College Park, Maryland June 6 - 10 , 2004 |
MP34: Neutron Residual Stress Measurements of Aluminum Cold Spray Coating
L. Li (State University of New York, Stony Brook, NY 11794-2275), V. Luzin (National Institute of Standards and Technology; State University of New York, Stony Brook, NY 11794-2275), R. Neiser (Sandia National Laboratories, Albuquerque, NM 87123), H.-J. Prask (National Institute of Standards and Technology), S. Sampath (State University of New York, Stony Brook, NY 11794-2275)
Cold spray technology is a novel method for producing dense, oxide free coatings with some other specific qualities that can not be easily achieved by the traditional thermal spray technique. Cold spraying process involves high particle velocities and impact momentum and less or no thermal input so that splat formation and coating deposition is very different from the “conventional” thermal spray process. Consequently residual stress formation is different for this process. It has been speculated that cold spraying produces significantly lower residual stresses than thermal spraying. This investigation was intended to elucidate this question and provide quantitative results on this subject.
In this study we investigated residual stress distribution in the aluminum-coating-on-aluminum-substrate sample by means of neutron diffraction. Neutron diffraction stress measurements were performed on the BT8 diffractometer at the NIST Center for Neutron Research (NCNR) with spatial resolution 0.5 mm through thickness using a gauge volume of 0.5x0.5x7 mm3. The substrate thickness is approximately 3 mm and the coating thickness is about 2 mm, so that this spatial resolution is sufficient to obtain reliable through-thickness profiles of the in-plane stress distribution. Special care was taken for measurements of near-surface points. Since sample surface preparation before spraying involves sand (grit) blasting, which is known to produce residual stresses too, additional experiments on a substrate-only sample were done to determine the initial stress state of the substrate before spraying. Other methods of material characterization (electron microscopy, indentation, etc.) were employed to understand better the coating performance.
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