JP3288567B2 - Composite thermal spray powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION This invention relates to boron nitride and aluminum nitride which are useful in the production of thermal spray powders, especially abrasive coatings.
The present invention relates to a composite thermal spray powder made of a silicon alloy.

[0002]

BACKGROUND OF THE INVENTION Thermal spraying, also known as flame spraying, involves the thermal softening or melting of a hot melt material, such as a metal or ceramic, and the spraying of the softened material in particulate form onto the surface to be coated. The hot particles hit the surface where they are quenched and bonded thereto. Conventional thermal spray guns are used for both heating and jetting of the particles. In one type of thermal spray gun, the hot melt material is supplied to the gun in powder form. Such powders are typically small particles, such as US standard screen size,
Molded between 00 mesh (149 microns) and about 2 microns.

[0003] Thermal spray guns typically use a combustion flame or a plasma flame to generate heat for melting powder particles. In powder-type combustion thermal spray guns, the carrier gas carrying the powder may be one of the combustion gases or an inert gas such as nitrogen, or simply compressed air. In a plasma spray gun, the primary plasma gas is typically nitrogen or argon. Usually, hydrogen or helium is added to the primary gas, and the carrier gas is generally the same as the primary plasma gas.

[0004] One form of thermal spray powder is a composite or agglomerated powder in which very fine particles are agglomerated into suitably sized powder particles. Such powders produced by spray drying are described in US Pat. No. 3,617,358 (Dit).
trich), again teaching a variety of useful flocculating polymeric (organic) binders. The agglomerated powder can also be obtained by mixing a slurry of the fine powder component with a binder and heating the mixture while continuing to mix until a dry powder of the agglomerate is obtained. In general, the binder for this mixing method may be the same as that disclosed for the spray drying method.

[0005] US Pat. No. 5,049,450 (Do)
rfman et al.) teach a homogeneous thermal spray powder made by mixing with a binder in a slurry, which powder is formed from complementary particles consisting of boron nitride and a silicon-aluminum alloy. This patent specifically relates to powders for producing thermally sprayed coatings which are abrasive, for example, for clearance control applications in gas turbine engines. Boron nitride is not fusible and can thus be introduced into the coating by a fusible metal component and a binder in a thermal spray process. Excellent, abrasive coatings can be achieved, but certain improvements are desired.

[0006] Thus, this US patent discloses that the binder is comprised of 2 to 2 binders.
Although it teaches that it may be 0%, it has been found in practice that a relatively high percentage of polymer binder (at least 15%) is required to incorporate boron nitride into the coating. However, if some amount of binder enters the coating, the sprayed coating becomes too soft, especially after exposure to high temperatures. A lower amount of binder results in a better abrasive coating but results in a relatively low adhesion effect and a higher hardness than desired.

If a particle is formed in which one of the components is approximately the same size as the final powder, the complex is not homogeneous, but instead is bound to it by the large particle as a core particle and a binder. And a fine second component.
An example of such a cladding powder is disclosed in US Pat.
No. 5 (Longo et al.), Wherein components such as boron nitride clad nickel alloy core particles. This patent teaches that the core is simply partially clad so that the core metal is exposed to the heat of the thermal spray process. In some cases, fine aluminum is added during cladding for improvement, but it is speculated in the specification that this is related to the exothermic reaction between aluminum and the core metal.

Other powders relating to abrasiveness are disclosed in US Pat.
Consists of a chemical cladding of a soft non-metallic nucleus nickel alloy (without binder) such as bentonite as disclosed in US Pat. No. 2,910,891 (Adamovic).
U.S. Pat. No. 3,322,515 (Ditrich)
Et al. Teach a cladding process using a polymer binder with aluminum complement particles of a metal core powder.
196471 (Rangaswamy et al.) Discloses a composite powder for thermal spraying of abrasive coatings, wherein the composite powder contains three components. One component is any of some metal or ceramic matrix materials, the other is a solid lubricant (eg, fluoride or boron nitride), and the third is a plastic. A wide range of particle sizes is disclosed for each component, specified as about 1 μm to about 150 μm,
The only specified example (Figure 1 of the specification) is a large aluminum embedded in the surface of the polyamide core particle - merely teaches the fine particles and the CaF ₂ fine particles of silicon alloys.

