On the Bonding Mechanism in Cold Spray of Deformable hex-BN-Ni Clusters

• Published in: Journal of thermal spray technology Vol. 25; no. 5; pp. 982 - 991
• Main Authors: Neshastehriz, M., Smid, I., Segall, A. E., Eden, T. J.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.06.2016
• Subjects: Analytical Chemistry; Characterization and Evaluation of Materials; Chemistry and Materials Science; Corrosion and Coatings; Machines; Manufacturing; Materials Science; Peer Reviewed; Processes; Surfaces and Interfaces; Thin Films; Tribology; nickel; self-lubricating coating; coefficient of friction; cold spray; hexagonal boron nitride; wear resistance; aluminum substrate; bond strength
• ISSN: 1059-9630; 1544-1016
• DOI: 10.1007/s11666-016-0416-6

Bond strength and the lubrication potential of coatings made of 7 µm Hexagonal Boron Nitride particles encapsulated with nickel (hBN-Ni), and deposited onto aluminum 6061 substrates via cold spray were examined; for all tests, N 2 was used as the carrier gas at a temperature of 480 °C and pressure of 2.4 MPa. Results showed significant improvement in both wear resistance and reduced surface friction. Coated samples also demonstrated unexpected high bond strength, which was much greater than pure nickel cold sprayed onto aluminum. However, while the results were truly promising, the primary reason for the observed high bond strength could not be explained using existing cold spray theories which were primarily developed for pure metal particles. Based on the present findings compared to cold-sprayed layers of composite nickel-nickel (nickel particles encapsulated with nickel), a mechanism for bonding of hBN-Ni particles to aluminum based on the level of plastic deformation and hardenability is proposed. Indeed, the high bond strength between the coating and substrate is related to the relatively high initial ductility of the nickel encapsulation, compliance of the hBN, as well as the ensuing significant plastic deformation of the composite particles during cold spray deposition.