JP7735147B2 - Manufacturing method for low thermal expansion additive manufacturing alloy - Google Patents

Description

The present invention relates to a method for producing a low thermal expansion additive manufacturing alloy suitable for components of precision instruments such as semiconductor manufacturing equipment.

As an example of Fe-Ni (including Fe-Ni-Co) low-thermal expansion layered alloy technology with an extremely low thermal expansion coefficient (hereinafter also referred to as α), Patent Document 1 discloses a low-thermal expansion alloy for additive manufacturing using powder bed fusion (PBF), which uses a laser beam or electron beam as a heat source to melt and layer the alloy.

The cooling rate during solidification of additive manufacturing alloys using PBF is said to be on the order of several hundred thousand K/s. Patent Document 1 utilizes this to reduce the dendrite secondary arm spacing (DAS) of the solidification structure to 5 μm or less, thereby minimizing segregation of the constituent elements and obtaining an Fe-Ni-based low-thermal expansion additive alloy with a small α value.

While there is a demand for industrially manufacturing large components using additive manufacturing, it is difficult to meet such demands using additive manufacturing based on PBF. While additive manufacturing based on PBF has the advantage of being able to precisely manufacture components with complex shapes, the manufacturing speed is slow because the thickness of each layer is small, resulting in long manufacturing times. Additionally, large equipment is expensive, making it difficult to apply PBF to the industrial manufacturing of large components.

In contrast, Non-Patent Document 1 describes an additive manufacturing method called Directed Energy Deposition (DED), which uses alloy powder or alloy wire as the building material and melts and layers it using a laser beam, electron beam, or even arc as a heat source. It also notes that DED functionality can be added to existing machining centers, making it relatively easy to build large components. Among these, DED using alloy wire as the building material (hereinafter referred to as wire-type DED) has lower building accuracy than DED using alloy powder, but offers a high building speed, utilizes nearly 100% of the supplied material in the built object, has good material yield, and has low porosity, making it useful as a method for industrially manufacturing components that require high density. Furthermore, DED using an electron beam requires building in a vacuum atmosphere, which precludes the use of gas for powder transport, making it a wire-type method.

As described above, wire-type DED has the advantage of being able to produce large, dense additive manufacturing components at high speed and with high yield, and can use a variety of heat sources such as laser beams, electron beams, and arcs.

Re-table 2019/044093 publication Japanese Patent Application Laid-Open No. 2003-19593

Materia, Vol. 36, No. 11 (1997) Internet <URL: https://www.jstage.jst.go.jp/article/materia1994/36/11/36_11_1080/_pdf Proceedings of the Japan Welding Society, Vol. 3 (1985) No. 1, pp. 78-81 PHYSICS AND APPLICATIONS OF INVAR ALLOYS, pp. 518-537, Maruzen, 1978

However, compared to PBF, wire-type DED has a lower energy density and a smaller temperature gradient in the laminate, making it more difficult to refine the crystal grains through rapid solidification and the associated segregation mitigation than with the additive manufacturing alloys using PBF described above. Furthermore, Non-Patent Document 2 states that because segregation tendencies are governed by the diffusion behavior of solutes in the solid phase, welding has a faster solidification rate than casting, and despite the small crystal grain size, the segregation ratio is large and the behavior is not simple. Therefore, with wire-type DED, which is assumed to have a similar form to welding and a solidification rate somewhere between casting and welding, it is difficult for those skilled in the art to devise a composition that will produce the target Fe-Ni-based low-thermal expansion additive alloy.

Furthermore, assembly welding and defect repair welding using low-thermal expansion alloy components as the base material have traditionally been performed using low-thermal expansion alloy wire whose main composition matches that of the base material. For example, Patent Document 2 discloses a welding material for a low-thermal expansion coefficient Fe-Ni alloy that is free of hot cracking during welding. However, in conventional welding, the welding material is added to the base material, and heat transfer occurs from the weld to the base material. In contrast, in wire-type DED, the entire additive manufacturing object is formed from the melted and solidified raw material wire. As described above, the solidification rate is slower than with welding, making it difficult to achieve low thermal expansion. Furthermore, as described in Non-Patent Document 3, it is known that adding other elements to an Fe-Ni alloy base for purposes such as crack prevention increases the thermal expansion coefficient. Therefore, considering the descriptions in Non-Patent Documents 2 and 3 and the fact that the α of Fe-Ni low-thermal expansion alloys varies significantly due to segregation of constituent elements, it is still difficult to obtain an alloy with an α equivalent to the target Fe-Ni low-thermal expansion alloy using wire-type DED.

