Isothermal compression of the alloys of iron up to 300 kilobars at room temperature: Iron-nickel alloys

The effect of pressure on the crystal structure and the molar volume of iron alloyed with 5 and 10% nickel was determined up to 300 kb at room temperature by means of X-ray diffraction techniques employing a diamond-anvil high-pressure cell. The alloys undergo a reversible bcc-hcp phase transformation, which is accompanied by a volume change of −0.36 ± 0.02 cm3/mole. The crystallographic axis ratio, c/a, of the hcp phase appears to increase with nickel content, whereas it appears to be unaffected by pressure. The bulk moduli calculated from the volume data for the bcc and hcp phases of the alloys do not differ significantly from those for the respective phases of iron. The bulk modulus value for the hcp phase evaluated at zero pressure has been calculated to be 2.06 ± 0.15 Mb and is about 20% greater than that for the bcc phase. The volume of the hcp phase at zero pressure has been calculated from the pressure-volume data by extrapolation. A value of 6.67 ± 0.02 cm3/mole has been obtained for iron and the alloys. The pressure-volume relationship obtained by this work is consistent with the results obtained by R. G. McQueen and S. P. Marsh (1960, 1966) using shock compression techniques.