No abstract

A nanostructured Ti50Ni25Fe25 phase (B2) was formed by mechanical alloying and its structural stability was studied as a function of pressure. The changes were followed by X-ray diffraction. The B2 phase was observed up to 7 GPa; for larger pressures, the B2 phase transformed into a trigonal/hexagonal phase (B19) that was observed up to the highest pressure used (18 GPa). Besides B2 and B19, elemental Ni or a SS-(Fe,Ni) and FeNi3 were observed. With decompression, the B2 phase was recovered. Using in situ angle-dispersive X-ray diffraction patterns, the single line method was applied to obtain the apparent crystallite size and the microstrain for both the B2 and the B19 phases as a function of the applied pressure. Values of the bulk modulus for the B2, B19, elemental Ni or SS-(Fe,Ni) and FeNi3 phases were obtained by fitting the pressure dependence of the volume to a Birch–Murnaghan equation of state (BMEOS).

The effect of pressure on mechanically alloyed nanostructured Gd3Fe5O12 was investigated using in situ angle-dispersive X-ray diffraction measurements at room temperature. No structural phase transitions were observed, but an anomalous behavior in the volume vs. pressure curve, attributed to nonhydrostatic effects, was observed in the pressure range between 4.4 GPa and 9.1 GPa. The analysis of effect of pressure on the Wickoff 23c sites, occupied by Gd3+ ions, 16a and 24d sites, occupied by Fe3+ ions, and 96h sites, occupied by O2– ions, was performed. The value of the bulk modulus B0 for nanostructured Gd3Fe5O12 could not be determined due to nonhydrostatic effects associated with the silicone oil used as a pressure transmitting medium.

A nanostructured Ti 50 Ni 25 Fe 25 phase (B2) was formed by mechanical alloying and its structural stability was studied as a function of pressure. The changes were followed by X-ray diffraction. The B2 phase was observed up to 7 GPa, and for larger pressures, the B2 phase transformed into a trigonal/hexagonal phase (B19) that was observed up to the highest pressure used (18 GPa). Besides B2 and B19, a segregation of elemental Ni and the formation of FeNi 3 were observed. With decompression, the B2 phase was recovered. Values of bulk modulus for the B2, B19, elemental Ni and FeNi 3 phases were obtained by fitting the pressure dependence of the volume to a Birch-Murnaghan equation of state (BMEOS).