阅读说明：本技术 用于γ-γ”镍基超级合金的电化学加工的电解质 (Electrolyte for electrochemical machining of gamma-gamma' nickel-based superalloys ) 是由 M·姆萨克尼马楼彻 J·勒康特 M·兰契奇 N·斯坦 C·鲍朗格 于 2019-12-17 设计创作，主要内容包括：本发明涉及用于γ-γ”镍基超级合金的电化学加工的电解质,其包含：-相对于电解质的总重量,含量在10重量％至30重量％之间的NaNO-(3)；-络合剂,其选自pH为3至10的磺基水杨酸,和pH为7至14的氨三乙酸,络合剂以相对于电解质的总重量在1重量％至5重量％之间的含量存在；-任选地,阴离子表面活性剂,其含量为相对于电解质的总重量在1重量％至5重量％之间；-任选地,NaOH,以获得所需的pH；-水性溶剂。本发明还涉及该电解质的用途和γ-γ”镍基超级合金的电化学加工的方法,以及使用该电解质对γ-γ”镍基超级合金进行精密电化学加工的方法。(The present invention relates to an electrolyte for electrochemical machining of gamma-gamma' nickel-based superalloys, comprising: -NaNO in a content comprised between 10% and 30% by weight with respect to the total weight of the electrolyte 3 (ii) a -a complexing agent selected from sulfosalicylic acid having a pH of 3 to 10, and nitrilotriacetic acid having a pH of 7 to 14, the complexing agent being such as to be opposite to the electrolyteIs present in a content of between 1% and 5% by weight; -optionally, an anionic surfactant in a content comprised between 1% and 5% by weight relative to the total weight of the electrolyte; -optionally NaOH, to obtain the desired pH; -an aqueous solvent. The invention also relates to the use of the electrolyte and a method for electrochemical machining of a gamma-gamma 'nickel-based superalloy, and to a method for precision electrochemical machining of a gamma-gamma' nickel-based superalloy using the electrolyte.)

1. An electrolyte for electrochemical machining of a gamma-gamma' nickel-based superalloy, comprising:

-NaNO in a content comprised between 10% and 30% by weight with respect to the total weight of the electrolyte₃；

-a complexing agent selected from sulfosalicylic acid having a pH ranging from 3 to 10, and nitrilotriacetic acid having a pH ranging from 7 to 14, the complexing agent being present in a content ranging from 1% to 5% by weight with respect to the total weight of the electrolyte;

-optionally, an anionic surfactant in a content comprised between 1% and 5% by weight relative to the total weight of the electrolyte;

-optionally NaOH, to obtain the desired pH;

-an aqueous solvent.

2. The electrolyte according to claim 1, characterized in that it comprises an anionic surfactant, advantageously selected from the group consisting of: saccharin, sodium lauryl sulfate, sulfonates, carboxylates, sulfinates, phosphates, and mixtures thereof, more advantageously selected from the group consisting of: saccharin, sodium lauryl sulfate, and mixtures thereof.

3. The electrolyte of any one of claims 1 to 2, wherein the complexing agent is sulfosalicylic acid having a pH between 3 and 10.

4. Use of the electrolyte according to any one of claims 1 to 3 in the electrochemical machining of a γ - γ "nickel-based superalloy, in particular in the precision electrochemical machining of a γ - γ" nickel-based superalloy, the electrochemical deposition of a γ - γ "nickel-based superalloy or the electrochemical grinding of a γ - γ" nickel-based superalloy.

5. A method for electrochemical machining of a gamma-gamma' nickel-based superalloy, comprising the sequential steps of:

a-providing a gamma-gamma' nickel-based superalloy workpiece as an anode;

b-providing a tool as a cathode;

c-providing an electrolyte according to any one of claims 1 to 3;

d-immersing the anode and cathode in the electrolyte with an electrode spacing of between 0.1mm and 1 mm;

e-applying a continuous current between the anode and the cathode to achieve anodic dissolution of the gamma-gamma' nickel-based superalloy work piece;

f-recycling the processed workpiece obtained in step e).

