Browsing by Author "Singer, Irwin L."

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    Evaluation of the durability of elastomeric easy-release coatings
    Christiaen, Anne-Claire (Virginia Tech, 1998-07-16)
    Novel coatings have been designed to solve problems associated with biofouling of marine structures, particularly ship hulls. The best candidates to date are multilayered coatings incorporating silicone rubber technology. These materials are efficient because they exhibit excellent release properties. However, they are very soft and tend to be more susceptible to various forms of mechanical damage. Fundamental analysis of the durability of these coatings has been done using standard laboratory tests. Simulative studies are essential to screen candidates as well as to predict the true life of the systems. The goal of this project was to develop a testing protocol for the evaluation of the durability of elastomeric easy release coatings and to implement it on selected candidate coatings. A brushing apparatus was designed and built to simulate the cleaning processes of ship hulls. Wear was measured with profilometry. The proposed methodology is valuable to study the processes of wear of the coatings, to screen various materials and to identify parameters, either functional or material, which would directly affect their durability. Two groups of candidate coatings were tested: the EXS series and the NRL series. The EXS samples showed better wear resistance than the NRL samples and showed no dependence on the rotational speed of the brushes. The NRL samples showed that increasing the sliding speed resulted in a decrease in wear. An increase in the applied load resulted in increased wear for both sample series. The effect of coating thickness was also investigated and discrimination between the proposed coatings could not be established because the tips of the bristles were sharp and irregular. Scratches matching the path of the brush bristles were observed in the wear scars of both sample types under all load and speed conditions. The NRL samples also exhibited ridges perpendicular to the sliding direction similar to the abrasion pattern.
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    Modeling of high fluence Ti ion implantation and vacuum carburization in steel
    Farkas, Diana; Singer, Irwin L.; Rangaswamy, M. (American Institute of Physics, 1985)
    Concentration‐versus‐depth profiles have been calculated for Ti and C in Ti‐implanted 52100 steel. A computer formalism was developed to account for diffusion and mixing processes, as well as sputtering and lattice dilation. A Gaussian distribution of Ti was assumed to be incorporated at each time interval. The effects of sputtering and lattice dilation were then included by means of an appropriate coordinate transformation. C was assumed to be gettered from the vacuum system in a one‐to‐one ratio with the surface Ti concentration up to a saturation point. Both Ti and C were allowed to diffuse. A series of experimental (Auger) concentration‐versus‐depth profiles of Ti‐implanted steel were analyzed using the above‐mentioned assumptions. A best fit procedure for these curves yielded information on the values of the sputtering yield, range, and straggling, as well as the mixing processes that occur during the implantation. The effective diffusivity of Ti was found to be 6×10− 1 5 cm2/sec, a value that is consistent with the cascade mixing mechanism. The effective diffusivity of C was found to be 6×10− 1 5 cm2/sec, and the sputtering yield by Ti atoms was best fit by a value of about 2. The observed range and straggling values were in very good agreement with the values predicted by existing theories, so long as the lattice was allowed to dilate.