The thermomechanical behavior of shape memory alloys is due to a martensitic-austenic phase transition and - at low temperature - to martensitic twinning. In single crystals the transition and the twins can be observed with the naked eye.
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	Cooling of a CuAl14Ni4.2 (wt%) crystal from 60°C to 20°C and appearance of arrow-shaped martensitic twins.(size 5cmx2cm)
	Martensitic plate groups in CuAl14Ni4.2 (wt%) single crystal in austenitic matrix.
	a. through l. Growth and decay of a martensitic arrow in an austenitic matrix upon cooling and subsequent heating.CuAl14Ni4.2 (wt%) single crystal.
	Martensitic arrow in austenitic matrix. CuAl14Ni4.2 (wt%) single crystal.