FORMATION OF NEW PHASES BY CHEMICAL LEACHING OF RAPIDLY SOLIDIFIED ALLOYS

Structural changes resulting from rapid solidification and subsequent leaching in sodium hydroxide water solution have been examined for ter nary systems: Al(almost-equal-to 70 at.%)-Cu(almost-equal-to 30 at.%)- X (X-0.8 at.% Ti, Zr, V, Nb, Pd), Al(75%)-Ni(0%-25%)-Fe(0%-25%) and Al (75%)-Co(0%-22.5%)-Cu (2.5%-18%). Intermetallic compounds in the Al-Cu -X alloy specimens obtained at slower solidification rates disappeared in rapidly solidified powders produced by rotating-water atomization. Leaching Al from the powders containing Ti, V and Pd yielding Cu soli d solution and showed a great increase in catalytic activity. In contr ast, a supersaturated b.c.c. phase and a metastable f.c.c. Co phase fo rmed in the Al-Ni-Fe and Al-Co-Cu systems. Some discussion has been ma de of the difference between the leaching of mechanically alloyed and rapidly solidified powders. The present method can become a new alloyi ng method, where new alloys are produced by subtracting chemical eleme nts from mother alloys, while the amounts of chemical elements are con stant or are added in the conventional alloying processes.