Iridium alloy thermocouple wire for high temperature measurement and preparation method thereof

Abstract

The present invention relates to an iridium alloy thermocouple wire for high-temperature temperature measurement and a preparation method thereof, wherein the thermocouple wire is composed of a positive electrode wire and a negative electrode wire, wherein the positive electrode wire is an IrRh alloy, and the weight percentage of each component in the alloy is: Rh is 10-40%, and the rest is Ir; the negative electrode wire alloy is composed of Ir, Pt and one or more of Pt, Cr, Ru, and Rh, and the weight percentage of each component in the alloy is: Pt content 5-15%, Ru content 0-10%, Cr content 0-10%, Rh content 0-10%, and the rest is Ir. The iridium alloy thermocouple wire of the present invention has the advantages of high strength and toughness, high temperature resistance, and oxidation resistance, and has good stability and long service life, which solves the problem that traditional high-temperature thermocouples are easy to break during use, have poor stability and short service life in high-temperature oxidizing atmosphere, and the upper limit of temperature measurement is above 2200°C.

Description

Technical Field

[0001] The invention belongs to the field of temperature measurement, and in particular relates to an iridium alloy thermocouple wire for high-temperature temperature measurement and a preparation method thereof. Background Art

[0002] With the technological progress in the fields of aerospace, the thrust-to-weight ratio of engines is constantly improving, and the temperature of the combustion chamber outlet, engine flame and other parts is getting higher and higher, and the demand for thermocouples used in high-temperature oxidizing environments is becoming more and more urgent. Iridium-rhodium 40-iridium thermocouple (the positive electrode is iridium-rhodium 40 alloy, and the negative electrode is pure iridium) is currently the most commonly used thermocouple with the highest temperature measurement upper limit (2100℃) that can be used directly in high-temperature oxidizing atmospheres. However, iridium has intrinsic brittleness at room temperature, is difficult to process into thin wires, and has poor bending ability during sensor assembly, and is easy to break; iridium is easy to form iridium oxide at high temperatures and volatilizes quickly, resulting in thermocouples that are easy to break when used, short high-temperature life, and fast signal drift. The existing technology hinders the oxidation and volatilization of iridium in iridium-rhodium 40-iridium thermocouple wires to a certain extent through the optimization design of the probe structure and the protection of the wire surface coating / thin film layer, but it still cannot solve the problem of easy breakage and short life of the wire during use, and cannot cope with ultra-high temperature measurements of 2200℃ and above.

[0003] The purpose of the present invention is to provide an iridium alloy thermocouple wire for high-temperature temperature measurement and a preparation method thereof. The iridium alloy thermocouple wire has the advantages of high strength and toughness, high temperature resistance, and oxidation resistance, and has good stability and long service life. It solves the problem that traditional high-temperature thermocouples are easy to break during use, have poor stability and short service life in a high-temperature oxidizing atmosphere, and the upper limit of temperature measurement is above 2200°C.

[0004] The technical solution of the present invention is:

[0005] Iridium alloy thermocouple wire used for high temperature measurement, the thermocouple wire consists of a positive wire and a negative wire, wherein:

[0006] The positive electrode wire is an IrRh alloy, and the weight percentage of each component in the alloy is: Rh is 10-40%, and the rest is Ir;

[0007] The negative electrode wire alloy is composed of Ir, Pt and one or more of Pt, Cr, Ru and Rh. The weight percentage of each component in the alloy is: Pt content 5-15%, Ru content 0-10%, Cr content 0-10%, Rh content 0-10%, and the rest is Ir.

[0008] A further technical solution is that the positive electrode wire is an IrRh alloy, and the weight percentage of each component in the alloy is: Rh is 30%, Ir is 70%;

[0009] The negative electrode wire alloy is composed of Ir, Pt and one or more of Pt, Cr, Ru and Rh. The weight percentage of each component in the alloy is: Pt content 5-15%, Ru content 0-10%, Cr content 0-5%, Rh content 0-5%, and the rest is Ir.

