Wang, Ling. Sink strength dependent coherency loss of precipitates during in-situ ion irradiation of fcc-structured model binary alloys

Principal Investigator
First Name:
Ling
Last Name:
Wang
Institution:
University of Tennessee-Knoxville
Title:
graduate research assistant
Team Members:
Name: Institution: Expertise: Status:
Ling Wang University of Tennessee-Knoxville Radiation Damage, Coherency Loss of Precipitates Graduate Student
Steven Zinkle University of Tennessee-Knoxville Irradiation-Induced Degradation, Structural Damage Faculty
Experiment Details:
Experiment Title:
Sink strength dependent coherency loss of precipitates during in-situ ion irradiation of fcc-structured model binary alloys
Describe the work that you are proposing in detail. Please include as many specifics as possible (e.g., dose, dose rate, ion energy, types of ions, beam line x-ray energy, irradiation temperature, analysis temperature, atmosphere, etc.):
Three classic fcc-structured (Cu-1at.%Co, Cu-1at.%Fe and Cu-0.4at.%Cr) binary alloys have been heat treated to produce a range of precipitate sink strengths (1013 ~1014 /m2), the coherent interface between the precipitate and the matrix are stated as neutral sink absorbing both interstitials and vacancies [Ref. Gary Was book]. Here, a smaller lattice parameter of a coherent “vacancy” type precipitate can sensor the interstitial type defects easily due to a dilatational strain (negative sign) around the precipitate. These thermally aged alloys will be irradiated at 25 and 350°C with 1MeV Kr ion to a mid-range dose of 1-10 dpa (corresponding fluences: 6×1014-6×1015 ions/cm2), separately. TEM samples will be prepared at University of Tennessee through jet-polish technique to suitable electron-transparent regions, where the thin foil thickness can be measured through thickness fringes under TEM dark field image conditions (average grain sizes are about 100 μm for these model binary alloys, thus, the grain boundary sink strengths can be ignored compared to higher order magnitude of that of initial coherent precipitates). Considering the precipitate number density in each of the binary alloys, tens of precipitates should be visible in the irradiated thin foil at the same time through certain two beam conditions when the sample is suitably tilted in the TEM holder. The selected temperatures will be used to investigate the effect of immobile vacancy clusters as matrix sink in the irradiated regions, since 25 °C is above recovery stage III and below recovery stage V, where monovacancies are mobile, and 350°C is well above recovery stage V, where vacancy clusters are also mobile. Each room temperature irradiation experiment will take one day (6 days for 25°C) since monovacancies are mobile at this temperature and will also act as sink in the matrix, absorbing interstitial defects, resulting in higher dpa dose to cause precipitate coherency loss. Experiment conducted at 350°C will cover a half day for each condition (3 days for 350°C) due to the higher mobility of vacancy clusters, leaving interstitial defects more easily been absorbed by the coherent precipitates other than vacancy clusters. We are expecting to see the coherency loss of the precipitates under high temperatures above specific threshold dose conditions whereas precipitates may remain coherent up to high doses at room temperature. The extra one day will be used to conduct cryo irradiation at 30K where interstitial and vacancy are immobile after the cascade, then sample will be annealed with increasing temperature to find out the recovery stage III temperature for binary alloy system.
Technical Abstract
Irradiation-induced loss of coherency of precipitates can serve as a ‘diagnostic monitor’ providing an indicator of point-defect (PD) cluster migration behavior due to the interaction between mobile PDs and coherent precipitates may induce precipitate coherency loss [1-3]. The precipitate coherency will be judged from the “no contrast line” appears in normal direction to the g vectors under dynamical diffraction condition [4]. Our previous ex situ TEM observations have shown that ion irradiations with 1MeV Ni ions at 25 and 350°C with doses of 1 to 10dpa result in the coherency loss for lower sink strengths (5.9×1013m-2) of matrix precipitates. The extent of the loss of coherency regimes are closer to the calculated 1-D migration mean free path ("λ" ~ (6𝛑2r4N2)-1/2) [5] of 2286nm for the initial precipitate size (r) and density (N), indicating that most of the radiation-produced clusters exhibit 1-D motion. However, precipitate coherency loss was not observed below 1dpa at 25 or 350°C, neither for the higher sink strength (>3×1014m-2). Thus, an innovative study is proposed by using in situ ion irradiation experiments to explore the threshold concentration of absorbed self-interstitial atoms to induce coherency loss as a function of precipitate size or sink strength. TEM foils of fcc-structured model binary alloys (Cu-1at.%Co, Cu-1at.%Fe and Cu-0.4at.%Cr) with similar sink strengths will be irradiated at 25 and 350°C with 1MeV Kr ions to midrange doses of 1-10dpa (corresponding fluences: 6E14-6E15 ions/cm2). TEM samples will be prepared through jet-polish technique to produce an electron-transparent region. Based on SRIM calculation results, the midrange dose region will start from 60nm from the surface, and the free surface effects will be avoided minimized in this condition. Considering the precipitate number density in each of the binary alloys, tens of precipitates should be visible in the irradiated thin foil at the same time through certain two beam conditions. This project will need 10 days of IVEM facility access. Three days for irradiation temperature at 25°C and 6 days at 350°C. These two different temperatures will be used to investigate the effect of immobile vacancy clusters as matrix sink in the irradiated regions. We are expecting to see the coherency loss of the precipitates at high temperatures above specific threshold dose conditions whereas precipitates may remain coherent up to high doses at room temperature. The extra one day will be used to conduct cryo irradiation at 30K where interstitial and vacancy are immobile after the cascade, then anneal the sample with increasing temperature to find out the recovery stage III temperature for dilute binary alloy system. The corresponding dislocation loops coming out from the precipitate/matrix interface should also be observed as the result of misfit relaxation of the initially coherent interface. The result will be a guidance in improving coherent oxide particles in oxide dispersion strengthened ferritic steels [6,7] or super high strength austenitic stainless steels with fcc precipitates [8] by exploring the stability behavior of coherent precipitates in model fcc-base binary alloys and the different responses to the in situ ion irradiation experiments compared to ex situ ion irradiation experiments. References: [1] G. R. Woolhouse. Loss of precipitate coherency by electron irradiation in the high voltage electron microscope. Nature, 220 (1986) 573-574. [2] G. R. Woolhouse and M. Ipohorski, On the interaction between radiation damage and coherent precipitates. Proceedings of the royal society of London. Series A, Mathematical and Physical Sciences, 324 (1971) 415-431. [3] R. Knoll thesis, Effects of heavy-ion irradiation on the phase stability of several copper-base alloys. (1981). [4] M. F. Ashby, L. M. Brown. Philosophy magazine, 8 (1963) 1083. [5] H.L. Heinisch, H. Trinkaus, B.N. Singh, Kinetic Monte Carlo studies of the reaction kinetics of crystal defects that diffuse one-dimensionally with occasional transverse migration, Journal of Nuclear Materials 367-370 (2007) 332-337. [6] P. Dou, A. Kimura, R. Kasada, T. Okuda, M. Inoue, S. Ukai, S. Ohnuki, T. Fujisawa, F. Abe, S. Jiang, Z. Yang, TEM and HRTEM study of oxide particles in an Al-alloyed high-Cr oxide dispersion strengthened ferritic steel with Hf addition. Journal of Nuclear Materials, 485 (2017) 189-201. [7] T. Chen, J.G. Gigax, L. Price, D. Chen, S. Ukai, E. Aydogan, S.A. Maloy, F.A. Garner, L. Shao, Temperature dependent dispersoid stability in ion-irradiated ferritic-martensitic dual-phase oxide-dispersion-strengthened alloy: Coherent interfaces vs. incoherent interfaces, Acta Materialia 116 (2016) 29-42. [8] P. Ou, L. Li, et. al., Steady-state creep behavior of super304H Austenitic steel at elevated temperatures. Acta Metallergy, 28 (2015), 1336-1343.