A. Davoodi, J. Pan,ch. Leygraf, Gh. R. Ebrahimi, M. Javidani,
Volume 6, Issue 3 (9-2009)
Abstract
Abstract: Localized corrosion of aluminum alloys is often triggered by intermetallic particles, IMP’s. To understandthe role of IMP’s in corrosion initiation of EN AW-3003, efforts were made to combine nano-scale ex-situ analysis ofthe IMP’s by SEM-EDS, SKPFM and in-situ AFM monitoring of the localized attack in chloride containing solution.The results showed that two distinct types of eutectically-formed constituent IMP’s exist the -Al(Mn,Fe)Si and theAl(Mn,Fe) phases. However, the exact chemical composition of the IMP’s varies with the particles size. Volta potentialdifference of surface constituents revealed that IMP’s have a higher Volta potential compared to the matrix, indicatingthe cathodic characteristic of the IMP’s. Noticeably, the boundary regions between the matrix and IMP’s exhibited aminimum Volta potential probably the sites for corrosion initiation. Localized corrosion attack monitored by in-situAFM clearly showed the trench formation occurrence around the large elongated IMP’s in the rolling direction.
R. Sarjahani, M. Sheikhattar, S. Javadpour, B. Hashemi,
Volume 13, Issue 1 (3-2016)
Abstract
Surface smoothness of ceramic glazes is always an important characteristic of ceramic glazes as a point of surface engineering studies. Surface roughness affects chemical resistivity, glossiness and stainabiliy of glazes. In fact, less surface roughness improves cleanability of the surface by the least usage amount of detergents. In this investigation, surface topography of two common opaque glazes, zirconia and titania-based, has been investigated. Crystallinity of the surface has been studied from SEM images, and comparison of EDS elemental results with phase analysis results of XRD. Surface roughness profile measured by Marsurf M300, shows that titania-based glaze is almost 24% percentage more smooth than zirconia based glaze. Surface smoothness is in relation with crystallinity of glaze surface, crystal type and crystal distribution in amorphous matrix phase
J. Ngoret, V. Kommula,
Volume 16, Issue 1 (3-2019)
Abstract
This paper investigates premature failure of High Pressure (HP) PT6A-114A Compressor Turbine (CT) blades used for short-haul aircraft fleet at 6378 hours, contrary to 10000 hours pre-set by the manufacturer. The CT blades were sectioned both transversely and longitudinally and subjected to several microstructural examinations; X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Energy Dispersive Spectroscopy-Scanning Electron Microscopy (EDS-SEM) of the tips, airfoils, as well as the bases. It was observed that from repeated elevated heating, incomplete solutioning and recrystallization of the substrate material, brittle carbides were initiated and developed. The tips were more affected, followed by the airfoils and least at the bases. Impingement of heat from the combustors on the CT blades led to rapid graining and rafting with eventual cracking upon cooling. The results further suggested that pores which are typically manufacturing defects were pronounced at the bases than either at the airfoils and the tips. However, contrary to the expectation that the bases would degrade more and rapider, a more near uniform distribution of the cuboidal phase was evident relative to the tips and airfoils, confirming that degradation of the CT blades originated from creep and fatigue.
