Self-Lubricating Cold-Sprayed Coatings Utilizing Microscale Nickel-Encapsulated Hexagonal Boron Nitride

Abstract

It is often beneficial to modify surfaces to gain desirable properties such as improved wear and friction resistance. Self-lubricating coatings can improve the performance of contacting surfaces and extend component lifetimes by reducing the coefficient of friction and/or improving resistance to specific wear modes. With these goals in mind, self-lubricating coatings of hexagonal boron nitride (hBN) particles in a deposited nickel matrix were investigated and optimized for friction and wear. These self-lubricating coatings were created via high-velocity particle consolidation or cold spray using micrometer-sized hBN powder encapsulated by nickel and nickel phosphorous alloys. Relatively thick nickel encapsulation via electrolesss Ni plating was required to aid in coating bonding/formation by “tricking” the hBN into acting as monolithic Ni during deposition. Once deposited on aluminum substrates, the coatings were analyzed and found to exhibit enhanced mechanical and tribological properties such as high bond strength and microhardness, a relatively low coefficient of friction, and improved reciprocating wear behavior relative to pure cold-sprayed Ni coatings. Furthermore, the encapsulation process was found to be both scalable and amenable to relatively small hBN particles.

KEYWORDS:

• Cold Spray
• Self-Lubricating Coatings
• Electroless Nickel
• Boron Nitride
• Coated Powders
• Wear Resistance
• Coefficient of Friction

ACKNOWLEDGEMENTS

The authors thank the Office of Naval Research under Award Number N00014-09-1-0019 for their support of this research.

Review led by Gary Doll