Determination of the stretch tensor for structural transformations

The transformation stretch tensor plays an essential role in the evaluation of conditions of compatibility between phases and the use of the Cauchy-Born rule. This tensor is difficult to measure directly from experiment. We give an algorithm for the determination of the transformation stretch tensor from x-ray measurements of structure and lattice parameters. When evaluated on some traditional and emerging phase transformations the algorithm gives unexpected results.Comment: 3 figures, 1 tabl

Modulated Martensite: Why it forms and why it deforms easily

Diffusionless phase transitions are at the core of the multifunctionality of (magnetic) shape memory alloys, ferroelectrics and multiferroics. Giant strain effects under external fields are obtained in low symmetric modulated martensitic phases. We outline the origin of modulated phases, their connection with tetragonal martensite and consequences for their functional properties by analysing the martensitic microstructure of epitaxial Ni-Mn-Ga films from the atomic to macroscale. Geometrical constraints at an austenite-martensite phase boundary act down to the atomic scale. Hence a martensitic microstructure of nanotwinned tetragonal martensite can form. Coarsening of twin variants can reduce twin boundary energy, a process we could follow from the atomic to the millimetre scale. Coarsening is a fractal process, proceeding in discrete steps by doubling twin periodicity. The collective defect energy results in a substantial hysteresis, which allows retaining modulated martensite as a metastable phase at room temperature. In this metastable state elastic energy is released by the formation of a 'twins within twins' microstructure which can be observed from the nanometre to millimetre scale. This hierarchical twinning results in mesoscopic twin boundaries which are diffuse, in contrast to the common atomically sharp twin boundaries of tetragonal martensite. We suggest that observed extraordinarily high mobility of such mesoscopic twin boundaries originates from their diffuse nature which renders pinning by atomistic point defects ineffective.Comment: 34 pages, 8 figure

Die nächste industrielle Revolution vorantreiben

Bis vor kurzem war Additive Manufacturing (AM) nichts weiter als eine praktische Möglichkeit für schnelles Prototyping. Heute ist zu erleben, wie sich AM zu einer bahnbrechenden Fertigungstechnologie entwickelt. Oerlikon hat sich zum Ziel gesetzt, die Industrialisierung von AM voranzutreiben. Im kürzlich eröffneten Innovations- und Technologiezentrum in München konzentriert sich das Unternehmen auf Forschung und Entwicklung entlang der gesamten AM-Prozesskette. Um sicherzustellen, dass alle additiv gefertigten Komponenten die erforderlichen geometrischen und mechanischen Eigenschaften bieten, werden Mikroskopie- und Metrologielösungen von Zeiss genutzt. </p

Combinatorial development and discovery of ternary and quaternary shape memory alloys

In dieser Arbeit wurden Methoden der kombinatorischen Materialforschung entwickelt und angewendet, um neue und/oder verbesserte Formgedächtnislegierungen zu erforschen. Für die Herstellung sogenannter Dünnschicht-Materialbibliotheken wurde das Katodenzerstäuben genutzt. Unter Verwendung keilförmiger Multilagenschichten konnten dabei komplette ternäre Legierungssysteme oder große Bereiche quaternärer Legierungssysteme abgeschieden werden. Zu deren Hochdurchsatz-Charakterisierung wurden automatisierte Messverfahren für die Bestimmung der Zusammensetzung (energiedispersive Röntgenanalyse), der Struktur (Röntgenbeugung) und des Phasenumwandlungsverhaltens (temperaturabhängige Widerstandsmessung) eingesetzt. Für die Charakterisierung des Formgedächtniseffektes fand die Biegebalken-Methode (temperaturabhängige Änderung der Schichtspannung) Anwendung und wurde unter Nutzung mikrostrukturierter Si-Biegebalken in Matrixanordnung zu einem parallelen Hochdurchsatz-Messverfahren weiterentwickelt.In the present work, combinatorial materials science methods were developed and applied for the discovery and development of new and/or improved ternary and quaternary TiNi-based shape memory alloys. Using a multilayer wedge-type thin film deposition approach, continuous composition spreads covering complete ternary systems or large portions of the quaternary composition space were fabricated and investigated by high-throughput characterization techniques: namely, automated energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and temperature-dependent resistance measurements (R(T)) for the characterization of thin film compositions, structure and phase transformation properties, respectively. Additionally, the cantilever deflection method was advanced to allow for a parallelized characterization of the temperature-dependent stress change ($\sigma$(T)) of thin-film SMA composition spreads using cantilever array wafers (CAW)

Extending the measurement capabilities of 3D X-ray microscopy to dimensional metrology

In the industry of manufactured and assembled devices, the miniaturization and integration of small components with feature sizes on the order of 10 mm or smaller leads to new demands for inspection measurement systems. There are requirements for higher levels of resolution, precision, and accuracy, ideally with technologies that measure internal features and avoid causing damage to the original device. Three-dimensional (3D) techniques such as X-ray computed tomography (CT) may be used to non-destructively inspect internal geometries, or features, that are difficult to reach (or impracticable to access) with tactile probes. Traditional CT systems are, however, limited in resolution and achievable measurement accuracy. One alternative would be to use higher resolution instruments such as 3D X-ray microscopes and expand their measurement capabilities to the field of high precision metrology. This paper demonstrates how to perform non-destructive inspection in small-scale volumes, using a field-of-view (FOV) of about 5 mm diameter, and achieve dimensional measurements that are highly repeatable and accurate (with deviations from calibrated data within the ±1 μm range). This capability is relevant for the electronic industry, e.g., for measurements of camera modules or injection molded connectors, and for manufacturing highly efficient components, e.g., fuel spraying injectors and additive manufactured components with small internal features