Fatigue of Cr-Mo-Si alloys
Project manager: M.Sc. David Heyerhoff
Motivation
Currently, as part of the GRK 2561 MatCom-ComMat research group at the IAM-WK of the Karlsruhe Institute of Technology, Cr-Mo-Si alloys are being investigated for use in high-temperature components due to their promising mechanical properties at room temperature and excellent oxidation and nitridation behaviour at elevated temperatures [1]. However, their brittle failure behaviour at low and intermediate temperatures poses a key limitation, rendering the material's mechanical reliability difficult to predict [1,2]. While these alloys exhibit noticeable compressive plasticity, their mechanical response under tensile loading remains unstudied to date. Nonetheless, the high strain-hardening rate observed under compression suggests potential for plastic deformation under tensile conditions [1,2].
To make Cr-Mo-Si alloys suitable for industrial applications, a systematic characterization of the material’s mechanical properties and effect of the respective microstructure is required [4].
In particular, for potential use in heavily loaded aerospace components, a precise description of the material’s behaviour under cyclic tensile loading is of central importance [6]. While the deformation behaviour under compressive loading has already been the subject of studies, the mechanical response of the material under tensile loads, as well as under cyclic loading, has not yet been analysed [1,2,7]. Therefore, this work aims to test refractory Cr-Mo-Si alloys under service-relevant tensile and fatigue loading and to determine the influence of microstructure on the failure mechanisms.
Methodology
A detailed understanding of the relationship between microstructure and failure mechanisms forms the basis for targeted materials development [3]. To this end, comprehensive materials characterization is conducted, combining microstructural analysis with mechanical testing. The experimental framework integrates scanning electron microscopy (SEM) methods, chemical analysis, and hardness measurements with quasi-static mechanical testing, including three-point and four-point bending, compression, and tensile tests. The resulting data serve to identify the microstructural factors governing the material's mechanical response and failure behaviour.
The experimental determination of failure behaviour requires a sequential testing approach: First, quasi-static bending and tensile tests are conducted to determine strength, modulus of elasticity, and elongation at break under monotonic loading. Knowledge of these static limit and deformation values is then an essential prerequisite for the precise parameterization of the subsequent fatigue tests [3,4,5].
Since, in Cr-Mo-Si alloys, twinning—in addition to dislocation motion—makes a significant contribution to the deformation behaviour, the microstructure is to be specifically adjusted using suitable heat treatment processes [1]. The goal is to maximize material deformation while simultaneously minimizing damage development in the material.
To characterize the fatigue behaviour of Cr–Mo–Si alloys, systematic cyclic fatigue tests are planned. These experimental investigations are intended to record the cyclic material response under alternating mechanical stress in order to subsequently analyse the fatigue mechanisms that occur in relation to the respective microstructural configuration.
Working Area & Research Group
The project will be conducted within the Graduate Research Training Group MatCom-ComMat (Project 13) at the Karlsruhe Institute of Technology (KIT). Its research is focussed on material characterization and material failure characteristics of refractory Cr-Mo-Si alloys.
Funding
Graduate School 2561 "Materials Compounds from Composite Materials" (MatCom-ComMat) by Deutsche Forschungsgemeinschaft.
Bibliography
[1] Hinrichs, F., Winkens, G., Kramer, L. K., Falcão, G., Hahn, E. M., Schliephake, D., ... & Heilmaier, M. (2025). A ductile chromium–molybdenum alloy resistant to high-temperature oxidation. Nature, 646(8084), 331-337.
[2] Zander, L., Kerbstadt, M., White, E. M., & Galetz, M. C. (2025). Cr-based high temperature alloys-The strengthening effect of molybdenum on chromium-silicon alloys. International Journal of Refractory Metals and Hard Materials, 132, 107287.
[3] Macherauch, E. (1970). Praktikum in Werkstoffkunde (Vol. 7). Braunschweig: Vieweg.
[4] Raj, S. V., Whittenberger, J. D., Zeumer, B., & Sauthoff, G. (1999). Elevated temperature deformation of Cr3Si alloyed with Mo. Intermetallics, 7(7), 743-755