Chemical treatment for optimization of TiAl bar machining
A chemical treatment with an acid mixture on titanium aluminide bars addresses the tool wear issue by removing the hard surface layer, ensuring efficient and cost-effective production of low-pressure turbine blades.
Patent Information
- Application Number
- FR2022010884
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2022-10-20
- Publication Date
- 2025-07-18
- Estimated Expiration
- 2042-10-20
AI Technical Summary
Traditional foundry processes for producing low-pressure turbine blades from titanium aluminide result in a hard surface layer that causes significant wear on machining tools, necessitating costly and non-viable solutions like using more resistant tools, which disrupt conventional production ranges.
A chemical treatment using a mixture of an acid oxidizing agent and a halogenated acid is applied to titanium aluminide bars to remove the hard surface layer before machining, maintaining conventional production ranges and reducing tool wear.
The chemical treatment effectively and economically removes the surface layer without altering conventional machining processes, minimizing tool wear and production costs.
Abstract
Description
Title of the invention: Chemical treatment for optimizing the machining of TiAl bars Technical field
[0001] The present invention relates to the general field of the manufacture of low-pressure turbine blades made of titanium aluminide. Prior art
[0002] Titanium aluminide is commonly used to produce moving blades of low pressure turbines because it has several advantages including: - good mechanical resistance when hot, and - a very low density in relation to its mechanical properties (3985 kg / m 3).
[0003] Traditional foundry processes do not allow the production of low-pressure turbine blades made of titanium aluminide. Consequently, these blades are entirely machined from the mass of parallelepiped titanium aluminide bars. In particular, after being produced, these bars undergo hot isostatic compaction and heat treatment before being sent for machining. At the end of the heat treatment, a layer may form on the outer surface of the bar. This layer, with an average thickness of between 15 μm and 50 μm, has a hardness greater than titanium aluminide. Due to this higher hardness, this layer impacts the conventional ranges for producing blades by machining and generates significant wear on the machining tools.
[0004] To address this problem, it has been proposed to use more resistant machining tools. However, this solution requires changing the conventional production ranges of moving blades by machining, it is therefore not easy to implement. In addition, the economic cost of this solution is so high that it is not industrially viable.
[0005] There is therefore a need for an effective, simple and economical solution to remove this layer.
[0006] It is thus to the credit of the inventors that they found that it was possible to meet this need using a chemical treatment of the bars before their machining. Summary
[0007] A method of producing a moving blade, in particular a low pressure turbine moving blade made of titanium aluminide, is provided, comprising the following steps: a) immersion of a titanium aluminide bar in an acid composition for get a treated bar, b) machining the treated bar to produce the moving blade, characterized in that the acid composition is a mixture of an acid oxidizing agent and a halogenated acid.
[0008] Advantageously, the acid composition of the process of the invention makes it possible to effectively, simply and economically remove the layer formed on the outer surface of the titanium aluminide bar.
[0009] Without wishing to be bound by any theory, the inventors are of the opinion that the layer formed on the outer surface of the titanium aluminide bar is effectively removed by the acidic composition because the chemical affinity between the acidic composition and the layer, mainly consisting of titanium oxide (TiO2) and alumina (A12O3) is good.
[0010] In addition, step b) can be implemented: - directly after step a), which minimizes the duration of the process of the invention, and - without modifying the conventional ranges of production of moving blades by machining, which minimizes the cost of the process of the invention. Description of the embodiments
[0011] A method of producing a titanium aluminide moving blade, in particular a low pressure turbine moving blade, is provided, comprising the following steps: a) immersing a titanium aluminide bar in an acidic composition to obtain a treated bar, and b) machining the treated bar to produce the moving blade, characterized in that the acid composition is a mixture of an acid oxidizing agent and a halogenated acid different from the acid oxidizing agent.
[0012] For the purposes of the present application, the term "acidic oxidizing agent" means a compound which receives an electron from another chemical species during an oxidation-reduction reaction and which accepts an electronic doublet during a reaction.
[0013] The acidic oxidizing agent may, for example, be chosen from nitric acid, sulfuric acid and mixtures thereof, in particular may be nitric acid.
[0014] For the purposes of the present application, the term "halogenated acid" means a halogenated compound which accepts an electronic pair during a reaction.
[0015] For example, the halogenated acid may be chosen from hydrogen fluoride, ammonium bifluoride, hydrochloric acid, iron chloride and mixtures thereof, in particular from hydrogen fluoride, ammonium bifluoride, hydrochloric acid and mixtures thereof.
[0016] Advantageously, the acidic composition comprising an acidic oxidizing agent from the above list and / or a halogenated acid from the above list effectively removes the layer formed on the outer surface of the titanium aluminide bar.
[0017] According to a particular embodiment, the acidic oxidizing agent may be nitric acid and the halogenated acid may be chosen from hydrogen fluoride, ammonium bifluoride, hydrochloric acid and mixtures thereof, in particular from hydrogen fluoride, ammonium bifluoride and hydrochloric acid, more particularly may be hydrogen fluoride.
