The answer is generally no, for reasons of cost. Only a small increase in lubricity is gained by coating both surfaces; however, part life may be doubled because of the greater thickness.

Remember: In most cases, it is easier and more economical to coat the exterior of a part rather than the interior (a shaft instead of a bearing).

When there is a difference in mating materials, it is usually preferable to coat the softer of the two surfaces, because this is the one which, given boundary lubrication failure, could suffer the greater damage.

The mating surface has a lot to do with the wear rate of a coating. For instance, the wear rate on a coated journal that supports an aluminum shaft is as much as 50 times that of an identical bearing that supports a carbon steel shaft.

The roughness of a mating surface also has an effect on coating wear. The optimum surface has 0.2-0.3 microns (rms)/8-12 micro-in. Surprisingly, hyper-smooth surfaces (less than 0.1 microns (rms)/4 micro in.) produce higher wear rates than those with a finish between 0.38-0.75 microns (rms)/15-30 micro-in.