Method of making an anti-friction coating on metal by plasma spraying powder having a solid lubricant core and fusable metal shell
Reference Number: N 01-02
Inventors: Rao, V. Durga N.; Kabat, Daniel M.; Rose, Robert A.
The invention, in a first aspect, is a thermally sprayable powder, having powder grains comprising: (a) a core of solid lubricant particles comprising at least graphite and MoS.sub.2 ; and (b) a thin, soft metal shell encapsulating such core. Additional powder grains can comprise other solid lubricants of the group consisting of hexagonal BN, LiF, CaF.sub.2, WS.sub.2, and eutectic mixtures of LiF/CaF.sub.2 or LiF/NaF.sub.2 ; additional powder grains can comprise hard, wear-resistant particles selected from the group consisting of SiC, NiCrAl, and intermetallic compounds such as FeWNiVCr, NiCrMoVW, FeCrMoWV, CoFeNiCrMoWV, NiCrMoV, and CoMoCrVW (known as lave phase). The soft metal for the shell is selected from the group consisting of Ni, Co, Cu, Zn, Sn, Mg, and Fe.
The invention in another aspect is a solid lubricant coating system for a metal wear interface subject to high temperatures and wet lubrication, comprising: (a) particles of oil-attracting solid lubricants comprised of at least graphite and MoS.sub.2, (b) soft metal shells encapsulating the particles and being fused together to form a network of grains constituting a coating fusably adhered to the metal interface, the coating having a porosity of 2-10% by volume. The coating has a deposited thickness in the range of 40-250 microns, and is desirably honed to a thickness of about 25-175 microns.
The invention in still another aspect is a method of making an anti-friction coating on a metal surface subject to sliding wear, comprising: (a) forming an encapsulated powder having grains comprising essentially a core of solid lubricants of graphite and MoS.sub.2, and a thin shell of fusable soft metal; (b) plasma spraying the powder onto a light metal surface to form a coating; and (c) finish-smoothing of the coating to a uniform thickness of about 25-175 microns. The light metal surface is constituted of a metal or alloyed metal selected from the group consisting of aluminum, magnesium, and titanium, the light metal surface being cleansed to freshly expose the light metal or metal alloy just prior to plasma spraying.
Yet another aspect of this invention is an engine block having one or more anti-friction coated cylinder bore walls, comprising: (a) a metal engine block having at least one metal cylinder wall; (b) a coating of grains fused to the cylinder bore wall, the grains each being comprised of solid lubricant particles encapsulated within a soft metal shell, the shells being fused together to form a network with limited porosity, the solid lubricant comprising graphite and MoS.sub.2 ; and (c) wet oil lubrication retained within the porosity of the coating. The soft metal of the coating will have a hardness no greater than 50 Rc (preferably Rc 20-30); the soft metal may additionally comprise a small amount of alloy metal adherently compatible with the cylinder bore wall metal.