Influence of twinning effects and grain size distribution on the crack propagation behavior of medium-entropy alloy CrCoNi through severe plastic deformation and heat treatment

• Applicant: Professor Dr.-Ing. Thomas Lampke
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 468469638

In more than 90% of cases, cyclic loading is the cause of component failure. In addition to fatigue strength, crack propagation resistance is of decisive importance for the technical applicability of a material. In order to further develop materials, it is necessary to intervene conceptually in the microstructure. Established approaches mainly consist of alloys with one property-determining base element. However, this classical alloyconcept has already reached its limits, while high-entropy alloys (HEAs) and medium-entropy alloys (MEAs) offer further potential for new developments. One promising representative of this alloy concept for application under cyclic loading is the MEA CrCoNi. On the one hand, it exhibits one of the highest measured fracture toughness values compared to established alloys, and on the other hand, CrCoNi is characterized by a high fatigue threshold. This is significantly influenced by both the chemical composition of the alloy and by the targeted introduction of lattice defects. In particular, the second aspect allows for the microstructure of a material to be tailored to the specific application. For this reason, the research focus is on microstructure adjustment in the CrCoNi system through severe plastic deformation in combination with a heat treatment route tailored to this process. The aim is to identify property-relevant microstructure elements for influencing the threshold value and to assess their influence as a function of the proportion in the microstructure. Thus, microstructure elements such as twins, grain size and their distribution as well as their interaction with other lattice defects, e.g. stacking faults, can be investigated in terms of their effect on the threshold against crack propagation. In particular, the effect of twins (twin (bundle) width, spacing, and orientation) will be determined, as these play a decisive role in the development of fatigue-resistant materials. In this way, structure-property relationships can be derived, providing a database for the development of a future qualitative as well as quantifiable model.

• DFG Programme: Research Grants