6. A method for precision electrochemical machining of a gamma-gamma' nickel-based superalloy, comprising the sequential steps of:

a, providing a gamma-gamma' nickel-based superalloy workpiece as an anode;

b-providing a tool as a cathode;

c-providing an electrolyte according to any one of claims 1 to 3;

d, immersing the anode and the cathode into the electrolyte;

e-applying a pulsed current between the anode and the cathode, synchronized with the possible oscillation of the cathode, accompanied by a possible rectilinear translational movement of the cathode towards the anode, so that a minimum electrode spacing of 10 to 200 μm can be obtained, thus achieving anodic dissolution of the gamma-gamma' nickel-based superalloy work piece;

f-recycling the processed workpiece obtained in step E).

7. The method according to claim 6, wherein step E) is carried out in a static mode, without a rectilinear translational movement of the cathode towards the anode.

8. The method according to claim 6, wherein step E) is carried out in a dynamic mode, there being a rectilinear translational movement of the cathode towards the anode.

9. The method according to any one of claims 6 to 8, wherein step E) is carried out by oscillation of the cathode.

Technical Field

The present invention relates to the field of electrolytes for electrochemical machining (ECM) of nickel-based superalloys of the gamma-gamma (gamma-gamma) type.

Prior Art

ECM is an unconventional process. The process is primarily directed to conductive materials. The principle of ECM is based on the anodic dissolution of a workpiece (anode) using a tool called a cathode in the presence of an ion conducting electrolyte. The electrode gap (gap) is defined as the distance between the workpiece to be machined and the cathode. It is about 0.1 to 1 mm.

Precision electrochemical machining (PECM) is based on the same principle as metal anodization. However, it differs from the ECM in the application of pulsed and discontinuous currents. The current is synchronized with the oscillation of the cathode. This oscillation is accompanied by a linear translational movement and also by a small gap (10 to 200 μm). Thus, the process becomes sensitive to the formation of hydrogen bubbles that form at the cathode and interfere with the efficiency of the process.

The current practice is to use NaNO in concentrations between 8% and 20% by weight with respect to the total weight of the solution₃The processing of the gamma-gamma' type nickel-based high-temperature alloy is realized in the base electrolyte solution.

In NaNO₃When ECM and its derivatives are carried out in media (precision ECM PECM, electrochemical deposition ECD, electrochemical milling ECG), anodic dissolution of gamma-gamma "superalloys produces soluble and insoluble products that form sludge, most of which remains adhered to the electrochemically processed surface. The latter mainly consists of oxides and hydroxides which hinder the optimal dissolution reaction. In addition, certain phases that make up these superalloys, such as the gamma prime phase, carbides, and nitrocarbides (nitrocarbides), are insoluble and fall off under the action of the electrolyte flow during machining, forming a rough surface. All these consequences lead to a reduction in efficiency and to additional operations for repairing the machined surface (chemical pickling, abrasive polishing).

This dissolution is also accompanied by the formation of hydrogen gas at the cathode surface, leading to process fluctuations and disturbances. These formed bubbles can cause process disturbances due to the small distance between the cathode and the workpiece to be machined (gap for precision electrochemical machining (PECM) is between 10 μm and 200 μm), thereby reducing efficiency.

Electrolytes for electrochemical machining of certain metals (Fe, Cu, Ni, Al, Sn, Cr and Zn) and alloys thereof are known. This electrolyte is based essentially on the addition of a mixture of a complexing agent, which may be EDTA, HEDTA, NTA or citric acid, and an inorganic salt based on NaNO₃、NaCl、NaClO₄、Na₂SO₄、KNO₃、KCl、KClO₄、K₂SO₄、LiNO₃、LiCl、LiClO₄And Li₂SO₄The concentration ranges from 100g/L to 500 g/L. The electrolyte also contains a reducing agent, such as ascorbic acid. However, the network is connected toThe binder is not able to complex Nb, which is the main element of γ "inclusions, especially since NTA is used in the pH range of 2 to 7, which makes good complexation impossible.

There is therefore a need to find a new electrolyte for the electrochemical machining of nickel-based superalloys of the gamma-gamma "type, which does not exhibit the drawbacks of the prior art.

Disclosure of Invention

The inventors have therefore surprisingly found that NaNO based₃And the electrolyte with specific composition is very suitable for electrochemical machining of gamma-gamma' type nickel base super alloy, without presenting the disadvantages of the prior art, and in particular, the electrolyte can reduce the overvoltage of hydrogen generated at the cathode surface, improve the dissolution efficiency, and produce the improved effect of reducing the roughness.

