In the gas turbine engine art, it is well known that the efficiency of certain components such as a compressor and a turbine is at least partially dependent on the extent to which compressed fluids such as air or combustion products leak through a space between blading members and cooperating shrouds. The clearance between such relatively moving parts can be designed within specific limits at a given temperature. However, during operation of a gas turbine engine from start up through various operating conditions to shut down, variation in temperatures cause non-uniform thermal expansion or contraction in a complex manner based on such factors as different materials of construction, different configurations, and different masses of materials. A number of reported arrangements have the object of reducing such an undesirable leakage.
One arrangement is described in U.S. Pat. No. 4,169,020--Stalker et al, issued Sept. 25, 1979, the disclosure of which is incorporated herein by reference. In such an arrangement, abrasive particles are provided on a projection such as a blade tip to cooperate with a relatively moving, opposed surface. The abrasive particles, when contacting such opposing surface, are intended to remove material from the surface in order to minimize clearance and reduce leakage between such relatively moving members.
A known method for applying such abrasive particles to a surface or a projection such as a blade tip is the codeposition of a bonding matrix and particles in an electrolyte bath onto a preselected surface. In one form of such an arrangement, the abrasive particles are suspended in the electrolyte bath and a metal matrix is codeposited with the particles at the selected surface to bond the particles to and entrap the particles at such surface. In another form of such method, abrasive particles are held in a bag about the surface and contact is provided under the electrolyte between the surface to be treated and the abrasive particles.
Abrasive particles which can be used for such purpose include oxides, nitrides, carbides, silicides, etc. Frequently used types include aluminum oxide, diamond and cubic boron nitride, one form of which is commercially available as Borazon material. Although some of such particles are relatively inexpensive, materials such as diamond and especially Borazon particles are very expensive. Use of known methods can result in a high loss or waste of such expensive materials.