NSUF 16-CINR-10480: Role of minor alloying elements on long range ordering in Ni-Cr alloys
High Cr, Ni-based alloys are an important class of structural materials due to their strength, toughness, and excellent corrosion resistance. Alloy 690 (~Ni-30wt.%Cr-10wt.%Fe) is used extensively in LWRs for steam generator tubing and as a replacement material for reactor control rod drive mechanism assemblies in the reactor pressure vessel head. The Ni-Cr binary system exhibits an ordered phase at temperatures below 590°C at the stoichiometry Ni2Cr. Alloy 690 has a similar Ni to Cr ratio as the ordered Ni2Cr binary and there is concern that an embrittling phase transformation may occur after many years in service. Previous thermal aging studies on Ni-Cr model alloys show that Ni2Cr can order in as little at 2000 hours at 475°C. The addition of Fe to the Ni-Cr binary system suppresses the critical temperature of the ordering transformation. The slow diffusion kinetics at lower temperatures requires long thermal aging to observe any phase transformation. Irradiation provides a way to accelerate the ordering phase transformation in Fe containing alloys while still maintaining a low temperature. This principle has been demonstrated by Frely who used electron irradiation to induce ordering in Ni-Cr-Fe alloys [1, 2]. Frely observed that model 690 alloys containing only Ni, Cr and Fe elements form the Ni2Cr-type ordered phase while commercial alloys irradiated under the same conditions do not. This finding suggests that minor alloying elements (Si, P, Mn, etc.) present in the commercial alloys are playing a critical role in delaying or preventing long range order. The focus of this work is to understand the role of different minor alloy elements in the formation of order phases. Additionally, the range of stability of the ordered phase is investigated by changing the Ni-Cr stoichiometry. This work proposes the irradiation of commercial alloy 690 and model Ni-Cr-Fe-X alloys (where X=Si, P) to understand the role of minor elements and stoichiometry in the ordering phase transformation kinetics. These irradiations will supplement an existing DOE-NEUP project titled “Modeling and Validation of Irradiation Damage in Ni-based Alloys for Long-Term LWR Applications”, which provides PI and student support.
Additional Info
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| Abstract | High Cr, Ni-based alloys are an important class of structural materials due to their strength, toughness, and excellent corrosion resistance. Alloy 690 (~Ni-30wt.%Cr-10wt.%Fe) is used extensively in LWRs for steam generator tubing and as a replacement material for reactor control rod drive mechanism assemblies in the reactor pressure vessel head. The Ni-Cr binary system exhibits an ordered phase at temperatures below 590°C at the stoichiometry Ni2Cr. Alloy 690 has a similar Ni to Cr ratio as the ordered Ni2Cr binary and there is concern that an embrittling phase transformation may occur after many years in service. Previous thermal aging studies on Ni-Cr model alloys show that Ni2Cr can order in as little at 2000 hours at 475°C. The addition of Fe to the Ni-Cr binary system suppresses the critical temperature of the ordering transformation. The slow diffusion kinetics at lower temperatures requires long thermal aging to observe any phase transformation. Irradiation provides a way to accelerate the ordering phase transformation in Fe containing alloys while still maintaining a low temperature. This principle has been demonstrated by Frely who used electron irradiation to induce ordering in Ni-Cr-Fe alloys [1, 2]. Frely observed that model 690 alloys containing only Ni, Cr and Fe elements form the Ni2Cr-type ordered phase while commercial alloys irradiated under the same conditions do not. This finding suggests that minor alloying elements (Si, P, Mn, etc.) present in the commercial alloys are playing a critical role in delaying or preventing long range order. The focus of this work is to understand the role of different minor alloy elements in the formation of order phases. Additionally, the range of stability of the ordered phase is investigated by changing the Ni-Cr stoichiometry. This work proposes the irradiation of commercial alloy 690 and model Ni-Cr-Fe-X alloys (where X=Si, P) to understand the role of minor elements and stoichiometry in the ordering phase transformation kinetics. These irradiations will supplement an existing DOE-NEUP project titled “Modeling and Validation of Irradiation Damage in Ni-based Alloys for Long-Term LWR Applications”, which provides PI and student support. |
| Award Announced Date | 2019-12-17T00:00:00 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | |
| Irradiation Facility | None |
| PI | Julie Tucker |
| PI Email | [email protected] |
| Project Type | CINR |
| RTE Number | 3037 |