Al-Ni-Fe 3元合金の急冷凝固組織とAlのアルカリリーチングによる非平衡相の生成

Abstract

A new approach for the metastable phase formation based on chemical reaction was proposed. Various ternary Al3(NixFe1−x) alloys were rapidly solidified and then aluminum atoms were leached from the alloys by the hot alkaline solution. The structure of the as-leached and heat treated specimens were examined by SEM and X-ray diffraction. The results are as follows.(1)In the as-leached state, the crystal structure varied with the value of x.In the range of x=0 to 0.33, a metastable bcc structure (supersaturated bcc in Ni) and magnetite were formed. Fcc and magnetite were formed between 0.33 and 0.5 of x. At a high values of x (more than 0.5), only the fcc phase was observed.(2)X-ray diffraction patterns of the fcc phase were very broad, and it was estimated that the grain size of the leached specimens were in the range of 5 and 10 nm. Since the specific surface area of the as-leached specimens was quite large, each grain might have a gap (free space) at the grain boundary.(3)The leached specimens showed high activity and sometimes ignited spontaneously in atomosphere due to their high specific surface area.(4)Rapidly solidified alloys were nonmagnetic, but after leaching they showed magnetism due to the formation of magnetite and ferromagnetic bcc and fcc phases.