Oxidation-induced Cu coating on steel surface

Copper is accumulated in recycled steels and is difficult to be removed during steelmaking processes when steel scrap is used as steel sources. Meanwhile, copper characteristics are of importance both to human beings and to animals and plants. In this paper, integrated copper coating was observed on the surface of copper-containing steels when the steels were heated at around 1150°C. However, the copper was separately scattered in and under the surface rust after heating at 1000°C. The forming mechanisms of copper coating are discussed in detail. By choosing a proper descaling reagent, self-generated oxidation-induced copper coating appeared on the steel surface. The method proposed in this work is environmentally friendly for nontoxic chemicals being used. In addition, this provides a new concept for producing protective composite by oxidizing from the substrate directly and there is no bonding problem.

Tribological Testing of Some Potential PVD and CVD Coatings for Steel Wire Drawing Dies

Cemented carbide is today the most frequently used drawing die material in steel wire drawing applications. This is mainly due to the possibility to obtain a broad combination of hardness and toughness thus meeting the requirements concerning strength, crack resistance and wear resistance set by the wire drawing process. However, the increasing cost of cemented carbide in combination with the possibility to increase the wear resistance of steel through the deposition of wear resistant CVD and PVD coatings have enhanced the interest to replace cemented carbide drawing dies with CVD and PVD coated steel wire drawing dies. In the present study, the possibility to replace cemented carbide wire drawing dies with CVD and PVD coated steel drawing dies have been investigated by tribological characterisation, i.e. pin-on-disc and scratch testing, in combination with post-test observations of the tribo surfaces using scanning electron microscopy, energy dispersive X-ray spectroscopy and 3D surface profilometry. Based on the results obtained, CVD and PVD coatings aimed to provide improved tribological performance of steel wire drawing dies should display a smooth surface topography, a high wear resistance, a high fracture toughness (i.e. a high cracking and chipping resistance) and intrinsic low friction properties in contact with the wire material. Also, the steel substrate used must display a sufficient load carrying capacity and resistance to thermal softening. Of the CVD and PVD coatings evaluated in the tribological tests, a CVD TiC and a PVD CrC/C coating displayed the most promising results.

Residual stress influence on fatigue lifetimes of electroplated AISI 4340 high strength steel

Residual stresses play an important role in the fatigue lives of structural engineering components. In the case of near surface tensile residual stresses, the initiation and propagation phases of fatigue process are accelerated; on the other hand, compressive residual stresses close to the surface may increase fatigue life. In both decorative and functional applications, chromium electroplating results in excellent wear and corrosion resistance. However, it is well known that it reduces the fatigue strength of a component. This is due to high tensile internal stresses and microcrack density. Efforts to improve hard chromium properties have increased in recent years. In this study, the effect of a nickel layer sulphamate process, as simple layer and interlayer, on fatigue strength of hard chromium electroplated AISI 4340 steel hardness - HRc 53, was analysed. The analysis was performed by rotating bending fatigue tests on AISI 4340 steel specimens with the following experimental groups: base material, hard chromium electroplated, sulphamate nickel electroplated, sulphamate nickel interlayer on hard chromium electroplated and electroless nickel interlayer on hard chromium electroplated. Results showed a decrease in fatigue strength in coated specimens and that both nickel plating interlayers were responsible for the increase in fatigue life of AISI 4340 chromium electroplated steel. The shot peening pre-treatment was efficient in reducing fatigue loss in the alternatives studied.

Effect of equal channel angular extrusion on wear and corrosion behavior of the orthopedic Ti-13Nb-13Zr alloy in simulated body fluid

We report investigations on the texture, corrosion and wear behavior of ultra-fine grained (UFG) Ti-13Nb-Zr alloy, processed by equal channel angular extrusion (ECAE) technique, for biomedical applications. The microstructure obtained was characterized by X-ray line profile analysis, scanning electron microscope (SEM) and electron back scattered diffraction (EBSD). We focus on the corrosion resistance and the fretting behavior, the main considerations for such biomaterials, in simulated body fluid. To this end. potentiodynamic polarization tests were carried out to evaluate the corrosion behavior of the UFG alloy in Hanks solution at 37 degrees C. The fretting wear behavior was carried out against bearing steel in the same conditions. The roughness of the samples was also measured to examine the effect of topography on the wear behavior of the samples. Our results showed that the ECAE process increases noticeably the performance of the alloy as orthopedic implant. Although no significant difference was observed in the fretting wear behavior, the corrosion resistance of the UFG alloy was found to be higher than the non-treated material. (c) 2012 Elsevier B.V. All rights reserved.

