METASTABLE TI-NI-FE-SI ALLOYS PREPARED BY MECHANICAL

The phase formation and physical properties of mechanically alloyed Ti 56Ni18Fe10Si16 have been investigated. The as-milled samples are amorp hous and undergo a transition to the icosahedral quasi-crystalline pha se on annealing at about 1025 K. Mechanical alloying in the presence o f an additive of 1% quasi-crystalline phase yielded the same phase dir ectly. Alloys have been studied by X-ray diffraction, Mossbauer spectr oscopy and magnetic susceptibility methods. These results may be compa red with those in the literature for amorphous and quasi-crystalline a lloys of similar composition prepared by rapid solidification from the melt. In all cases the alloys produced by mechanical alloying show a greater concentration of open volume defects and, in the icosahedral p hase, a greater degree of disorder and larger phason strains. Hydrogen diffusion studies of these alloys have shown that the mean interatomi c distance increases for short hydrogenation times, but that for longe r hydrogenation times the hydrogen increases local atomic order which results in a reduction of mean interatomic distances.