Characterization Of Oxide Scales Research Articles

Secondary ion mass spectrometry and surface profilometry characterization of oxide scales developed over various regions of weldments of 2.25Cr1Mo steel

Microstructurally different regions (namely the weld metal, the heat-affected zone (HAZ) and the base metal) were characterized in weldments of 2.25Cr1Mo steel and composite specimens comprising the three regions were oxidized in air at 773 K for durations from 2 to 100 h. For all exposures a thicker oxide scale developed over the HAZ than on the weld metal and base metal. As measured by a surface profilometer, the thickness difference was found to be a fraction of a micrometre higher over the HAZ after 2 h of exposure but had increased to more than 5 μm after 100 h. Detailed secondary ion mass spectrometry (SIMS) depth profiles of Fe and Cr in the scales developed over the various regions of the weldments suggest a considerably higher Cr content of the inner scales on the weld metal and base metal than that of the scale over the HAZ. SIMS profiles have also corroborated the formation of a thicker scale over the HAZ as assessed earlier by surface profilometry. Secondary ion images of Cr acquired from an area comprising the boundary between the scales grown over the weld metal and HAZ have confirmed the formation of a Cr-rich scale over the weld metal. The higher Cr content of the weld metal scale has been further confirmed by combined scanning electron microscopy and energy-dispersive X-ray examinations.

Use of the mechanical properties microprobe for characterization of oxide scales

A mechanical properties microprobe (MPM) based on low-load, depth-sensing submicrometre indentation testing is an extremely powerful instrument for examining surface mechanical behaviour and offers several advantages for determining the elastic and plastic properties of protective oxide scales. Its high spatial and force resolutions allow measurements on thin scales and, for thicker surface oxides, determination of gradients in properties. Under optimal conditions, hardness and modulus values can be determined with an overall accuracy of about 10%. A key factor in analysis of the load-displacement data is an accurate determination of the indenter contact area. Because of this, companion indentations into bulk oxides using the same indenter reduce uncertainties associated with comparing the elastic and plastic properties of such materials with their corresponding scales. Use of a standard MPM is currently limited to near room temperature. More effective depth-sensing indentation testing of oxide scales at ...

Characterization of oxide scales on coatings for gas turbine blades by infrared reflection-absorption spectroscopy

The oxidation of chromia (Cr2O3) and alumina (Al2O3) forming alloys for the protection of gas turbine blades has been studied by Infrared Reflection Absorption Spectroscopy (IRAS). The Berreman-Effect (i. e. minimum of reflectivity of p-polarized light at oblique incidence) allows an unambiguous distinction between Al2O3 and Cr2O3 for thin scales (<0.1 μm) as well as for thick scales (∼6 μm). The position of interference fringes in the non-absorbing region of the spectrum results in simultaneous thickness determinations.

The influence of yttrium on oxide scale growth and adherence

Alloys and coatings for high-temperature service are designed to form selectively chromia scales, alumina scales, or, to a limited extent, silica scales upon exposure to the environment. For such oxide scales to be protective, they should be both slow growing and adherent. It turns out that the addition of yttrium to such alloys can often impart both characteristics to the oxide scale. However, the actual operating mechanisms continue to be a matter of controversy among researchers in the area of oxidation. In the present study, the growth and adherence of alumina and chromia scales on alloys containing yttrium, either as an oxide dispersion or as an intermetallic phase, have been investigated in conjunction with detailed oxide scale characterization using the techniques of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and secondary ion mass spectrometry (SIMS). The results of the study are used for critical assessment of the proposed mechanisms, especially the more recent ones, and to suggest some new mechanisms for adherence.

Eignung von Tiefenprofilanalysen zur Charakterisierung von Oxidschichten an Hochtemperaturlegierungen

The characterization of oxide scales by their composition and structure is necessary in order to predict their protective behaviour for the high temperature alloys in various corrosive media. For this purpose information obtained by classical methods, such as metallography, X-ray diffraction and microprobe analysis can be supplemented by depth profiles determined by various spectroscopical methods. In this paper, HASTELLOY X und INCONEL 617 were oxidized for relatively short times in two different atmospheres. Depth profiles were determined by GDOS (Glow Discharge Optical Spectroscopy), SNMS (Secondary Neutral Mass Spectrometry) and SIMS (Secondary Ion Mass Spectrometry). The measured profiles were compared with the results of non-destructive X-ray diffraction analysis to characterize the scales and the oxide-metal interface.

Characterization of oxide scales on complex alloys using multiple microanalytical techniques

The alloys used as coatings to protect gas turbine components from high temperature oxidation and from sulfur-related hot corrosion attack are, in most cases, complex multiphase materials, which form complex oxide scales. A study of the effects of alloy composition and microstructure on the mechanisms controlling oxidation of such a system is greatly aided by the use of complimentary information from several microanalytical methods, each of which has its own strengths and weaknesses.In investigations of oxide scales, scanning Auger microanalysis (SAM), in conjunction with Ar-ion milling gives semiquantitative composition vs. sputtering time for each of the phases detected. However, since various metals and their oxides can sputter at different rates, only relative depth scales can be obtained. Rutherford backscattering spectroscopy (RBS), on the other hand, provides absolute depth scales and quantitative composition information for the heavier elements in the specimens.