NSUF 14-505: Investigation of Cr segregation and thermal stability and hardening effects of nanoscale solute clusters and a' precipitates in irradiated Fe-Cr alloys
High chromium ferritic/martensitic (F-M) steels are one of the strong contenders for structural components of the next generation of nuclear reactors and future fusion reactors. The long-term use of these steels in intense neutron irradiation environments requires reliable predictions of the evolution of their microstructures and mechanical properties. Developing accurate models that can predict phase transformations, accelerated diffusion, and other irradiation-affected phenomena, requires experimental insight and validation. The structural changes induced by irradiation in Fe-Cr steels, which have been extensively reported, are complex and include Ni and Si clustering, solute segregation to dislocations, grain boundary Cr segregation or Cr depletion. Prior work on multicomponent steels, such as austenitic stainless steels and low alloy ferritic pressure vessel steels, has also revealed a sensitivity of the radiation response to small variations, not only in alloy solute contents, but also trace impurity concentrations. A number of outstanding questions remain concerning the microstructural features, specifically the mechanisms by which they form: radiation induced segregation or radiation enhanced diffusion. Prior work by the PI on a series of neutron irradiated Fe-Cr alloys has demonstrated the impact of using atom probe tomography to determine the phase boundary for the a/a’ decomposition [Bachhav et al. Scripta Materialia 2013], to quantitatively measure dislocation loop distribution and habit planes, and to quantify solute segregation to dislocations, grain boundaries or second phase particles [Bachhav et al. submitted 2014]. Therefore using the same experimental approach in combination with microhardness measurements, the proposed work focuses on quantifying the effects of post irradiation annealing on three Fe-Cr alloys. The objectives of these experiments are 2) to investigate the thermal stability of Si-P clusters and segregation to dislocation loops and their contributions to hardening in Fe-3 and 6Cr, 2) to follow the coarsening kinetics of a’ precipitate to measure Cr diffusion kinetics in fe-18Cr, and 3) to finally establish the origin of Cr segregation to grain boundaries observed after irradiation. The work requested at CAES is limited to the use of the FIB instrument for liftout of small volumes of materials, while initial specimen preparation, atom probe tomography specimen sharpening, and atom probe tomography data collection and analyses will be performed at the PIs institutions. The proposed work directly addresses the programmatic need for developing and benchmarking predictive models for material degradation through quantitative microstructure evolution and microstructure/ hardening relationships.
Additional Info
| Field | Value |
|---|---|
| Abstract | High chromium ferritic/martensitic (F-M) steels are one of the strong contenders for structural components of the next generation of nuclear reactors and future fusion reactors. The long-term use of these steels in intense neutron irradiation environments requires reliable predictions of the evolution of their microstructures and mechanical properties. Developing accurate models that can predict phase transformations, accelerated diffusion, and other irradiation-affected phenomena, requires experimental insight and validation. The structural changes induced by irradiation in Fe-Cr steels, which have been extensively reported, are complex and include Ni and Si clustering, solute segregation to dislocations, grain boundary Cr segregation or Cr depletion. Prior work on multicomponent steels, such as austenitic stainless steels and low alloy ferritic pressure vessel steels, has also revealed a sensitivity of the radiation response to small variations, not only in alloy solute contents, but also trace impurity concentrations. A number of outstanding questions remain concerning the microstructural features, specifically the mechanisms by which they form: radiation induced segregation or radiation enhanced diffusion. Prior work by the PI on a series of neutron irradiated Fe-Cr alloys has demonstrated the impact of using atom probe tomography to determine the phase boundary for the a/a’ decomposition [Bachhav et al. Scripta Materialia 2013], to quantitatively measure dislocation loop distribution and habit planes, and to quantify solute segregation to dislocations, grain boundaries or second phase particles [Bachhav et al. submitted 2014]. Therefore using the same experimental approach in combination with microhardness measurements, the proposed work focuses on quantifying the effects of post irradiation annealing on three Fe-Cr alloys. The objectives of these experiments are 2) to investigate the thermal stability of Si-P clusters and segregation to dislocation loops and their contributions to hardening in Fe-3 and 6Cr, 2) to follow the coarsening kinetics of a’ precipitate to measure Cr diffusion kinetics in fe-18Cr, and 3) to finally establish the origin of Cr segregation to grain boundaries observed after irradiation. The work requested at CAES is limited to the use of the FIB instrument for liftout of small volumes of materials, while initial specimen preparation, atom probe tomography specimen sharpening, and atom probe tomography data collection and analyses will be performed at the PIs institutions. The proposed work directly addresses the programmatic need for developing and benchmarking predictive models for material degradation through quantitative microstructure evolution and microstructure/ hardening relationships. |
| Award Announced Date | 2014-08-11T00:00:00 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Yaqiao Wu |
| Irradiation Facility | None |
| PI | Emmanuelle Marquis |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 505 |