Displacive transformations in Fe–Ni nanophase alloys
Abstract The crystallisation behaviour and subsequent transformation of the crystalline phase of amorphous alloys in the series (Fe 100− x Ni x ) 93− y Zr 7 B y , where y =16 and x =30 or y =12 and x =40,50 have been studied. The fabrication of amorphous precursors was performed using melt-spinning. The primary crystallisation products were α (b.c.c.) for x =30 and 40 but γ (c.c.p.) in the x =50 sample. In each of the alloys, the fully crystalline structure consisted of the γ phase and a metastable boride that could be removed by annealing at elevated temperature with the result of improved ductility. Attempts have been made to induce martensitic transformation in the nanophase and nanocrystalline γ structures. No evidence of transformation on quenching to liquid nitrogen temperature has been found in any of the samples across the composition range, regardless of the degree of devitrification. Transformation was observed in the fully crystalline x =30 alloy, induced by 20 min deformation in a high velocity ball-mill, but this was not possible at higher Ni contents. The partially crystalline, c.c.p. x =50 alloy has been found to be stable against transformation. A preliminary investigation into the effects of hydrostatic pressure on the devitrification behaviour has provided evidence that pressure acts to stabilise the γ phase at lower Ni contents than is required in the vacuum-annealed samples.