[0010] The preparation method of the thermocouple wire comprises the following steps:

[0011] S1 Alloy Casting

[0012] The thermocouple wire of claim 1 or 2 is prepared by mixing the components in a uniform ratio, briquetting, vacuum induction melting, and bottom casting to obtain positive and negative electrode alloy ingots, respectively;

[0013] S2 Homogenization annealing

[0014] The positive electrode and negative electrode alloy ingots are vacuum annealed at 1200-1600°C for 1-3h;

[0015] S3 Hot Forging

[0016] 1) Free forging

[0017] The initial forging temperature is 1450-1650°C, the final forging temperature is 1200-1400°C, the forging ratio is 5-10%, and the positive and negative square bars are forged;

[0018] 2) Die forging

[0019] The die forging temperature is 1450-1650°C, and the die spacing is 0.1-0.8 mm to obtain positive and negative electrode rods;

[0020] S4 Hot Pull

[0021] The positive and negative electrode rods are drawn at a temperature of 1050-1250°C with a deformation of 5-10% per pass to obtain positive and negative electrode wires.

[0022] S3 The dimensions of the positive and negative electrode bars are 7.0×7.0 to 12.0×12.0 mm 2 .

[0023] The diameter of the positive electrode and negative electrode rods described in S3 is 3.0 to 3.5 mm.

[0024] The diameter of the positive electrode and negative electrode wires in S4 is 0.3 to 1.0 mm.

[0025] In the positive electrode wire of the present invention: the Rh content in Ir is controlled at 10% to 40%, so that the thermocouple has a large thermoelectromotive force output value while ensuring that the melting point of the alloy is above 2200°C; in the negative electrode wire: Pt, Ru, Cr, and Rh can all play a role in solid solution strengthening and improve the strength and toughness of the wire.

[0026] Among them, Pt can increase the pairing thermoelectric potential, and it itself has extremely high oxidation resistance; the Pt content must be above 5% to have a more significant solid solution strengthening effect, but when it is higher than 15%, it will significantly reduce the melting point of the alloy, which is not conducive to high-temperature application of the pair wire.

[0027] Ru has a high melting point and can also increase the pairing thermoelectric potential, and has a significant solid solution strengthening effect; Cr forms a dense chromium oxide layer on the surface of the pair wire at high temperature to prevent the wire from being further oxidized; the Ru / Cr content must be controlled below 10%, otherwise it will be difficult to distribute evenly in the Ir matrix, affecting the temperature measurement accuracy.

[0028] Rh can significantly improve the oxidation resistance of the thermocouple wire, especially effectively reduce the volatilization rate of Ir, thereby improving the stability of the thermocouple. The Rh content in the negative electrode wire must be controlled below 10%, otherwise it will cause a significant decrease in the thermoelectric potential value, which is not conducive to the sensitivity of the thermocouple.

[0029] The experiment of the applicant shows that: the positive and negative electrode wires of the present invention and the traditional iridium-rhodium 40-iridium couple wires are subjected to 2200℃ high temperature oxidizing atmosphere conditions. After 10 minutes, the negative electrode wire near the positive and negative electrode welding points of the traditional iridium-rhodium 40-iridium couple wire breaks and its diameter is significantly reduced, and the thermocouple electrical signal disappears; the thermocouple wire of the present invention is still working normally after 6 hours under 2200℃ high temperature oxidizing atmosphere conditions, and the thermocouple remains intact. Therefore, the iridium alloy thermocouple wire of the present invention has the advantages of high strength and toughness, high temperature resistance, and oxidation resistance, and has good stability and long life in high temperature oxidizing atmosphere. DETAILED DESCRIPTION

[0030] Example 1: φ0.5 mm IrRh40-Ir thermocouple wire (comparative example);

[0031] The positive electrode wire is formulated with 60% Ir and 40% Rh; the negative electrode wire is formulated with 100% Ir.

[0032] S1 alloy casting

[0033] The raw materials are uniformly mixed and pressed into blocks for vacuum induction melting, and the melt is introduced into a water-cooled copper mold by bottom pouring casting to solidify into positive and negative electrode alloy ingots.

[0034] S2 Homogenization annealing

[0035] The positive electrode and negative electrode alloy ingots are vacuum annealed at 1200-1600° C. for 1-3 hours.

[0036] S3 hot forging

[0037] 1) Free forging

[0038] The initial forging temperature of the positive and negative electrode alloy ingots after homogenization annealing is 1450-1650°C, the final forging temperature is 1200-1400°C, the forging ratio is 5%-10%, and the forging is 7.0×7.0-12.0×12.0mm 2 After the square bars are formed, hot die forging is performed;

[0039] 2) Die forging

[0040] The die forging temperature is 1450-1650°C, the die spacing is 0.1-0.8 mm, and the positive and negative electrode iridium alloy bars with a diameter of 3.0-3.5 mm are obtained;

[0041] S4 hot pull

[0042] The positive and negative iridium alloy rods obtained in S3 are hot drawn at a drawing temperature of 1050-1250°C and a deformation amount of 5-10% to obtain a φ0.5mm IrRh40-Ir thermocouple wire.

