of the FeNiAl9 after 624 hours at 450 C. Improvements in alloy strength and stability are attributed to the presence of fine scale similar to 30 nm oxides and carbides introduced during MA, and which are distributed uniformly throughout the matrix, at matrix- intermetallic interfaces, and on sungrain boundaries. This fine-scale dispersoid provides effective resistance to dislocation bowing Orowan mechanism below 300 C. At higher temperatures, dislocation climb is the controlling mechanism and the small oxidescarbides are no longer effective barriers to climb. Processing mode does not significantly alter the as-extruded microstructure, but it does influence strength and strength retention. A combination of low degassing and extrusion temperatures results in superiority with respect to strength and stability.
- Properties of Metals and Alloys