Chair of

High Temperature Materials

The complex oxidation behavior of vanadium is the reason why vanadium-based alloys cannot be considered for use at high temperatures, despite their high strength and low density. In addition, vanadate changes very easily between different oxidation states and thus extremely accelerates the high-temperature corrosion of Ni, Co or Fe-based materials, especially when it is present in molten form. This also rules out the use of current vanadium alloys in the environment of these materials.
In order to make vanadium alloys usable at high temperatures, a completely new and innovative approach to oxidation protection with simultaneous oxide particle reinforcement is therefore to be pursued: The development of Mg- and Ca-containing oxide particles for the production of oxidation-resistant ODS vanadium-silicon alloys. The ODS particles introduced in sufficient concentration should prevent liquid phase formation at high temperatures. At the same time, the ODS particles are expected to have a strength-enhancing effect, which is to be quantified in the potential application area of such alloys from room temperature to 1050 °C.
The project aims to clarify (1) up to what volume fraction of MgO, CaO or magnesium orthosilicate particles homogeneous microstructures can be achieved in vanadium materials, (2) how high the necessary MgO, CaO or magnesium orthosilicate concentration is in order to prevent liquid phase formation or to provoke a self-protecting mechanism, (3) how great the strength-enhancing effect of the addition of oxide dispersoids is and how the ODS particles affect creep formation. to provoke a self-protecting mechanism, (3) how great the strength-enhancing effect is through the addition of oxide dispersoids and how the ODS particles affect the creep behavior of vanadium alloys.
This text was translated with DeepL

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Since the CCAs are being actively explored for next-generation structural materials for high-temperature applications and therefore, they should have a high creep resistance besides that a comprehensive understanding of their creep and fracture behaviors is also indispensable.
Among the several anomalies existing in the creep behavior of HEAs, the foremost important is the stress exponent, n, calculated from the Berkovich nanoindentation creep tests turns out to be much larger than that calculated based on the uniaxial stress relaxation and spherical nanoindentation creep tests, and this could not be explained using classical creep theory for crystalline metals. It is still uncertain whether the classical creep theory for conventional metals are applicable for the HEAs.
The Fe32.3Al29.3Cu11.7Ni10.8Ti15.9 CCA, developed by OVGU-HT Materials group – whose compression behavior was studied under a constant displacement test with quasi static strain rate between room temperature (RT) and 1100°C revealed a stable single phase bcc microstructure with precipitates at the grain boundaries. The high temperature deformation and creep behavior of this material will be studied during a 3 months visit of Prof. Puspendu Sahu, Professor of Physics), Jadavpur University, Kolkata, India. In addition, TEM analyses are planned to perform at Jadavpur University with the deformed materials to get insights into the deformation mechanisms.

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The sub-project is related to Engineering Materials to be used in a wide temperature range and under complex mechanical loading. The project will focus on the microstructure/properties relationship of single and multi-phase metallic materials. Theoretical considerations of microstructure evolution or phase stability/transition will be done by Phase-Field Simulation and/or DFT, MD, or other nanoscale-related numerical methods. Mechanical properties will be determined from (micro and nano) indentation, bending, compression as well as creep tests.

A simulation-supported approach shall be used to develop further these materials.

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