Report on coating from Teer

A trial coating run has been performed at Teer Coating LTD to assess the use of a barrel coating system as a viable option to coat multilayer spheres. Hollow glass spheres (3M K15) ranging in diameter from 70-120 microns were cleaned in a process using a 0.1 M HCl solution. Comparative photos before and after the cleaning process are shown in figure 1. Approximately, 2 liters of cleaned spheres were sent to Teer for the trial coating in their barrel coater. A picture of barrel coating system is shown in figure 2. The coating process was one layer of titanium followed by one layer of aluminum. The target thickness for each layer is 500 nm, however, no rate runs were performed to calibrate the parameters. Each layer was sputtered for 10 hours, for a total of 20 hours. After the coating process, the coated spheres were sent back to LLNL for SEM analysis. In order to quickly examine the coating in cross-section, the spheres were broken with a spatula. Photos of the broken spheres are shown in Fig 3. One sphere was chosen to look at the uniformity around the sphere. As can be seen in Figure 4, there is fairly good uniformity around the sphere. You can also distinguish between the Ti (lighter) and Al layers, however it appears the Al is quite a bit thicker. This result is not too surprising because in general Al deposits faster than Ti. Figure 4 also shows the surface morphology of the top Al layer. Although it is still quite rough, it appears to be smoother than the Teer coating with just Al on glass. Based on this analysis, we believe that the barrel coating system can produce uniform coatings and is the correct deposition configuration to coat large quantities of microspheres. However, given the variation in thickness and surface roughness of the current coatings, the process needs further development in order to produce the high quality multilayers required. Other variables including optimum material combinations, layer pair thickness, optimum surface preparation, cleaning, and coating parameters need to be optimized to fully assess this technology

Multiple slip in copper single crystals deformed in compression under uniaxial stress

Uniaxial compression experiments on copper single crystals, oriented to maximize the shear for one slip system, show some unexpected results. In addition to the expected activity on the primary slip system, the results show appreciable activity perpendicular to the primary system. The magnitude of the activity orthogonal to the primary varies from being equal to the primary for the as-fabricated samples to 1/5 of the primary in the samples annealed after fabrication

Calculation of the Slip System Activity in Deformed Zinc Single Crystals Using Digital 3-D Image Correlation Data

A 3-D image correlation system, which measures the full-field displacements in 3 dimensions, has been used to experimentally determine the full deformation gradient matrix for two zinc single crystals. Based on the image correlation data, the slip system activity for the two crystals has been calculated. The results of the calculation show that for one crystal, only the primary slip system is active, which is consistent with traditional theory. The other crystal however, shows appreciable deformation on slip systems other than the primary. An analysis has been conducted which confirms the experimental observation that these other slip system deform in such a manner that the net result is slip which is approximately one third the magnitude and directly orthogonal to the primary system

Image Correlation Applied to Single Crystal Plasticity Experiments and Comparison to Strain Gage Data

Full-field optical techniques are becoming increasingly popular for measuring the deformation of materials, especially in materials that exhibit non-uniform behavior. While there are many full-field techniques available (e.g. moire interferometry, electronic speckle pattern interferometry (ESPI), holography, and image correlation [1]), for our study of the deformation of single crystals, the image correlation technique was chosen for its insensitivity to vibrations and ability to measure large strains. While the theory and development of the algorithms for image correlation have been presented elsewhere [2,3] a comparative study to a conventional strain measurement device, such as a strain gage rosette, is desired to test the robustness and accuracy of the technique. The 6 Degrees of Freedom (6DOF) experiment, which was specifically designed to validate dislocation dynamics (DD) simulations [4], is ideally suited to compare the two methods. This experiment is different from previous experiments on single crystals in that it allows the crystal to deform essentially unconstrained, in both the elastic and plastic regimes, by allowing the bottom of the sample to move as the sample is being compressed. This unconstrained motion prevents the internal crystal planes from rotating during the deformation as typically seen in the pioneering work of Schmid [5] and Taylor [6]. In the early development of the 6DOF apparatus, stacked strain gage rosettes were used to provide the strain data [7]. While very accurate at small strains, strain gages provide an averaged measurement over a small area and cannot be used to measure the inhomogeneous plastic strains that typically occur during the 6DOF experiment. An image correlation technique can measure the full-field in-plane and out-of-plane deformation that occurs in single crystals, and a comparison to the strain gage data at small strains can test the accuracy of the method

Multiscale Characterization of bcc Crystals Deformed to Large Extents of Strain

In an effort to help advance the predictive capability of LLNL's multiscale modeling program a new experimental technique has been developed to provide high fidelity data on metallic single crystals out to relatively large extents of strain. The technique uses a '6 Degrees of Freedom' testing apparatus in conjunction with a 3-D image correlation system. Utilizing this technique, a series of experiments have been performed that reveal unexpected behavior which cannot be explained using traditional crystal plasticity theory. In addition, analysis and characterization techniques have also been developed to help quantify the unexpected behavior. Interactions with multiscale modelers include the development of a possible mechanism that might explain the anomalous behavior, as well as the discovery of a new 4-node dislocation junction

Generating and measuring the anisotropic elastic behaviour of Co thin films with oriented surface nano-strings on micro-cantilevers

In this research, the elastic behaviour of two Co thin films simultaneously deposited in an off-normal angle method was studied. Towards this end, two Si micro-cantilevers were simultaneously coated using pulsed laser deposition at an oblique angle, creating a Co nano-string surface morphology with a predetermined orientation. The selected position of each micro-cantilever during the coating process created longitudinal or transverse nano-strings. The anisotropic elastic behaviour of these Co films was determined by measuring the changes that took place in the resonant frequency of each micro-cantilever after this process of creating differently oriented plasma coatings had been completed. This differential procedure allowed us to determine the difference between the Young's modulus of the different films based on the different direction of the nano-strings. This difference was determined to be, at least, the 20% of the Young's modulus of the bulk Co