NSUF 17-922: Effect of grain boundary character and surface treatment on irradiation tolerance of nuclear alloys
The objective of this project is to determine the influence of the grain boundary character distribution (GBCD) and surface treatments on irradiation resistance. Tailoring the GBCD by increasing the volume fraction of special coincident site lattice (CSL) boundaries, particularly S3 and related boundaries, can substantially enhance a material’s strength, stress corrosion cracking (SCC) resistance, and oxidation resistance. There is a growing interest in implementing tailored GBCDs to nuclear-relevant austenitic steels and Ni-base alloys to reduce their SCC and IASCC susceptibility. One of the most common means of tailoring the GBCD is via grain boundary engineering (GBE), but the resultant CSL boundaries, especially S3 coherent twins, though resistant to RIS, void denuded zones and corrosion are remarkably poor sinks for irradiation defects. How the irradiation behavior is altered at grain boundaries of various types (from special to random) is not well understood at all. Surface treatments such as laser shock peening (LSP) and ultrasonic nanocrystal surface modification (UNSM) can tailor compressive residual stresses and the GBCD while also producing surface nanocrystalline grains, which are known to promote radiation tolerance. The main objective of this project is to gain new scientific insights into how grain boundary character, surface grain size and residual stress affect the irradiation behavior of a workhorse nuclear alloy.
To meet the objectives of this project, we will compare irradiated microstructures in a Ni-base Alloy 600 untreated specimen, specimens containing a high volume density of CSL boundaries (produced by GBE), and specimens containing both a high volume density of CSL boundaries and nanocrystalline grains (produced by LSP or UNSM). This plan allows us to isolate the roles of GBCD and grain size on irradiation tolerance, leading to a fundamental, mechanistic understanding of irradiation tolerance and sink strength. Specimens have already been irradiated with 2.0 MeV protons at 400°C to 7 displacements per atom (dpa). We will conduct a comprehensive irradiated microstructure and microchemistry characterization on all six specimens using transmission electron microscopy (TEM) and scanning TEM (STEM). The project outcome is a first-of-its-kind understanding of the effect of grain boundary character and surface treatments on irradiation tolerance, enabling science-based design of processing routes to optimize strength, SCC resistance, and irradiation tolerance. It will also generate a database for experimental validation of microstructural models of GBE and surface treated alloys for MARMOT.
Additional Info
| Field | Value |
|---|---|
| Abstract | The objective of this project is to determine the influence of the grain boundary character distribution (GBCD) and surface treatments on irradiation resistance. Tailoring the GBCD by increasing the volume fraction of special coincident site lattice (CSL) boundaries, particularly S3 and related boundaries, can substantially enhance a material’s strength, stress corrosion cracking (SCC) resistance, and oxidation resistance. There is a growing interest in implementing tailored GBCDs to nuclear-relevant austenitic steels and Ni-base alloys to reduce their SCC and IASCC susceptibility. One of the most common means of tailoring the GBCD is via grain boundary engineering (GBE), but the resultant CSL boundaries, especially S3 coherent twins, though resistant to RIS, void denuded zones and corrosion are remarkably poor sinks for irradiation defects. How the irradiation behavior is altered at grain boundaries of various types (from special to random) is not well understood at all. Surface treatments such as laser shock peening (LSP) and ultrasonic nanocrystal surface modification (UNSM) can tailor compressive residual stresses and the GBCD while also producing surface nanocrystalline grains, which are known to promote radiation tolerance. The main objective of this project is to gain new scientific insights into how grain boundary character, surface grain size and residual stress affect the irradiation behavior of a workhorse nuclear alloy. To meet the objectives of this project, we will compare irradiated microstructures in a Ni-base Alloy 600 untreated specimen, specimens containing a high volume density of CSL boundaries (produced by GBE), and specimens containing both a high volume density of CSL boundaries and nanocrystalline grains (produced by LSP or UNSM). This plan allows us to isolate the roles of GBCD and grain size on irradiation tolerance, leading to a fundamental, mechanistic understanding of irradiation tolerance and sink strength. Specimens have already been irradiated with 2.0 MeV protons at 400°C to 7 displacements per atom (dpa). We will conduct a comprehensive irradiated microstructure and microchemistry characterization on all six specimens using transmission electron microscopy (TEM) and scanning TEM (STEM). The project outcome is a first-of-its-kind understanding of the effect of grain boundary character and surface treatments on irradiation tolerance, enabling science-based design of processing routes to optimize strength, SCC resistance, and irradiation tolerance. It will also generate a database for experimental validation of microstructural models of GBE and surface treated alloys for MARMOT. |
| Award Announced Date | 2017-04-26T10:11:03.22 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Yaqiao Wu |
| Irradiation Facility | None |
| PI | Vijay Vasudevan |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 922 |