UBC Theses and Dissertations
Thermal cycling of cadium. Evans, Dewi Gordon Sutcliffe
The thermal cycling of cadmium and dilute Cd-Pb alloys was studied by measuring the length change of a specimen as a function of the number of cycles a specimen had undergone. The majority of the experiments were performed using material which had been swaged to 90% reduction in area followed by various amounts of drawing reduction, and which were cycled from 0°C to -190°C. Other areas of interest were the effect of temperature range and grain size on the growth rate, and the effect of cycling on the microstructure and on the axial thermal expansion coefficient. It was found that swaged-and-drawn material cycled from 0 to -190°C, exhibited a three-stage growth curve. The growth rates in Stages 2 and 3 were constant; Stage 1 was ill-defined and was not investigated to any extent. The transition from stage to stage was abrupt and was accompanied by a decrease in growth rate, a lower incidence of non-basal slip and a change in the expansion coefficient. Both the Stage 2 and the Stage 3 growth rates showed a (grain size)¯ ½ dependence and reacted in approximately the same way to alloying in that maxima in both growth rates were indicated for alloys containing between 10 and 50 ppm Pb. The results were interpreted in terms of an idealized model of a textured specimen. The model consisted of a bicrystal representing all grains possessing a given orientation, surrounded by a matrix representing all other grains in the specimen. Stresses are set up in the specimen since the expansion of the textured grains and the matrix grains differ in a given reference direction. These expansion stresses are then relaxed at the upper temperature by creep processes. Stage 3 was identified with the overall cycling mechanism. Stage 2 was considered to result from the interaction of the swaged and the drawn portions of the swaged-and-drawn texture. Stage 1 was believed to result from boundary stresses arising from the differential expansion of adjacent grains. Some experiments were carried out using rolled, drawn and swaged material. The results of these experiments as well as those results obtained by changing the temperature range were used primarily for purposes of comparison to the results obtained from cycling swaged-and-drawn specimens from 0 to -190° C.
Item Citations and Data