Search NASA⌕ Search

SEARCH · Search NASA

Results for “stacking faults”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1966

Stacking faults in TiC.

Stacking faults in titanium carbide shown by electron microscopy bounded by partial dislocations

TITANIUM CARBIDE↗
NASA NTRS1982

The measurement of the stacking fault energy in copper, nickel and copper-nickel alloys

The relationship of hydrogen solubility and the hydrogen embrittlement of high strength, high performance face centered cubic alloys to the stacking fault energy of the alloys was investigated. The stacking fault energy is inversely related to the distance between the two partial dislocations which are formed by the dissociation of a perfect dislocation. The two partial dislocations define a stacking fault in the crystal which offers a region for hydrogen segregation. The distance between the partial dislocations is measured by weak beam, dark field transmission electron microscopy. The stacking fault energy is calculated. Pure copper, pure nickel and copper-nickel single crystals are used to determine the stacking fault energy.

Leighly, H. P., Jr.↗
NASA NTRS1982

The determination of the stacking fault energy in copper-nickel alloys

Methods for determining the stacking fault energies of a series of nickel-copper alloys to gain an insight into the embrittling effect of hydrogen are evaluated. Plans for employing weak beam dark field electron microscopy to determine stacking fault energies are outlined.

Leighly, H. P., Jr.↗
NASA NTRS1982

Pre- and post-annealing of mechanical damage in silicon wafers

Basic properties of mechanical damage in silicon consisting of cracks and abrasion were studied using transmission electron microscopy. The crystallographic structure of mechanical damage was determined before and after high temperature annealing. The main findings include that stresses in silicon around crack tips are not plastically relieved at room temperature and that abrasion at room temperature introduces shear loops into the silicon. It was also found that cracks of micron size can be annealed out, specifically, if cleavage occurs on 111 planes. The healing products of such cracks are 60 deg and 90 deg dislocations. Submicron cracks transform into stacking faults during annealing. Likewise high concentrations of shear loops due abrasion were found to anneal into stacking faults. A one to one correlation between surface areas containing small cracks and stacking faults was made. Measurements of damage removal on silicon surfaces through chemical-mechanical etching techniques are presented. It is shown that silicon dioxide repolishes damaged silicon surfaces most effectively.

Schwottke, G. H.↗
NASA NTRS1980

Dislocation dissociation in some f.c.c. metals

The dissociation of a perfect screw dislocation into a stacking fault in an f.c.c. lattice is modeled by the modified lattice statics. The interatomic potentials are obtained from the work of Esterling and Swaroop and differ substantially from those empirical potentials usually employed in defect simulations. The calculated stacking fault widths for aluminum, copper, and silver are in good agreement with weak beam microscopy results.

Esterling, D. M.↗
NASA NTRS1978

The impact of defects on the photovoltaic potential of RTR silicon ribbon

Silicon ribbon grown at a high rate by the ribbon-to-ribbon (RTR) method contains a variety of defects and can exhibit an unusual dendritic morphology. This paper is a study of the effect of the defect structure and dendritic morphology on the photovoltaic potential of RTR ribbon. Defects found in RTR ribbon include grain boundaries, twin planes, stacking faults and dislocations. The electrical activity of these defects is investigated by measuring the diffusion length in the ribbon; by fabricating small area diodes on the ribbon and evaluating their photoresponse; and by using a scanning electron microscope in the electron beam induced current mode. It is concluded that although grain boundaries serve very effectively as recombination centers, they do not occur frequently enough in RTR ribbons to significantly affect the generation current. Dislocation densities up to 1,000,000/sq cm can be tolerated without strongly reducing the photoresponse. Similarly, linear boundaries such as twin planes or stacking faults do not affect the cell performance up to densities of 1000/sq cm.

Baghdadi, A.↗
NASA NTRS1975

Oxide nucleation on thin films of copper during in situ oxidation in an electron microscope

Single-crystal copper thin films were oxidized at an isothermal temperature of 425 C and at an oxygen partial pressure of 0.005 torr. Specimens were prepared by epitaxial vapor deposition onto polished faces of rocksalt and were mounted in a hot stage inside the ultrahigh-vacuum chamber of a high-resolution electron microscope. An induction period of roughly 30 min was established which was independent of the film thickness but depended strongly on the oxygen partial pressure and to exposure to oxygen prior to oxidation. Neither stacking faults nor dislocations were found to be associated with the Cu2O nucleation sites. The experimental data, including results from oxygen dissolution experiments and from repetitive oxidation-reduction-oxidation sequences, fit well into the framework of an oxidation process involving the formation of a surface charge layer, oxygen saturation of the metal with formation of a supersaturated zone near the surface, and nucleation followed by surface diffusion of oxygen and bulk diffusion of copper for lateral and vertical oxide growth, respectively.

Heinemann, K.↗
NASA NTRS1976

Oxidation of metals and alloys in controlled atmospheres using in situ transmission electron microscopy and Auger spectrography

Single-crystalline thin films of copper were oxidized at an isothermal temperature of 425 C and at an oxygen partial pressure of .005 Torr in situ in a high-resolution electron microscope. The specimens were prepared by epitaxial vapor deposition onto polished 100 and 110 faces of rocksalt and mounted in a hot stage inside an ultra-high-vacuum specimen chamber of the microscope. Large amounts of sulfur, carbon, and oxygen were detected by Auger electron spectroscopy on the surface of the as-received films and were removed in situ by ion-sputter etching immediately prior to the oxidation. The nucleation and growth characteristics of Cu2O on Cu were studied. Results show that neither stacking faults nor dislocations are associated with the Cu2O nucleation sites. The growth of Cu2O nuclei is linear with time. The experimental findings, including results from oxygen dissolution experiments and from repetitive oxidation-reduction-oxidation sequences, fit well into the framework of an oxidation process involving (a) the formation of a surface-charge layer, (b) oxygen saturation in the metal and (c) nucleation, followed by surface diffusion of oxygen and bulk diffusion of copper for lateral and vertical oxide growth, respectively.