[0043] Example 2: IrRh30-IrPt15 thermocouple wire of φ0.5 mm;

[0044] The positive electrode wire is formulated according to 70% Ir and % Rh30, and the negative electrode wire is formulated according to 85% Ir and 15% Pt.

[0045] The preparation method is the same as that in Example 1, and a φ0.5 mm IrRh40-IrPt15 thermocouple wire is obtained.

[0046] Example 3: IrRh30-IrPt10Ru10 thermocouple wire of φ0.5 mm;

[0047] The positive electrode wire is formulated according to 70% Ir, % Rh30, and the negative electrode wire is formulated according to 80% Ir, 10% Pt, and 10% Ru.

[0048] The preparation method is the same as that in Example 1, and a φ0.5 mm IrRh40-IrPt10Ru10 wire is obtained.

[0049] Example 4: IrRh30-IrPt5Ru5Cr5Rh5 thermocouple wire of φ0.5 mm;

[0050] The positive electrode wire is formulated according to 70% Ir and 30% Rh; the negative electrode wire is formulated according to 80% Ir, 5% Pt, 5% Ru, 5% Cr, and 5% Rh.

[0051] The preparation method is the same as that in Example 1, and a φ0.5 mm IrRh30-IrPt5Ru5Cr5Rh5 thermocouple wire is obtained.

[0052] High temperature stability test:

[0053] After the positive and negative electrode wires of Examples 1-4 were welded and assembled into temperature probes, they were placed in a high-temperature fuel gas (high-temperature oxidizing atmosphere) above 2200°C. After 10 minutes, in Example 1, the negative electrode wire broke near the hot junction of the thermocouple and its diameter was significantly reduced as seen by the naked eye, the thermocouple electrical signal disappeared, and the thermocouple could not work normally. In Examples 2-4, no obvious change in the diameter of the negative electrode wire was observed to the naked eye after 6 hours, the electric thermocouple could still work normally, and the thermocouple remained intact.

Claims

1. An iridium alloy thermocouple wire for high temperature measurement, characterized in that: The thermocouple wire is composed of a positive wire and a negative wire, wherein: The positive electrode wire is an IrRh alloy, and the weight percentage of each component in the alloy is: Rh is 10-30%, and the rest is Ir; The negative electrode wire alloy is composed of Ir, Pt and one or more of Pt, Cr, Ru and Rh, and the weight percentage of each component in the alloy is: Pt content is 5-15%, and the rest is Ir; Or the weight percentage of each component of the negative electrode wire alloy is: Pt content 5-15%, Ru content 10%, and the rest is Ir; Or the weight percentage of each component of the negative electrode wire alloy is: Pt content 5-15%, Ru content 5%, Cr content 5%, Rh content 5%, and the rest is Ir.

2. The thermocouple wire according to claim 1, characterized in that The positive electrode wire is an IrRh alloy, and the weight percentage of each component in the alloy is: Rh is 30%, and Ir is 70%.

3. The method for preparing the thermocouple wire according to claim 1 or 2, characterized in that: There are the following steps: S1 Alloy Casting The thermocouple wire of claim 1 or 2 is prepared by mixing the components in a uniform ratio, briquetting, vacuum induction melting, and bottom casting to obtain positive and negative electrode alloy ingots, respectively; S2 Homogenization annealing The positive electrode and negative electrode alloy ingots are vacuum annealed at 1200-1600°C for 1-3h; S3 Hot Forging 1) Free forging The initial forging temperature is 11450-1650°C, the final forging temperature is 1200-1400°C, the forging ratio is 5-10%, and the positive and negative square bars are forged; 2) Die forging The die forging temperature is 1450-1650°C, and the die spacing is 0.1-0.8 mm to obtain positive and negative electrode rods; S4 Hot Pull The positive and negative electrode rods are drawn at a temperature of 1050-1250°C with a deformation of 5-10% per pass to obtain positive and negative electrode wires.

4. The preparation method according to claim 3, characterized in that: S3 The dimensions of the positive and negative electrode bars are 7.0×7.0 to 12.0×12.0 mm 2 .

5. The preparation method according to claim 3, characterized in that: The diameter of the positive electrode and negative electrode rods described in S3 is 3.0 to 3.5 mm.

6. The preparation method according to claim 3, characterized in that: The diameter of the positive electrode and negative electrode wires in S4 is 0.3 to 1.0 mm.