Characterization of Alumina Scale Formed on FeCrAl Steel

Abstract

In this paper the morphology of the oxide scale formed at 850• C on the foil surface of FeCrAl steel is described. Two types of samples have been used: one covered with an Al nano-layer and the second without. Microscopic observations of the cross-sections of scales have demonstrated that in the case of foil without Al nano-layer there is a remnant of an amorphous Al 2 O 3 nano-layer, from which γ and θ crystallites of Al 2 O 3 have been grown. In the case of foil covered with the Al nano-layer, α-Al 2 O 3 phase is present and θ-phase forms a forest of whiskers on the surface.Keywords: A. steel, B. TEM, B. SEM, C. oxidation, alumina W pracy opisano morfologię warstw tlenkowych, które powstały na folii FeCrAl pod wpływem jej utleniania w temperaturze 850• C. Badania dotyczyły folii pokrytej nanowarstwą Al oraz nie pokrytej. Przekroje warstw i podłoża stalowego badane za pomocą transmisyjnej mikroskopii elektronowej wykazały, że w przypadku folii nie pokrytej warstwą Al występuje pozostałość amorficznej nanowarstwy Al 2 O 3 , z której następuje wzrost krystalitów γ i θAl 2 O 3 . W przypadku folii z osadzoną nanowarstwą Al stwierdzono obecność fazy α Al 2 O 3 oraz występującej na powierzchni folii fazy θAl 2 O 3 , w postaci lasu whiskerów.

Processing of Porous SiC by Aluminum‐Derived Binders and Sacrificial Porogen Leaching Method

“…Figure c shows the uniform and lengthy nano thickness whiskers of metastable θ‐Al 2 O 3 formed on the surface of porous SiC above 850°C. Similar type of metastable θ‐Al 2 O 3 and α‐Al 2 O 3 were observed in earlier studies of alumina‐coating formation over steel surfaces . Analysis of XRD pattern of porous SiC sintered at 1000°C reveal the presence of more α‐Al 2 O 3 peaks along with few θ‐ Al 2 O 3 .…”

“…27 Figure 6c www.ceramics.org/ACT Processing of Porous SiC studies of alumina-coating formation over steel surfaces. 28 Analysis of XRD pattern of porous SiC sintered at 1000°C reveal the presence of more a-Al 2 O 3 peaks along with few h-Al 2 O 3 . In selective regions, fine and uniformly arranged whiskers of h-Al 2 O 3 were observed over outer surface of spherically shaped alumina (Fig.…”

Transmission Electron Microscopy of Meta-stable Al2O3 Scale Formed on NiCoCrAl Coated Layer During Isothermal Oxidation

“…Such phase has monoclinic symmetry (space group C2/m) which is a structural isomorphs of b-Ga 2 O 3 with the lattice parameters a = 0.56 nm, b = 0.29 nm, c = 1.19 nm and b = 103.7 [2]. Rhombohedral a-alumina with lattice parameters of a = 0.48 nm and c = 1.29 nm [16][17][18] is the most thermodynamically stable phase of alumina. The SAED pattern is shown in Fig.…”

Characterization by Photoluminescence and Raman Spectroscopy of the Oxide Scales Grown on the PM2000 at High Temperatures

“…It is believed that at high temperatures (above 950 C), the form is the stable form existing, while at lower temperatures, the aluminum oxide metastable phases, such as theta, delta, and gamma are formed. 7 At the beginning of the reaction, it develops transition alumina such as -Al 2 O 3 , -Al 2 O 3 and -Al 2 O 3 for a duration which depends on the temperature. 8 The growth of -Al 2 O 3 scales that form on FeCrAl alloys during high temperature oxidation is generally considered to be controlled by oxygen inward di®usion through oxide grain.…”