2元系Mg-14Ca亜共晶合金におけるクリープ特性

抄録

The binary Mg-14Ca (mass％) hypoeutectic alloy exhibits a fine lamellar structure of α-Mg and C14 (Mg₂Ca) phases with the lamellar spacing of 0.9 µm, together with a small amount of the primary α-Mg phase. Tensile creep tests were conducted for the alloy at temperatures between 473-523 K and stresses between 30-50 MPa. The overall creep rate vs. time in a log-log diagram for the alloy shows a downward curvature from stress application until creep rupture. A well-defined steady-state is barely evident. The decrease in the creep rate during the transient stage is emphasized at lower temperatures and lower stresses. The coarse lamellar structure with the lamellar spacing between 1.5-2.5 µm is evident at colony boundaries during the accelerating creep stage. It is found that the stress exponent of the minimum creep rate, n, is 7, and the activation energy for creep, Q_c, is 146 kJ/mol. The value of Q_c is close to that for the lattice self-diffusion of magnesium (136 kJ/mol). It is deduced that the creep for the alloy is controlled by dislocation climb.

Fig. 5　FE-SEM image of the Mg-14Ca alloy creep-ruptured at 498 K under a stress of 40 MPa. The rupture life is 180 h (6.5 × 10⁵ s).