The following specification particularly describes the nature of invention and the manner in which it is to be performed.

This invention relates to the development of a novel method of preparing an aluminium silicon powder for providing a high temperature chemical coating on gas turbine engines parts operating in medium and high-temperature environments.

Background of the invention

In gas turbine engines there are components requiring hot corrosion resistance, oxidation and creep resistance. The chances for the hot end components to get corroded and eroded are very high due to the catalytic environment of heat and corrosive gaseous mixture. So there is a need for high temperature stable coatings capable of preventing hot corrosion and oxidation.
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Summary of invention

A novel method comprising of following features is introduced. To prevent the oxidation, sulphidation, corrosion and carburization of hot end components of gas turbine engines an efficient coating is required. Aluminium-silicon diffusion coating is found suitable for the purpose and thus an aluminium-silicon powder suitable for the process is developed.

Objective of invention

Main objective is to introduce a novel material to be coated on hot end parts of gas turbine engines to prevent Hot Corrosion, Metal Dusting, Oxidation, Carburization, Sulphidation etc.

To develop a novel method for the diffusion coating of aluminium- silicon powder on hot end parts of gas turbine engines.

Detailed Description of the invention
The hot end part of gas turbine engines is to be protected from hot corrosion, oxidation, sulphidation, carburization etc. This can be done by providing different coatings which is capable of withstanding the mentioned problems. Thorough study and analysis is done and is found that aluminium silicon coating is suitable for the very purpose. Addition of silicon increased resistance to acidic corrosion. This is a high temperature diffusion coating. This coating is done by pack cementation process.

Pack Cementation process is the most widely used in which the process is performed in either a glass seal box in an air furnace or in a reducing/inert gas atmosphere retort.

The chosen components are embedded in newly developed powder mixture referred to as the 'pack' or 'compound' which consists of:

• A source metal: Al (may be moderated)

• An activator (e.g. Halide)

• An inert diluent (e.g. A1203; prevents pack powder particles sintering together)

At the required coating temperature, the activator reacts with the source metal to form a gaseous halide compound, which is transferred to the substrate surface. As this gas decomposes, the halogen activator is released and the coating, element is deposited at the substrate surface, leaving the activator to return to the pack and react with the source metal again. Coating thickness is controlled by temperature and time at temperature.

Procedure for making aluminium silicon powder. NOTE:

a. Total powder quantity shall be 20 kg. Same proportion to be maintained if less or more quantity of power is mixed.

b. Before weighing, the balance shall be calibrated and accuracy shall be ± lgm
shall be maintained.

c. Ratio of powder to steel balls shall be 1:1 by weight.
1. Weigh the following powders and keep in separate polythene bags.
• Alumina (A1203) 8.80Kg
• Silica (Si02) 2.00Kg
• Aluminium (Al) 4.80Kg
• Silicon (Si) 3.20Kg
• Sodium Fluoride (NaF) 0.86Kg
• Potassium Bi-Fluoride (KHF2) O.lOKg
• Ammonium Chloride (NH4CI) 0.24Kg

2. Vapour degrease the steel balls and dry. Weigh 20Kg of cleaned steel balls.

3. The powders and balls shall be loaded into jar in following sequence.
STEP A: Pour approximately 2.4 Kg of Aluminium (Al).
STEP B: Add approximately 0.43 Kg of sodium fluoride (NaF).
STEP C: Add approximately 1.6 Kg of silicon (Si).
STEP D: Add approximately 0.12 Kg of AmmoniumChloride (NH4CL).
STEP E: Add approximately 4.4 Kg of Alumina (A1203).
STEP F: Add approximately 0.005 Kg of Potassium Bi-flouride(KHF2).
STEP G: Add approximately 1.0 Kg of silica. (Si02).
STEP H: Over these powders keep 10 Kg of steel balls.
STEP I: Repeat steps A to H using remaining powder and steels balls.

4. Mix in ball mill for 48 Hours.

5. Separate the balls and powder.

6. Pack the powder in moisture free polythene bags. Seal bags.

Claims: We Claim

1) Development of a novel material to be coated on hot end parts of gas turbine engines to prevent Hot Corrosion, Metal Dusting, Oxidation, Carburization, Sulphidation etc.

2) Development of a novel method for the diffusion coating of aluminium- silicon powder on hot end parts of gas turbine engines.