JPS6333987B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to abrasive materials, and more particularly to particulate abrasive materials dispersed within a metal matrix to provide a useful product with superior abrasive properties.

Improving efficiency has become an increasingly important factor in the development of gas turbine engines. A gas turbine engine has several rows of rotating blades within a generally cylindrical case, and gas leakage between the tips of the blades and the case reduces efficiency. In modern engine designs, such leakage is minimized by a blade-seal system in which the tip of the blade slides against a seal mounted inside the engine case.
Such systems generally have blade tips that are harder and more abrasive than the seal, thus grinding the seal at some stage of engine operation so that there is little gap between them. It has been found that it is most desirable to configure Conventional abrasive blade tips have been made of various materials, including certain nickel-based superalloys, as in U.S. Pat. No. 2,994,605, or randomly dispersed tungsten carbide particles, as in U.S. Pat. No. 3,199,836. It was composed of nickel matrix. However, in a gas turbine engine, especially in the turbine section, the temperature is high and corrosive gas is present, so the effectiveness of such polishing or grinding action on the tip of the blade has not been sufficient. Prior art blade tips are particularly inefficient when used in conjunction with ceramic seal materials, such as zirconia-based graded ceramic seals developed for use in gas turbine engines. It turns out that it is.

The present invention relates to an improved abrasive material particularly useful as a dispersed phase within a metal matrix to provide a useful product with superior abrasive properties, especially at elevated temperatures. The present invention utilizes abrasive silicon carbide particles in which each individual particle has a coating of substantially alumina (Al ₂ O ₃ ). The alumina coating acts to prevent such dispersed silicon carbide particles from diffusing or dissolving into the metal matrix during use at high temperatures, thereby reducing the useful life of the particles as an abrasive dispersed phase. increase. In addition, the present invention attempts to improve high-temperature bonding by forming a mullite phase (3Al ₂ O ₃ .2SiO ₂ ) between the particles and the alumina coating, thereby providing an intermediate coating of silica (SiO ₂ ) between the particles and the alumina coating. It is something. According to the invention, the alumina coating and the silica coating are preferably applied by sputtering or vapor deposition.

Alumina-coated silicon carbide particles can be dispersed within a wide variety of metal matrices to suit specific requirements. Dispersion of such particles may be carried out by powder metallurgy, casting or other methods.

The invention is particularly applicable to abrasive blade tips used in gas turbine engines. Such blade tips are made to have a nickel-based or cobalt-based superalloy matrix in which alumina-coated silicon carbide particles are dispersed. Abrasive blade tips formed in accordance with the present invention have been found to be highly effective in abrasively grinding ceramic seal materials at elevated temperatures.

The present invention will now be described in detail with reference to its preferred embodiments.

As discussed above, the improved abrasive materials of this invention are particularly useful as a dispersed phase within a metal matrix to provide a useful product with excellent high temperature abrasive properties. One such useful product is an abrasive blade tip used in modern gas turbine engine blade-seal systems. Below, the present invention will be explained in detail regarding such a blade tip.

In modern gas turbine engines, abrasive blade tips must be capable of effectively abrading and abrading the seal material at very high temperatures. In the turbine section of a gas turbine engine, for example, the temperature at the blade tip is 1093 during normal engine operation.
It may reach or exceed ℃. Under such harsh conditions, the blade tip of the prior art
This was particularly unsatisfactory when used in combination with ceramic sealing materials. The present invention provides an abrasive blade tip characterized by its superior ability to abrade and grind seal materials, including ceramic seal materials, at very high temperatures such as during engine operation. To this end, an improved abrasive material is provided which is dispersed within a nickel-based or cobalt-based superalloy matrix or other suitable matrix. More particularly, the present invention provides that silicon carbide particles exhibit superior abrasive ability when dispersed within a nickel-based or cobalt-based superalloy matrix, and that individual particles of silicon carbide are coated with alumina. This includes the discovery that such superior abrasive properties can be maintained even at turbine engine operating temperatures.

