Ceramic coating for foundry core

Patent metadata

Field	Value
Publication number	US-11752541-B2
Application number	US-201917266020-A
Country	US
Kind code	B2
Filing date	Aug 7, 2019
Priority date	Aug 7, 2018
Publication date	Sep 12, 2023
Grant date	Sep 12, 2023

Abstract

A process for coating a refractory alloy part is provided and includes coating an area of a refractory alloy part by means of a treatment composition including a type of preceramic polymer and a solvent, and heat treating the part coated with the treatment composition. The heat treating partially converts the preceramic polymer and forms a ceramic coating obtained by conversion, the ceramic coating protecting the refractory alloy from oxidation. The treatment composition also includes active fillers to form an alloy coating on a surface of the part by solid diffusion in addition to the ceramic coating obtained by conversion, and the alloy coating generates a protective oxide layer when subjected to oxidizing conditions.

First claim

The invention claimed is:

1. A process for coating a refractory alloy part, the process comprising:
coating at least one area of a refractory alloy part by a treatment composition, the treatment composition comprising at least one type of preceramic polymer and a solvent, and
heat treating the refractory alloy part coated with the treatment composition, the heat treating being configured to at least partially convert the preceramic polymer and form a ceramic coating obtained by conversion, the ceramic coating being configured to protect the refractory alloy from oxidation,
wherein the treatment composition also comprises active fillers configured to migrate by diffusion to the refractory alloy part during the heat treatment, the active fillers being configured to form an alloy coating on a surface of the refractory alloy part, and the alloy coating being located between the refractory alloy part and the ceramic coating obtained by conversion, and
the alloy coating being configured to generate a protective oxide layer when subjected to oxidizing conditions.

2. The process as claimed in claim 1 , comprising removing the ceramic coating obtained by conversion by mechanical or chemical action to leave only the alloy coating.

3. The process as claimed in claim 1 , wherein the treatment composition further comprises passive fillers configured to modulate a coefficient of expansion of the ceramic coating so as to exhibit a difference between a coefficient of expansion of a substrate and the coefficient of expansion of the ceramic coating of less than 3*10 −6 K −1 .

4. The process as claimed in claim 1 , wherein the ceramic coating comprises at least a first coating step and a second consecutive coating step, and at least one cross-linking step carried out between the first coating step and the second coating steps,
the cross-linking step being configured to generate an infusible polymer network capable of supporting subsequent pyrolysis steps, and
the second coating step being applied to obtain a layer thicker than the first coating step.

5. The process as claimed in claim 4 , wherein a treatment composition used in the second coating step has a lower viscosity than a viscosity of a treatment composition used during the first coating step.

6. The process as claimed in claim 4 , wherein the cross-linking step is carried out in the presence of air at a temperature greater than or equal to a highest cross-linking temperature among different cross-linking temperatures of different preceramic polymer species of the treatment solution.

7. The process as claimed in claim 1 , wherein the refractory alloy comprises molybdenum, and wherein the ceramic coating is configured to protect the refractory alloy from a diffusion phenomena.

8. The process as claimed in claim 1 , wherein the heat treatment step comprises:
cross-linking at a first temperature configured to evaporate the solvent and accelerate cross-linking;
conversion carried out at a second temperature configured to convert the preceramic polymer to ceramic and remove organic species, so as to obtain a ceramic with an amorphous structure; and
structuring carried out at a third temperature, configured to convert the ceramic with an amorphous structure to ceramic having a crystalline structure.

9. The process as claimed in claim 1 , wherein the process comprises at least a first coating step and a second coating steps and a ceramization step carried out between the first coating step and the second coating steps,
the second coating step being configured to fill or heal defects and porosity that may be generated by the ceramization step.

10. The process as claimed in claim 1 , wherein the heat treating step is carried out under a controlled atmosphere so as to avoid oxidation of a foundry core while having an oxygen partial pressure sufficient to ensure the conversion of the preceramic polymer to an oxycarbide ceramic or oxide ceramic.

11. The process as claimed in claim 1 , wherein the treatment composition comprises, based on a total weight of the treatment composition:
a mass proportion comprised between 45% and 70% of the solvent,
a mass proportion comprised between 15% and 40% of the preceramic polymer,
a mass proportion comprised between 10% and 30% of a passive filler.

12. The process as claimed in claim 1 , wherein the treatment composition comprises, based on a total weight of the treatment composition:
a mass proportion comprised between 30% and 70% of the solvent,
a mass proportion comprised between 15% and 40% of a polysiloxane preceramic polymer, having a theoretical conversion rate from ceramic to silicon dioxide, and
a mass proportion comprised between 15% and 60% of aluminum with a grain size of less than 20 microns.

13. The process as claimed in claim 1 , wherein the refractory alloy part is a refractory alloy mechanical part.

14. The process as claimed in claim 1 , wherein the refractory alloy part is a refractory alloy foundry core.

Assignees

• Commissariat Energie Atomique
• Safran

Inventors

• Bechelany Mirna
• Jaquet Virginie
• Saboundji Amar
• Soulier Mathieu
• Boidot Mathieu
• Laucournet Richard

Classifications

• B22C1/00 Primary

  Compositions of refractory mould or core materials; Grain structures thereof (refractory materials in general C04B35/00); Chemical or physical features in the formation or manufacture of moulds · CPC title

• B22C9/12 Primary

  Treating moulds or cores, e.g. drying, hardening · CPC title

• B22C3/00

  Selection of compositions for coating the surfaces of moulds, cores, or patterns · CPC title

• B22C9/101

  Permanent cores · CPC title

• B22C9/10

  Cores; Manufacture or installation of cores {(breaker cores B22C9/084)} · CPC title