Microstructure-Wear Resistance Correlation and Wear Mechanisms of Spark Plasma Sintered Cu-Pb Nanocomposites

The dispersion of a softer phase in a metallic matrix reduces the coefficient of friction (COF), often at the expense of an increased wear rate at the tribological contact. To address this issue, unlubricated fretting wear tests were performed on spark plasma sintered Cu-Pb nanocomposites against bearing steel. The sintering temperature and the Pb content as well as the fretting parameters were judiciously selected and varied to investigate the role of microstructure (grain size, second-phase content) on the wear resistance properties of Cu-Pb nanocomposites. A combination of the lowest wear rate (similar to 1.5 x 10(-6) mm(3)/Nm) and a modest COF (similar to 0.4) was achieved for Cu-15 wt pct Pb nanocomposites. The lower wear rate of Cu-Pb nanocomposites with respect to unreinforced Cu is attributed to high hardness (similar to 2 to 3.5 GPa) of the matrix, Cu2O/Fe2O3-rich oxide layer formation at tribological interface, and exuding of softer Pb particles. The wear properties are discussed in reference to the characteristics of transfer layer on worn surface as well as subsurface damage probed using focused ion beam microscopy. Interestingly, the flash temperature has been found to have insignificant effect on the observed oxidative wear, and alternative mechanisms are proposed. Importantly, the wear resistance properties of the nanocomposites reveal a weak Hall-Petch-like relationship with grain size of nanocrystalline Cu. (C) The Minerals, Metals & Materials Society and ASM International 2013

Evaluation of the Interfacial Adhesion between Brittle Coating and Ductile Substrate by Cross-Secitional Indention

The cross-sectional indentation method is extended to evaluate the interfacial adhesion between brittle coating and ductile substrate. The experimental results on electroplated chromium coating/steel substrate show that the interfacial separation occurs due to the edge chipping of brittle coating. The corresponding models are established to elucidate interfacial separation processes. This work further highlights the advantages and potential of this novel indentation method.

Evaluation of the Interfacial Adhesion between Brittle Coating and Ductile Substrate by Cross-Secitional Indention

The cross-sectional indentation method is extended to evaluate the interfacial adhesion between brittle coating and ductile substrate. The experimental results on electroplated chromium coating/steel substrate show that the interfacial separation occurs due to the edge chipping of brittle coating. The corresponding models are established to elucidate interfacial separation processes. This work further highlights the advantages and potential of this novel indentation method

An Instrumented Indentation Method for Young's Modulus Measurement with Accuracy Estimation

The relationships between indentation responses and Young's modulus of an indented material were investigated by employing dimensional analysis and finite element method. Three representative tip bluntness geometries were introduced to describe the shape of a real Berkovich indenter. It was demonstrated that for each of these bluntness geometries, a set of approximate indentation relationships correlating the ratio of nominal hardness/reduced Young's modulus H (n) /E (r) and the ratio of elastic work/total work W (e)/W can be derived. Consequently, a method for Young's modulus measurement combined with its accuracy estimation was established on basis of these relationships. The effectiveness of this approach was verified by performing nanoindentation tests on S45C carbon steel and 6061 aluminum alloy and microindentation tests on aluminum single crystal, GCr15 bearing steel and fused silica.

Medição de espessura de filmes eletrodepositados em suporte metálico por EDXRF

Esse trabalho apresenta a técnica de fluorescência de raios X por dispersão de energia (EDXRF) para calcular a espessura de filmes metálicos finos por ser de custo relativamente baixo, não destrutiva e que permite também uma análise qualitativa e até quantitativa dos elementos do revestimento. As espessuras do Níquel, Zinco e Cromo sobre aço, foram calculadas utilizando cinco procedimentos diferentes e todas as relações matemáticas obtidas foram baseadas na lei de atenuação de Beer-Lambert, que relaciona as intensidades Kα e/ou Kβ e as relações específicas do material (coeficiente de atenuação, μm). Os resultados experimentais para as espessuras do Zinco e Níquel, utilizando somente a intensidade Kα, apresentaram valores próximos dos valores estimados. Quando foi considerada a razão Kα/Kβ, os resultados experimentais divergiram bastante do estimado. Para calcular a espessura do Cromo foi necessário utilizar um método em que as camadas são calculadas separadamente, pois o revestimento de Cromo é composto por múltiplas camadas (Cromo, Cobre e Níquel), Os resultados para a espessura do Cromo foram satisfatórios.

Tratamento de soluções de cromo (III) por flotação a ar dissolvido

O presente trabalho estuda a viabilidade da utilização do processo de flotação a ar dissolvido (FAD) no tratamento de efluentes contendo cromo. Tal processo é analisado comparativamente à sedimentação. Urna revisão dos diferentes tipos de processos de separação ou de recuperação do cromo é, também, aqui apresentada. Soluções contendo 200 mg.l" de cromo tri ou hexavalente foram estudadas quanto às condições ideais de precipitação, às características de sedimentação e de flotação a ar dissalvido em regime descontínuo e contlnuo. Agentes poliméricos foram testados no intuito de melhorar as condições de clarificação. O processo de FAD foi o que apresentou melhores resultados no que se refere a cinética de separação sólido/líquido, e em termos de clarificação das soluções. Estudos de separação sólido/líquido de soluções contendo cromo VI foram feitos por estes dois processos empregando sulfato ferroso e sulfito de sódio como agentes redutores. A FAD mostrou ser eficiente para tratar as soluções quando reduzidas com sulfito de sódio. Porém, no caso da utilização do sulfato ferroso como redutor, o rendimento da FAD diminuiu no tratamento de soluções que continham sólidos suspensos acima de uma concentração crítica. Polímeros também foram empregados neste caso, e confirmaram sua atuação melhorando a cinética de separação sólido/líquido e como agentes que beneficiam a clarificação das soluções. Os resultados dos estudos de flotação por ar dissolvido em uma unidade contínua mostraram que é viavel a FAD sem agentes floculantes ou tensoativos. No entanto, estes aumentam os níveis de clarificação das soluções. Apenas os floculantes a base de amido mostraram-se ineficientes nesta aplicação. Conclui-se que o processo de FAD pode ser utilizado no tratamento de efluentes contendo cromo permitindo obter efluentes finais dentro dos padrões de emissão da legislação brasileira.

