Metal-to-metal spherical bearings are used in the aerospace industry and have particular application to landing gear bearings in aircraft. Conventional materials used in the production of landing gear metal-to-metal bearings are stainless steel and copper alloy for the inner and outer races. These materials are used because they do not gall in areas where no lubricant is present. However, these are relatively heavy materials, so solutions have been sought in the past to use more lightweight materials. In this respect, it is possible to replace such relatively heavy materials on a strength basis with titanium alloy bearings which are approximately 40% lighter. Although there is a significant weight saving, these materials tend to gall very quickly under the loading conditions experienced in landing gears. U.S. Pat. No. 4,848,934 gives an example of a titanium alloy bearing. Since the titanium alloy is too soft for metal-to-metal contact, it is provided with a hard coating of chromium oxide.
Other coatings have been investigated but considerable problems are encountered with the adhesion of the hard coating to the relatively soft titanium alloy.
In a conventional metal-to-metal bearing, the bearing housing is manufactured from copper or a copper alloy and the ball held within the housing manufactured from stainless steel. Lightweight versions are available where the stainless steel component is replaced by a titanium alloy but this is a relatively soft material and is therefore provided with a relatively hard coating of chromium oxide so as to provide a good bearing surface at the interface between the bearing housing and the ball.
The use of chromium oxide and chromium plating techniques are environmentally unfriendly and entail considerable manufacturing costs so it is preferred not to use chromium oxide.