Low thermal expansion alloy

Abstract

To provide a low thermal expansion alloy that is cow cost, has high oxidation resistance at high temperature and, when bonding the alloy to alumina and operating a composite member thereof with alumina in a temperature range of 20 to 600°C, hardly generates defects such as cracking and peeling due to a difference in α between the alloy and alumina in a temperature range of 20 to 600°C.SOLUTION: A low thermal expansion alloy is provided, containing in mass%, 0.05% or less of C, 0.40% or less of Si, 0.50% or less of Mn, 27.0 to 30.0% of Ni, 18.0 to 22.0% of Co, 1.0 to 2.0% of Cr, and the remainder of Fe and inevitable impurities, wherein Ni+Co×0.8-Cr×0.8 is 43.0 to 46.0%, and wherein an absolute value of a difference between an average α of the alloy and an average α of alumina in each temperature range of 20 to 100°C, 20 to 200°C,20 to 300°C, 20 to 400°C, 20 to 500°C, and 20 to 600°C is less than 2.0×10-6 / °C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a low thermal expansion alloy suitable for bonding with alumina ceramics. [Background technology]

[0002] Traditionally, Fe alloys containing specific amounts of Ni or Ni and Co have been used in various applications due to their low thermal expansion properties. These include so-called high-temperature, low-thermal-expansion alloys, such as Fe-42%Ni alloy (42Alloy) and Fe-29Ni-17Co alloy (Kovar).

[0003] These alloys are sometimes used in applications such as brazing and sealing, where they are intended to combine dissimilar materials. In such cases, if the difference in thermal expansion coefficients (α) between the materials constituting the composite is large, defects such as cracking and delamination are more likely to occur during manufacturing or operation. To prevent this, the α difference of the materials constituting the composite is restricted to be below a certain value.

[0004] For example, Patent Document 1 describes how to adjust α from room temperature to 300°C for glass and porcelain, ranging from 4 to 8 × 10⁻¹⁰ -6 / ℃, α at room temperature to 500℃ is 8-12 × 10 -6 An alloy consisting of 28-34% Ni, 2-15% Cu, and the remainder Fe has been proposed, with a temperature of / ℃.

[0005] Furthermore, Patent Document 2 describes a method for bonding a ceramic substrate mainly composed of alumina to a metal, in order to prevent cracks caused by thermal cycling, such as the average α of the metal at 40-800°C being 7-10 × 10 -6 A composite alloy of Mo and Cu with a temperature of / ℃ has been proposed. Patent document 3 concerns brazing the end face of an alumina ceramic cylinder to a metal flange using activated metal brazing material, and it is stated that the material of the metal flange to be joined is an iron-nickel alloy that approximates the α of alumina.

[0006] Furthermore, Non-Patent Document 1 discloses an alloy having a composition of Ni: 35.0 to 40.0%, Co: 12.0 to 16.0%, Nb: 4.3 to 5.7%, and Ti: 1.3 to 1.8% with α from room temperature to 600 °C being 9.5×10 -6 / °C.

[0007] When these materials are applied to the bonding of alumina, there are the following problems.

[0008] The α of the alloy of the example disclosed in Patent Document 1 is 9.3 to 12.0×10 -6 / °C in the range of 30 to 500 °C, and the difference from the α of alumina, which is 7.2 to 7.5×10 -6 / °C, is relatively large, so there is a risk of problems such as cracking and peeling.

[0009] Also, the α of the alloy disclosed in Patent Document 2 is 7.3 to 9.5×10<000000�> / °C in the range of 40 to 800 °C, and the difference from the α of alumina is relatively small, so the risk of problems such as cracking and peeling is small. However, it is an alloy containing 70% of the rare metal Mo, and there is a problem of high material cost.

