Studies of tin coated brass contacts in fretting conditions under different normal loads and frequencies

The fretting corrosion behavior of tin-plated brass contacts is studied at various normal loads (0.25, 0.5, 1.0 and 1.5 N) and fretting frequencies (1, 3 and 8 Hz). The typical characteristics of the change in contact resistance with fretting cycles and time are explained. Irrespective of the frequencies under study, 1 N normal load suppressed the fretting corrosion of tin contacts by maintaining the mechanical stability and good electrical contact between the contacting members which makes less accumulation of wear debris at the fretted zone. For a given normal load, the fretting corrosion of tin-plated contacts occur much faster at higher frequencies as it provides more fresh metal for oxidation and generates more accumulation of oxide wear debris at the contact zone. The failure time, i.e. the time for contact resistance at the fretted surface to reach 0.1 Ω is delayed with increasing normal loads at the studied frequencies. For a given normal load, the failure time reaches early at 8 Hz, i.e. at higher fretting frequencies. The fretted surface is examined using laser scanning microscope, scanning electron microscope and energy dispersive X-ray analysis to assess the surface profile, extent of fretting damage, extent of oxidation and elemental distribution across the contact zone. From the surface profile data, the fretted area and the wear rate is calculated and correlated with the observed extent of oxidation and earlier failure of electrical contacts. The surface morphology and EDX analysis results of the fretted surface clearly revealed the severe fretting damage at 0.25 N and 8 Hz.