Abstract
Relaxation phenomena have been studied in an Fe-25% Ni alloy containing up to 42 ppm boron and in two type AISI 316 austenitio stainless steels, one containing 1 ppm boron and the other 22 ppm boron. The temperature range used was 300°C to 1200°C. The individual constituents of the complex internal friction peaks have been separated with the help of a computer. The relaxation spectrum of the Fe-25% Ni alloy has been shown to consist of only one relaxation peak occurring in the temperature region of 750°C. The relaxation spectrum of the type 516 stainless steel has been split into three regions. A grain boundary relaxation peak spectrum, which consists of a number of peaks, was found to occur in the temperature range 802°-858°C, a high temperature peak in the region 930°-980°C and a further high temperature peak in the region 992°-1027°C. These relaxation peaks have been explained in terms of current theories of grain boundary sliding and migration which have been extended to explain the additional effects observed in this, work. The high temperature peak has been attributed to the relaxation effects of molybdenum. It has been observed that the high temperature background damping is strongly dependent on the grain size and composition of the alloy. The effect of cooling rate on the distribution of boron in the type 516 stainless steel has also been studied and it has been shown that on vacuum quenching from 1000°C and above, the boron segregates to the grain boundary in atomic form, causing a reduction in the height of the high temperature peak. On slower cooling, however, the boron diffuses back into the matrix with a consequent increase in the height of the high temperature peak.