An experimental protocol development of three-dimensional transmission electron microscopy methods for ferrous alloys

Towards quantitative microstructural characterization in three dimensions

Satoshi Hata, Kazuhisa Sato, Mitsuhiro Murayama, Toshihiro Tsuchiyma, Hideharu Nakashima

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

The majority of engineering steels are ferromagnetic and structurally inhomogeneous on scales ranging from nanometers to micrometers, and their physical properties depend on the three-dimensional (3D) features in their microstructures. Thus, obtaining a 3D image with a large field of view is desirable for transmission electron microscopy (TEM) based microstructure characterization in order to establish the relationship between the microstructure and the physical properties with a reasonable statistical relevancy. Here, we use a conventional sample preparation process, i.e., mechanical polishing followed by electropolishing, and optimizing experimental protocols for electron tomography (ET) of ferromagnetic materials, to carry out microstructural characterization of engineering steel. We determined that the sample thickness after the mechanical polishing step is a critical experimental parameter affecting the success rate of tilt-series image acquisitions. For example, for ferritic heat-resistant 9Cr steel, mechanical thinning down to 30 μm or less was necessary to acquire an adequate tilt-series image of the carbide precipitates in the annular dark-field scanning TEM (ADF-STEM) mode. However, acquiring tilt-series images of dislocation structures remains a challenge due to an unavoidable, significant electron beam deflection during specimen tilt, even with a thinned sample. To overcome the electron beam deflection problem, we evaluated several relatively accessible approaches including the "Low-Mag STEM and Lorentz TEM" modes. Although rarely used for ET, both modes reduce or even zero the objective lens current, likely weakening the magnetic interference between the ferromagnetic specimen and the objective lens magnetic field. The advantages and disadvantages of these experimental components are discussed.

Original languageEnglish
Pages (from-to)623-631
Number of pages9
Journalisij international
Volume55
Issue number3
DOIs
Publication statusPublished - Jan 1 2015

Fingerprint

Iron alloys
Steel
Transmission electron microscopy
Polishing
Microstructure
Tomography
Electron beams
Lenses
Physical properties
Electrolytic polishing
Ferromagnetic materials
Electrons
Image acquisition
Carbides
Precipitates
Magnetic fields
Scanning electron microscopy

All Science Journal Classification (ASJC) codes

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

Cite this

@article{7a48bf8435fc44c7a0b55e9f9f24e780,
title = "An experimental protocol development of three-dimensional transmission electron microscopy methods for ferrous alloys: Towards quantitative microstructural characterization in three dimensions",
abstract = "The majority of engineering steels are ferromagnetic and structurally inhomogeneous on scales ranging from nanometers to micrometers, and their physical properties depend on the three-dimensional (3D) features in their microstructures. Thus, obtaining a 3D image with a large field of view is desirable for transmission electron microscopy (TEM) based microstructure characterization in order to establish the relationship between the microstructure and the physical properties with a reasonable statistical relevancy. Here, we use a conventional sample preparation process, i.e., mechanical polishing followed by electropolishing, and optimizing experimental protocols for electron tomography (ET) of ferromagnetic materials, to carry out microstructural characterization of engineering steel. We determined that the sample thickness after the mechanical polishing step is a critical experimental parameter affecting the success rate of tilt-series image acquisitions. For example, for ferritic heat-resistant 9Cr steel, mechanical thinning down to 30 μm or less was necessary to acquire an adequate tilt-series image of the carbide precipitates in the annular dark-field scanning TEM (ADF-STEM) mode. However, acquiring tilt-series images of dislocation structures remains a challenge due to an unavoidable, significant electron beam deflection during specimen tilt, even with a thinned sample. To overcome the electron beam deflection problem, we evaluated several relatively accessible approaches including the {"}Low-Mag STEM and Lorentz TEM{"} modes. Although rarely used for ET, both modes reduce or even zero the objective lens current, likely weakening the magnetic interference between the ferromagnetic specimen and the objective lens magnetic field. The advantages and disadvantages of these experimental components are discussed.",
author = "Satoshi Hata and Kazuhisa Sato and Mitsuhiro Murayama and Toshihiro Tsuchiyma and Hideharu Nakashima",
year = "2015",
month = "1",
day = "1",
doi = "10.2355/isijinternational.55.623",
language = "English",
volume = "55",
pages = "623--631",
journal = "ISIJ International",
issn = "0915-1559",
publisher = "Iron and Steel Institute of Japan",
number = "3",

