Talk given by Dr. Julia Ivanisenko Abstract: Nanomaterials have properties that are dominated by surfaces and interfaces. As a rule such materials are crystalline, but recently a novel concept of amorphous materials with nanometer-size internal structure - nanoglasses, was introduced. In regard to the mechanical properties, nanomaterials reveal specific deformation behavior. Nanocrystalline materials being compared with their coarse grained counterparts demonstrate a pronounced compression-tension asymmetry, an extended microplasticity stage, an inverse Hall-Petch relationship, strain induced grain growth and a strong temperature dependence of the flow stress. The development of these features is related to the difficulty for dislocations to nucleate and to propagate in very small grains, which leads to the emergence of an unusual deformation mechanism – grain boundary sliding (GBS). Metallic nanoglasses demonstrate the enhanced plasticity as compared with rapidly quenched glasses due to the occurrence of multiple intersecting shear bands. By contrast, in rapidly-quenched samples only a single shear band is typically observed. Nanomaterials can be produced using a variety of methods, which can be divided into two large groups. Bottom-up methods include inert gas condensation, deposition of layers, chemical or microwave plasma syntheses, and top-down methods are generally based on the application of severe plastic deformation (SPD) involving heavy straining under a high imposed pressure for microstructure refinement in bulk metals and alloys. Furthermore, SPD offers a powerful tool for microstructure design on different hierarchical levels. In addition to grain size refinement, it also enables mechanically driven phase transformations with formation of metastable phases, grain boundary design and texture formation. For example, using high pressure torsion (HPT) technique, the nano-structuring of ferrite, dissolution of carbides and formation of grain boundary segregations of carbon was achieved in a plain carbon steel. As a result, HPT-processed nano-steel has record-breaking strength and fatigue life endurance. In this respect up-scaling of HPT is a necessary condition for industrial processing of advanced nanocrystalline materials. The technical approach is currently being developed, it will allow the continuous processing of long rods.

This event is part of the eventgroup INT Talks

Homepage
https://www.int.kit.edu/events.php

Speaker
Dr. Julia Ivanisenko

Karlsruhe Institute of Technology (KIT)
Institute of Nanotechnology (INT)

Organizer
Prof. Dr.-Ing. Horst Hahn
Institute of Nanotechnology (INT)
Karlsruhe Institute of Technology (KIT)
Eggenstein-Leopoldshafen
Mail: horst hahn ∂does-not-exist.kit edu

Targetgroup
Interested / Everyone