[0009] The basic and general opposite goals of abrasive coatings are to achieve both abrasive properties and resistance to gas and particulate corrosion. The resistance of the gas turbine engine to corrosive environments is also required. Although current coatings have been fairly successful for this purpose, full requirements have been difficult to achieve as a whole, and research on improved abrasive coatings continues.

[0010]

Accordingly, it is an object of the present invention to provide an improved thermal spray powder useful for clearance control applications in gas turbine engines. A further object is to provide a powder for producing a coating which improves abrasiveness while retaining corrosion resistance. A further object is to provide a powder for producing a corrosion resistant coating in a gas turbine engine environment. A particular object is to provide an improved composite powder consisting of an aluminum-silicon alloy and boron nitride. A more specific object is to provide a boron nitride powder in a form that allows the amount of polymer binder to be reduced for optimal coating, and to provide an abrasive coating having a hardness that is retained after exposure to high temperatures. It is to provide a powder for production.

[0011]

SUMMARY OF THE INVENTION The foregoing and further objects are at least in part, mainly in the form of clad particles,
Each of the particles is achieved with a composite thermal spray powder consisting of core particles consisting of boron nitride and complement particles consisting of an aluminum-silicon alloy. The complement particles are bonded to the core particles with a polymer binder.

Aluminum-silicon alloys useful for the cladding particles contain about 10 to 14 weight percent silicon, with the balance being aluminum and associated impurities (less than 1%).
Generally, the boron nitride core material comprises about 5 to 25% by weight, and preferably 15 to 2% by weight, based on the total weight of boron nitride and the alloy.
It is present in an amount of 0% by weight. Boron nitride has a lower density than aluminum alloys, and the volume percentage of boron nitride is higher. The polymer binder is 2 to 1 based on the total weight of the alloy and boron nitride, measured as the solids content in the powder.
It is 2% by weight, preferably 6 to 10%.

[0013] Boron nitride is of the normal hexagonal BN type.
The size of the core particles is essentially between 44 and 210 μm, preferably predominantly distributed in the range 74 to 177 μm, and is preferably the nearer end region. Aluminum alloy complement particles are in the range of 1 to 44 μm. (The powder particle size corresponds to a conventional convenient screen size except for 1 μm, which is almost the minimum that can be measured by conventional optical equipment.) The powder is clad bonded by a polymer suitable for thermal spraying Manufactured by conventional or desired methods for manufacturing powders. This agglomerate should not be too brittle so that it does not collapse during processing and feeding. An advantageous method is to stir a slurry of the fine powder component with a binder,
And while continuing to mix, agglomerate by heating the mixture until a dry powder of agglomerates is obtained. The polymeric binder may be conventional and is selected, for example, from those mentioned in the aforementioned patent specifications. The amount of liquid binder introduced into the initial slurry is selected to achieve a suitable percentage of polymer solids in the final dried agglomerated powder. One or more additives to the slurry, such as a neutralizing agent as taught in any of the aforementioned references, may be advantageous. Although the powder is primarily composed of boron nitride nuclei clad with aluminum alloy complement particles, we recognize that some of the powder particles are aggregates of smaller boron nitride and alloy complement particles.

[0014]

EXAMPLE A composite powder was produced by agglomerating a core powder of boron nitride (BN) 17% by weight and a fine powder of aluminum-12% by weight silicon alloy. The particle size of each of boron nitride and alloy powder is 74 to 177 μm and 1 to
It was 44 μm. Table 1 shows the particle size distribution of these powders.

[0015]

[Table 1]

The powder components were premixed for 30 minutes and then a polymeric binder (UCAR Latex 879) was added to the mixture along with distilled water and acetic acid to neutralize the slurry. This ratio was selected as shown in Table 2.

