Critical voltage analysis of precipitation in certain nickel-base alloys

The critical voltage in quenched (single phase) binary nickel alloys containing Au, Ta, Pt, Nb, Al, and Be has been determined in the AEI EM7 high voltage electron microscope. For the {400} reflection, Au and Ta cause a significant decrease of ≈ 10 kV per 1% addition. The resultant calibration curves have been used to follow the compositional changes of the nickel-rich phase produced by ageing, and in the Ni-Ta alloy the critical voltage measurements show that compositional gradients exist around the precipitate particles. Le microscope electronique a haut voltage AEI EM7 a ete utilise pour determiner le voltage critique dans des solutions solides d'alliages binaires a base de nickel contenant Au, Ta, Pt, Nb, Al ou Be. Des courbes de calibration (voltage critique vs. pourcentage solute) furent determinees pour tous les alliages. Une addition de 1% de Au ou Ta cause une diminution considerable de ≈ 10 kV du voltage critique de la reflexion de Bragg du second ordre {400}. Il est alors possible de detecter le changement de composition dans la phase riche en nickel produit pendant le vieillissement et dans le systeme NiTa, les mesures du voltage critique demontrent l'existance d'un prfil de concentration de solute autour des particles precipitees.

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