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Hren, J. J.

Publications and source records attributed to Hren, J. J..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Determination of Burgers vectors in close-packed metals using g.b = 2 contrast.

Reexamination of dislocation images giving double contrast in the electron microscope for g.b = 2 as a possible means for Burgers vector determinations. In fcc foils which have been cut parallel to an active slip plane, the g.b = 2 criterion provides a quick positive Burgers vector analysis which can be carried out during observation. The method is also applicable to basal dislocations in hcp. A comparison between calculated two-beam profiles and experimental images in aluminum is discussed, and several commonly observed characteristics of g.b = 2 contrast are described.

Kestenbach, H.-J.↗
NASA NTRS1972

Anomalous FIM images of tungsten.

Observation of unusual field-ion images consisting of bright bands of variable width parallel to the 111 (in carets) zones in tungsten at 78 K. Typical conditions for the effect are: pulse width from 1 to 50 microsec and pulse height adjusted so that five to ten pulses are required to remove one (110) plane. The influence of a number of accessible variables was studied and the results lead to a two-mechanism model for field evaporation involving (1) a slow process requiring helium promotion and (2) unpromoted evaporation when the local helium supply is depleted at high rates. The model implies that helium diffusion is rate-limiting in the promotion mechanism and leads to a migration energy of about 0.15 eV during field evaporation. There is a measurable difference in end form in the limits of high- and low-field evaporation rates. High rates are nearly isotropic and yield a more hemispherical end form.

Hren, J. J.↗
NASA NTRS1971

Field-ion microscopy of ordered Cu-Au alloy.

A method is proposed for overcoming current difficulties in measuring atomic order parameters of nonrefractory metals when using the field-ion microscope (FIM). Near stoichiometric CuAu and Cu3Au were tested by means of this method. Images of substantially fully ordered CuAu and Cu3Au thus obtained are presented and discussed.

Son, U. T.↗