A metal used in hydrodynamic bearings, characterized by its resistance to galling. It is soft and easily damaged, which suggests it might be unsuitable for a bearing surface. However, it is made up of small, hard crystals dispersed in a softer metal, making it a metal matrix composite. As the bearing wears, the softer metal erodes, creating paths for lubricant between the hard high spots that provide the actual bearing surface. When tin is used as the softer metal, friction causes the tin to melt and function as a lubricant, protecting the bearing from wear when other lubricants are absent.