Commercially available silicon carbide particles having an average diameter on the order of 203-762 microns are sufficient, although the particular particle size used may vary depending on the particular polishing application. Individual particles were coated with commercially available alumina (Al ₂ O ₃ ) to prevent diffusion and dissolution of the particles into the metal matrix at high temperatures, thereby preserving polishing performance. Alternatively, it may be coated first with a first layer of silica (SiO ₂ ) and then with a second layer of alumina to improve the bond.
By applying a silica coating in the middle, a mullite phase (3Al ₂ O ₃・2SiO ₂ ) is formed between the alumina coating and the particles during use at high temperatures, and the alumina-coated particles at high temperatures Improved connectivity. Alternatively, if desired, such double coated particles may be suitably heat treated before being dispersed within the matrix to effect the formation of the mullite phase. Such alumina or silica coatings are suitably applied onto individual silicon carbide particles by sputtering, physical vapor deposition, chemical vapor deposition (in which case the particles are gently rotated during application), or the like. Of course, the thickness of the coating may be varied as desired. About the use of the abrasive blade tip
An alumina coating thickness of 2.5μ has been found to be sufficient.

As will be understood by those skilled in the art, dispersing alumina-coated silicon carbide particles within a nickel-based or cobalt-based superalloy matrix may include powder metallurgy, casting, or other methods. (However, the method is not limited to this method.) Various methods may be used. Powder metallurgy is preferred because it allows particles to be randomly dispersed in an optimal state. For example, one preferred method is to mix the coated silicon carbide particles with the superalloy powder in the required amount and then hot press the mixture into the final or intermediate solidified shape.
However, in some cases it may be desirable to have a non-random distribution or particles localized in certain areas of the blade tip, such as near the end where it contacts the sealing material. One important advantage of the present invention is that the alumina-coated silicon carbide particles are dispersed within a wide range of matrix alloys and no deleterious reactions occur between them. These features allow matrix alloys to be selected and matched to particular environments and conditions of use, resulting in an overall improved abrasive blade tip or other useful product. Various nickel-based or cobalt-based alloys may be used for the abrasive blade tip; examples of such alloys include 21-25% Cr by weight;
4.5~7%Al, 4~10%W, 2.5~7Ta, 0.02~
Nickel-based alloy with a nominal composition of 0.15% Y, 0.1-0.3% C balance nickel, and also 18-30% by weight.
Cr, 10~30% Ni+Fe, 5~15% W+Mo, 1~
5%Ta+Cb, 0.05~0.6%C, 3.5~8.0%Al, 0.5
It is a cobalt-based alloy with a nominal composition of ~2.0% Hf, 0.02-0.1% Y, and the balance cobalt. A blade tip with alumina-coated silicon carbide particles dispersed in such an alloy can be bonded to a nickel-based or cobalt-based superalloy by solid state diffusion bonding, TLP bonding, brazing, or other methods. Can be attached to the end of a turbine blade.

It will be appreciated that the amount of alumina coated silicon carbide particles dispersed within the alloy matrix may be varied as desired. In blade tip applications, such amounts range from 45% by volume for 203μ diameter particles to 30% by weight for 381μ diameter particles. Additionally, other abrasive particles may be simultaneously dispersed within the matrix to provide useful properties. For example, hot-pressed silicon nitride may be dispersed with alumina-coated silicon carbide. Abrasive blade tips according to the invention were tested and the results
It was found to have acceptable polishing properties for a tip temperature of 1149°C (matrix alloy was a cobalt alloy).

Although the present invention has been described in detail with respect to specific embodiments above, the present invention is not limited to such embodiments, and various modifications and omissions can be made within the scope of the present invention. This will be clear to those skilled in the art.

Claims (1)

Claims: 1. An abrasive material useful as a dispersed phase within a metal matrix, particularly at high temperatures, comprising silicon carbide particles, the individual particles of which are dispersed within said matrix at high temperatures. 1. An abrasive material characterized in that it has a coating thereon consisting primarily of alumina to inhibit diffusion in the abrasive phase and thereby increase the useful life of said particles as an abrasive dispersed phase. 2. The abrasive material of claim 1, characterized in that an intermediate coating containing silica is disposed between the particles and the alumina coating to improve high temperature bonding between the particles and the alumina coating. Abrasive material. 3. The abrasive material of claim 1, wherein an interphase substantially comprising mullite is disposed between the particles and the alumina coating to improve high temperature bonding between the particles and the alumina coating. An abrasive material characterized by: 4. In the abrasive material according to any one of claims 1 to 3, the thickness of the alumina coating is
An abrasive material characterized by up to 2.5μ.