Microstructural transitions in Pt-C alloys during high-voltage-electron-microscope irradiation

Abstract

Radiation-induced microstructural changes in Pt-C alloys under irradiation inside a high-voltage electron microscope were investigated as a function of energy and temperature. Electrons of energy > 380 keV can displace C atoms from the monolayer carbon platelets previously created by co-precipitation of C and vacancies on {100} planes. The collapsed vacant sites left behind in the platelets by this direct displacement process amalgamate after a certain incubation dose. At higher energies, > 560 keV, the electrons can impart a considerable energy to the C atoms, which, in turn, become sufficiently energetic to displace the Pt atoms via secondary C-Pt collisions. Consequently, in these energy regimes, significant changes in the alloy microstructure, such as stimulated precipitate coarsening and formation of interstitial loops in the matrix, take place, even though the incident electrons have energies far below the displacement threshold of the matrix element ( ~ 1.3 MeV). The incubation doses for the formation of visible defect clusters inside the C precipitates and in the matrix were measured and fitted to simple analytical formalisms. The present work indicates the importance of accounting for secondary-collision processes in the assessment of radiation damage in alloys in which the alloying elements are drastically different in atomic mass.