Creep and stress relaxation in alpha-brass at low temperatures

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Abstract
Creep of vacuum annealed polycrystalline 65/36 alpha-brass was studied at constant stress in the range 77–30°k, close to the yield point, at elongations not exceeding 3%. The tensile strain σ increased logarithmically with time, and the characteristic strain 8cr ≡ de/d log10 t, given by the slope of the creep curves in semi-logarithmic representation, decreased approximately linearly with increasing temperature, from 29 × 10−4 at 77°k to 11 × 10−4 at 300°k. The creep was correlated with logarithmic stress relaxation, and the relation 8Cr = - 8rel/χ was established. where χ ≡ d[sgrave]/d σ in the coefficient of work-hardening, and 8 rel≡ d[sgrave]/d log10 t the slope of the corresponding curve obtained with stress relaxation at constant elongation. Both the creep and the relaxation are ascribed to a process of residual slip propagation in which the migration of edge disclocations impeded by the drag of conservatively moving jogs is rate determining. The driving force on the jog is the component of the line tension of the dislocation, which impels the jog in the direction of its Burgers vector; the effective stress on the dislocation is the difference between that necessary to tear it from its looked site and the stress, due to the intragranular sub-structure, which opposes its movement through the lattice in the unlocked state. At temperatures exceeding about 300°k, when dislocation locking is weak, both 8cr and 8rel tend to very small values.