Bismuth-based composite coating for overlay applications in plain bearings

A plain bearing 1 with an overlay 2 of a composite coating comprising a bismuth or Bi-based alloy matrix and one or more soft particles 5 with a Mohs hardness of ≤ 5 dispersed within the matrix. A further aspect relates to a method of manufacturing the coating and overlay 2 via electro-deposition or electroless plating from a bath in which the particles are dispersed by ultrasound or megasound and potentially a further agitation method. The ultrasound or megasound and optional further agitation method may be applied during or before the electrodeposition stage. The soft particle 5 may be PTFE, a metal fluoride or sulphate, graphite, hexagonal boron nitride, phyllosilicate or lead or zinc oxide. The coating 2 may also contain hard particles with a Mohs hardness of ≥5.5, such as metal oxides, borides, carbides, nitrides and silicides, diamond, CNTs, or graphene. The soft lubricant particles 5 and optional hard particles may be between 1 nm and 5 µm in size, and take up 0.0001 to 30 % of the volume of the composite coating. The bearing 1 may have a bronze-based or aluminium-based alloy lining material 3, and possibly an interlayer between 5 nm and 15 µm thick comprising Ni, Cu, Ag, Cr, Co. Fe, Mn, Au, Zn or alloys thereof located between the bearing lining 3 and composite coating. The composite coating 2 forming part of the plain bearing 1 may be between 1 and 50 µm thick.