TY - JOUR A1 - Pelegrina, J.L. A1 - Yawny, A. A1 - Olbricht, Jürgen A1 - Eggeler, G. T1 - Transformation activity in ultrafine grained pseudoelastic NiTi wires during small amplitude loading/unloading experiments N2 - Martensitic phase transformations were studied in ultrafine grained Ni-rich pseudoelastic NiTi wires during cyclic deformation under small imposed strain amplitudes. Small strain variation tests were complemented by a thermographic analysis of the emerging temperature distributions in the specimens. The characteristics of the observed thermal profiles result from the specific phase transitions which take place at different stress levels. Homogeneous temperature changes, corresponding to a non-localized transformation activity along the specimen length, were observed throughout the whole range of applied stresses, starting from values as low as 100 MPa. This behavior is in line with previous literature reports for the stress-induced transformation from B2 austenite to R-phase as long as the critical stress for B19' martensite formation is not reached. In the present study, similar type of transformation activity could also be demonstrated at higher strains/stresses, even after the stress induced transformation to B19' was apparently completed. These findings suggest that transformation activity involving the B2 phase is present throughout the whole pseudoelastic stress–strain cycle; i.e., it is not restricted to the initial loading portion. Finally, non-localized transformation to or from B19' was identified during small amplitude strain variations in the plateau-like coexistence ranges of the pseudoelastic cycle. KW - NiTi shape-memory alloys KW - Pseudoelasticity KW - Stress-induced phase transformations KW - R-phase KW - Thermal analysis PY - 2015 DO - https://doi.org/10.1016/j.jallcom.2015.08.159 SN - 0925-8388 SN - 1873-4669 VL - 651 SP - 655 EP - 665 PB - Elsevier Sequoia CY - Lausanne AN - OPUS4-34012 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pelegrina, J.L. A1 - Yawny, A. A1 - Olbricht, Jürgen T1 - Comment on: "Isothermal nature of the B2-B19' martensitic transformation in a Ti-51.2 Ni (at.%) alloy" N2 - Fukuda et al. published a paper (Scripta Mater. 68 (2013) 984–987) in which they claimed to be able to determine the isothermal nature of the martensitic transformation in a Ti–Ni alloy. They analyzed the evolution of electrical resistance during isothermal holding stages and concluded that the variations were a consequence of the isothermal transition between austenite and martensite. In the following we will demonstrate that the discussed data do not allow the interpretation presented and that the isothermal nature is not proved. KW - Thermal activation KW - Titanium–nickel alloy KW - Shape memory alloy KW - Nucleation PY - 2015 DO - https://doi.org/10.1016/j.scriptamat.2014.10.009 SN - 1359-6462 SN - 1872-8456 VL - 98 SP - 68 EP - 70 PB - Elsevier Ltd. CY - Oxford AN - OPUS4-32401 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Olbricht, Jürgen A1 - Bismarck, Marc A1 - Skrotzki, Birgit T1 - Size effects in miniature specimen creep testing of heat resistant ferritic-martensitic steels N2 - The use of miniaturized specimen geometries in mechanical testing allows extracting the sample material directly from the sidewall of critical components of power plants, like e.g. headers and steam pipes. In this way, both the impacts of the processing of the component (including all shaping and tempering influences) and of the exposure to the complex aging/loading/oxidation conditions in the plant (in case of post-Service tests) can be analyzed and representative mechanical properties are obtained. T2 - CREEP 2015 - 13th International conference on creep and fracture of engineering materials and structures CY - Toulouse, France DA - 31.05.2015 PY - 2015 SP - 163 EP - 164 AN - OPUS4-33528 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Olbricht, Jürgen A1 - Kranzmann, Axel A1 - Skrotzki, Birgit T1 - Metallic high temperature materials for energy applications - current research activities at BAM T2 - 2nd European Steel Technology and Application Days (ESTAD) 2015 CY - Düsseldorf, Deutschland DA - 2015-06-15 PY - 2015 AN - OPUS4-33467 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Olbricht, Jürgen A1 - Bismarck, M. A1 - Skrotzki, Birgit T1 - Size Effects in Miniature Specimen Creep Testing of Heat Resistant Ferritic-Martensitic Steels T2 - 13th International Conference on Creep and Fracture of Engineering Materials and Structures CY - Toulouse, France DA - 2015-05-31 PY - 2015 AN - OPUS4-33466 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Jürgens, Maria A1 - Olbricht, Jürgen A1 - Fedelich, Bernard A1 - Skrotzki, Birgit T1 - FLEXIKON - Teil 2: Ermüdungsverhalten, Schädigungsentwicklung und Lebensdauer von 9-12% Cr-Stählen im zyklischen Kraftwerksbetrieb N2 - Schnelle Lastwechsel führen v.a. in dickwandigen Kraftwerksbauteilen zu starken thermischen und mechanischen Beanspruchungen, da sich hohe Temperaturgradienten über der Wand des Bauteils einstellen. Es ergeben sich komplexe Lastkollektive aus zeitlich veränderlichen Spannungen/Dehnungen und Temperaturen, die formal einer Kombination aus Kriechbeanspruchung, Kriechermüdung und thermomechanischer Ermüdung (TMF) entsprechen. T2 - 47. Kraftwerkstechnisches Kolloquium CY - Dresden DA - 13.10.2015 KW - TMF KW - LCF KW - P91 KW - P92 PY - 2015 AN - OPUS4-35613 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -