ELECTRON MICROSCOPE OBSERVATIONS OF QUENCHED AND AGED GOLD AND GOLD-PALLADIUM ALLOYS,
PENNSYLVANIA UNIV PHILADELPHIA SCHOOL OF METALLURGICAL ENGINEERING
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A review of past work on the behavior of vacancies in quenched metals is presented, with emphasis upon gold and transmission electron microscopy data. Results are presented on Au, Au-5 at Pd, and Au-10 at Pd foils quenched from 0.875 Tm Tm absolute melting temperature and examined in an electron microscope. It is found that increasing palladium content causes an increase in the number of faulted dislocation loops in the quenched and aged material and in the concentration of vacancies annihilated at such loops. However stacking fault tetrahedra represent the most important sinks in all cases. Some reasons for the increased importance of dislocation loops as vacancy sinks in the alloys are discussed. Changes in stacking fault energy due to alloying are not thought significant in producing this effect. Possible roles of nucleus configurations are discussed and a model is presented in which tetrahedra become less effective as sinks as their growth proceeds, owing to changes in solute concentration near them. However the effectiveness of loops as sinks is not expected to change significantly during ageing with the result that dislocation loops can become the main sinks in the later stages of ageing.
- Metallurgy and Metallography