Irradiation-induced nanoclusters and their evolution in compound forming ni-base and cu-base alloys

Lee, Jae Yel

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Description

Title

Irradiation-induced nanoclusters and their evolution in compound forming ni-base and cu-base alloys

Author(s)

Lee, Jae Yel

Issue Date

2016-10-07

Director of Research (if dissertation) or Advisor (if thesis)

Averback, Robert S.

Doctoral Committee Chair(s)

Bellon, Pascal

Committee Member(s)

• Dillon, Shen
• Stubbins, James F.

Department of Study

Materials Science and Engineering

Discipline

Materials Science and Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Irradiation
• clusters
• precipitation
• alloys
• nickel tungsten (Ni-W)
• copper molybdenum silicon (Cu-Mo-Si)
• copper niobium silicon (Cu-Nb-Si)
• silicide
• electron microscopy
• Transmission electron microscopy (TEM)
• Calphad

Abstract

Nanostructured alloys with finely dispersed precipitates are actively studied for designing materials tolerant to irradiation at high temperatures. The challenge is that nanostructures will often coarsen under elevated temperature irradiation or annealing, owing in part to radiation-enhanced diffusion. In this thesis, we propose a scheme to enhance the stability of nanostructure at high temperature or irradiation by forming stable compound formation. Thermal coarsening of precipitates of nominally pure alloy constituents and compounds were systematically studied in three systems: Ni-W binary, Cu-Mo-Si, Cu-Nb-Si ternary. 1) In the Ni-W system, which forms compounds at low temperature but undergoes phase separation at high temperature, pre-irradiation at RT and post-annealing at 850 °C induced finely dispersed nanoprecipitation with a high number density inside grains. The precipitates were identified as carbides, however, these carbides experienced significant coarsening during high temperature annealing. The microstructures of the Cu alloys containing silicide forming constituents were more controllable and expected to have better thermal coarsening resistance. 2) In the Cu-Mo-Si system, where Mo is highly immiscible in Cu and forms stable silicides with Si, Si-rich Mo-Si nanoclusters were induced by RT irradiation. These pre-irradiated alloys revealed remarkable thermal coarsening resistance, which I attribute to a narrow initial particle size distribution, and a significantly reduced solubility of Mo in the Cu-rich matrix, owing to silicide formation, which is predicted by thermodynamic calculations using CALPHAD method. 3) I employed the same strategy to the Cu-Nb-Si system, where the immiscibility between Cu and Nb is less strong than Cu-Mo, and the Nb forms various stable silicides with Si. Si-rich Nb-Si clusters were still induced by RT Kr irradiation despite the reduced immiscibility in the Cu-Nb system, The Si-rich Nb-Si clusters also revealed much improved thermal coarsening resistance in comparison to (nearly) pure Nb in Cu-Nb binary. The findings in Cu-Mo-Si and Cu-Nb-Si demonstrated that coarsening resistance of nanoprecipitates can be significantly enhanced by taking advantage of stable compound formation and it can be used in the design of novel nanostructured materials for high temperature and nuclear application.

Graduation Semester

2016-12

Type of Resource

text

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Copyright 2016 Jae Yel Lee

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