high strain RAte, TEmperature and Small-scale mechanical properties of materials – RATES

The project puts together a unique collection of expertise in nanomechanical testing (LTDS & LGF) and small scale simulations of mechanical properties (LaMCoS & SIMaP). RATES will take advantage of the original nanoindentation set-up designed to perform measurements up to 1000 °C in LTDS (bought in 2019, only a few exists in the world) and of the micro-pillar compression set-up of LGF updated to allow measurements up to 1000 s-1. It is worth noting that these cutting-edge devices ask for intense development efforts to make possible measurements of small-scale behaviours of materials under such extreme conditions, which is the aim of tasks T1 & T2.
Only a few being known about the materials response in such conditions, small-scale computational modelling will be used to interpret the results. Development of such computational models (Discrete Dislocation Dynamics, extended Molecular Dynamics) will be the aim of tasks T3 & T4.
The task T5 will be dedicated to the investigation of the relation between small scale materials properties, high strain rate and high temperature for the two kinds of materials investigated. For that purpose both micro-pillar compression and nanoindendation tests will be run. FIB-TEM characterization will also be required.
It has to be noted here that we will restrict our project to “model” materials : FCC Copper or Nickel single crystals provided by LGF and metallic glasses (CuXZrY) provided by SIMaP. Applications of these techniques to more complex (industrial) materials will be treated in a second step, once a significant level of maturity has been reached thanks to the RATES project. This will be within a framework including industrial partners that have already expressed their interest for this kind of measurements.

The first 18 months of ANR RATES were mainly devoted to experimental developments.
Regarding high temperature indentation, a new method called High Temperature Scanning Indentation (HTSI) was developed as part of the thesis of Gabrielle Tiphene (PhD0). This method allows to follow the evolution of mechanical properties of materials (hardness, modulus of elasticity, sensitivity to the strain rate) along predefined thermal ramps. It is based on the use of fast indentation cycles (< 1s) designed to measure the desired properties, inspired by the work developed in this field by the LTDS and the LGF for over 10 years now. The evolution of mechanical properties being intrinsically linked to the evolution of the microstructure of materials, the HTSI technique can be seen as a complementary technique to DSC or X-ray diffraction, to track the transformation (or stability) of materials in temperature and which is adapted to materials at small scales (thin films, gradient materials).
The first results have already been published in two publications during these 18 months, one on the method itself and its application to the recrystallization of metals, the other on the monitoring of the crystallization of thin layers of metallic glasses at temperature. The method is now fully operational up to temperatures of 600°C (or even 800°C) and work is continuing on the metallurgical modelling aspect to quantify the kinetics of microstructural evolution as a function of the materials.
Regarding the high strain rate component, a new mechanical characterization micro-test inspired by macroscopic shear-compression tests has been developed. This one is based on the micro-machining of notches on micropillars in order to induce a localization of the deformation in a small volume of material during the micro-compression. Thus, the deformation and the deformation speed are multiplied. This method has been validated on silica micropillars (amorphous materials well known by the members of the consortium) allowing to go up to speeds of 2 000 /s but the objective of 10 000 /s is clearly attainable and can even be exceeded. This work has been published. Work is continuing on increasing the capabilities of the device in terms of acquisition speed, steering and indentation speed in the context of the thesis Benédicte Adogou.

In parallel with these experimental developments, the first modeling work «at the right scale« could start. A microcompression model based on discrete dislocation dynamics (Tridis software developed by Marc Fivel, SIMAP) has been designed by Bénédicte Adogou and will soon be used to study the effects of strain rate in copper (face-centered cubic structure) and in iron (face-centered cubic structure) Meta-dynamic simulations, to study strain rate effects in amorphous materials, are also under development at LaMCoS (Matias Sepulveda).

Outstanding features:

The development of the HTSI (High Temperature Scanning Indentation) method and its potential for applications in materials science and tribology with first proofs of concept on the (re)crystallization of aluminum alloys, copper alloys and thin film metallic glasses. This innovative method already shines academically through the invited papers of ANR RATES members and new collaborations in the making.

The development of micro-shear tests: this work is now taking on a life of its own in the field of tribology through the CISASURF project (Labex Manutech-SISE, 2021-2023) which has benefited from the developments made in RATES.

The recruitment and assignment of Szilvia Kalacska (CR CNRS) to LGF in 2021 to work on micromechanical tests under extreme conditions, in line with the developments made in RATES, with an additional component on durability under aggressive environments. SK has just been awarded the ANR JCJC project entitled INSTINCT.

1. Tiphéne, Gabrielle, et al. «High-Temperature Scanning Indentation: A new method to investigate in situ metallurgical evolution along temperature ramps.« Journal of Materials Research 36.12 (2021): 2383-2396.
2. Comby-Dassonneville, Solene, et al. «Real-time high-temperature scanning indentation: Probing physical changes in thin-film metallic glasses.« Applied Materials Today 24 (2021): 101126.
3. Guillonneau, Gaylord, et al. «Plastic Flow Under Shear-Compression at the Micron Scale-Application on Amorphous Silica at High Strain Rate.« JOM 74.6 (2022): 2231-2237.

Investigating small mechanical properties of materials under extreme conditions, such as high strain rate and/or high temperature, is of primary importance regarding the upcoming challenges in tribology and materials processing in the framework of energy efficiency. The RATES project proposes a coupled experimental/numerical approach to pave the way in this very broad but exciting field. It lies on new and almost unique experimental facilities developed by the different partners as well as their expertise in small-scale simulations (Molecular Dynamics, Discrete Dislocation Dynamics). Beside the goal of developing nanomechanical characterization methods up to extreme conditions that have almost never been reached before, this project will help to address some rising scientific issues, such as the effect of high strain rate/temperature on size effects in metallic single crystals or in inorganic glasses.