Materials

Surface modification of titanium alloy for biomedical application, Image: Alicona measurement, Claudia Ramskogler 2015 - ©TU Graz / IMAT

The materials development group represents an interdisciplinary team, working on the alloy development as well as the optimisation of production and processing technologies of high performance metallic materials. The objectives of our activities are the characterisation, understanding and modelling of the relationships between microstructure and mechanical properties in order to design new alloys exhibiting optimal properties with regards to service conditions. Of special interests are materials, providing high strength and/or toughness for applications under extreme conditions (e.g. high temperature applications). Most advanced experimental characterisation techniques are applied together with new sophisticated modelling tools, in order to characterize the mechanical and structural properties.

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Creep restistant materials

Since the 1980’s the Institute for Materials Science and Welding is a well-established partner in numerous National, European and International projects in the field of materials development for thermal power stations. For such applications, the microstructure and the related creep resistance of the used materials play a crucial role. The main working fields are:

To design new alloys (optimise the chemical composition and find the optimal process chain)
To investigate the creep behaviour of creep resistant steels and Nickel-based alloys
To improve the understanding of creep mechanisms
To analyse the microstructure evolution along process chain and during creep loading
To study the damage of creep exposed welded joints
To model the microstructure evolution during production and in service (phase transformation and precipitation kinetics).

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Thermo-mechanical processing

Metallic parts are generally submitted to thermomechanical treatments mainly to achieve certain desired shapes and properties. The deformation parameters such as temperature, strain rate and the number of steps have a direct influence on the microstructure and on the precipitation state with direct impact on the mechanical properties of the final product. Optimization of the whole process is done by finding a compromise between cheap and easy thermomechanical treatments stages to achieve both the required shape and desired mechanical properties for the product without damage.

The main objectives of the thermomechanical group are:

to optimize thermomechanical processing such as forging, rolling, continuous casting and heat treatments from the energetic point of view
to find the optimal temperature, strain, strain rate, holding time and heating/cooling rates combination to achieve desired mechanical properties (microstructure engineering)
to model physically and phenomenologically the microstructural changes and flow response as a function of the processing parameters
to study and avoid damage during thermomechanical processing
to describe the dynamic and static mechanisms which lead to softening (recrystallization, recovery, coarsening, etc.) as well as the ones which result in hardening (precipitation, cold deformation, among others)

The group works with:

Materials: low alloyed steels and titanium, aluminium and magnesium alloys
Characterization methods (more information click here):
- Microstructure characterization: metallography using LOM, SEM, EBSD, TEM (the last two in cooperation with FELMI and USTEM) ; 3D characterization and phase characterization by means of synchrotron radiation (ESRF, DESY)
- Thermomechanical simulators: Beta, Gleeble ®3800, Bähr dilatometer
- Mechanical testing: Zwick 250 universal machine, EMCO test hardness,
Modelling and simulation tools: FEM by means of DEFORMTM, cellular automata, precipitation kinetics with MatCalc

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Kinetics precipitation of phase transformation

Precipitates are the most promising way to increase the creep resistance of creep-exposed steels and alloys. The size and the amount of precipitates drastically influence the strength of such materials. The Institute for Materials Science and Welding is able to predict the phase fraction, size and amount of different precipitate classes after various heat treatments and for different chemical compositions. To do so, the precipitation kinetics-software MatCalc is used for the calculation of the evolution of the precipitates as a function of aging time and temperature. Phase transformations are handled in terms of phase diagrams and phase fraction diagrams.

Our long lasting experience in the field of precipitation kinetics makes us able to predict the evolution of precipitates and different phases in many steels and alloys on a profound basis.

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