Nondestructive, Rapid Identification of Aluminum Nitride and Internal Alumina Scales on a Heat-Resistant Alloy Using Cathodoluminescence

Characterization of <i>α</i>-Al₂O₃ in Structural Isomers of Alumina Formed by Oxidation of Fe–Cr–Al Alloys

“…Details of the SEM-CL have been previously reported. 11,17,[23][24][25][26] A spectrometer (QE65Pro, Ocean Optics Inc., Largo, Florida, USA) attached through an optical fiber to the SEM equipment (Mighty-8DXL, TECHNEX, Tokyo, Japan) was used to acquire the CL spectra. A parabolic mirror was used to collimate the light emitted from the samples, and plano-convex lenses that were attached to the tip of the optical fiber were used to collect the collimated light.…”

“…1) These Al 2 O 3 scales, which are notably formed on nickel-aluminum intermetallic compounds and nickel-based heat-resistant aluminum, act as corrosion-protective layers. [2][3][4][5][6][7][8][9][10][11] Al 2 O 3 exhibits several structural isomers at different temperatures. 6,10) Some Al 2 O 3 isomers, such as γ-Al 2 O 3 and θ-Al 2 O 3 , show less resistance to high temperature corrosion owing to their high reactivity and unstable structure, whereas α-Al 2 O 3 show high corrosion resistance owing to its high structural stability.…”

“…The formation of Al 2 O 3 in iron-based alloys and heatresistant steels has also been investigated. [10][11][12][13][14][15][16][17][18][19] It is often necessary to understand and analyze the structural changes of Al 2 O 3 on the surfaces of iron-based alloys at high tem-peratures because of the practical applications of these alloys. For example, X-ray diffraction, which is practically applied to on-line analysis of galvannealed coating layers, 20) would be applicable to the on-site identification of a specific structural isomer of Al 2 O 3 .…”

Determination of the maximum surface chromia thickness for the nondestructive identification of internal alumina scales on a heat-resistant alloy using cathodoluminescence

“…As an alternative method to identify and determine the thickness of α-Al 2 O 3 and SiO 2 scales on heatresistant alloys, the author has previously focused on SEM-cathodoluminescence (CL) analysis [15][16][17][18][19][20], which provides spectra and projection images of the light emission induced by bombarding electrons from the electron gun of the SEM device on a material. Compared with photostimulated luminescence spectroscopy, the SEM-CL system is simple and versatile because it can be assembled by attaching an off-axis parabolic mirror, an optical ber, and a portable spectrometer to a conventional SEM instrument or an electron probe microanalyzer [21], which allows conducting an elemental analysis together with the CL analysis.…”

“…Compared with photostimulated luminescence spectroscopy, the SEM-CL system is simple and versatile because it can be assembled by attaching an off-axis parabolic mirror, an optical ber, and a portable spectrometer to a conventional SEM instrument or an electron probe microanalyzer [21], which allows conducting an elemental analysis together with the CL analysis. The author has previously revealed that SEM-CL analysis can be used to identify an internal α-Al 2 O 3 layer beneath surface Cr 2 O 3 scales on an Ni-Cr-Al alloy (Inconel 601 alloy) by observing a CL peak at 695 nm [19], which originates from the substitution of chromium(III) ions (Cr 3+ ) for aluminum(III) ions (Al 3+ ) in the α-Al 2 O 3 scales [22][23][24]. Although the CL peak intensity at 695 nm was expected to decrease with increasing the thickness of the surface Cr 2 O 3 scale layer, no effect of the latter on the CL peak intensity at 695 nm was observed in a thickness range of 0.74-1.25 µm owing to the rough surface of the Cr 2 O 3 scales [19].…”