In addition, with conventional welding, the welding operator can adjust welding conditions such as wire feed speed while observing the welding situation, but with wire-type DED, additive manufacturing is performed automatically based on a pre-entered program, making it difficult to apply operating conditions that respond quickly to the melting situation. Wires for wire-type DEDs must be able to operate stably even under such conditions, and the resulting products must be of high quality and free of cracks, etc.

As described above, it is difficult to conceive of a low thermal expansion laminated alloy for wire-type DED based on the above prior art.

The present invention aims to provide a method for producing a low-thermal expansion additive manufacturing alloy that, when producing a low-thermal expansion additive manufacturing alloy using wire-type DED, can obtain a low-thermal expansion additive manufacturing alloy with a low thermal expansion coefficient equivalent to that of a target thermal expansion coefficient alloy, which is an existing Fe-Ni-based low-thermal expansion alloy, even when adding the required amount of alloy elements to prevent cracking.

After extensive research to solve the above-mentioned problems, the inventors discovered the following: In compositions in which crack-preventing alloy elements are added to the target Fe-Ni low-thermal expansion alloy, α increases compared to compositions in which no alloy elements are added, depending on the type and amount of the alloy elements. Furthermore, due to factors such as segregation, the α of the molded product increases compared to the raw wire. However, by adjusting the alloy composition based on a certain relationship depending on the type and amount of alloy elements added to prevent cracking, it is possible to prevent an increase in α and obtain a low-thermal expansion additive manufacturing alloy with a thermal expansion coefficient equivalent to that of the target Fe-Ni low-thermal expansion alloy.

The present invention was completed based on the above findings and provides the following means:

A method for manufacturing a low thermal expansion alloy using Invar or Super Invar, an existing Fe-Ni based low thermal expansion alloy, as a target thermal expansion coefficient alloy , and manufacturing a low thermal expansion additive manufacturing alloy using a wire-type DED with the target thermal expansion coefficient.
The low thermal expansion laminate alloy is
In mass%,
C: 0.05-0.20%,
Si: 0.3% or less,
Mn: 0.2 to 0.4%,
Ni: 29.5-40%,
Nb: 7.74 x [C] ~ 1.6%,
Co: [CoA] + (0.84 × [Nb] - 4.269 × [C] + 0.1) / (0.25 - 0.0004 × [T]) ~ [CoA] + (0.84 × [Nb] - 4.269 × [C] + 0.1) / (0.25 - 0.0004 × [T]) + 0.5%,
Contains
Furthermore, the Ni equivalent expressed by [Ni] + 0.8 × [Co] is in the range of 35.945 − 0.00025 × [T] + 0.0000375 × [T] ^2.026 −0.5 to 35.945 − 0.00025 × [T] + 0.0000375 × [T] ^2.026 + 0.5%,
A method for producing a low thermal expansion additive manufacturing alloy, characterized in that the balance consists of Fe and unavoidable impurities.
where [C], [Nb], and [Co] are the C content, Nb content, and Co content (all in mass %), respectively; [CoA] is the Co content (mass %) of the alloy with the target thermal expansion coefficient , and when the alloy with the target thermal expansion coefficient is Invar, [CoA] = 0.00 mass %; when the alloy with the target thermal expansion coefficient is Super Invar, [CoA] = 5.17 mass %; and [T] is the upper limit temperature T (°C) of the thermal expansion measurement temperature range of the alloy with the target thermal expansion coefficient, and when the alloy with the target thermal expansion coefficient is Invar or Super Invar, [T] = 40°C.

