Friction Behavior of Boric Acid and Annealed Boron Carbide Coatings Studied by In Situ Raman Tribometry

• Published in: Tribology transactions Vol. 45; no. 3; pp. 354 - 362
• Main Authors: Dvorak, S. D., Wahl, K. J., Singer, I. L.
• Format: Journal Article
• Language: English
• Published: Colchester Taylor & Francis Group 01.01.2002; Taylor & Francis
• Subjects: Applied sciences; Carbide Coatings; Exact sciences and technology; Friction Coefficient; Friction, wear, lubrication; Machine components; Mechanical engineering. Machine design; Raman Spectroscopy; Relative humidity; Solid lubricant; Sliding wear; Wear test; Tribochemical reaction; Third body; Ceramic coating; Experimental study; Coatings; Boron carbide; Boric acid; Humidity effect; Reciprocating movement machine; Raman spectrometry; Air humidity; Sliding friction; Tribology
• ISSN: 1040-2004; 1547-397X
• DOI: 10.1080/10402000208982560

The sliding friction behavior of boric acid and annealed boron carbide coatings has been investigated by in situ Raman tribometry. Reciprocating sliding tests were performed in air (∼20% relative humidity) at 1 mm/s with a transparent sapphire hemisphere dead weight loaded against the coated substrates. A homebuilt micro-Raman tribometer recorded the friction force as well as allowed both visualization and Raman spectroscopy of the contacts during sliding. Friction coefficients for the boric acid films remained low (μ ∼ 0.06) throughout sliding until failure (μ ∼ 0.7), at which time boric acid was lost from the contact and substrate material (aluminum) transferred to the slider. Friction coefficients for the annealed boron carbide, known to form boric acid surface films upon cooling, were initially low (0.08), then gradually increased and leveled out at about 0.2. Raman spectroscopy revealed a mixture of boric acid and carbon initially; but as the friction coefficient rose, the boric acid intensity decreased to zero while the carbon intensity increased. Correlations between friction coefficients and amounts of solid lubricating material in the contact are presented, and the role of third bodies in controlling friction is discussed.