In-situ beobachtung der thermo- und spannungs-induzierten martensitischen phasenumwandlung

Cu_81.8Al_14.0Ni_4.2 (wt.%) single crystals are grown in a self-made furnace by the Bridgman method. The phase transformation austenite ↔ martensite of a single martensite plate in the CuAlNi single crystals are observed by light optical microscopy. We have identified two different forms of metallographic irreversible phase transformation: (i) the transformation martensite → austenite takes place by nucleation of austenite at the middle line between the single martensite variantes upon heating, and (ii) by decay of one of the martensite variantes. Stress-induced martensitic phase transformation of CuAlNi single crystals is observed by use of an in-situ optical observation apparatus. The results show that long before the transformation of the austenite phase becomes macroscopically noticeable, interfaces arise, while the martensitic transformation is completed only at a stress which is much higher than the yield stress.