Structural relaxation by interphase boundary migration in pure tin

Abstract

It is well known that tin exhibits an allotropic transformation from white tin which has a tetragonal lattice to grey tin which has a cubic diamond type lattice at about 13.2 ° C. The relaxation effects and the internal friction developed near the phase transition temperature is generally characterized by the form and volume of the new phase and its internal structure [1]. Many theories [2-4] discussed the atomic origin controlling the mechanism responsible for such a relaxation process. The present work aims to throw more light on the role of phase change on the mechanical properties of tin through a study of the temperature dependence of internal friction, elastic modulus and steady creep rate near the phase transition temperature. thare tin wires of 0.025 cm in diameter were used in the present tests. The test samples were pre.annealed for 2h at 85 ° C. A vibration detector circuit previously described [5] was used to measure both the internal friction, Q-I, and elastic modulus changes, AE. The elastic modulus was traced through changes in the square of the natural frequency of test samples having frequencies of vibration ranging between 20 and 120 Hz. Internal friction and elastic modulus changes of tin wire samples were measured as a function of temperature in the range 0-45 ° C. Measurements were taken while the temperature was gradually increased. The standing time for observation at each temperature did not exceed two minutes. Different degrees of deformation by pre-plastic extension was effected by a locally made tensile