Table 2 Alloy 36 g BN 9 g Binder 9 g Water 9 g Heat the vessel to about 135 ° C., continue stirring and mixing until the slurry and binder are dry, and combine the composite powder with approximately 8 wt% polymer solids. Molded. After making the powder, the powder was sieved at a maximum of 210 μm (70 mesh) and a minimum of 44 μm (325 mesh).

The powder is applied to a plasma spray gun (Metco type 9 MB) using a GH nozzle and # 1 powder lance.
Sprayed. Spray parameters were: argon primary gas, pressure 7 kg / cm ² and flow rate 96 l / min, hydrogen secondary gas, pressure 3.5 kg / cm ² and the flow required to maintain about 80 volts (about 10 l / min). ), 500 amps, spray rate 3.6 kg / h, spray distance 13c
m. These parameters are described in US Pat.
The same as recommended and used for the agglomerated powders prepared according to the examples described in US Pat. No. 4,049,450. Table 3 compares the chemical properties and some coating properties for the conventional agglomerated powder and the cladding powder of the present invention.

Table 3 Powder Chemical Properties Agglomerated Powder Clad Powder Boron Nitride (1) 10-12% 16-18% Polymer Solid (1) 15-17% 8-10% Silicon (1) 8-10% 8- 10% Aluminum Residue Residue Coating properties Nonmetal (2) 35-40% 30-35% Porous (2) 2-4% 2-4% Polymer solid (2) 4-8% <4% Metal phase residue Min. Residue Hardness (R15y) 50-60 60-70 (1)... Weight% (2)... Volume% Compared to agglomerated powder, the cladding powder coating of the present invention clearly has a lower amount of polymer bonding Agent. The cladding powder coating has a high hardness which results in improved corrosion resistance. The microstructure shows relatively coarse boron nitride embedded in an aluminum alloy matrix. For hardness measurement, the clad powder coating slightly densified (compressed) the surface
Showed that it became harder.

Although the present invention has been described in detail with respect to particular embodiments, many variations and modifications within the spirit and scope of the invention will be apparent to those skilled in the art. Accordingly, the invention is limited only by the claims and the equivalents.

──────────────────────────────────────────────────続 き Continued on the front page (72) Burton A. Inventor. Kushner USA New York Old de Vestpage East Park Drive 23 (72) Inventor George E. Garcia USA New York Farmingdale Cresswood Blvd. 70 (56) References JP-A-4-254568 (JP, A) (58) Fields studied (Int. Cl. ⁷ , DB name) C23C 4/04 C01B 21 / 064 C22C 21/02

Claims (4)

(57) [Claims] 2. The method according to claim 1, wherein each of the core particles comprises a core particle made of hexagonal boron nitride and a complementary particle made of an aluminum-silicon alloy. The alloy contains 10 to 14% by weight of silicon, based on the weight of the alloy, the balance of the alloy being aluminum and less than 1% of concomitant impurities, boron nitride comprising boron nitride and alloy 5 to 25% by weight based on the total weight of the alloy, the size of the core particles is 74 to 177 μm, and the size of the alloy complement particles is 1
Composite thermal spray powder of ~ 44 [mu] m. 2. The composite thermal spray powder according to claim 1, wherein the boron nitride is present in an amount of 15 to 20% by weight based on the total weight of the boron nitride and the alloy. 3. The composite thermal spray powder according to claim 1, wherein the polymer binder is present at from 6 to 12% by weight polymer solids based on the total weight of boron nitride and the alloy. 4. Mainly in the form of clad particles, each of which comprises core particles comprising hexagonal boron nitride and complement particles comprising an aluminum-silicon alloy, wherein the complement particles are added to the core particles with a polymer binder. Bonded, the alloy contains 10 to 14% by weight of silicon, based on the weight of the alloy, the balance of the alloy being aluminum and less than 1% of accompanying impurities, The polymer binder is present at 15 to 20% by weight based on the total weight, the polymer binder is present at 6 to 12% polymer solids by weight based on the total weight of boron nitride and alloy, and the core particle size is 74 to 177 μm.
m, and the size of the alloy complement particles is from 1 to 44 μm.