Synchrotron X-ray diffraction studies on the transition metal alloy Mo-Re under high pressures

The effect of the addition of a d-rich transition metal Re to Mo on the bcc to hcp phase transformation at high pressures is investigated using Mo-Re alloys with 5, 11, 18, and 26 at. pct Re, fabricated by arc melting. The alloys were cold rolled to a 50-micron-thick foil for studies of transformations under high pressure in a diamond anvil cell. The energy dispersive X-ray diffraction pattern (recorded at Corness High-Energy Synchrotron Source) at the lowest pressure of 0.9 GPa showed that the Mo-26Re was single phase bcc. Typically 15 diffraction peaks of the bcc phase were observed to 70 keV at each pressure, and these peaks were followed to the highest applied pressure of 64 GPa. No discontinuity in the spacing and no new diffracton peaks were observed to 64 GPa, implying that the bcc phase is stable. Theoretical estimates of the transition pressure indicate that studies employing pressures up to several megabars are needed on this alloy to observe the bcc-hcp boundary. 16 refs