NSUF 18-1412: Irradiated Microstructure Evolution in Cast Compared to PM-HIP Alloy 625
The objective of this study is to determine the influence of processing method – casting or powder metallurgy with hot isostatic pressing (PM-HIP) on the irradiated microstructure evolution in Alloy 625. Recently, PM-HIP alloys have been developed and introduced for pressure-retaining applications in the electric power industry. PM-HIP alloys exhibit excellent structural uniformity, no chemical segregation during processing, superior mechanical properties, and enhanced weldability as compared to conventional cast or forged alloys. In addition, PM-HIP components are produced near-net shape, which offers distinct advantages of minimizing the need for machining and enhancing the ease of component inspectability. Because of these exceptional properties and features, PM-HIP alloys are of interest to the nuclear power industry as potential structural materials for light water reactors (LWRs), advanced LWRs (ALWRs), small modular reactors (SMRs), and advanced (e.g. Generation IV) reactors. NSUF is supporting neutron irradiation qualification of PM-HIP alloys through the ongoing project “Irradiation Influence on Alloys Fabricated by Powder Metallurgy and Hot Isostatic Pressing for Nuclear Applications”. In advance of the neutron irradiated samples being available for post-irradiation examination (PIE), NSUF has also supported accelerated ion irradiations of PM-HIP alloys as a scoping study to enable a more informed and strategic PIE effort of the high-value neutron irradiated specimens once they become available. Now, this proposal seeks to conduct the necessary PIE of these ion irradiated PM-HIP alloys, leveraging previous NSUF investments.
In this project, we will compare the irradiated microstructure in PM-HIP Inconel alloy 625, to that of the cast (i.e. conventionally fabricated) counterpart. Although Ni-base alloys, including IN625, are not known for irradiation tolerance, their high temperature corrosion resistance has made them candidates for in-core components of Generation IV plants and SMRs, where they will receive high irradiation doses. As such, their microstructural response to irradiation must be understood, and has accordingly been noted as a high-priority knowledge gap in a 2012 Electric Power Research Institute report, justifying the purpose of the work proposed herein. Thus far, we have conducted a scanning electron microscopic (SEM) investigation of the cast and PM-HIP IN625; electron backscatter diffraction (EBSD) grain orientation mapping has revealed a refined grain size and more twinning in the PM-HIP version. Because of the finer grain structure in PM-HIP IN625, which serves as a strong point defect sink, we hypothesize that: (1) the PM-HIP alloy will be more resistant to void and dislocation loop nucleation than the cast alloy, but that (2) the PM-HIP alloy will exhibit more radiation-induced segregation (RIS). Our design of experiments enables a thorough investigation of this hypothesis, by characterizing microstructure evolution in PM-HIP and cast IN625 following 5 MeV Ni+ ion irradiation at 450°C to 50, 100, and 200 displacements per atom (dpa). Transmission electron microscopy (TEM) will allow us to ascertain the relationship between grain boundary sink strength, RIS, and void and loop nucleation. More broadly, we will gain some of the first insight into the effect of processing method on irradiated microstructure evolution, enabling more scientifically informed studies of forthcoming neutron irradiated PM-HIP materials.
Additional Info
| Field | Value |
|---|---|
| Abstract | The objective of this study is to determine the influence of processing method – casting or powder metallurgy with hot isostatic pressing (PM-HIP) on the irradiated microstructure evolution in Alloy 625. Recently, PM-HIP alloys have been developed and introduced for pressure-retaining applications in the electric power industry. PM-HIP alloys exhibit excellent structural uniformity, no chemical segregation during processing, superior mechanical properties, and enhanced weldability as compared to conventional cast or forged alloys. In addition, PM-HIP components are produced near-net shape, which offers distinct advantages of minimizing the need for machining and enhancing the ease of component inspectability. Because of these exceptional properties and features, PM-HIP alloys are of interest to the nuclear power industry as potential structural materials for light water reactors (LWRs), advanced LWRs (ALWRs), small modular reactors (SMRs), and advanced (e.g. Generation IV) reactors. NSUF is supporting neutron irradiation qualification of PM-HIP alloys through the ongoing project “Irradiation Influence on Alloys Fabricated by Powder Metallurgy and Hot Isostatic Pressing for Nuclear Applications”. In advance of the neutron irradiated samples being available for post-irradiation examination (PIE), NSUF has also supported accelerated ion irradiations of PM-HIP alloys as a scoping study to enable a more informed and strategic PIE effort of the high-value neutron irradiated specimens once they become available. Now, this proposal seeks to conduct the necessary PIE of these ion irradiated PM-HIP alloys, leveraging previous NSUF investments. In this project, we will compare the irradiated microstructure in PM-HIP Inconel alloy 625, to that of the cast (i.e. conventionally fabricated) counterpart. Although Ni-base alloys, including IN625, are not known for irradiation tolerance, their high temperature corrosion resistance has made them candidates for in-core components of Generation IV plants and SMRs, where they will receive high irradiation doses. As such, their microstructural response to irradiation must be understood, and has accordingly been noted as a high-priority knowledge gap in a 2012 Electric Power Research Institute report, justifying the purpose of the work proposed herein. Thus far, we have conducted a scanning electron microscopic (SEM) investigation of the cast and PM-HIP IN625; electron backscatter diffraction (EBSD) grain orientation mapping has revealed a refined grain size and more twinning in the PM-HIP version. Because of the finer grain structure in PM-HIP IN625, which serves as a strong point defect sink, we hypothesize that: (1) the PM-HIP alloy will be more resistant to void and dislocation loop nucleation than the cast alloy, but that (2) the PM-HIP alloy will exhibit more radiation-induced segregation (RIS). Our design of experiments enables a thorough investigation of this hypothesis, by characterizing microstructure evolution in PM-HIP and cast IN625 following 5 MeV Ni+ ion irradiation at 450°C to 50, 100, and 200 displacements per atom (dpa). Transmission electron microscopy (TEM) will allow us to ascertain the relationship between grain boundary sink strength, RIS, and void and loop nucleation. More broadly, we will gain some of the first insight into the effect of processing method on irradiated microstructure evolution, enabling more scientifically informed studies of forthcoming neutron irradiated PM-HIP materials. |
| Award Announced Date | 2018-05-17T11:00:31.673 |
| Awarded Institution | Idaho National Laboratory |
| Facility | Advanced Test Reactor |
| Facility Tech Lead | Alina Zackrone, Catou Cmar |
| Irradiation Facility | None |
| PI | Janelle Wharry |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1412 |