Neural network detection of grinding burn from acoustic emission

An artificial neural network (ANN) approach is proposed for the detection of workpiece `burn', the undesirable change in metallurgical properties of the material produced by overly aggressive or otherwise inappropriate grinding. The grinding acoustic emission (AE) signals for 52100 bearing steel were collected and digested to extract feature vectors that appear to be suitable for ANN processing. Two feature vectors are represented: one concerning band power, kurtosis and skew; and the other autoregressive (AR) coefficients. The result (burn or no-burn) of the signals was identified on the basis of hardness and profile tests after grinding. The trained neural network works remarkably well for burn detection. Other signal-processing approaches are also discussed, and among them the constant false-alarm rate (CFAR) power law and the mean-value deviance (MVD) prove useful.

Chromizing of Steels

In recent years, considerable thought and study have been given to the use of chromized articles in place of chromium stainless steel articles. The present extensive application of chromizing, indeed, helps greatly to conserve this valuable metal.

SLM von Polylactiden zur Herstellung von resorbierbaren Implantaten

Rapid Manufacturing von individuellen Implantaten mittels Selective Laser Melting (SLM) wurde für metallische Standardwerkstoffe in der Medizintechnik (Titanlegierungen, Kobalt-Chrom-Legierungen, Stahl) realisiert. Dies sind permanente Implantate, die entweder dauerhaft im Körper verbleiben oder in einer zweiten Operation entfernt werden. Eine vom ILT mittels SLM hergestellte Hüftpfanne aus TiAl6V4 konnte bereits erfolgreich im Patienten implantiert werden. Die regenerative Therapie ist jedoch die klinisch bevorzugte Strategie. Das bedeutet, dass der Selbstheilungsprozess des menschlichen Körpers für die Heilung von großen Knochendefekten genutzt wird. Ein neuer Ansatz zur Implantatfertigung folgt dieser Strategie. Der SLM-Prozess wird für die Verarbeitung von bioresorbierbaren Werkstoffen entwickelt um individuelle Implantate zu fertigen, die im Körper abgebaut und durch körpereigenes Knochengewebe ersetzt werden. Diese Arbeit beschreibt die Qualifizierung des SLM Verfahrens für die Verarbeitung von einem Kompositmaterial aus Polylactid / β-Tricalciumphosphat (PDLLA/β-TCP).

Microstructural degradation of aluminide coatings on single crystal nickel based superalloys during high temperature exposure

An investigation, employing edge-on transmission electron microscopy, of the microstructure of aluminide diffusion coatings on a single crystal y' strengthened nickel base super alloy is reported. An examination has been made of the effect of postcoating exposure at 1100°C on the stability of the coating matrix, a B2 type phase, nominally NiAl. Precipitation in the coating is considered with respect to both decomposition of the B2 matrix to other Ni-Al (plus titanium) phases and the formation of chromium bearing precipitates. A comparison is drawn with behaviour at lower temperatures (850-950°C). © 1995 The Institute of Materials.

Study of the physical properties of metals and oxides at extreme pressure and temperature conditions

The high-pressure and temperature investigations on transition metals, metal doped-oxide system, nanocrystalline materials are presented in this dissertation. The metal-doped oxide systems are technologically important because of their applications, e.g. LSC, opto electronic applications, luminescence from lasers, etc., and from the earth sciences point of view, e.g. the study of trace elements in the MgO-SiO2 system, which accounts for 50% of the Earth's chondritic model. We have carried out thorough investigations on Cr2O3 and on chromium bearing oxides at high PT-conditions using in situ X-ray diffractometry and florescence spectroscopy techniques. Having obtained exciting results, an attempt to focus on the mechanism of the coordination of transition metals in oxides has been made. Additionally, the florescence from the metals in host oxides was found to be helpful to obtain information on structural variations like changes in the coordination of the doped element, formation of new phases, the diffusion processes. The possible reactions taking place at extreme conditions in the MgO-SiO2 system has been observed using florescence as markers. A new heating assemblage has been designed and fabricated for a precise determination of temperature at high pressures. An equation combining pressure shifts of ruby wavelength and temperature has been proposed. We observed that the compressibility of nanocrystalline material (MgO and Ni) is independent of crystallite size. A reduction in the transition pressure of nanocrystalline ceria at high-pressure has been observed as compare to the corresponding bulk material. ^