[0018] Advantageously, the acid composition of this particular embodiment is very effective in removing the layer formed on the outer surface of the titanium aluminide bar.
[0019] Typically, the composition may be aqueous-based and comprise: - the acid oxidizing agent at a concentration of between 50 g / L and 400 g / L, in particular between 75 g / L and 350 g / L, more particularly between 100 g / L and 325 g / L, and - halogenated acid at a concentration between 5 g / L and 100 g / L, in particular between 10 g / L and 80 g / L, more particularly between 20 g / L and 75 g / L.
[0020] According to a particular embodiment, the composition may be aqueous-based and comprise nitric acid at a concentration of between 100 g / L and 320 g / L and hydrogen fluoride at a concentration of between 20 g / L and 75 g / L.
[0021] According to a very particular embodiment, the composition may be aqueous-based and comprise nitric acid at a concentration of between 100 g / L and 125 g / L and hydrogen fluoride at a concentration of between 55 g / L and 65 g / L.
[0022] According to a very particular embodiment, the composition may be aqueous-based and comprise nitric acid at a concentration of between 300 g / L and 320 g / L and hydrogen fluoride at a concentration of between 20 g / L and 25 g / L.
[0023] During step a), the titanium aluminide bar may be immersed in the acid composition for a period of between 5 min and 120 min, in particular between 10 min and 90 min, more particularly between 15 min and 60 min.
[0024] The duration of step a) is therefore advantageously short.
[0025] The duration can also be adapted to the acid composition. For example, a duration of between 5 min and 90 min, in particular between 10 min and 65 min, more particularly between 15 min and 40 min is suitable for a composition comprising nitric acid and hydrogen fluoride. For example, a duration of between 10 min and 120 min, in particular between 20 min and 90 min, more particularly between 40 min and 70 min is suitable for a composition comprising nitric acid and ammonium bifluoride or nitric acid and hydrochloric acid.
[0026] During step a), the temperature of the acid composition may be the tem- room temperature, i.e. a temperature between 20°C and 25°C.
[0027] Alternatively, during step a), the acid composition may be heated and presented at a temperature of between 30°C and 70°C, in particular between 30°C and 60°C, more particularly between 30°C and 45°C.
[0028] According to one embodiment, the method may comprise, before step a), a step of pretreating the titanium aluminide bar to obtain a pretreated titanium aluminide bar, said pretreated titanium aluminide bar then being implemented in step a).
[0029] For example, the step of pretreating the titanium aluminide rod may comprise the following substeps: - hot isostatic compaction of the titanium aluminide bar to obtain a compacted titanium aluminide bar, and - heat treatment of the compacted titanium aluminide bar to obtain the pre-treated titanium aluminide bar.
[0030] These sub-steps of the pre-processing step are conventional steps known to those skilled in the art.
[0031] Machining step b) is also a conventional step known to those skilled in the art.
[0032] Thus the sub-steps of the pre-processing step and step b) do not modify advan considerably not the conventional ranges of production of moving blades by machining. Thus, the method of the invention can be implemented easily and at low cost by those skilled in the art.
Claims
Claims
1. A method of producing a titanium aluminide moving blade comprising the following steps: a) immersing a titanium aluminide bar in an acidic composition to obtain a treated bar, and b) machining the treated bar to produce the moving blade, wherein the acidic composition is a mixture of an acidic oxidizing agent and a halogenated acid different from the acidic oxidizing agent, the acidic oxidizing agent is a compound which receives an electron from another chemical species during a redox reaction and which accepts an electron pair during a reaction, and the halogenated acid is a halogenated compound which accepts an electron pair during a reaction, characterized in that the acidic composition is aqueous-based and comprises: - the acidic oxidizing agent at a concentration of between 50 g / L and 400 g / L, and - the halogenated acid at a concentration of between 20 g / L and 75 g / L.
2. The method of claim 1, wherein the acidic oxidizing agent is selected from nitric acid, sulfuric acid and mixtures thereof.
3. A method according to claim 1 or claim 2, wherein the halogenated acid is selected from hydrogen fluoride, ammonium bifluoride, hydrochloric acid, iron chloride and mixtures thereof.
4. A method according to any one of claims 1 to 3, wherein the acidic oxidizing agent is nitric acid and the halogenated acid is selected from hydrogen fluoride, ammonium bifluoride, hydrochloric acid and mixtures thereof.
5. A method according to any one of claims 1 to 4, wherein, during step a), the titanium aluminide bar is immersed in the acid composition for a period of between 5 min and 120 min.
6. A method according to any one of claims 1 to 5, wherein, during step a), the acid composition has a temperature of between 30 C and 70 C.
7. A method according to any one of claims 1 to 6 comprising, before step a), a step of pretreating the titanium aluminide rod to obtain a pretreated titanium aluminide rod, said pretreated titanium aluminide bar then being implemented in step a).
8. The method of claim 7 wherein the step of pretreating the titanium aluminide rod comprises the following substeps: - hot isostatic compaction of the titanium aluminide rod to obtain a compacted titanium aluminide rod, and - heat treatment of the compacted titanium aluminide rod to obtain the pretreated titanium aluminide rod.