Phase transformations and local deformation mechanisms - A case study on Cu 20 m.% Sn

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Investigating thermally activated deformation mechanisms by high temperature nanoindentation – A Study on W-Re alloys

Since the advent of indentation at elevated temperatures the technique of high-temperature nanoindentation has been further developed, currently enabling testing temperatures above 1000 °C. Due to small sample sizes and a variety of different testing techniques this method provides the opportunity for alloy development at a new level regarding composition variety or efficiency. In this study the thermally activated deformation mechanisms in binary W-Re alloys will be investigated by using a high-end in-situ nanoindenter. For that purpose, three different materials were tested, namely commercially pure W, W5Re and W10Re, all of them in both, coarse grained and ultra-fine grained condition. Nanoindentation experiments were conducted from ambient temperatures up to 800 °C, thereby overcoming the critical temperature TC of tungsten at around 450 °C. With temperature increments of 100 °C a large range of the normalized temperature with respect to TC is covered, allowing general conclusions regarding the appearing deformation mechanisms in bcc metals. Additionally to constant indentation strain rate tests, strain rate jump tests were utilized to determine the mechanical properties and to evaluate the impact of temperature and microstructure on rate-dependent parameters. A strong influence of the alloying level with Re as well as the grain size on both, the thermal and athermal contribution to the flow stress, is observed. The origin and effects, such as solid solution softening for W5Re at temperatures far below TC, will be discussed in detail. Furthermore, the dominating deformation mechanisms in dependence of temperature and grain size are determined. In the coarse grained materials a change in deformation processes from kink-pair mechanism to dislocation-dislocation interaction at higher temperatures can be observed, while in ultra-fine grained materials grain boundary/dislocation interactions are responsible for the maintained time-dependent mechanical behavior

High-Temperature Nanoindentation of an Advanced Nano-Crystalline W/Cu Composite

The applicability of nano-crystalline W/Cu composites is governed by their mechanical properties and microstructural stability at high temperatures. Therefore, mechanical and structural investigations of a high-pressure torsion deformed W/Cu nanocomposite were performed up to a temperature of 600 °C. Furthermore, the material was annealed at several temperatures for 1 h within a high-vacuum furnace to determine microstructural changes and surface effects. No significant increase of grain size, but distinct evaporation of the Cu phase accompanied by Cu pool and faceted Cu particle formation could be identified on the specimen′s surface. Additionally, high-temperature nanoindentation and strain rate jump tests were performed to investigate the materials mechanical response at elevated temperatures. Hardness and Young′s modulus decrease were noteworthy due to temperature-induced effects and slight grain growth. The strain rate sensitivity in dependent of the temperature remained constant for the investigated W/Cu composite material. Also, the activation volume of the nano-crystalline composite increased with temperature and behaved similar to coarse-grained W. The current study extends the understanding of the high-temperature behavior of nano-crystalline W/Cu composites within vacuum environments such as future fusion reactors