Constitutive Relation for Ambient-Temperature Creep in Hexagonal Close-Packed Metals

Abstract

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 À9 s À1 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. Ambienttemperature 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.

Accumulation of plastic strain in Zircaloy-4 at low homologous temperature

“…In this condition, two n values were observed: the high stress region showed that n ¼ 20, which belongs to the power-law breakdown (PLB) region; the low stress region showed n ¼ 3. Because the latter n value corresponded not only to "threepower-law" creep brought about by viscous motion of dislocation in solid solution alloys [18,19,21] but also to ambient-temperature creep in HCP metals where it is rate-controlled by dislocation absorption at GB [20,22,23], the following discussion was undertaken to identify the rate-controlling process.…”

Intragranular Deformation Mechanisms during Ambient-Temperature Creep in Hexagonal Close-Packed Metals

“…Therefore, to continue the ambient-temperature creep deformation, an accommodation process must be activated at the grain boundaries. However, abnormally low values of the apparent activation energies of ambienttemperature creep, about 20 kJ/mol, 2) might not activate conventional diffusional accommodation processes. Mordike et al 30) and Koike et al 31) reported exceptionally low apparent activation energies that are close to 20 kJ/mol in several Mg alloys around room temperature.…”

“…metals and alloys show creep behavior at ambient temperature. 1,2) Using Ti-6Al-4V alloy for some critical parts, e.g. bolts and nuts, will bring about stress relaxation, possibly leading a structural component to destruction.…”

Creep properties of biodegradable Zn-0.1Li alloy at human body temperature: implications for its durability as stents

“…In fact, creep resistance has been an important consideration in evaluation of polymeric stent materials [13,14]. It has long been known that Zn, like other hcp metals such as Mg, Ti and Zr, tends to exhibit discernible creep at room temperature [15][16][17]. Room temperature creep has also been reported in Zn alloys, such as rolled Zn-(0.3-2.0)Cu alloys [18], rolled Zn-0.15Cu-0.07Ti alloy [19], extruded Zn-28.7Al-1.9Cu alloy [20] and die-cast Zn-4Al-(0-3Cu) alloys [21].…”