Friction behavior of boric acid and annealed boron carbide coatings studied by in situ Raman tribometry

摘要

The sliding friction behavior of boric acid and annealed boron carbide coatings has been investigated by in situ Roman 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 oat 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.