Shape memory alloys are fascinating materials, which exhibit the shape-memory effect and a superelasticity not common for ordinary metals. The former effect is the ability to recover automatically a certain shape, whenever the external conditions are identical to those under which the material has been trained. The broad range of applications includes sensors and actuators in medicine and astronautics. The currently used materials (e.g. NiTi) use the temperature as a parameter to trigger the shape change. The incorporated transformations are diffusionless, martensitic phase transitions, for which the crystallographic unit cell undergoes large deformations.