Abstract: Ceramic particles useful as abrasives in a metal matrix layer are described. The particles are coated with an oxide monolayer and a metal duplex layer. Preferably, the particles are silicon carbide; the oxide monolayer is aluminum oxide, and the metal duplex layer is a nickel-boron alloy over pure nickel.

Abstract: Porous metal structures are especially useful as abradable seals in axial flow compressors. Carefully defined oxide content and density provide a superior combination of abradability and particulate erosion resistance. The seals are comprised of 1-30 weight percent oxide and have 27-38 percent of the solid metal density. A preferred seal is made by plasma arc spraying a mixture of 80Ni-20Cr and polymethylmethacrylate powders and then heating the resultant deposit in air to about 315.degree. C. to cause the polymer to flee. The nichrome seal will have less than 15 percent oxide and a density of about 2.7 g/cm.sup.3, about 32 percent of the solid metal density.

Abstract: A combination of sintering, plasma arc spraying, hot isostatic pressing and chemical milling is used to form an abrasive surface on an article. Alumina coated silicon carbide particulates are clad with nickel and sinter bonded to the surface of a superalloy turbine blade tip. An impermeable layer of plasma arc sprayed superalloy matrix is deposited over the particulates and then has its inherent voids eliminated by hot isostatic pressing. The abrasive material so formed on the surface is then machined to expose the particulates. Next, a portion of the matrix is removed so that the machined particulates project into space and are thus best enabled to interact with abradable ceramic air seals in a gas turbine engine. The ceramic particulates are sized so they are larger than the finished thickness of the abrasive and they have small aspect ratios. Thus, a high density spacing can be achieved while at the same time it is insured that matrix adequately surrounds the particles and holds them in place during use.

Abstract: Disclosed is a process for plasma spraying small metal fibers, to adhere them to the surface of a workpiece, and articles made using the process. The process is especially useful for improving the strength of plasma arc coatings, as well as for improving the bonding of plasma arc coatings to substrates. To make an improved ceramic faced metal article, fibers are sprayed onto the workpiece by injecting fibers into the plasma stream external to the plasma gun nozzle. Then, plasma sprayed ceramic particles are caused to surround the fibers as a matrix. The optional interposition of a removable polymer material on the workpiece surface, after the fibers are sprayed but before the ceramic matrix is sprayed, provides an effective way of providing a low stiffness connector between a low thermal expansion coefficient ceramic material and a high expansion coefficient metal substrate. The connector alleviates strains from thermal expansion differences.

Abstract: Outer air seal structures of particular suitability for use in gas turbine engines are disclosed. Techniques for improving resistance to erosion while maintaining good abradability are discussed.In one particular structure the ceramic facing material of an outer air seal (30) at the leading edge region (36) is densified by a plasma gun to produce a glazed area (52) which is resistant to erosion.

Abstract: Methods for applying grit containing abrasive coatings by plasma spray techniques are disclosed. Various concepts for obtaining good adherability of the coating to an underlying substrate and for maintaining angularity of the grit particles are discussed. The concepts employ simultaneous contact of the grit particles with matrix material at the surface of the substrate to be coated. In coating narrow substrates, the substrate is offset from the axis of the plasma stream discharging from the plasma gun.