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Full-Text Articles in Physics

Lattice-Dynamical Study Of The Premartensitic State Of The Cu-Al-Be Alloys, Lluís Mañosa, Jerel L. Zarestky, Thomas A. Lograsso, Dwight W. Delaney, C. Stassis Dec 1993

Lattice-Dynamical Study Of The Premartensitic State Of The Cu-Al-Be Alloys, Lluís Mañosa, Jerel L. Zarestky, Thomas A. Lograsso, Dwight W. Delaney, C. Stassis

Ames Laboratory Publications

Neutron-scattering techniques have been used to study the premartensitic state of a family of Cu-Al-Be alloys, which transform from the bcc phase to an 18R martensitic structure. We find that the phonon modes of the TA2[110] branch have very low energies with anomalous temperature dependence. A slight anomaly at q=2/3 was observed; this anomaly, however, does not change significantly with temperature. No elastic peaks, related to the martensite structure, were found in the premartensitic state of these alloys. The results are compared with measurements, performed under the same instrumental conditions, on two Cu-Al-Ni and a Cu-Zn-Al ...


Dynamical X-Ray Diffraction From An Icosahedral Quasicrystal, S. W. Kycia, Alan I. Goldman, Thomas A. Lograsso, Dwight W. Delaney, D. Black, M. Sutton, E. Dufresne, R. Brüning, B. Rodricks Aug 1993

Dynamical X-Ray Diffraction From An Icosahedral Quasicrystal, S. W. Kycia, Alan I. Goldman, Thomas A. Lograsso, Dwight W. Delaney, D. Black, M. Sutton, E. Dufresne, R. Brüning, B. Rodricks

Ames Laboratory Publications

We present direct evidence of dynamical diffraction of x rays from a quasicrystal. High-resolution x-ray-diffraction measurements of the Al-Pd-Mn face-centered icosahedral quasicrystal were performed, revealing a mosaic full width at half maximum of less than 0.001°. In a second experiment, the anomalous transmission of x rays (the Borrmann effect) was observed. These measurements show that nearly perfect quasicrystals may be grown to centimeter-size dimensions allowing x-ray techniques based upon dynamical diffraction to be brought to bear on the analysis of icosahedral structures.


Interatomic Forces And Atomic Structure Of Grain Boundaries In Copper-Bismuth Alloys, Min Yan, Mojmír Šob, David E. Luzzi, Vaclav Vitek, Graeme J. Ackland, M. Methfessel, C. O. Rodriguez Mar 1993

Interatomic Forces And Atomic Structure Of Grain Boundaries In Copper-Bismuth Alloys, Min Yan, Mojmír Šob, David E. Luzzi, Vaclav Vitek, Graeme J. Ackland, M. Methfessel, C. O. Rodriguez

Departmental Papers (MSE)

The many-body empirical potentials that describe atomic interactions in the copper-bismuth system were constructed using both experimental data and physical quantities obtained by ab initio full-potential linear muffin-tin orbital calculations for a metastable Cu3Bi compound. These potentials were then used to calculate the structure of a grain boundary in copper containing bismuth, which was at the same time studied by high-resolution electron microscopy (HREM). Excellent agreement between the calculated and observed structures is shown by comparing a through-focal series of observed and calculated images. This agreement validates the constructed potentials, which can be used with a high confidence ...


Deconvolution Of X-Ray Backscatter Diffraction Data For Nde Of Corrosion, Feng Qiu, W. L. Anderson, P. S. Ong Jan 1993

Deconvolution Of X-Ray Backscatter Diffraction Data For Nde Of Corrosion, Feng Qiu, W. L. Anderson, P. S. Ong

Review of Progress in Quantitative Nondestructive Evaluation

The problem of corrosion of steel surfaces under thermal insulation is one that plagues the petroleum, petrochemical, chemical and pipeline industries [1,2]. Often internal surfaces, as well, are subject to attack by moisture, acids or other corrosive influences. Thermal insulation renders traditional NDE methods mostly ineffective but is essentially transparent to x-rays in the energy ranges commonly used for industrial radiography. Since transmission radiography is severely hampered by the need for access to “both sides” of the object being tested, the use of NDE methods employing Compton backscattered x-rays is strongly suggested [3,4]. Through appropriate collimation of incident ...


X-Ray Ct For Quantitative Casting Material Evaluation, Gary Georgeson, Richard Bossi Jan 1993

X-Ray Ct For Quantitative Casting Material Evaluation, Gary Georgeson, Richard Bossi

Review of Progress in Quantitative Nondestructive Evaluation

Casting is an economical way to manufacture parts. However, castings are rarely used as primary structure in aircraft because of the large safety factors that are required for design allowables. This conservatism in utilization is due, in part, to the traditional limitations in evaluation technology for castings. The safety factor increases the overall weight of the casting, which defeats the cost and weight savings that castings offer. Significant gains in casting utilization are possible by a combination of control of the casting microstructure and proper nondestructive evaluation (NDE) of the product. The presently applied NDE criteria for accepting castings involves ...


Theoretical Study Of The Noble Metals On Semiconductor Surfaces And Ti-Base Shape Memory Alloys , Yungui Ding Jan 1993

Theoretical Study Of The Noble Metals On Semiconductor Surfaces And Ti-Base Shape Memory Alloys , Yungui Ding

Retrospective Theses and Dissertations

The electronic and structural properties of the (√3 x √3) R30° Ag/Si(111) and (√3 x √3) R30° Au/Si(111) surfaces are investigated using first principles total energy calculations. We have tested almost all experimentally proposed structural models for both surfaces and found the energetically most favorable model for each of them. The lowest energy model structure of the (√3 x √3) R30° Ag/Si(111) surface consists of a top layer of Ag atoms arranged as "honeycomb-chained-trimers" lying above a distorted "missing top layer" Si(111) substrate. The coverage of Ag is 1 monolayer (ML). We find ...