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5392 |
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Evaluation of low-pressure cold spray MMC coatings by acoustic emission-coupled four-point flexural testing |
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Roy Lee* / University of Alberta, Canada Yik Tung Roy Lee / University of Alberta, Canada Mohamed Shibly/ University of Nottingham, United Kingdom Tanvir Hussain/ University of Nottingham, United Kingdom André McDonald/ University of Alberta, Canada |
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Low-pressure cold spray has been investigated as an innovative method to deposit metal matrix composite (MMC) coatings: boron carbide-nickel (B4C-Ni) and tungsten carbide-cobalt-nickel (WC-Co-Ni) composites. The coatings were investigated using scanning electron microscopy, X-ray diffraction with Rietveld refinement, and acoustic emission coupled four-point flexural test. Indentation fracture toughness tests were performed on the WC-Co-Ni coatings only. The results showed that the composites had a reinforcing particle volume fraction of 45.8 ± 1.6 vol.% and 22.7 ± 2.2 vol.% for the WC-Co-Ni and B4C-Ni MMC coatings, respectively. The flexural tests were used to evaluate the fracture strain of the composites. In these tests, the WC-Co-Ni composite failed by brittle facture at approximately 0.5% nominal strain. The B4C-Ni composite showed similar flexural behavior to that of an unreinforced Ni matrix. These results suggest that there was insufficient B4C within the coating to affect the ductile failure mode of Ni matrix significantly. Post bending fracture analysis showed the presence of straight, continuous cracks on the WC-Co-Ni surface and the indentation fracture toughness of WC-Co-Ni was found to be 1.2 ± 0.2 MPa-m0.5. Discontinuous, random cracks were observed on the B4C-Ni surface. The quantification of these properties is essential in evaluating the performance of the low-pressure cold spray coatings to determine its potential applications. |