[0010] The iron-nickel-based alloys disclosed in Patent Document 3 are the above-mentioned 42Alloy and Kovar. According to Non-Patent Document 2, the α of the former at 20 to 500 °C is 8.0×10 -6 / °C, and the latter is​​​​​​​​​​​​​is / °C, and although it is possible to make the difference from α of alumina relatively small, it contains approximately 1.5% of Ti which is extremely easy to oxidize. Since Ti becomes an oxide in atmospheric melting, there is a constraint that a melting furnace capable of melting in a vacuum or an inert atmosphere is required. In addition, as described above, this type of composite material may be exposed to a high temperature of 600°C or higher during manufacturing or operation. Since the surface of the member oxidizes in the atmosphere, there is a problem that depending on the application, it must be manufactured or operated under a vacuum or an inert atmosphere.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0013]

Non-Patent Document 1

Non-Patent Document 2

[0015] In other words, the present invention aims to provide a low thermal expansion alloy that is low-cost, has high oxidation resistance at high temperatures, and is less prone to defects such as cracking and delamination due to the difference in α between the alloy and alumina when joining with alumina and when operating composite members with alumina in the temperature range of 20 to 600°C. [Means for solving the problem]

[0016] To solve the above problems, the inventors first investigated the difference in thermal expansion between the target low thermal expansion alloy and alumina. As a result, to prevent problems when joining the target low thermal expansion alloy and alumina, and when the composite member with alumina is in operation, it is preferable that the α difference between the materials be small, but an α difference of 2.0 × 10⁻⁶ -6 We found that it is sufficient if the temperature is less than / ℃. This is because the α difference is 2.0 × 10 -6 It is presumed that below / ℃ the stress generated at the bonding interface is relieved by the elastic deformation of the metal side, resulting in a level below which defects occur. However, the difference in average α between 20 and 600℃ is 2.0 × 10⁻⁶. -6 Even if the temperature is below / ℃, if the manufacturing or operation takes place within a specific temperature range of the applicable temperature range, the α difference between the two materials in that temperature range will be 2.0 × 10⁻⁶. -6It was found that malfunctions are more likely to occur when the temperature is above / ℃. Therefore, in order to suppress such malfunctions, the average α difference for every 100℃ in the applicable temperature range is set to 2.0 × 10 -6 We found that it is sufficient if the temperature is below / ℃.

[0017] Next, we investigated a composition range that prevents problems caused by such α differences, is low-cost, and has high oxidation resistance at high temperatures. As a result, we found that it is effective to include appropriate amounts of Ni and Co, which are used to adjust the thermal expansion coefficient characteristics in conventional 42 Alloy and Kovar, and then add Cr within a predetermined range.

[0018] The present invention is based on the above findings and provides the following means (1) to (4).

[0019] (1) In mass%, C: 0.05% or less, Si: 0.40% or less, Mn: 0.50% or less, Ni: 27.0-30.0% Co: 18.0~22.0%, Cr: 1.0~2.0%, Furthermore, the ratio of Ni+Co×0.8-Cr×0.8 is 43.0~46.0%, The remainder consists of Fe and unavoidable impurities. The average thermal expansion coefficient of alumina in the temperature ranges of 20-100°C, 20-200°C, 20-300°C, 20-400°C, 20-500°C, and 20-600°C is 6.1 × 10⁻⁶. -6 / ℃、6.7×10 -6 / ℃、7.0×10 -6 / ℃、7.3×10 -6 / ℃、7.6×10 -6 / ℃、7.8×10 -6 When set to / ℃, In the temperature ranges of 20-100°C, 20-200°C, 20-300°C, 20-400°C, 20-500°C, and 20-600°C Average thermal expansion coefficient and alumina Average thermal expansion coefficient The absolute value of the difference is 2.0 × 10 -6 A low thermal expansion alloy characterized by having a temperature of less than / ℃. (2) Oxidation gain when a test specimen measuring φ25mm x height 15mm is held in air at 600°C for 100 hours.but, In mass%, it consists of C: 0.03%, Si: 0.25%, Mn: 0.31%, Ni: 29.1%, Co: 17.0%, Ni + Co × 0.8 - Cr × 0.8: 42.7%, with the remainder being Fe and unavoidable impurities. The low thermal expansion alloy according to (1), characterized in that it is 1 / 30 or less of that of Kovar. (3) The low thermal expansion alloy according to (1) or (2), characterized in that the mass percentage is Cr: 1.5 to 2.0%. (4) Oxidation gain when a test specimen measuring φ25mm x height 15mm is held in air at 600°C for 100 hours. but, In mass%, it consists of C: 0.03%, Si: 0.25%, Mn: 0.31%, Ni: 29.1%, Co: 17.0%, Ni + Co × 0.8 - Cr × 0.8: 42.7%, with the remainder being Fe and unavoidable impurities. The low thermal expansion alloy described in (3), characterized in that it is 1 / 50 or less of that of Kovar. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a low thermal expansion alloy that is low-cost, has high oxidation resistance at high temperatures, and is less prone to cracking, delamination, and other defects due to the difference in α between it and alumina when joining with alumina and when operating composite members with alumina in the temperature range of 20 to 600°C. Therefore, it can exhibit higher reliability than conventional alloys, is low-cost, and can be manufactured or operated in the atmosphere without requiring special melting equipment. [Brief explanation of the drawing]

