Grain Boundary Relaxation in Four High Purity, Face-Centered Cubic Metals

摘要

The grain boundary relaxation in high purity aluminum, nickel, copper, and silver was studied by means of a low frequency torsion pendulum. Both internal friction and creep at constant stress tests were conducted on all the metals. A lognormal distribution in relaxation times was used to explain the relativity wide experimental internal friction peaks and the gradual relaxation behavior during the creep tests. The lognormal distribution in relaxation times was separated further into a lognormal distribution of relaxation time constants and a normal distribution in activation energies. A spread of from = 4 to = 6 Kcal/mole accounted for the major part of the distribution. The distribution parameter was observed to increase with increasing grain size in copper. Grain boundary segregation is suspected to be the cause. A 'double peak' internal friction phenomenon observed in copper is explained by the segregation of minute quantities of oxygen to the grain boundary. The preferred orientation of grains in the wire specimens also appears to be an important factor. A similar double peak was also observed in high purity silver. The activation energy of the second peak is H sub m = 55.5 = 4 Kcal/mole. (Author)