A high-temperature air flow temperature sensor based on iridium alloy shielding cover

Abstract

The invention discloses a high-temperature airflow temperature sensor based on an iridium alloy shielding cover, which belongs to the field of temperature measurement. The invention comprises a thermocouple wire, a shielding cover, an insulating porcelain tube, a housing, and a mounting flange. The shielding cover is provided with a shielding cover shell, an air inlet, and an air outlet. The invention adopts an iridium-niobium-tungsten-thorium-aluminum five-element alloy as the shielding cover material of the sensor, and through alloying, the recrystallization temperature of the material is increased, the grain growth is suppressed, and the welding performance of the material is improved, thereby avoiding the problem of insufficient mechanical properties and processing properties of pure iridium. Tungsten is used to promote that the iridium alloy will not recrystallize during high-temperature processing. Adding the element thorium increases the bonding force of the grain boundary; and can further improve the plasticity of iridium; adding the element aluminum can promote the segregation of thorium to the grain boundary, effectively improving the plasticity and impact toughness of iridium; adding niobium improves the welding performance of the alloy. The invention ensures that the high-temperature airflow temperature sensor has good strength, plasticity, toughness and processing properties while being resistant to a high temperature of 2300K.

Description

Technical Field

[0001] The invention relates to a high-temperature airflow temperature sensor based on an iridium alloy shielding cover, in particular to a high-temperature airflow temperature sensor suitable for high-temperature measurement of airflow, and belongs to the field of temperature measurement. Background Art

[0002] In the development, production test and use of high-performance aircraft engines, turboramjet combined cycle engines, etc., airflow high temperature is a key test parameter, usually used for engine performance evaluation, status monitoring, combustion diagnosis, etc. Airflow high temperature measurement uses a high-temperature airflow temperature sensor. Due to the harsh working environment of engines and other equipment, in order to reduce the radiation error and speed error of the high-temperature airflow temperature sensor, and to protect the thermocouple wire from the harsh environment, the high-temperature airflow temperature sensor generally adopts a shielded structure, that is, a shielding cover is coated on the outside of the thermocouple wire head. At present, the high-temperature airflow temperature sensor generally uses platinum-rhodium alloy, platinum-iridium alloy, corundum and other materials to make the shielding cover, but the above materials cannot be used normally at a temperature of 2300K due to the limitation of melting point. Although the temperature of the shielding cover can be reduced by cooling the back end, the result of doing so is the introduction of a large thermal conductivity error, which makes the measurement error of the temperature sensor larger. The operating temperature of metal iridium can reach 2300K, but due to the high brittleness of iridium, it is very easy to break during processing and use, which greatly limits its reliable use. In summary, there is currently a lack of effective means for measuring high temperature of 2300K airflow. Summary of the invention

[0003] The main purpose of the present invention is to provide a high-temperature airflow temperature sensor based on an iridium alloy shielding cover, which ensures that the high-temperature airflow temperature sensor has good strength, plasticity, toughness and processability while being resistant to a high temperature of 2300K.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] The invention discloses a high-temperature airflow temperature sensor based on an iridium alloy shielding cover, comprising a thermocouple wire, a shielding cover, an insulating porcelain tube, a shell, and a mounting flange. The shielding cover is provided with a shielding cover shell, an air inlet, and an air outlet.

[0006] The shielding cover is in the shape of a thin-walled tube with a wall thickness of 0.8 mm to 1.8 mm. The circumferential and axial distances between adjacent air outlet holes of the shielding cover are not less than 5 times the hole diameter.

[0007] The shielding cover is connected to the shell by welding. The thermocouple wire is inserted into the insulating porcelain tube and then installed into the shell. It is bent 90 degrees at the head and inserted into the shielding cover. The mounting flange is connected to the shell by welding.

[0008] The shielding cover is an iridium alloy shielding cover, and the manufacturing method is as follows:

[0009] Step 1: Prepare shielding cover material based on iridium-niobium-tungsten-thorium-aluminum quinary alloy, wherein the content of niobium is 0.4%-0.8% by weight, the content of tungsten is 0.2%-0.4% by weight, the content of thorium is 30ppm-50ppm, the content of aluminum is 40ppm-60ppm, and the rest is iridium.

[0010] Step 2: Use powder metallurgy to cold isostatically press pure iridium powder to prepare iridium pre-sintered blocks. The cold isostatic pressing pressure is 50MPa~100MPa, and the holding time is 100s~150s. Then, the iridium sintered blocks are pre-sintered in a hydrogen atmosphere at a sintering temperature of 950℃~1100℃ and a holding time of 1h~2h.

[0011] Step 3: sinter the pre-sintered iridium block in a high-temperature vacuum furnace at a high temperature of 1450° C. to 1550° C., a holding time of 3 h to 4 h, and a vacuum degree better than 0.3 Pa.

[0012] Step 4: Use arc melting to melt the sintered iridium block to prepare pure iridium button ingots, and the weight of each button ingot is controlled at 50g to 100g.