[0021] [Figure 1] This figure compares the α value of the example alloy and comparative alloy of the present invention with that of alumina. [Modes for carrying out the invention]

[0022] The present invention will be described in detail below. In the following explanation, unless otherwise specified, percentages in the ingredients refer to mass percentages.

[0023] [Chemical composition] C: 0.05% or less Carbon (C) is an element that inhibits the low thermal expansion properties of low thermal expansion alloys and is also thought to cause dimensional changes in components over time. However, these adverse effects can be ignored if the C content is 0.05% or less. Therefore, the C content should be kept within the range of 0.05% or less.

[0024] Si:0.40% or less Si is typically added as a deoxidizing agent, but if its content exceeds 0.40%, the increase in α becomes significant. Therefore, the Si content should be kept within the range of 0.40% or less. However, in the case of cast alloys, it is preferable to include 0.15% or more to improve the fluidity of the molten metal.

[0025] Mn: 0.50% or less Mn is usually added as a deoxidizing agent, but if its content exceeds 0.50%, the increase in α becomes significant. Therefore, the Mn content should be kept within the range of 0.50% or less. However, in the case of forged alloys, it is preferable to include 0.30% or more to prevent hot cracking.

[0026] Ni: 27.0~30.0% Ni is the element that determines the basic α of an alloy, and it is added along with Co to adjust α. However, if the Ni content is less than 27.0%, the structure becomes unstable even at room temperature, leading to an increase in α, and if it exceeds 30.0%, the desired thermal expansion properties cannot be obtained even if the amount of Co is adjusted. Therefore, the Ni content should be in the range of 27.0 to 30.0%.

[0027] Co: 18.0~22.0% Co, along with Ni, is an element necessary for adjusting the thermal expansion properties of alloys, and is added particularly to improve thermal expansion properties at high temperatures. However, if the Co content is less than 18.0%, the low thermal expansion effect at high temperatures is not sufficiently obtained, and if it exceeds 22.0%, α becomes large, and in either case, the desired thermal expansion properties cannot be obtained. Therefore, the Co content should be set between 18.0% and 22.0%.

[0028] Cr: 1.0~2.0% In the alloy of the present invention, Cr is an element used to adjust α by utilizing the nearly linear relationship between its content and α. It also has the effect of reducing high-temperature oxidation by forming a stable oxide film on the alloy surface, and by adding an appropriate amount, the oxidation resistance at 600°C can be reduced to 1 / 30 or less of Kovar, a typical high-temperature, low-thermal-expansion material. However, if the Cr content exceeds 2.0%, it becomes impossible to adjust α to an appropriate range. Also, if the content is less than 1.0%, it is not possible to reduce the oxidation resistance at 600°C to 1 / 30 or less of Kovar, and it becomes difficult to adjust α to an appropriate range. Therefore, the Cr content should be in the range of 1.0 to 2.0%. Furthermore, a Cr content of 1.5% or more is preferable. The oxidation resistance-improving effect of Cr becomes even higher at 1.5% or more, and it can be reduced to 1 / 50 or less of Kovar.