Rao, D. B.↗
NASA NTRS1977

The effect of oxidation-expanded defects upon MOS parameters

Implantation of Ne ions was chosen as a means of introducing a uniformly distributed quantitatively controllable and reproducible amount of microdefects at the silicon surface. Each wafer was ion-implanted on one half of its surface, the other half remaining as a control. Seven implant fluences from 1 trillion to 5 by 10 to the 14th power Ne ions/sq cm were used. The fluences, as well as the concentrations of defects expanded by the subsequent gate oxidation, were correlated with seven different MOS parameters. For implant fluences of 10 to the 14th power per sq cm and above, increasing stacking-fault densities were found. The oxide defect density associated with time-dependent breakdown increased significantly with Ne dose. The presence of oxidation-expanded defects drastically increases the surface-generation velocity and decreases the bulk lifetime. Slight increases in flatband voltage and surface-state density occurred only for the wafers having the greatest defect concentrations. Oxidation of a P-containing damaged silicon surface results in a greater pileup of P at the surface than occurs for the oxidation of a similar but undamaged surface. It appears that the expanding defects restrain the diffusion of P inward from the surface.

Prussin, S.↗
NASA NTRS1979

Fatigue crack propagation behaviour of unidirectionally solidified gamma/gamma-prime-delta eutectic alloys

Fatigue crack propagation studies were carried out on unidirectionally solidified gamma/gamma-prime-delta (Ni-Nb-Al) alloys over an aluminum content range of 1.5-2.5% by weight. The variation of Al content of as-grown alloys did not significantly affect the crack growth behavior of these eutectic composites. The results indicate that the addition of Al to the eutectic dramatically improved the FCP behavior. The gamma/gamma-prime-delta alloy exhibited crack growth rates for a given stress intensity range that are an order of magnitude lower than those for the gamma-delta alloy. It is suggested that this difference in FCP behavior can be explained on the basis of stacking fault energy considerations. Extensive delaminations at the crack tip were also revealed, which contributed to the superior fatigue response. Delamination was predominantly intergranular in nature.

Bretz, P. E.↗
NASA NTRS1978

Flow stress model in metal cutting

A model for the plastic deformation that occurs in metal cutting, based on dislocation mechanics, is presented. The model explains the fundamental deformation structure that develops during machining and is based on the well known Cottrell-Stokes Law, wherein the flow stress is partitioned into two parts; an athermal part which occurs in the shear fronts (or shear bands); and a thermal part which occurs in the lamella regions. The deformation envokes the presence of a cellular dislocation distribution which always exists in the material ahead of the shear process. This 'alien' dislocation distribution either exists in the metal prior to cutting or is produced by the compressive stress field which operates in front of the shear process. The magnitude of the flow stress and direction of the shear are shown to be correlated to the stacking fault energy of the metal being cut. The model is tested with respect to energy consumption rates and found to be consistent with observed values.

Black, J. T.↗
NASA NTRS1981

EBIC and HVTEM studies of RTR silicon ribbon

The defect structure of RTR ribbon #6-731, run 803 was studied. Prior to laser recrystallization the defect structure consists of closely spaced twin and grain boundaries. Precipitation of impurities occurs after laser recrystallization. The observation of electrically active defects in EBIC was correlated with HVTEM studies. Pairs of electrically active defects in twin boundaries are due to stacking faults connecting the twin boundaries.

Cunningham, B.↗
NASA NTRS1984

The role of cobalt on the creep of Waspaloy

Cobalt was systematically replaced with nickel in Waspaloy (which normally contains 13% Co) to determine the effects of cobalt on the creep behavior of this alloy. Effects of cobalt were found to be minimal on tensile strengths and microstructure. The creep resistance and the stress rupture resistance determined in the range from 704 to 760 C (1300 to 1400 C) were found to decrease as cobalt was removed from the standard alloy at all stresses and temperatures. Roughly a ten-fold drop in rupture life and a corresponding increase in minimum creep rate were found under all test conditions. Both the apparent creep activation energy and the matrix contribution to creep resistance were found to increase with cobalt. These creep effects are attributed to cobalt lowering the stacking fault energy of the alloy matrix. The creep resistance loss due to the removal of cobalt is shown to be restored by slightly increasing the gamma' volume fraction. Results are compared to a previous study on Udimet 700, a higher strength, higher gamma' volume fraction alloy with similar phase chemistry, in which cobalt did not affect creep resistance. An explanation for this difference in behavior based on interparticle spacing and cross-slip is presented.

Jarrett, R. N.↗
NASA NTRS1985

New adatom model for Si(11) 7X7 and Si(111)Ge 5X5 reconstructed surfaces

A new adatom model differing from the conventional model by a reconstruction of the substrate is proposed. The new adatom structure provides an explanation for the 7x7 and 5x5 size of the unit cells seen on annealed Si(111) and Si(111)-Ge surfaces, respectively. The model is consistent with structural information from vacuum-tunneling microscopy. It also provides simple explanations for stacking-fault-type features expected from Rutherford backscattering experiments and for similarities in the LEED and photoemission spectra of 2x1 and 7x7 surfaces.

Chadi, D. J.↗