Published by De Gruyter

Volume 50 Issue 6

Issue of Practical Metallography

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Contents
Journal Overview

Contents/Inhalt

August 12, 2013

Page range: 365-366

Editorial

August 12, 2013

Editorial

Karen Pantleon

Page range: 367-368

Technical Contributions/Fachbeiträge

August 12, 2013

Quality Control of Thermal Spray Coatings in Diesel Engines

J. V. Carstensen, M. Lindegren

Page range: 369-390

Abstract

Thermal spraying is a method, which is suitable for coating of large components. The coatings can e. g. improve the wear, friction and/or corrosion properties of components so that they can withstand the increased loads. The quality of the coatings is essential to ensure reliable operation of the components. However, quality control of thermally sprayed coatings is indeed nontrivial and sample preparation is a key issue. This paper shows examples of thermal spray coated components in large diesel engines and provides insight into the methods used in preparing samples for quality control.

August 12, 2013

Mapping the Local Structure of Nanowires

J. M. Persson, J. B. Wagner

Page range: 391-409

Abstract

The crystallographic and compositional structure of heterostructured semiconductor nanowires has been studied by means of transmission electron microscopy. The native geometry of the studied InP-GaAs nanowires (80–100 nm in diameter) is in general too thick for reliable high-resolution TEM imaging. Nano Beam Electron Diffraction (NBED) is shown to be a powerful technique to reveal strain near the interface of compositional change in heterostructured semiconductor nanowires. Furthermore, the relative orientation of the nanowires is studied by means of NBED revealing the nanowires to be very flexible. NBED proves to be a good alternative to convergent beam electron diffraction and electron backscatter diffraction in terms of crystal orientation determination and mapping.

August 12, 2013

Application of Complementary Techniques for Advanced Characterization of White Etching Cracks

O. H. E. West, A. M. Diederichs, H. Alimadadi, K. V. Dahl, M. A. J. Somers

Page range: 410-431

Abstract

White etching crack (WEC) networks were characterized in heavy loaded bearings for wind turbines. Both conventional techniques as reflected light microscopy and (scanning and transmission) electron microscopy as well as electron backscatter diffraction and ion channelling contrast imaging were applied. The complementary use of the techniques in unravelling the complicated failure mechanisms is explored in the present work.

August 12, 2013

Identification of Precipitates in an IN792 Gas Turbine Blade after Service Exposure

K. V. Dahl, J. Hald

Page range: 432-450

Abstract

Plate-like precipitates were found in an exposed IN792 gas turbine blade after service exposure for 40,000–60,000 service hours at a temperature of 680–760 °C. The blade was heavily oxidised and therefore removed. During subsequent metallurgical investigations extensive precipitation was found in the metallic region beneath the outer oxide layer. Further investigations were undertaken in order to understand the failure mechanism, especially the precipitate type and formation mechanism. Cross sections prepared from the turbine blade were studied using LOM and SEM. Composition profiles across the interface between bulk material and oxide layer revealed significant depletion of chromium below the oxide. Thermodynamic equilibrium calculations were used as a practical tool supporting the investigations. Chemical mapping using energy filtered TEM and selected area diffraction were used to prove that the precipitates were carbides and not an intermetallic phase like σ. The extensive oxidation resulted in dissolution of carbides near the outer surface, while reactive elements, e. g. chromium, released from this process would then diffuse outwards towards the oxide, carbon diffused inwards resulting in extensive re-precipitation of carbides.

Meeting Diary/Veranstaltungskalender

August 12, 2013

Meeting Diary

Page range: 458-459

About this journal

Practical Metallography is a bilingual (German-English) journal that informs you thoroughly on materialographic preparation, imaging and analysis of microstructures. The journal covers the development and improvement of metallographic methods and equipment, possibilities of optical and electron microscopy, spectroscopy, diffraction techniques, non-destructive testing, metallographic investigations of materials, problems of specimens preparation and evaluation including useful laboratory advice and recipes, failure analysis including damage detection and elimination.
All articles are subject to thorough, independent peer review.
Practical Metallography works closely with Deutsche Gesellschaft für Materialkunde e.V. (DGM)