La fatigue à haute température des superalliages à base nickel – avec une attention particulière sur les modes de déformation et de l’oxydation

ScienceDirect – Engineering Failure Analysis : High temperature fatigue of nickel-base superalloys – A review with special emphasis on deformation modes and oxidation

Andre Pineaua, Corresponding Author Contact Information, E-mail The Corresponding Author, Stephen D. Antolovichb

Abstract

Low cycle fatigue, high cycle fatigue, fatigue crack propagation and thermo-mechanical fatigue in Ni-base superalloys are reviewed in terms of fundamental deformation mechanisms, environmental effects, and interactions between environment and deformation mode. These factors are related to the chemical composition and underlying microstructure for all currently-used product forms (i.e. powder metallurgy, wrought, conventionally cast and single crystal). The basic principles that are developed are used to show how both intrinsic and extrinsic variables can be manipulated to control fatigue behaviour and as a guide for formulation of engineering life prediction models.

Keywords: Ni-base superalloys; Low cycle fatigue; High cycle fatigue; Fatigue crack propagation

Publicités

Une étude sur la corrosion électrochimique comparée d’un alliage de titane (TA6V) et un alliage de magnésium moulé (AZ91D)

Electrochemical corrosion behavior of alloys either used in industry or as implants in human body

Faculty of Science-Cairo University
Published on 29 March 2010

Electrochemical corrosion behavior of alloys either used in industry or as implants in human body

The main problem in our life is the corrosion of many types of alloys either industrial or biological. Corrosion behavior had been studied using open circuit potential, electrochemical impedance (EIS) spectroscopy, Potentiondynamic polarization, cyclic voltammetry measurements. Many electrodes have been studied as Titanium and its alloys as one of the best engineering materials for use in industrial applications [1]. Titanium is widely used in the equipment of chemical enterprises, petroleum-refining industries and food industry. A study to investigate the stability of the Titanium and Ti-6Al-4V in aqueous solutions of oxalic acid has been done. Oxalic acid is a relatively strong organic acid used as purifying agent in pharmaceutical industry, it is a metabolite of the catalytic oxidation of phenol [2] and other aromatic substrates like, for instance, coumaric acid (a by-product of olive oil manufacturing). It was found that the corrosion rate increase with either increasing oxalic acid concentration or temperature. EIS results of titanium and its alloy in 0.01 M oxalic acid containing either SO 4 2 or Cl ions showed that oxide film resistance decreases with the increase of the sulphate ion concentration. However, for Cl ion, it decreases from 0.001 till 1 mM, then increases at higher concentration for both Ti and its alloy [3].

The titanium alloys have been increasingly used in aerospace, biomedical, and chemical industries due to their very high strength to weight ratio, biocompatibility, and high corrosion resistance due to the formation of titania on its surface. The nature, composition and thickness of the protective oxide scales depend on environmental conditions [4]. It was previously reported [5] that titanium has a high resistance to corrosion in physiological saline and artificial saliva. Metallic materials are being increasingly used in medical applications as implants to restore lost functions or replace organs functioning below acceptable levels. Titanium alloys are among the most used metallic biomaterials, particularly for orthopaedic applications [6]. Magnesium alloys as potential biodegradable material provides both biocompatibility and suitable mechanical properties [7]. Mg 2+ is an essential element and present in large amounts in the human body. The presence of magnesium in the bone system is beneficial to bone strength and growth. Magnesium alloys have specific density (1.74–2 g/cm 3) and Young’s modulus (41–45 GPa) most close to those (1.8–2.1 g/cm 3, 3–20 GPa) of human body’s bone. Therefore, in orthopedic and bone repairing or replacement applications magnesium alloys are particularly superior to any other metallic or polymer implants in terms of physical and mechanical properties, as the dissimilarity in Young’s modulus between an implant and natural bone can result in stress shielding effects, leading to concentration of stress at the interface between the bone and implant reducing stimulation of new bone growth and decreasing implant stability [7].

The electrochemical behavior of AZ91D and Ti–6Al–4V alloys was investigated in simulated body fluid (SBF) at 37 C. The study is aimed to improve knowledge for the nature of the corrosion films in those systems by comparing the behavior of AZ91D alloy (biodegradable material for temporary implant) and Ti–6Al–4V alloy (passive alloy for permanent human use) and tried to correlate the electrochemical behavior to their structure, using conventional electrochemical techniques complemented with surface examination. Very low current density was obtained for Ti–6Al–4V alloy compared to that of AZ91D alloy, indicating a typical passive behavior for Ti alloy. EIS results exhibited high corrosion resistance indicating a highly stable film on titanium alloy compared to magnesium alloy in SBF [8].

