title: The effect of severe grain refinement on the damage tolerance of a superelastic NiTi shape memory alloy.
abstract: Nickel-titanium (NiTi) shape memory alloys are widely used for medical components, as they can accommodate large strains in their superelastic state. In order to further improve the mechanical properties of NiTi, grain refinement by severe plastic deformation is applied to generate an ultrafine-grained microstructure with increased strength. In this work comprehensive fracture and fatigue crack growth experiments were performed on ultrafine-grained NiTi to assess its damage tolerance, which is essential for the safe use of this material in medical applications. It was found, that equal channel angular pressing of NiTi for 8 passes route BCincreases the transformation stress by a factor of 1.5 and the yield stress of the martensite by a factor of 2.6, without significantly deteriorating its fracture and fatigue crack growth behavior. The fatigue crack growth behavior at high mean stresses is even improved, with lower fatigue crack growth rates and higher threshold stress intensity factor ranges, however, beneficial contributions from crack closure are slightly reduced.
authors.affiliation: Department of Materials Physics, Montanuniversitaet Leoben, Austria. Electronic address: thomas.leitner@unileoben.ac.at.
authors.forename: Thomas
authors.initials: T
authors.lastname: Leitner
authors.affiliation: Madrid Institute for Advanced Studies of Materials, Madrid, Spain.
authors.forename: Ilchat
authors.initials: I
authors.lastname: Sabirov
authors.affiliation: Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben, Austria.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Pippan
authors.affiliation: Department of Materials Physics, Montanuniversitaet Leoben, Austria.
authors.forename: Anton
authors.initials: A
authors.lastname: Hohenwarter
mesh_terms: D000497:Alloys / Q000032:analysis*; D004548:Elasticity; D008422:Materials Testing; D009532:Nickel; D013314:Stress, Mechanical; D014025:Titanium
chemical_list: D000497:Alloys; D009532:Nickel; D014025:Titanium
keywords: ECAP; Fatigue crack growth; Fracture; NiTi; Severe plastic deformation; Shape memory alloy