Abstract: Gas turbine engines employ a variety of abradable liners to decrease the clearance between the rotating components and the surrounding casing. There is normally a trade-off between porosity, (and concomitant permeability) and the abradability of the liner material, such that materials with good abradability are permeable to gas flow--resulting in performance losses. Permeability of porous liners is decreased by infiltrating the liner with a low-viscosity liquid containing a metal or metal oxide. After infiltration, the viscosity of the liquid is substantially increased to prevent its egress from the porous liner. Thereafter, the liner is heated at an elevated temperature to drive off the remaining liquid and provide an oxide which blocks the passages and decreases the permeability of the liner.

Abstract: An improved method of forming a composite body of a metal, intermetallic or ceramic matrix reinforced with niobium filaments, particles, platelets or mixtures thereof, the method comprising admixing the niobium reinforcing material with powders of the matrix component elements, forming the admixture into a desired shape and converting the powders to a matrix reinforced with the niobium material, the improvement wherein the reinforcing material has a surface coating thereon of a compound Nb.sub.2 O.sub.5, wherein the compound NbO reacts during formation of the matrix with a portion of at least one of the powdered elements to form a barrier layer at the reinforcer-matrix interface to prevent further reaction between the reinforcer and the matrix component elements. Also disclosed is a method of treating niobium particles, filaments, platelets or mixtures thereof by exposing the surface thereof to molecular O.sub.2 at temperatures and pressure conditions such that the niobium and molecular O.sub.