Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

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JUNE 28 WEDNESDAY AFTERNOON JS1-WeA-P.7 UHV REACTIVE EVAPORATION GROWTH OF TITANIUM NI- TRIDE THIN FILMS, LOOKING FOR MULTIPACTOR EFFECT SUPPRESSION IN SPACE APPLICATIONS. Ana Ruiz and Elisa Román. Instituto de Ciencia de Materiales de Madrid. Consejo Superior de Investigaciones Científicas. Cantoblanco. E-28049-Madrid. Spain Pilar Lozano*, Mariano García and Luis Galán. Departamento de Física Aplicada. Universidad Autónoma de Madrid.Cantoblanco. E-28049 Madrid. Spain. Isabel Montero. Instituto de Ciencia de Materiales de Madrid. Consejo Superior de Investigaciones Científicas. Cantoblanco. E-28049-Madrid. Spain. David Raboso. ESA/ESTEC. Keplerlaan, 1. 2200 AG Noordwijk. The Netherlands. A low secondary electron emission yield which remains stable after exposure to ambient, as well as a good electrical conductivity, have proved to be basic criteria for selecting a reliable coating in RF components for space applications, in order to reduce the multipactor effect. Although titanium nitride is among the most appropriate materials, its actual performance is very much dependent on the deposition conditions. Standard deposition techniques used for TiN thin films or coatings often produce layers that are far from optimal, specially concerning secondary emission yield and its stability when exposed to air. In this work, an ultra-high vacuum reactive evaporation procedure has been tested and optimized for the growth of TiN thin films, throwing very good results both in composition of the TiN layers and SEY values and performance. Sublimation of Ti filaments is carried out in a ultra-high vacuum chamber in which a controlled leak of high purity N 2 is placed close to the substrate surface, thus maintaining the overall pressure in the high vacuum range and preventing nitridation of the Ti filaments. Detailed description of the growth procedure, substrate preparation and deposition protocol will be described with special emphasis on the relevant growth parameters and practical hints and how to achieve them. We present a study of the samples grown, such as stoichiometry and composition obtained by means of XPS and AES, and secondary electron emission measurements versus time in the scale of several months. The results obtained show that the deposition technique throws the best results towards the multipactor effect suppression. *present address: Instituto Universitario de Investigación en Nanociencia de Aragón. Universidad de Zaragoza. Edificio Interfacultativo II. c/ Pedro Cerbuna,12.E-50009 Zaragoza (Spain) 130
JUNE 28 WEDNESDAY AFTERNOON JS1-WeA-P.6 DC-PULSED PLASMA NITRIDING (DCPPN) OF STANLESS STEEL: MICROSTRUCTURE, CORROSION A WEAR BEHAVIOUR. P. Corengia 1 , E. De Las Heras 2 , M. Brizuela 1 , D. González 1 , A. García-Luis 1 , G. <strong>Ybarra</strong> 2 , C. Moina 2 . 1 Fundación INASMET- Tecnalia, Paseo de Mikeletegi 2, 20009 San Sebastián, Spain. 2 Instituto Nacional de Tecnología Industrial, Av. Gral. Paz 5445, C.C. 157, (B1650 WAB) San Martín, Argentina. Stainless steels are usually employed as engineering materials due to high corrosion resistance. However, low wear resistance and poor tribological behaviour limit their use in some industrial applications. Therefore, there is an increasing interest in improving surface properties through plasma assisted treatments, notably ion nitriding. Although stainless steels can be nitrided with the consequential increase in surface hardness, which improves their tribological performance, this is accompanied by a loss of corrosion resistance of the nitrided case. Nitriding of stainless steels leads to a depletion of chromium content in the matrix, thus reducing the corrosion resistance of the nitrided layer. In the present work, industrial-scale DC-pulsed plasma nitriding for 20 h at 673K was used to improve the surface properties of both martensitic (AISI 410) and austenitic (AISI 316L) stainless steels. The effect of nitriding on structural and mechanical properties of the nitrided layer was investigated by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and microhardness. The tribological behaviour was studied and compared to the behaviour of the same steel in asreceived condition. The wear resistance was investigated using an Amsler-disc-machine, employing a dry combined contact of rolling–sliding with three different applied loads. The wear mechanisms involved during the test of unnitrided and plasma nitrided steels were investigated by microscopic observation of the surfaces, the corresponding cross-sections and the produced wear debris. In addition microhardness profiles were done in order to evaluate the work hardening effect during the wear process. Electrochemical experiments in 3% NaCl solution were carried out to characterize the corrosion behaviour of unnitrided and nitrided stainless steels. Analysis and discussion of the tribological results show that plasma nitriding improves the wear resistance of the surface on stainless steels and the main wear mechanism appears to be delamination. Consequences on the load bearing capacity are discussed. The modified layers of the nitrided AISI 316L steel were composed of “expanded austenite”, while the nitrided AISI 410 samples were characterized by the presence of “expanded ferrite”, CrN and Fe 4 N. The DCPPN samples of both AISI 316L and AISI 410 revealed a surface hardness above 1000 HV and a sharp interface between the case (nitrided layer) and the core (matrix). Results of electrochemical measurements of unnitrided and DCPPN specimens were analysed and related to the microstructural characteristics of the nitrided case. Corresponding author: Tel: +34 943 003700; fax: +34 943 003800, e-mail: pablo.corengia@inasmet.es <strong>129</strong>
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Sigilum Universitatis Studii Salama
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