Morphology and Chemical Composition of Nanoprecipitate in AerMet100 Steel by Separation of the Nuclear and Magnetic Small-Angle Neutron Scattering Data

doi:10.11900/0412.1961.2024.00062

Acta Metall Sin

2024, Vol. 60

Issue (8): 1109-1118 DOI: 10.11900/0412.1961.2024.00062

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Morphology and Chemical Composition of Nanoprecipitate in AerMet100 Steel by Separation of the Nuclear and Magnetic Small-Angle Neutron Scattering Data

KE Yubin¹^,²(

), LI Bin³, DUAN Huiping³(

)

1 Spallation Neutron Source Science Center, Dongguan 523803, China
2 Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
3 School of Materials Science and Engineering, Beihang University, Beijing 100191, China

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KE Yubin, LI Bin, DUAN Huiping. Morphology and Chemical Composition of Nanoprecipitate in AerMet100 Steel by Separation of the Nuclear and Magnetic Small-Angle Neutron Scattering Data. Acta Metall Sin, 2024, 60(8): 1109-1118.

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Abstract

AerMet100 ultrahigh-strength steel is widely used in aircraft landing gears because of its excellent mechanical properties. Its high strength mainly results from the secondary hardening effect of a large amount of needle-shaped M₂C-type precipitates generated during the alloy tempering process. Given the nanoscale size and coherency with the martensitic matrix, the size and composition of the precipitates in the AerMet100 steel are difficult to extract and accurately characterize by using traditional imaging techniques. In this study, the size, distribution, and composition of M₂C-type needle-like precipitates in AerMet100 steel tempered for 5 h at 454, 482, 486, and 498^oC were quantitatively characterized by combining TEM, XRD, and small-angle neutron scattering (SANS) techniques. By applying a transverse magnetic field of 1.1 T during the SANS experiment and reducing the data along the parallel and perpendicular magnetic field directions, the separation of nuclear and magnetic scattering data was achieved. Model fitting of the nuclear scattering curves revealed an average length of 6-16 nm and an average diameter of 1-2 nm for the needle-like precipitates in the alloy. The volume fraction of the needle-like phase increases with the tempering temperature ranging from 0.54% to 5.19%. Given the nanodomains between the precipitates and matrix phase with spin misalignment, the structural parameters obtained from magnetic scattering data are much bigger than the nuclear ones. Furthermore, by comparing the neutron scattering length densities of the carbides and matrix phases, the possible chemical composition and physical density of the needle-like precipitates within are (Cr_0.4Mo_1.6)C and 8.55 g/cm³, respectively. This study demonstrates nondestructive quantitative neutron scattering analysis of the nanoscale morphology and chemical composition of nanophases in ferromagnetic alloys.

Key words: AerMet100 steel nanoscale precipitate small-angle neutron scattering separation of nuclear and magnetic scattering chemical composition of nanophase

Received: 01 March 2024

ZTFLH:

TG142

Fund: National Key Research and Development Program of China(2021YFB3501201);National Natural Science Foundation of China(12275154);Guangdong Basic and Applied Basic Research Foundation(2021B1515140028);Youth Innovation Promotion Association, CAS(2020010)

Corresponding Authors: KE Yubin, associate professor, Tel: (0769)88931334, E-mail: keyb@ihep.ac.cnDUAN Huiping, professor, Tel: (010)82339822, E-mail: hpduan@buaa.edu.cn

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https://www.ams.org.cn/EN/10.11900/0412.1961.2024.00062 OR https://www.ams.org.cn/EN/Y2024/V60/I8/1109

Fig.1 Transmission curve and Bragg-edge feature of CoNi_454 sample (a), integration and normalization within 10° azimuth angle along the 0° and 90° orientations (b) (Q_x, Q_y —scattering vector moduli in x and y axes, repectively)

Fig.2 TEM images and SAED patterns (insets) of AerMet100 steel samples tempered at 486^oC (a) and 498^oC (b) for 5 h (White and black arrows indicate precipitates and reverted austenite films (RAFs), respectively)

Fig.3 XRD spectra of the AerMet100 steel tempered at different temperatures

Fig.4 TEM images and SAED patterns (insets) of the needle-like M₂C precipitates in tempered AerMet100 steel along different crystallographic orientations of the matrix phase (White arrows indicate the needle-like precipitates)
(a) 486^oC, [001] _α (b) 486^oC, [011] _α (c) 498^oC, [001] _α (d) 498^oC, [011] _α

Fig.5 Magnetic hysteresis curves (a) and the 1D SANS scattering curves measured under no field application (5 mT remanence) and 1.1 T magnetic field of AerMet100 steel tempered at different temperatures (b) (SANS—small-angle neutron scattering; Q—scattering vector modulus)

Table 1 Chemical compositions, densities and neutron scattering length densities of phases in AerMet100 steel

Fig.6 2D SANS patterns of 498^oC-tempered AerMet100 steel under different magnetic field strengths (I—integral intensity)
(a) no field application (5 mT) (b) 50 mT (c) 0.1 T (d) 1.1 T

Fig.7 SANS results of AerMet100 tempered steel under magnetic field application
(a) total SANS 1D scattering data
(b, c) experimental and fitted nuclear (b) and magnetic (c) SANS results
(d) observed ratio between SANS nuclear scattering intensity (I_N) and magnetic scattering intensity (I_M)

Table 2 Fitted structural parameters of nanoprecipitates from the nuclear SANS data of AerMet100 steel

Table 3 Fitted structural parameters of nanodomains from the magnetic SANS data of AerMet100 steel

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