Al-Fe-based bulk quasicrystalline alloys with high elevated temperature strength

An icosahedral (I) phase in coexistence with Al phase was found to precipitate in atomized Al93Fe3Cr2Ti2 and Al93Fe3Cr2V2 powders. The mixed structure was formed in the size fraction range up to 125 mum for the AI-Fe-Cr-V alloy, while the increase of the particle size to 125 IJ-m for the Al-Fe-Cr-Ti powder led to the precipitation of Al23Ti9. The replacement of Cr by Mn for the Al93Fe3Cr2Ti2 powder caused a mixed structure of Al + I + Al23Ti9 + Al6Mn even for the -26 mum powder. The formation tendency of the I-phase increased in the order of AI-Fe-Cr-V > Al-Fe-Cr-Ti > Al-Fe-Mn-Ti system. The decomposition temperature of the I-phase was about 790 K. The I particles were analyzed to have approximate compositions of Al84.2Fe7.0Cr6.3Ti2.5 and Al82.9Fe9.0Mn6.4Ti1.7, and the use of the analytical compositions enabled the formation of a mostly single I phase with an average grain size of 90 to 130 nm in the melt-spun state. Bulk I alloys in a cylindrical rod form were produced by extrusion of the atomized powders at 673 K and an extrusion ratio of 10. The extruded Al93Fe3Cr2Ti2 alloys exhibited good mechanical properties; i.e., sigma (0.2) of 550 MPa, sigma (UTS) of 660 MPa, and epsilon (p) of 4.5% at room temperature, and sigma (0.2) of 330 MPa, sigma (UTS) of 350 MPa, and epsilon (p) of 1.5% at 573 K. The high sigma (UTS) exceeding 350 MPa at 573 K was superior to the final target of the United States Air Force and hence the I-based Al93Fe3Cr2Fe2 alloy is expected to be extended as a new type of high elevated temperature strength material.