}

TY - JOUR

T1 - An experimental protocol development of three-dimensional transmission electron microscopy methods for ferrous alloys

T2 - Towards quantitative microstructural characterization in three dimensions

AU - Hata, Satoshi

AU - Sato, Kazuhisa

AU - Murayama, Mitsuhiro

AU - Tsuchiyma, Toshihiro

AU - Nakashima, Hideharu

PY - 2015/1/1

Y1 - 2015/1/1

N2 - The majority of engineering steels are ferromagnetic and structurally inhomogeneous on scales ranging from nanometers to micrometers, and their physical properties depend on the three-dimensional (3D) features in their microstructures. Thus, obtaining a 3D image with a large field of view is desirable for transmission electron microscopy (TEM) based microstructure characterization in order to establish the relationship between the microstructure and the physical properties with a reasonable statistical relevancy. Here, we use a conventional sample preparation process, i.e., mechanical polishing followed by electropolishing, and optimizing experimental protocols for electron tomography (ET) of ferromagnetic materials, to carry out microstructural characterization of engineering steel. We determined that the sample thickness after the mechanical polishing step is a critical experimental parameter affecting the success rate of tilt-series image acquisitions. For example, for ferritic heat-resistant 9Cr steel, mechanical thinning down to 30 μm or less was necessary to acquire an adequate tilt-series image of the carbide precipitates in the annular dark-field scanning TEM (ADF-STEM) mode. However, acquiring tilt-series images of dislocation structures remains a challenge due to an unavoidable, significant electron beam deflection during specimen tilt, even with a thinned sample. To overcome the electron beam deflection problem, we evaluated several relatively accessible approaches including the "Low-Mag STEM and Lorentz TEM" modes. Although rarely used for ET, both modes reduce or even zero the objective lens current, likely weakening the magnetic interference between the ferromagnetic specimen and the objective lens magnetic field. The advantages and disadvantages of these experimental components are discussed.

AB - The majority of engineering steels are ferromagnetic and structurally inhomogeneous on scales ranging from nanometers to micrometers, and their physical properties depend on the three-dimensional (3D) features in their microstructures. Thus, obtaining a 3D image with a large field of view is desirable for transmission electron microscopy (TEM) based microstructure characterization in order to establish the relationship between the microstructure and the physical properties with a reasonable statistical relevancy. Here, we use a conventional sample preparation process, i.e., mechanical polishing followed by electropolishing, and optimizing experimental protocols for electron tomography (ET) of ferromagnetic materials, to carry out microstructural characterization of engineering steel. We determined that the sample thickness after the mechanical polishing step is a critical experimental parameter affecting the success rate of tilt-series image acquisitions. For example, for ferritic heat-resistant 9Cr steel, mechanical thinning down to 30 μm or less was necessary to acquire an adequate tilt-series image of the carbide precipitates in the annular dark-field scanning TEM (ADF-STEM) mode. However, acquiring tilt-series images of dislocation structures remains a challenge due to an unavoidable, significant electron beam deflection during specimen tilt, even with a thinned sample. To overcome the electron beam deflection problem, we evaluated several relatively accessible approaches including the "Low-Mag STEM and Lorentz TEM" modes. Although rarely used for ET, both modes reduce or even zero the objective lens current, likely weakening the magnetic interference between the ferromagnetic specimen and the objective lens magnetic field. The advantages and disadvantages of these experimental components are discussed.

UR - http://www.scopus.com/inward/record.url?scp=84928167679&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84928167679&partnerID=8YFLogxK

U2 - 10.2355/isijinternational.55.623

DO - 10.2355/isijinternational.55.623

M3 - Article

VL - 55

SP - 623

EP - 631

JO - ISIJ International

JF - ISIJ International

SN - 0915-1559

IS - 3

ER -