[0029] Ni + Co × 0.8 - Cr × 0.8: 43.0~46.0% In this invention, the desired thermal expansion characteristics can be obtained by including Ni and Co within the above range and keeping the Ni equivalent, expressed as Ni + Co × 0.8 - Cr × 0.8, within a certain range. If the Ni equivalent is less than 43.0% or more than 46.0%, the α difference with alumina will exceed 2.0 ppm / °C in either temperature range. Therefore, the Ni equivalent is set in the range of 43.0 to 46.0%.

[0030] In this invention, the remainder of the components other than C, Si, Mn, Ni, Co, and Cr is Fe and unavoidable impurities.

[0031] [Manufacturing conditions] In the present invention, the manufacturing conditions are not particularly limited. For example, the alloy of the above composition may be melted according to a conventional method and then cast into a mold to be used as a cast material, or it may be cast and then plastically deformed to form a plastically deformed material. The manufacturing conditions for casting or plastic deformation, including heat treatment, can be the same as those for conventional Fe-Ni low thermal expansion alloys. It is preferable to perform heat treatment to relieve stress in order to reduce deformation during use.

[0032] [Thermal expansion coefficient α] The average difference in α between 20 and 600°C is 2.0 × 10⁻⁶ -6 Even if the temperature is below / ℃, if the manufacturing or operation takes place within a specific temperature range of the applicable temperature range, the α difference between the two materials in that temperature range will be 2.0 × 10⁻⁶. -6 While problems are more likely to occur above / ℃, as shown in Table 1, the absolute value of the difference between the average α in each temperature range of 20-100℃, 20-200℃, 20-300℃, 20-400℃, 20-500℃, and 20-600℃ and the average α of alumina is 2.0 × 10 -6 If the temperature is below / ℃, no problems will occur during joining or operation. Therefore, in this invention, the average α difference for every 100℃ increments of 20~100℃, 20~200℃, 20~300℃, 20~400℃, 20~500℃, and 20~600℃ is set to 2.0 × 10⁻⁶. -6 The temperature should be below / ℃, and the α difference between the two materials should be 2.0 × 10⁻⁶. -6 Ensure that the temperature does not exceed / ℃.

[0033] [Table 1] [Examples]

[0034] The following describes embodiments of the present invention. Alloys with the chemical compositions shown in Table 2 were melted in an air atmosphere using a high-frequency induction melting furnace, and then cast into an alumina-silica artificial sand mold in accordance with Figure 1b) of JIS G0307 to produce test specimens measuring φ35 mm × L220 mm. In Table 2, Nos. 1 to 7 are examples of the present invention, while Nos. 11 to 22 are comparative examples that do not satisfy the present invention. All of the above test specimens were held at 850°C for 2 hours, then water-cooled, held at 550°C for 2 hours, and then slowly cooled before being processed, and the α and oxidation weight were measured.

[0035] [Alpha difference with alumina] First, for α, test specimens measuring φ6 mm × length 50 mm were prepared, and thermal expansion was measured in the range of 20 to 600°C using a push-rod type thermal expander. The average α was calculated for each 100°C interval (20 to 100°C, 20 to 200°C, 20 to 300°C, 20 to 400°C, 20 to 500°C, and 20 to 600°C), and then the difference from the average α of alumina in the same temperature range was calculated. The results are shown in Table 2. For examples No. 1 to 7 of the present invention, the difference from the average α of alumina in the same temperature range was 2.0 × 10⁻⁶. -6 The temperature was found to be below / ℃, and it was confirmed that defects such as crack formation during bonding with alumina and during operation of the composite member could be effectively prevented. On the other hand, in comparative examples No. 11, 12, 13, 15, 17, 19, and 21, the C, Si, Mn, Ni, Co, Cr, and Ni equivalents exceeded the range specified in the present invention, respectively. In comparative examples No. 14, 16, and 20, the Ni, Co, and Ni equivalents were below the range specified in the present invention, respectively. In No. 18, the Cr was less than 1.0%, so in some temperature ranges, the difference from the average α of alumina was 2.0 × 10⁻⁶. -6 The temperature was above / ℃. Furthermore, Comparative Example No. 22, Kovar, is a typical low-thermal-expansion material for high-temperature applications. However, because the Cr content was at an impurity level and the Ni equivalent was below the range specified in this invention, the difference from the average α of alumina was 2.0 × 10⁻⁶. -6 The temperature rose above / ℃.