[0013] Step 5: Add appropriate amounts of niobium, thorium, tungsten and aluminum according to the ratio described in step 1 to prepare iridium alloy button ingots. Each button ingot is repeatedly smelted 6 to 8 times, and then the button ingot is washed in aqua regia for 5 to 8 minutes to remove surface impurities.

[0014] Step 6: Electron beam melting of iridium alloy button ingots and casting into water-cooled molds Iridium alloy round ingot.

[0015] Step 7: Prepare the iridium alloy rod by hot working methods such as jacket extrusion, hot forging or hot rolling, the jacket extrusion temperature is 1250℃~1350℃, the initial forging temperature of hot forging or the blanking temperature of hot rolling is 1500℃~1750℃, the final forging temperature of hot forging or the final rolling temperature of hot rolling is not less than 1300℃.

[0016] Step 8: Annealing the iridium alloy rod at a temperature of 1200°C to 1300°C for a holding time of 1h to 2h, and then cooling to room temperature with the furnace.

[0017] Step nine: Prepare an iridium alloy tube by mechanical processing, and make a shielding cover based on the iridium alloy tube.

[0018] The mechanical processing means include laser cutting, electric spark drilling and mechanical grinding.

[0019] Beneficial effects:

[0020] 1. To solve the problem of insufficient upper temperature limit of shielding covers of platinum-rhodium alloy, platinum-iridium alloy, corundum, silicon carbide, etc. in the current 2300K airflow high temperature measurement, and poor strength, plasticity, toughness and processability of iridium shielding covers. The present invention discloses a high-temperature airflow temperature sensor based on an iridium alloy shielding cover, which uses iridium-niobium-tungsten-thorium-aluminum five-element alloy as the shielding cover material of the high-temperature airflow temperature sensor. By alloying, the recrystallization temperature of the material is increased, the grain growth is suppressed, and the welding performance of the material is improved at the same time, and the problem of insufficient mechanical properties and processing properties of pure iridium is avoided. While being resistant to 2300K high temperature, it has the advantages of good strength, plasticity, toughness and processability.

[0021] 2. The present invention discloses a high-temperature airflow temperature sensor based on an iridium alloy shielding cover. In the shielding cover material, the main function of tungsten is to strengthen the solid solution and increase the recrystallization temperature, so that the iridium alloy will not recrystallize during high-temperature processing. Adding the element thorium has two functions: one is to increase the recrystallization temperature, segregate at the grain boundary, and increase the bonding force of the grain boundary; the other is to precipitate iridium and thorium phases, pin them at the grain boundary, inhibit grain growth, play a role in refining grains and increasing the bonding force of grain boundaries, and can further improve the plasticity of iridium; adding the element aluminum can promote the segregation of thorium to the grain boundary, effectively improving the plasticity and impact toughness of iridium; the main function of adding niobium is to improve the welding performance of the alloy.

[0022] 3. The present invention discloses a high-temperature airflow temperature sensor based on an iridium alloy shielding cover. After a large number of tests and analyses, it is found that when the shielding cover is in the shape of a thin-walled tube with a wall thickness of 0.8 mm to 1.8 mm, and the circumferential and axial distances between adjacent air outlets of the shielding cover are not less than 5 times the hole diameter, the strength and processability of the shielding cover and the measurement accuracy of the sensor can be guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the structural diagram of the high temperature air flow temperature sensor. Figure 2 A schematic diagram of the structure of the shielding cover.

[0024] 1—thermocouple wire, 2—shielding cover, 3—insulating porcelain tube, 4—housing, 5—mounting flange, 6—shielding cover shell, 7—air inlet, 8—air outlet. DETAILED DESCRIPTION

[0025] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to examples and drawings.

[0026] like Figure 1 As shown, the high-temperature air flow temperature sensor based on the iridium alloy shielding cover disclosed in this embodiment includes a thermocouple wire 1, a shielding cover 2, an insulating porcelain tube 3, a housing 4, and a mounting flange 5. Figure 2 As shown, the shielding cover 2 is provided with a shielding cover shell 6, an air inlet 7, and an air outlet 8.

[0027] The shielding cover 2 is in the shape of a thin-walled tube with a wall thickness of 1 mm. The circumferential distance between adjacent air outlet holes 8 of the shielding cover 2 is 6 times the diameter of the hole. Figure 2 6 is the shielding shell, 7 is the air inlet, and 8 is the air outlet.

[0028] The shielding cover 2 is connected to the shell 4 by welding. The thermocouple wire 1 is inserted into the insulating porcelain tube 3 and then installed into the shell 4. It is bent 90 degrees at the head and inserted into the shielding cover 2. The mounting flange 5 is connected to the shell 4 by welding.

