Solid lubricant and hardenable steel coating system
Reference Number: N 01-02
Inventors: Rao, V. Durga N.
The invention, in a first aspect, is a thermally sprayable powder (particularly by plasma) for coating surfaces such as cylinder bores of an internal combustion engine. The powder comprises grain size agglomerates of (i) a plurality of solid lubricant particles selected from the group consisting of graphite, MoS.sub.2, hexagonal BN, CaF.sub.2, LiF, and eutectic mixtures of LiF/CaF.sub.2 or LiF/NaF.sub.2 ; and (ii) fusable ingredients adjacent the solid lubricant particles, the ingredients being air-hardenable upon friction-promoting-use, and the lubricants and fusable ingredients being agglomerated together by a low melting medium in the grains.
The invention, in a second aspect, comprises a solid lubricant coating system for use with a metal interface subject to high temperatures. The coating system comprises agglomerates of particles forming grains adhered to a metal substrate or interface, said particles being comprised of (i) solid lubricant particles selected from the group consisting of graphite, hexagonal boron nitride, molybdenum disulfide, lithium fluoride, calcium fluoride, and eutectic mixtures of LiF/CaF.sub.2 or LiF/NaF.sub.2 ; and (ii) steel particles fused together and bounding said solid lubricant particles at least at certain intersections, certain portions of said steel particles being air-hardened to a high hardness upon exposure of the coating to the interface at high temperatures. It is desirable that the steel particles be of a stainless steel character consisting preferably of 70% iron, 15-24% chromium, and about 8% nickel. The agglomerates preferably comprise by volume: 15-25% solid lubricant particles and 74-84% stainless steel particles. The air-hardened hardness of the steel is about Rc 60, and the coefficient of friction achieved by the coating system is about 0.14 dry and 0.060-0.08 under partially wet lubricated conditions.
Another aspect of this invention is a method of making anti-friction coated surfaces subject to sliding wear. The method comprises: (a) forming grains of agglomerated solid lubricant particles and air-hardenable, fusable ingredients such as steel particles, the particles being agglomerated by a low melting, easily combustible, ash-free binder or medium such as wax; (b) providing a light metal-based component surface; (c) thermally spraying such grains onto said surface in a thickness range of 100-250 microns to form a coating substantially devoid of the binder (the temperature of said thermal spraying eliminating the wax by ash-free combustion); (d) removing at least a portion of the fusable particles by honing to expose edges of such particles; and (e) subjecting the exposed particles to air hardening (i.e., by available interfacing friction resulting from the thermal spray deposition process).
Yet another aspect of this invention is an engine block with one or more anti-friction coated cylinder bores. The block comprises: (a) a cast aluminum based cylinder block having at least one cylinder bore wall; (b) an oil-attracting coating of grains fused to each other and to said bore wall, said grains comprising agglomerates of solid lubricant particles and hardened, fused particles, the solid lubricant particles being selected from the group consisting of graphite molybdenum disulfide, boron nitride, lithium fluoride, calcium fluoride, and eutectic mixtures of LiF/CaF.sub.2 or LiF/NaF.sub.2, the coating having been finish-honed to expose certain margins of the fused particles.