Particle coarsening in rapidly solidified Al-Fe-Ce alloys
The objective of this study was to examine the stability of the strengthening dispersoids with respect to phase change and Ostwald ripening at elevated temperatures in rapidly solidified Al-Fe-Ce alloys containing 7-9 wt. % Fe and 3-7 wt. % Ce. Five dispersed phases were observed in the as-extruded Al-8.8Fe-3.7Ce and Al-8.9Fe-6.9Ce alloys: metastable Al/sub 6/Fe, two metastable Al-Fe-Ce phases, and equilibrium Al/sub 13/Fe/sub 4/ and Al/sub 10/Fe/sub 2/Ce. By convergent beam electron-diffraction studies, the structure of one of the metastable Al-Fe-Ce phases was found to be orthorhombic, having a = 1.02 nm, b = 1.62 nm, and c = 0.42 nm. The structure of Al/sub 10/Fe/sub 2/Ce was determined to be orthorhombic, having a = 0.894 nm, b = 1.022 nm, and c = 0.906 nm. After aging 2160 hours at 316/sup 0/C, no Al/sub 6/Fe was detected and only rarely were the metastable orthorhombic Al-Fe-Ce particles found. The other metastable Al-Fe-Ce phase persisted. Aging 24 hours at 425/sup 0/C gave only the equilibrium phases. Coarsening of the dispersed phases in the rapidly solidified Al-Fe-Ce alloys occurs much more rapidly than expected by the Modified Lifshitz-Slyozov-Wagner theory for bulk-diffusion-controlled coarsening, although the expected linear relation between particle dimension cubed and time is followed for aging temperatures of 475/sup 0/C and higher. Experimental particle-size distributions are broadened and skewed in the opposite sense to that predicted by the theory.
- Research Organization:
- Northwestern Univ., Evanston, IL (USA)
- OSTI ID:
- 5574469
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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