Microstructure tailoring; Solid-state transformation; secondary carbide precipitation

• Applicant: Dr.-Ing. Maria Agustina Guitar
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins ; Synthesis and Properties of Functional Materials
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 466487393

The strengthening of materials can be improved by many different mechanisms. Some of them (e.g., Orowan mechanism or Zener effect) are directly related to the presence of second phase (SP) particles, wherein, their volume fraction, morphology, size, and distribution play a funda-mental role. These parameters can be controlled during the material production (e.g., metal matrix composites) or during heat treatment (HT) processes, where the particles are forced to precipitate, as in the case of white cast irons. In these materials, controlling the SP particle features is the major and challenging task, especially those related to the shape and distribu-tion, since they are dominated by thermodynamic and kinetic parameters that include chemical composition, temperature, cooling/heating rate, etc. The major focus of this work will be devot-ed in designing a multi-step HT using thermodynamic and kinetic calculations, for tailoring the microstructure of high chromium cast irons (HCCI). HCCI presents a fairly complex multi-component and multiscale microstructure with a matrix capable of being hardened by both phase transformation and the precipitation of SP particles. These materials can be considered as a kind of ‘composite’, from the point of view of the mechanical interaction between the di-verse components. All these features, added to its chemical composition (which can be simpli-fied to a ternary Fe-C-Cr system), makes these class of materials feasible to be used for the study of microstructural tailoring, carbide precipitation, and the associated characteristic strengthening mechanisms. The objective of the present project is focused on tailoring and predicting the microstructure of HCCI to ensure the best properties and material response with the aim of customizing the alloy for engineering components subjected to strong-abrasive con-ditions. We aspire to design the thermal treatments by combining thermodynamic and kinetic calculations with experimental work, for tailoring the microstructure of HCCI (16 wt.% Cr and 26 wt.% Cr). Subsequently, the results obtained can be used as a steppingstone for transferring the gained knowledge to materials of the same family with different chemical compositions and varied initial microstructures. From this point of view, it will be possible to vary and control several critical processes in the microstructural design, such as the carbon partitioning, car-bide precipitation and final matrix morphology with emphasis placed on understanding the un-derlying precipitation characteristics and the strengthening mechanisms, for an optimal per-formance. The design of the HT, focused in controlling the amount of retained austenite, and fraction, size and distribution of SC, will be implemented at the laboratory scale in combination with an extensive microstructural, mechanical and tribological characterization.

• DFG Programme: Research Grants