INVESTIGATION OF THE DISTRIBUTION AND THE STATE OF SMALL AMOUNT OF RARE EARTH ELEMENTS IN PURE IRON BY THE METHOD OF INTERNAL FRICTION

Abstract
Eleven kinds of pure iron specimens dopted with a small amount of rare earth elements were used in present research. Internal frictions were measured with a torsion pendulum. Experimental results showed that the nitrogen Snoek peak becomes broadened and the optimum internal friction shifts to a higher temperature. When the rare earth elements are increased the nitrogen peak tends to separate into two parts. In general, the height of nitrogen Snoek peak decreases with the increase of rare earth contents. On the basis of the experimental results it is suggested that the rare earth elements in the interior of pure iron grains is in a state of solid solution. The high temperature internal frictions were measured in two pure iron specimens containing different content of Lanthanum. Two internal friction peaks were obtained in each specimen. One internal friction peak around 550°C is the grain boundary peak of pure iron, while the other internal friction peak around 700°C is a new one. After treating one of the above two specimens into very large grains in specimen both the internal friction peaks of pure iron and new one were all disappeared. Only the pure iron grain boundary peak around 500°C was observed in the pure iron specimen containing no rare earth elements. Therefore, the new internal friction peak may be associated with the grain boundary which adsorbed a small amount of rare earth elements. Based on the results presented as above, it may be concluded that the rare earth elements in pure iron distribute not only in the interior of grains in a state of solid solution, but also segregate slightly at the grain boundary area in a state of adsorption.