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AbstractAbstract
[en] Currently, attempts are made to develop hardfacing cobalt-free alloys for coating the contact areas of moving parts of nuclear installations. In fact, under neutron flux, cobalt 59 is activated into cobalt 60, a highly radioactive isotope. Consequently, the coating debris generated by friction are likely to contaminate parts of the installation. Existing cobalt-free hardfacing alloys, nickel or iron bases, do not exhibit tribological properties competing with those of stellite, a commonly used hardfacing cobalt base alloy. HEA (High Entropy Alloy) and CCA (Complex Concentration Alloy) may be good candidates. Indeed, compare to conventional alloys, they show vast composition domain giving access to a large range of properties. After an initial selection of elements, the phases of selected alloys were calculated by CALPHAD software (Calculation of Phase Diagram). The compositions favoring the presence of hard intermetallic phases beneficial to tribological behavior were selected. Then several alloys were fabricated using different processes. From microstructural and tribological characterizations, one composition has been selected as the best potential cobalt-free hardfacing alloy candidate. Coatings of this composition were then fabricated by DLD (Direct Laser Deposition) and HIP (Hot Isostatic Pressing). Their microstructure and tribological behavior were measured and compared to those of stellite. (author)
[fr]
Il est necessaire de developper des revetements sans cobalt possedant une bonne resistance a l'usure afin de remplacer les alliages de type stellite qui sont utilises dans les centrales nucleaires. En effet, les debris de cet alliage sont actives sous flux neutronique et forme du 60Co, un isotope radioactif susceptible de contaminer le reste de l'installation. Les materiaux sans cobalt, base nickel ou base fer, proposes pour le moment ne presentent pas des proprietes tribologiques concurrentes a celles du stellite. Les AHE (Alliage a Haute Entropie) et ACC (Alliage a Composition Complexe) peuvent etre de bons candidats. En effet, ces alliages possedent des domaines de compositions particulierement etendus par rapport aux alliages conventionnels, qui donnent alors acces a un vaste espace de proprietes, en particulier mecaniques. Dans un premier temps, l'etude de plusieurs ACC par la methode CALPHAD (CALculation of PHAse Diagram) a ete realisee afin de determiner des compositions favorisant la presence de phases intermetalliques dures benefiques au comportement tribologiques. Le travail s'est poursuivi par la realisation de plusieurs series d'alliages. Des caracterisations microstructurales et tribologiques ont permis de retenir une unique composition comme meilleure candidate potentielle au remplacement des alliages base cobalt. Cette composition a alors ete elaboree sous forme de poudre puis de revetement en utilisant les procedes de DLD (Direct Laser Deposition) et compression isostatique a chaud. Leur microstructure et leur comportement tribologique a ete compare a celui du stelliteOriginal Title
Etude et selection d'alliages a composition complexe sans cobalt a finalite tribologique
Primary Subject
Source
2 Dec 2020; 166 p; 191 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; Science des Materiaux
Record Type
Report
Literature Type
Thesis/Dissertation
Report Number
Country of publication
ALLOYS, BETA DECAY RADIOISOTOPES, BETA-MINUS DECAY RADIOISOTOPES, COBALT ALLOYS, COBALT BASE ALLOYS, COBALT ISOTOPES, ELEMENTS, FABRICATION, INTERMEDIATE MASS NUCLEI, INTERNAL CONVERSION RADIOISOTOPES, ISOMERIC TRANSITION ISOTOPES, ISOTOPES, MATERIALS WORKING, METALS, MINUTES LIVING RADIOISOTOPES, NUCLEI, ODD-ODD NUCLEI, PRESSING, RADIOISOTOPES, SIMULATION, TRANSITION ELEMENT ALLOYS, TRANSITION ELEMENTS, YEARS LIVING RADIOISOTOPES
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