Effect of heat treatment on carbides in 23-8-N steel

Galerie

Abstract Metal carbides play an important role in deciding the end properties and ultimately the suitability of the austenitic stainless steels for various applications. Austenitic stainless steels, being nonhardenable via phase transformation, are subject to solution annealing to ensure maximum … Lire la suite

Failure Analysis of Low Pressure Evaporator Tubes in a Typical Combined Cycle Power Plant

Failure Analysis of Low Pressure Evaporator Tubes in a Typical Combined Cycle Power Plant

Failure Analysis of Low Pressure Evaporator Tubes in a Typical Combined Cycle Power Plant

Journal Applied Mechanics and Materials (Volumes 110 – 116)
Volume Mechanical and Aerospace Engineering
Edited by Wu Fan
Pages 4607-4614
DOI 10.4028/www.scientific.net/AMM.110-116.4607
Citation M. Nematollahi et al., 2011, Applied Mechanics and Materials, 110-116, 4607
Online since October, 2011
Authors M. Nematollahi, M. Rezaeian
Keywords Droplet Impingement Erosion, Power Plant, Steam Generator Tube Failure, Two-Phase Flow Pattern
Abstract

Flow-induced corrosion is one of the most prevalent tube damage mechanisms in steam generators of power plants. In this study, tube failure of a steam generator in Fars Combined Cycle Power Plant is evaluated. In addition to analysis of the measured tube thicknesses and the failure statistics data, computational fluid dynamic (CFD) methods are used to simulate flow distribution inside and outside of the tubes in one header of the low pressure circuit of the plant steam generator. The results show that regarding the created two-phase flow pattern inside the tubes, the droplet impingement erosion is the main source of tube failures in the bending areas where the extrados surface of the tubes are partially prone to the droplets. The results are useful for modifying the design of the steam generator from different viewpoints such as, optimal design for appropriate configuration of downcomer, header and footer and tube bending. Also, selecting suitable material for the steam generator tubes and implementation of protective coating in risky areas would benefit from the present results.

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Study of fatigue damage in wind turbine blades

Citation

ScienceDirect – Engineering Failure Analysis : Study of fatigue damage in wind turbine blades

J.C. Marín Corresponding Author Contact Information, E-mail The Corresponding Author, A. Barroso, F. París, J. Cañas

School of Engineering, University of Seville, Camino de los Descubrimientos s/n, 41092 Seville, Spain

Available online 29 February 2008.

Abstract

The inspection of damages detected in some blades of 300 kW wind turbines revealed that the nature of these damages was probably due to a fatigue mechanism. The causes that had originated the failure (superficial cracks, geometric concentrator, abrupt change of thickness) have been studied, verifying, by means of the simplified evaluation procedure of fatigue life of the “Germanischer Lloyd” (GL) standard, that these causes can explain the failure detected in the period of time in which it happened.

Keywords: Blade failures; Composites; Fatigue life

Article Outline

Failure analysis of stress corrosion cracking in a gas transmission steel pipeline

Engineering Failure Analysis : Failure analysis of stress corrosion cracking occurred in a gas transmission steel pipeline

Abstract

In January 2010, stress corrosion cracking was occurred in a high-pressure gas pipeline steel in northern regions of Iran, after almost 40 years since its installation. In this study, failure mechanisms were determined based on available documents and metallographic studies conducted on this pipeline. The results showed that the applied polyethylene tape coating on the external surface of the pipeline became opened and disbonded in the corroded area causing external surface of buried pipeline to be exposed to wet soil around it. As a result of the chemical interactions and formation of carbonate/bicarbonate solution and with the presence of tensile stresses, stress corrosion cracking occurred in the longitudinal direction and at the outer surface of the pipe. In addition, mechanisms and morphology of cracks propagation due to stress corrosion cracking to internal side of the pipe wall were studied.

Keywords: API 5L X60; Stress corrosion cracking; Pipeline; Intergranular

Corrosion des goussets d’assemblage de fermes de toit dans les bâtiments d’élevage

www.omafra.gov.on.ca/french/engineer/facts/10-072.pdf

PROBLÈME DE CORROSION
La détérioration des goussets de fermes de toit en
métal est une préoccupation majeure dans les
bâtiments dont l’intérieur constitue un milieu très
humide et corrosif. Après cinq à dix ans, bon nombre
de ces bâtiments montrent des signes d’une grave
corrosion. Les goussets en tôle d’acier galvanisé exposés
à l’humidité, à la condensation et à une circulation
d’air chargé de gaz de fumier se corrodent rapidement.
Cette corrosion peut affaiblir un bâtiment et conduire
à une défaillance structurale.

Failure analysis of duplex stainless steel weld

 

[PDF] Automatic Segmentation of the Secondary Austenite-phase

 Island Precipitates in a Superduplex StainlessSteel Weld Metal

Failure analysis of duplex stainless steel weld used in flexible pipes in off shore oil production.
Engineering Failure Analysis 17, p. 1500–1506. 6

A NOVEL MANUFACTURING TECHNIQUE TO IMPROVE BEARING STRENGTH OF PIN LOADED WOVEN COMPOSITES

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The bearing strength of pin-loaded woven glass-fibre reinforced epoxy composites was investigated. As an alternative to the hole-drilling procedure, a novel composite manufacturing technique has been implemented for pin-hole creation. The bearing performance of composite joints manufactured using both techniques was compared. Specimen with various edge- distances to pin-hole diameter ratios (e/d) and, width to pin-hole diameter ratios (w/d) were tested. It was observed that composite joints manufactured using the novel technique sustained more load compared to the joints manufactured by the hole-drilling procedure. Geometrical parameters were found to be effective on failure modes, bearing strength and magnitude of sustained load.