Critical Voltage Effect in Cu-Al and Cu-Au Alloys

Abstract

The critical voltages, V_c, for 222 and 400 reflections from pure Cu and Al and Cu-based alloys with 15 at%Al, and 5 or 15 at%Au were measured by JEM-1000 HVEM to investigate the effect of alloying on the critical voltage effect. The addition of 15 at%Al to Cu causes V_c for the 222 and 400 reflections to increase by 15 and 32 kV, respectively. The addition of 5 at%Au results in decreases of V_c for the 222 and 400 reflections by about 44 and 77 kV, respectively. A decrease as much as 176 kV occurs for the 400 reflection by the addition of 15 at%Au. These results agree with the expectation that the addition of an element with a smaller (or larger) scattering factor than that of the matrix will produce an increase (or decrease) of V_c. The measured V_c was analyzed by the many beam dynamical theory by taking into account systematic 10 beams. From the measured V_c of Cu-Al and Cu-Au alloys, we estimated the B factors and the Debye temperatures by using the corrected scattering factors. In the case of Cu-Al alloy, a fairly good agreement is obtained between the result of the present work and the one obtained by X-ray measurement. The effect of temperature on V_c has also been investigated by using a liquid nitrogen cold stage. The V_c increases with a decrease in temperature, and the temperature dependence of V_c is more pronounced in Cu-Al alloy than in Cu-Au alloy. In order to investigate the effect of short range order on V_c, the differrence in V_c in Cu-15 at%Au alloy between the specimens furnace-cooled and quenched from 400°C has been measured and the change of 5 kV for the 400 reflection has been obtained.