High elevated-temperature strength of Al-based nanoquasicrystalline alloys

A new icosahedral (I) quasicrystalline alloy was found around thr Al-rich composition of Al84.2Fe7.0Cr6.3Ti2.5 by melt spinning. The I-phase consists of a spherical shape with a particle size of about 250 nm and contains a high density of internal defects. The I-phase is a metastable phase and decomposes to Al + Al13Cr2 + Al23Ti9 + Al13Fe4 phases in the temperature range of 620 to 1005 K by continuous heating at a heating rate of 0.67 K/s. The use of further Al-rich Al-Fe-Cr-Ti alloys enabled the production of metastable phase powders consisting mainly of Al + I phases in a wide particle size fraction of 26 to 125 mu m by high-pressure Ar gas atomization. The bulk Al93Fe3Cr2Ti2 alloys prepared by extrusion of the 26 mu m powder at 67.3 K consist of Al, I and Al23Ti9 phases and the I-phase keeps a particle size of about 300 nm. The extruded bulk I-base alloy exhibits high elevated-temperature strength of 510 MPa at 473 K and 360 MPa at 573 K as well as high room-temperature strength of 650 MPa. The elevated-temperature strength exceeds the air-force goal level (400 MPa at 473 K and 350 MPa at 573 K) for Al-based alloys. The high elevated-temperature strength and wear resistance remain almost unchanged even after annealing at 573 K for 1000 h. The extremely good elevated temperature strength is thought to result from high elevated-temperature strength of the Al-based I-phase itself containing Fe, Cr, and Ti elements which have low diffusivities in Al phase, The success of developing the new type of high elevated temperature strength Al-based alloys containing the I-phase as a main constituent phase by the use of the stoichiometric Al-Fr-Cr-Ti icosahedral alloy is promising For the future development as a new high elevated-temperature strength material. (C) 1999 Acta Metallurgica Inc.