Abstract: Porous plasma arc sprayed powder metal abradable materials used in knife edge labyrinth seals of gas turbine engines have their resistance to erosion improved when a thin ceramic surface layer containing fine aluminum particulate is applied. The fine equiaxed particulate and ceramic are applied as an aqueous liquid so that both the particulate and cermic matrix material fill the surface pores, without penetrating further into the powder metal material and thereby adversely affecting desirable abradability characteristics.

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.