Material design of shape-memory ceramics

The authors have studied the shape-memory phenomena of ceramics, mainly of glass ceramics. They found that most polycrystalline ceramics exhibit shape-memory phenomenon. The starting temperature of shape recovery corresponded to the starting temperature of stress relaxation in every shape-memory ceramics. These experimental results showed the shape recovery process as follows. If a specimen is deformed in the high temperature range and cooled to the room temperature and released, the viscosity change of the glass matrix or boundary restrains the elastic deformation of the crystal. The specimen in this condition can recover its original shape upon reheating. The authors also found that two factors of mica glass ceramics enabled the network of mica crystals to behave like a high compliance mechanical spring system. One is the 'card-house-type' microstructure; the other is the connected form of mica crystals. This is why mica glass ceramics can recover their shape 5 to 20 times better than ordinary polycrystalline ceramics. Based on these results, this paper describes a guideline for designing the shape-memory ceramics and shape-memory composite materials.