Constitutive relation for ambient-temperature creep in hexagonal close-packed metals

This paper reports creep tests on three kinds of polycrystalline hexagonal close-packed metals, i.e. commercially pure titanium, pure magnesium, and pure zinc, in the vicinity of ambient temperature even below their 0.2% proof stresses. These materials showed significant steady state creep rates around 10^-9 s^-1 and had stress exponents of about 3.0. Arrhenius plots in the vicinity of ambient temperature indicate extremely low apparent activation energies, Q, of about 20 kJ/mol, which is at least one-fourth of the Q of dislocation-core diffusion. Ambient-temperature creep also has a grain-size effect with an exponent of 1.0. These parameters indicate that ambient-temperature creep is a new creep deformation mechanism in h.c.p. materials.