Ceramic Joining by Gas Phase Pulsed Laser Processing

The method of Selective Area Laser Deposition (SALD) and Vapor Infiltration (SALDVI) has been successfully used to fabricate small three-dimensional SiC/SiC and SiC/metal powder parts. Ceramic joints made by this technique have been limited by the throwing power of the laser resulting in incomplete joint penetration. Studies were performed to show the effectiveness of a fiber laser, with a wavelength of 1070 nm, for a joining process. The ability of the laser to penetrate a powder bed was utilized in the joint fabrication. The combination of powder fill, and deep laser penetration into the powder bed shows potential in the field of ceramic joining.Mechanical Engineerin

On the self-pinning character of synchro-Shockley dislocations in a Laves phase during strain rate cyclical compressions

Strain rate cyclical tests in compression, between 1350 and 1500 degrees C, have been employed to study the self-pinning character of thermally activated synchro-Shockley dislocations in the C15 Cr2Nb Laves phase. An average minimum effective (pinning) stress was calculated to be necessary for their propagation. The dislocation velocity cannot respond instantly to the strain rate changes and requires variations in the mobile dislocation density because the synchro-Shockleys can be pinned if the cooperating motion of their two Shockley components is hindered. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

The mechanical properties and the deformation microstructures of the C15 Laves phase Cr2Nb at high temperatures

Compression tests between 1250 and 1550 degrees C and 10(-5) and 5 x 10(-3) s(-1) and transmission electron microscopy have been employed to investigate the high temperature mechanical properties and the deformation mechanisms of the C15 Cr2Nb Laves phase. The stress-peaks in the compression curves during yielding were explained using a mechanism similar to strain aging combined with a low initial density of mobile dislocations. The primary deformation mechanism is slip by extended dislocations with Burgers vector 1/2 <110 >, whereas twinning is more frequent at 10(-4) s(-1). Schmid factor analysis indicated that twinning is more probable in grains oriented so as to have two co-planar twinning systems with high and comparable resolved shear stresses. Twinning produced very anisotropic microstructures. This may be due to synchroshear: a self-pinning mechanism which requires co-operative motion of zonal dislocations. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Studies of heteroepitaxial films of silicon and cadmium telluride on sapphire

SIGLEAvailable from British Library Document Supply Centre- DSC:DX92480 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Analysis of the reference structure adopted by a mixed tilt-twist vicinal high-angle grain boundary in titanium

A transmission electron microscopy study and geometric analysis has been performed on a vicinal 78.7° high-angle grain boundary in pure Ti which has mixed tilt-twist character and exhibits a characteristic dislocation arrangement. There is no feasible constrained coincident site lattice which could be adopted as the reference structure by this boundary and an alternative structure is proposed which corresponds to a two-dimensional atomic arrangement inclined at about 18° to the boundary plane. The dislocation configuration required to accommodate the deviation from the reference structure orientation was predicted using an O-lattice algorithm for class 1 interfacial dislocations and this matched well the arrangement observed experimentally

A Modified Approach to the Modeling of Grain-Boundary Structure in Materials with an Hexagonal Crystal-Structure

No abstract available

Determination of Beam Directions and Axis/Angle Pairs for Grain-Boundaries in Hexagonal Materials

The method of Ball which is used widely to obtain accurate measurements of beam directions for electron diffraction patterns from cubic crystals has been modified for hexagonal crystals. This modification employs Frank's four-vector method for hexagonal crystallography and does not require complex conversions between reference frames. Use of this method simplifies the determination of axis/angle pairs from grain boundaries in hexagonal crystals and one example from a boundary in Ti is presented

Identification of the Reference Structure for a High Angle Grain Boundary in Titanium

A high angle grain boundary in titanium containing a regular dislocation network has been studied using transmission electron microscopy. It was shown that the reference structure for this grain boundary was unlikely to be a CCSL and that a more feasible reference structure corresponded to the existence of near-2d periodicity in a plane which made a small angle with the grain boundary plane. The dislocation arrangement that would be required to accommodate the angular deviation from the relative orientation for this reference structure was calculated using an 'O' lattice method. This showed a good semi-quantitative agreement with that which was observed experimentally indicating that the proposed reference structure was the one adopted by this grain boundary