[0036] Figure 1 shows the results of calculating the average α at 100°C intervals for alumina, Invention Examples No. 3 and 6, and Comparative Examples No. 13 and 22.

[0037] [Oxidation resistance] For the oxidation test, a test specimen measuring φ25mm × height 15mm (▽▽▽ finish) was prepared, placed in a magnetic crucible (with lid), and its pre-test weight was measured using an electronic balance. The specimen was then placed in an electric furnace and maintained at 600°C for 100 hours in air. The oxidation weight increase was calculated by measuring the post-test weight using an electronic balance while the specimen was placed in the magnetic crucible, as before the test, and then using the formula ([post-test weight] - [pre-test weight]) / [test specimen surface area]. All of the present invention alloys No. 1 to 7 showed excellent oxidation resistance, with oxidation weight increases of less than 1 / 30 of comparative example alloy No. 22 (Kovar), a typical low-thermal-expansion material for high temperatures. In particular, No. 6 and No. 7, with a Cr content of 1.5% or more, showed extremely good oxidation resistance, with oxidation weight increases of less than 1 / 50 of comparative example alloy No. 22 (Kovar). On the other hand, the oxidation resistance of comparative alloy No. 18 was better than that of comparative alloy No. 22 (Kovar) because its Cr content was below the component composition range of the present invention, but it did not achieve the same level of oxidation resistance as the alloy of the present invention.

[0038] [Table 2]

Claims

1. In mass percent, C: 0.05% or less, Si: 0.40% or less, Mn: 0.50% or less, Ni: 27.0-30.0%, Co: 18.0-22.0%, Cr: 1.0-2.0%, Furthermore, the ratio of Ni + Co × 0.8 - Cr × 0.8 is 43.0 to 46.0%, The remainder consists of Fe and unavoidable impurities. If the average thermal expansion coefficients of alumina in the temperature ranges of 20-100°C, 20-200°C, 20-300°C, 20-400°C, 20-500°C, and 20-600°C are 6.1 × 10⁻⁶ / °C, 6.7 × 10⁻⁶ / °C, 7.0 × 10⁻⁶ / °C, 7.3 × 10⁻⁶ / °C, 7.6 × 10⁻⁶ / °C, and 7.8 × 10⁻⁶ / °C, respectively, then the absolute difference between the average thermal expansion coefficient in each temperature range and the average thermal expansion coefficient of alumina is 2.0 × 10⁻⁶ / °C. －６ A low thermal expansion alloy characterized by having a temperature of less than / °C.

2. The low thermal expansion alloy according to Claim 1, characterized in that, when a test piece measuring φ25 mm × height 15 mm is held in air at 600°C for 100 hours, the oxidation weight gain is less than or equal to 1 / 30 of Kovar, which consists of C: 0.03%, Si: 0.25%, Mn: 0.31%, Ni: 29.1%, Co: 17.0%, Ni + Co × 0.8 - Cr × 0.8: 42.7%, with the remainder being Fe and unavoidable impurities.

3. A low thermal expansion alloy according to claim 1 or 2, characterized in that the mass percentage of Cr is 1.5 to 2.0%.

4. The low thermal expansion alloy according to Claim 3, characterized in that, when a test piece measuring φ25 mm × height 15 mm is held in air at 600°C for 100 hours, the oxidation weight increase is less than or equal to 1 / 50 of Kovar, which consists of C: 0.03%, Si: 0.25%, Mn: 0.31%, Ni: 29.1%, Co: 17.0%, Ni + Co × 0.8 - Cr × 0.8: 42.7%, with the remainder being Fe and unavoidable impurities.

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