The present invention therefore relates to an electrolyte for the electrochemical machining of a γ - γ "nickel-based superalloy, comprising, advantageously consisting essentially of, in particular consisting of:

-NaNO in an amount of 10 to 30% by weight relative to the total weight of the electrolyte₃；

-a complexing agent chosen from sulfosalicylic acid having a pH ranging from 3 to 10, advantageously a pH of 6, and nitrilotriacetic acid (NTA) having a pH ranging from 7 to 14, advantageously a pH of 10, the complexing agent being present in a content ranging between 1% and 5% by weight, advantageously between 2% and 3% by weight, with respect to the total weight of the electrolyte;

-optionally, an anionic surfactant in a content comprised between 1% and 5% by weight relative to the total weight of the electrolyte;

optionally, NaOH, to obtain the desired pH (depending on the complexing agent chosen);

-an aqueous solvent, advantageously water.

The gamma-gamma "nickel-based superalloy may be, for example, Inconel sold by International Wire of InternationalThis is a precipitation hardenable nickel-iron-a chromium alloy having a high creep rupture strength at high temperatures of about 700 ℃, advantageously having the following composition in weight percent: 50-55 parts of Ni, 17-21 parts of Cr, 2.8-3.3 parts of Mo, 4.75-5.5 parts of Nb, 0.65-1.15 parts of Ti, 0.2-0.8 part of Al, less than or equal to 0.08 part of C, less than or equal to 0.35 part of Mn, less than or equal to 0.35 part of Si, less than or equal to 0.015 part of P, less than or equal to 0.015 part of S, less than or equal to 1.00 part of Co, less than or equal to 0.05 part of Ta, less than or equal to 0.006 part of B, less than or equal to 0.30 part of Cu, less than or equal to 0.0005 part of Pb, less than or equal to 0.00003 part of Bi, less than or equal to 0.003 part of Se, and the balance of Fe.

Sulfosalicylic acids can complex Ni at a pH between 3 and 10, advantageously at a pH of 6₃The main element of the Nb phase, which is niobium, is insoluble in the nitrate medium alone.

NTA can complex all metal cations, e.g. Ni, Al, Fe, Cr, more easily at pH values between 7 and 14, advantageously at an optimal pH value of pH 10.

Advantageously, the complexing agent is sulfosalicylic acid at a pH of 3 to 10, more advantageously at a pH of 6.

Anionic surfactants may be present in the electrolyte. Which can lower the surface tension and promote the dissolution reaction. The anionic surfactant can also reduce overvoltage of hydrogen generated at the surface of the cathode and causing interference during processing, and improve dissolution efficiency. In an advantageous embodiment, the anionic surfactant is selected from the group consisting of: saccharin, sodium lauryl sulfate, sulfonates, carboxylates, sulfinates (sulfonates), phosphates, and mixtures thereof; advantageously, it is selected from the group consisting of: saccharin, sodium lauryl sulfate, and mixtures thereof.

The electrolyte according to the invention can ensure a homogeneous anodic dissolution of all phases of the gamma-gamma' nickel-based superalloy. It also ensures a good surface finish by optimizing efficiency and dissolution rate and reducing the formation of residues.

The electrolyte according to the present invention is prepared by simply adding and mixing various components in an aqueous solvent by a method well known to those skilled in the art. If NaOH is required, it is added at the end until the target pH is reached.

The invention further relates to the use of the electrolyte according to the invention in the electrochemical machining of a gamma-nickel-based superalloy, in particular in the precision electrochemical machining of a gamma-nickel-based superalloy, the electrochemical deposition (ECD) of a gamma-nickel-based superalloy or the electrochemical grinding (ECG) of a gamma-nickel-based superalloy.

It also relates to a method for electrochemical machining of a gamma-gamma' nickel-based superalloy, comprising the following sequential steps:

a-providing a gamma-gamma' nickel-based superalloy workpiece as an anode;

b-providing a tool as a cathode;

c-providing an electrolyte according to the invention;

d-immersing the anode and the cathode in the electrolyte, wherein the electrode distance is between 0.1mm and 1 mm;

e-applying a continuous current between the anode and the cathode to achieve anodic dissolution of the gamma-gamma' nickel-based superalloy work piece;

f-recycling the processed workpiece obtained in step e).

The tool that can be used as the cathode in step b) of the electrochemical machining process of the present invention is mainly made of stainless steel, but may also be made of a titanium alloy, a platinum alloy, a copper-based alloy, or a copper-tungsten alloy.

