摘要:

AbstractThe metal dusting of two low alloy steels was investigated at 475°C in flowing CO‐H2‐H2O mixtures at atmospheric pressure and aC>1. The reaction sequence comprises: (1) oversaturation with C, formation of cementite und its decomposition to metal particles and carbon, and (2) additional carbon deposition on the metal particles from the atmosphere. The metal wastage rate r1was determined by analysis of the corrosion product after exposures, this rate is constant with time und virtually independent of the environment. The carbon deposition from the atmosphere was determined by thermogravimetry, its rate r2increases linearly with time, which can be explained by the catalytic action of the metal particles – periodic changes are superposed. The rate of carbon deposition r2is proportional to the carbon activity in the atmosphere. The metal dusting could not be suppressed by increasing the oxygen activity or preoxidation, even if magnetite should be stable. Addition of H2S, however, effectively suppresses the

ISSN:0947-5117    

DOI:10.1002/maco.19940450402

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractThe presence of the structural interconnected porosity causes serious problems in the use of traditional bath compositions or usual deposition methods for protecting sintered iron pieces.The corrosion protection of steel is traditionally obtained by different surface treatment methods such as painting, electroplating, dipping or spraying, which cannot always be easily transposed for sintered metal parts.The aim of this work is to study in detail a wide range of industrially produced coatings, covering all the main proposed treatments, in order to evaluate the microstructural characteristics and in particular to point out the structural defects which can affect the corrosion behaviour of the protected sintered metal parts.The samples studied in this work were obtained by industrial production; both the sintered substrates and the corrosion protection treatments were carried out by specialized factories.

ISSN:0947-5117    

DOI:10.1002/maco.19940450403

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractThe oxidation induced loss in wall thickness of alumina forming high temperature alloys is in most cases not a limiting factor for component life because of the slow growth rates of the alumina surface scales. However, scale growth and repealing after spalling lead to depletion of the scale forming element, aluminium, in the bulk alloy. If, during long time service at high temperatures, the concentration of aluminium has decreased beneath a critical level, the protective alumina scale can no longer be formed and oxidation of the base elements Fe, Ni or Co occurs, leading to a catastrophic breakaway oxidation of the component. A model is presented which allows the calculation of the time at which this breakaway occurs using FeCrAl based ODS alloys as an example. The parameters which are necessary for the calculations, such as scale growth rates, scale spalling und bulk aluminium diffusion can be determined from relatively short time laboratory experiments. The calculated und measured results for the commercial ODS alloys ODM 751, PM 2000 und MA 956 at 11.00 und 1200°C are presented in form of Oxidation Diagrams in which the time to breakaway oxidation is plotted as a function of component wall thickness. On the basis of the theoretical considerations possible measures for increasing the oxidation limited life of the mentioned alumina forming alloys are discussed

ISSN:0947-5117    

DOI:10.1002/maco.19940450404

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Abstract76Ni‐24P amorphous alloys have been electrodeposited from solutions containing sodium lauryl sulphate (SLS) and triton‐X 100 (TX‐100) to improve the surface quality of the specimens. Corrosion behaviour of electrodeposited amorphous alloys in sulphate and chloride solutions at 25°C has been studied by potential‐time decay, linear polarization resistance and potentiodynamic techniques. Anodic polarization curves show that the specimens exhibit mild passivity at potentials between approximately −200 mV and 200 mV (SCE) and dissolve transpassively above 200 mV (SCE). The sulphate solution was found to increase the dissolution of the samples treated by the surfactants during the substrate brass plating. The nonanionic surfactant increases the corrosion current by 10 times compared to the anionic one which enhances the current by 400 times; the interpretation was based on the enhanced dissolution of the microcrystals of the specimens in the sulphate solution and to the steric hindrance of the surfactants. In addition, the alloys are more resistant to chlorides due to the formation of a phosphate/hypophosphite film which protects the surface from d

ISSN:0947-5117    

DOI:10.1002/maco.19940450405

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19940450406

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19940450407

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19940450408

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19940450401

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY