Volume 43, Issue 12

In the present study we investigate microstructures of NiTi-based shape memory alloys (SMAs) using scanning electron microscopy (SEM) in combination with mechanical polishing and electropolishing. The results show that electropolishing is quite useful for microstructural characterization of NiTi-based SMAs revealing morphologies of second phases, characteristic features of eutectic regions, growth mechanisms of primary carbides and coarsening of second phases. Furthermore, three-dimensional morphologies of martensitic variants, twins, and substructures can be identified in electropolished high temperature SMAs like NiTiHf and NiTiZr.

Kurzfassung Dünne kornwachstumsresistente Tantaldrähte werden zur Herstellung von elektrischen Tantalkondensatoren verwendet. Um den Herstellungsprozess zu optimieren, ist es wichtig, die Mikrostruktur von dotiertem Tantal nach unterschiedlichen Herstell- bzw. Wärmebehandlungsschritten zu untersuchen. Dies setzt jedoch voraus, dass eine geeignete artefaktfreie Präparationsmethode für dotiertes Tantal vorliegt, beziehungsweise die bestehenden Methoden verbessert werden. In der vorliegenden Arbeit werden optimierte Präparationsmethoden für licht- und rasterelektronenmikroskopische Untersuchungen vorgestellt. Neben der Beschreibung der Probenpräparation wird auch auf die wichtigsten Ergebnisse der anschließenden mikrostrukturellen Untersuchungen eingegangen.

The impact tensile test was carried out on hot-rolled commercially pure titanium at temperature from 293 K to 77 K. The microstructures after fracture were examined by transmission electron microscope to determine the deformation modes. Strength and ductility increase with decreasing temperature from 293 K to 77 K. The investigation on the microstructure shows that slip cooperates with twinning in the deformation, and twinning becomes more active at lower temperature. At high strain rate titanium exhibits obvious strain hardening and twinning plays an important role in strain hardening. {1012} twin is identified in the microstructure at room temperature and three types of twins were identified at 77 K, which are {1011}, {1012}, {1121} twins.