When the surfaces of the bearing are separated by a fluid film, the bearing materials do not have any effect on its operation so long as the parts have sufficient strength to withstand the imposed loads and sufficient rigidity to maintain alignment.
On account of strength and rigidity requirements, journals are generally made of steel. For the bushing, however, there are other requirements, as discussed below that must be considered in selecting the best material for bearing.
Low Coefficient of friction
The bearing materials combination of sliding surfaces, along with the lubricant should provide a low friction coefficient for reducing damage and lower running costs.
High Compressive Strength
The bearing material should have high compressive strength to withstand this maximum pressure to prevent extrusion or other permanent deformation of the bearing.
High Fatigue Strength
The bearing material should have sufficient fatigue strength so that it can withstand repeated loads without developing surface fatigue cracks. It is of major importance in aircraft and automotive engines.
Low Thermal Expansion
The size of bearing should remain nearly constant during periods of temperature change.
High Thermal Conductivity
The ability to bear material to dissipate heat quickly due to friction.
Bearing material should be elastic enough to allow the bearing to return to original shape upon relief of stresses that may cause temporary distortion, such as misalignment and overloading.
It is the ability of the bearing material to accommodate shaft deflections and bearing inaccuracies by plastic deformation (or creep) without excessive wear and heating.
It is the ability to bearing material to accommodate (or embed) small particles of dust, grit, etc. without scoring the material of the journal.
Bearing materials have varying degrees of resistance to corrosion; this should be considered where corrosive oils must be used.