Phase evolutions and steady state diagrams in ion irradiated nanocrystalline alloys

Under irradiation, the competition between several kinetic processes and their non-linear coupling to a high density of defect phases in nanostructured alloys leads to complex, non-equilibrium open systems which are susceptible to display a wide range of evolutions and microstructures in the long term limit, i.e. steady or quasi-steady state. These states can be systematically represented by building dynamical phase diagrams (DPD) that specify the phases and microstructures an alloy system attain under irradiation, in analogy to how equilibrium phase diagrams work for systems relaxing towards equilibrium. This thesis explores experimentally the formation of such steady or near steady states in dilute, immiscible, nanograined Al-Sb and Cu-Zr alloys under ion irradiation. These systems show the consequences of strong coupling of the solute with point defect fluxes, denoted radiation induced segregation, which had not been previously studied experimentally in this context, and it is identified to be a key kinetic process in the evolution of the microstructure of nanograined alloys. In the Al-Sb system, the steady states are comprised of precipitate phases of varying composition at defect structures such as grain boundaries (GBs) and defect clusters and loops. A novel steady state is identified where the nano-precipitates at the GBs and defect clusters in the grain interior are stabilized under irradiation, i.e. they have a fixed size and composition. This steady state portrays a novel precipitate patterning phenomenon at the GBs, similar to compositional patterning (CP) observed previously in Cu-based immiscible systems but now influenced strongly by the high density of defects. For the Cu-Zr system, the defect microstructure is found to be even more complex with the presence of high density of nanotwins, where the steady states under irradiation portray evolution of amorphous, Zr-rich precipitates at various defect interfaces. This system also evolves to a similar self-organized steady state comprising of discrete amorphous precipitates at the defect phases having similar morphology and composition. Both systems thus acquire an invariant, highly stable nanostructured microstructure under prolonged irradiation, indicating that they are self-healing and highly resistant to additional irradiation.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science & Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Das, Sourav

Contributors dc:contributor

• Bellon, Pascal
• Averback, Robert S
• Shoemaker, Daniel P
• Charpagne, Marie A
• Dillon, Shen J

• Na

Statement dc:rights

• Copyright 2024 Sourav Das

Language dc:language

eng, en

Handle dc:identifier

https://hdl.handle.net/2142/127373

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F127373