FORMATION OF METASTABLE L12 PHASES IN AL3ZR AND AL-12.5-PERCENT-X-25-PERCENT-ZR (X = LI, CR, FE, NI, CU)

The intermetallic Al3Zr crystallizes in the tetragonal DO23 structure but can be produced as a metastable cubic L1(2) structure by rapid solidification. We have studied the effects of mechanical alloying, a low-temperature isothermal processing method, and ternary additions of lithium, chromium, iron, nickel and copper on the phase stability of the L1(2) phase. Mechanically alloyed Al3Zr is single-phase L1(2) which is stable up to 550-degrees-C. The additions of lithium or chromium increase the stability of the L1(2) phase to 750 and 740-degrees-C, respectively. The addition of iron or nickel leads to the formation of amorphous, rather than L1(2), phases. Mechanically alloyed Al-12.5%Cu-25%Zr is single-phase L1(2) and this phase is stable up to at least 1300-degrees-C.