The current of step e) may have a voltage in the range of 4V to 30V. The current density is advantageously 12.8A/cm². The application of a continuous current in the electrochemical process according to the invention allows the continuous passage of electrolyte between the cathode and the anode during step e) at a sufficient flow rate, in particular using a pressure of between 3.5 and 4 bar (between 350000 and 400000 Pa), to evacuate the residues of anodic dissolution (sludge and hydrogen) and ensure an optimal dissolution rate. The dissolution rate is the difference in mass before and after processing divided by the processing time. It is advantageously greater than or equal to 80 mg/min.

The optimum dissolution efficiency advantageously obtained by the process according to the invention is greater than or equal to 60% by mass. It is calculated by the following formula:

for simplicity, nickel is considered only as an electroactive element. Thus, the anodic reaction is:

Ni→Ni²⁺2e^-

theoretical mass loss Δ W of the sample_theoDetermined by the following relationship:

m is the atomic molar mass of nickel, I is the applied current, t is the duration of oxidation, n is the valence of the dissolved ion (n-2), F is the faraday constant, equal to 96500C/mole. Assuming 100% faradaic efficiency.

The efficiency is defined as:

wherein, Δ W_expIs the difference between the quality before the test and the quality after the test and after the final surface cleaning.

Finally, the invention relates to a method for the precision electrochemical machining of a gamma-gamma' nickel-based superalloy, comprising the following successive steps:

a, providing a gamma-gamma' nickel-based superalloy workpiece as an anode;

b-providing a tool as a cathode;

c-providing an electrolyte according to the invention;

d, immersing the anode and the cathode into the electrolyte;

e-applying a pulsed current between the anode and the cathode, synchronized with the possible oscillation of the cathode, accompanied by a possible rectilinear translational movement of the cathode towards the anode, so that a minimum interpolar distance of 10 to 200 μm can be obtained, thus achieving anodic dissolution of the gamma-gamma' nickel-based superalloy work piece;

f-recycling the processed workpiece obtained in step E).

The tool that can be used as the cathode in step B) of the electrochemical machining process of the present invention is mainly made of stainless steel, but may also be made of a titanium alloy, a platinum alloy, a copper-based alloy, or a copper-tungsten alloy.

The current of step E) may have a voltage in the range of 6V to 18.7V. The amplitude of the oscillations may be between 0.2 and 0.8mm, preferably 0.4 mm. The oscillation frequency may be between 27 and 70Hz and the pulse duration may be between 2 and 10 ms.

Step E) can be carried out with or without cathode oscillation, advantageously with cathode oscillation. If implemented without oscillation, a continuous displacement of the cathode (using only current pulses) may occur.

Step E) can also be carried out in dynamic mode (linear translational motion of the cathode towards the anode) or in static mode (no linear translational motion of the cathode towards the anode) with current pulses and optionally with associated oscillations for surface repair or polishing operations (removal <1 mm). Thus, step E) of the method according to the invention can be carried out in a static mode without a rectilinear translational movement of the cathode towards the anode, or step E) of the method according to the invention can be carried out in a dynamic mode with a rectilinear translational movement of the cathode towards the anode.

The invention will be better understood from the following description of examples.

Examples

Under slightly different conditions than ECM (gap greater than 2mm and low current density (178 mA/cm)²) In an ECM process in InconelThree electrolytes were tested:

-solution a: 2.35M NaNO₃Aqueous solution

-solution B: 2.35M NaNO₃+0.1M aqueous solution of sulfosalicylic acid, pH 6

-solution C: 2.35M NaNO₃+0.1M aqueous nitrilotriacetic acid, pH 10.

SEM analysis of the surface finish obtained after machining can demonstrate that the use of solutions B and C significantly reduces corrosion products at the surface compared to sodium nitrate medium (solution a). In the presence of complexing agents, these products have reduced adhesion and are easily removed by electrolyte flow.

Chemical analysis of the dissolved elements in the spent electrolyte (concentration in mg/L) showed that the solubility of niobium was 7 times higher than that in the nitrate medium alone in the presence of the sulfosalicylic acid based complexing agent (solution B). Also, the Ti and Mo concentrations in the electrolyte increased, indicating that their entry into solution was promoted in the presence of the complexing agent. The results are collated in Table 1 below.

[ Table 1]

	Ni	Fe	Cr	Mo	Nb	Ti
							Solution A	11.9	4.6	4.7	0.6	0.1	0.0
Solution B	11.5	5.1	5.0	1.0	0.7	0.1