The Effect of High Pressure on the Order-Disorder Transformation in Alloys

With electrical resistance as an index of degree of order, the behavior of the order-disorder transformation under high hydrostatic pressure has been investigated with the three alloys, CuAu, ${\mathrm{Cu}}_3$Au and CuZn. Measurements were made under pressures up to 10,000 kg/${\mathrm{cm}}^2$ and over the temperature range 50°C to 426°C. For temperatures below the critical point the course of the transition under pressure may be predicted from reported thermal expansion data and deductions from the Bragg-Williams' theory. The observed behavior of the alloys seems to be consistent with these predictions. Measurements made near the critical temperature with the alloys CuAu and ${\mathrm{Cu}}_3$Au show that the critical point is raised by pressure in both cases. One alloy, alpha brass (${\mathrm{Cu}}_3$Zn), not hitherto included in the class of the three alloys above mentioned has been examined. The conclusion is reached that a slight ordering of the constituents of the alloy occurs under high pressure.