[0029] The shielding cover material is an iridium alloy shielding cover, and the manufacturing method is as follows:

[0030] The shielding cover material is a five-element alloy of iridium-niobium-tungsten-thorium-aluminum as the shielding cover material, wherein the niobium content is 0.5% by weight, the tungsten content is 0.3%, the thorium content is 30ppm, and the aluminum content is 50ppm. The main function of tungsten is solid solution strengthening and increasing the recrystallization temperature, which prevents the iridium alloy from recrystallizing during high-temperature processing. Adding the element thorium has two functions: one is to increase the recrystallization temperature, segregate at the grain boundary, and increase the bonding force of the grain boundary; the other is to precipitate iridium and thorium phases, pin them at the grain boundary, inhibit grain growth, play a role in refining grains and increasing grain boundary bonding force, and can further improve the plasticity of iridium. Adding the element aluminum can promote the segregation of thorium to the grain boundary, effectively improving the plasticity and impact toughness of iridium. The main function of niobium is to improve the welding performance of the alloy.

[0031] Pure iridium powder was cold isostatically pressed by powder metallurgy to prepare iridium pre-sintered blocks. The cold isostatic pressing pressure was 80 MPa and the holding time was 120 s. The iridium sintered blocks were then pre-sintered in a hydrogen atmosphere at a sintering temperature of 1000°C and a holding time of 1 h.

[0032] The pre-sintered iridium block is sintered in a high-temperature vacuum furnace at a sintering temperature of 1500°C for 4 hours at a vacuum degree of 0.2Pa.

[0033] The sintered iridium block is melted by arc melting to prepare pure iridium button ingots, each weighing 60g.

[0034] Iridium alloy button ingots were prepared by adding appropriate amounts of niobium, thorium, tungsten and aluminum according to the ratio. Each button ingot was smelted repeatedly for 6 times to remove gas and high vapor pressure impurity elements. The button ingot was then washed in aqua regia for 5 minutes to remove surface impurities.

[0035] Iridium alloy button ingots are electron beam melted and cast into water-cooled molds. Iridium alloy round ingot.

[0036] The iridium alloy rods are prepared by hot forging process, with the initial forging temperature of 1650℃ and the final forging temperature not less than 1300℃.

[0037] The iridium alloy rod is annealed at a temperature of 1300°C for 1 hour and then cooled to room temperature in the furnace.

[0038] Iridium alloy tubes are prepared by laser cutting and electric spark drilling.

[0039] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-temperature airflow temperature sensor based on an iridium alloy shield, characterized in that: It includes a thermocouple wire, a shielding cover, an insulating porcelain tube, a shell, and a mounting flange; the shielding cover is provided with a shielding cover shell, an air inlet, and an air outlet; The shielding cover is in the shape of a thin-walled tube with a wall thickness of 0.8 mm to 1.8 mm, and the circumferential and axial distances between adjacent air outlet holes of the shielding cover are not less than 5 times the hole diameter; The shielding cover is connected to the shell by welding, the thermocouple wire is inserted into the insulating porcelain tube and then installed into the shell, and then turned 90 degrees at the head to insert into the shielding cover, and the mounting flange is connected to the shell by welding; The shielding cover is an iridium alloy shielding cover, and the manufacturing method is as follows: Step 1: Making a shielding cover material based on a five-element alloy of iridium-niobium-tungsten-thorium-aluminum, wherein the content of niobium is 0.4% to 0.8% by weight, the content of tungsten is 0.2% to 0.4% by weight, the content of thorium is 30ppm to 50ppm, the content of aluminum is 40ppm to 60ppm, and the rest is iridium; Step 2: cold isostatic pressing the pure iridium powder by powder metallurgy to prepare an iridium pre-sintered block, the pressure of the cold isostatic pressing is 50MPa-100MPa, the holding time is 100s-150s, and then the iridium sintered block is pre-sintered in a hydrogen atmosphere, the sintering temperature is 950°C-1100°C, and the holding time is 1h-2h; Step 3: sinter the pre-sintered iridium block in a high-temperature vacuum furnace at a high temperature of 1450°C to 1550°C, with a holding time of 3h to 4h and a vacuum degree better than 0.3Pa; Step 4: Using arc melting to melt the sintered iridium block to prepare pure iridium button ingots, the weight of each button ingot is controlled at 50g to 100g; Step 5: Add appropriate amounts of niobium, thorium, tungsten and aluminum according to the ratio described in step 1 to prepare iridium alloy button ingots, and smelt each button ingot repeatedly for 6 to 8 times, and then wash the button ingot in aqua regia for 5 to 8 minutes to remove surface impurities; Step 6: Electron beam melting of iridium alloy button ingots and casting into water-cooled molds Iridium alloy round ingots; Step 7: preparing the iridium alloy rod by hot working methods such as jacket extrusion, hot forging or hot rolling, wherein the jacket extrusion temperature is 1250° C. to 1350° C., the initial forging temperature of hot forging or the blanking temperature of hot rolling is 1500° C. to 1750° C., and the final forging temperature of hot forging or the final rolling temperature of hot rolling is not less than 1300° C.; Step 8: annealing the iridium alloy rod at a temperature of 1200°C to 1300°C for a holding time of 1h to 2h, and then cooling to room temperature with the furnace; Step nine: Prepare an iridium alloy tube by mechanical processing, and make a shielding cover based on the iridium alloy tube.

2. A high-temperature airflow temperature sensor based on an iridium alloy shielding cover as claimed in claim 1, characterized in that: The mechanical processing means include laser cutting, electric spark drilling and mechanical grinding.

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