Fracture behaviour of Ti - 50.7 Ni under plain strain conditions

A. BARUJ; J. FRENZEL; CH. SOMSEN; G. EGGELER

Munich

Congreso; Materials Week 2004; 2004

Werkstoffwoche Tagungsbüro

Studies on the fracture mechanisms of NiTi alloys have been mainly performed on small samples or devices where plain stress conditions prevail. The present study focuses on the fracture characteristics of NiTi bulk samples in the as-cast and processed conditions. Understanding the fracture behavior of the as-cast material is necessary to optimize all subsequent steps of processing such as rolling, swaging or wire drawing. In addition, knowing the fracture properties of the processed material is important to predict the service life of components. We are also interested in studying the possible formation of martensite under a triaxial stress state such as the one occurring at the tip of a growing crack. A Ti – 50.7 Ni (at. %) alloy containing low impurity levels has been selected in order to have fully austenitic at ambient temperature. The critical stress intensity level resulting from fracture experiments on fatigue pre-cracked as-cast CT samples is near 20 MPa m. X-ray diffraction experiments and electron microscopy observations of the fracture surface are carried out in order to study the occurrence of martensitic transformation during the fracture process.