According to the present invention, a method for producing a low thermal expansion additive manufacturing alloy is provided, which, when producing a low thermal expansion additive manufacturing alloy using wire-type DED, can obtain a low thermal expansion additive manufacturing alloy having a low thermal expansion coefficient equivalent to that of the target thermal expansion coefficient alloy, which is an existing Fe-Ni based low thermal expansion alloy, even if the necessary amount of alloy elements are added to prevent cracking .

10A and 10B are diagrams illustrating shapes of objects in the examples. FIG. 2 is a diagram showing how to collect evaluation test pieces in the examples.

This embodiment will be described in detail below.
Unless otherwise specified, percentages for components are mass % and the thermal expansion coefficient (α) is the average thermal expansion coefficient (ppm/°C) between 10°C and T°C.

In the present invention, a low-thermal expansion additive manufacturing alloy is manufactured by wire-type DED using an existing Fe-Ni low-thermal expansion alloy as the target thermal expansion coefficient alloy (target α alloy), with the target thermal expansion coefficient being that alloy . When manufacturing a low-thermal expansion additive manufacturing alloy using wire-type DED, an alloy wire having the composition described below is melted and laminated using a heat source such as a laser beam, electron beam, or arc. Existing Fe-Ni low-thermal expansion alloys serving as the target α alloy include Ni-Fe alloys and Fe-Ni-Co alloys. Specific examples of such Fe-Ni low-thermal expansion alloys include Invar and Super Invar . Invar and Super Invar have the compositions shown, for example, in Nos. 31 and 32 in Table 1 (described below). These alloys can achieve the desired low thermal expansion characteristics in the temperature range of 10 to 40°C . The low-thermal expansion additive manufacturing alloy manufactured in the present invention is specified to correspond to the target α alloy, Invar or Super Invar .

Next, the reason for the limitation will be explained.
・C: 0.05-0.20%
As will be described later, C is an element that, when added in conjunction with Nb, forms an appropriate amount of NbC to prevent hot cracking during welding by adjusting the amount added. However, if the C content is less than 0.05%, this effect is insufficient, and if it exceeds 0.20%, the increase in α cannot be ignored. Therefore, the C content is set to the range of 0.05 to 0.20%.

Si: 0.3% or less. Si is an element added to the low-thermal expansion additive manufacturing alloy of the present invention for the purpose of deoxidizing and improving the flowability of the alloy. However, if the Si content exceeds 0.3%, the increase in α cannot be ignored. Therefore, the Si content is set to 0.3% or less.

・Mn: 0.2-0.4%
Mn is an element effective in deoxidizing the low-thermal expansion additive manufacturing alloy of the present invention. However, if its content is less than 0.2%, the effect is small, and if its content exceeds 0.4%, the increase in α becomes significant. Therefore, the Mn content is set to the range of 0.2 to 0.4%.

・Ni: 29.5-40%
Ni, together with Co, is an important element that determines α. By adjusting the Ni equivalent and Co content (described below), it is possible to compensate for the increase in α that accompanies the addition of alloys to prevent cracking during additive manufacturing, and achieve an α equivalent to that of the target α alloy. However, if Ni is less than 29.5% or more than 40%, α cannot be made equivalent to that of the target α alloy, even if other components are adjusted. Therefore, the Ni content is set to the range of 29.5 to 40%.

・Nb: 7.74×[C] ~ 1.6%
As mentioned above, Nb is an element that forms NbC with C to prevent cracking during additive manufacturing. However, if Nb dissolves in the matrix, the effect of preventing weld cracking cannot be obtained and instead leads to an increase in α, so Nb must be dispersed in the structure in the form of NbC. When the C content is expressed as [C], if the Nb content is less than 7.74 × [C], the amount of dissolved C is large, and if it exceeds 1.6%, the amount of dissolved Nb is excessive, both of which increase α and lead to a decrease in weldability. Therefore, the Nb content is set to the range of 7.74 × [C] to 1.6%.

・Co: [CoA]+(0.84×[Nb]-4.269×[C]+0.1)/(0.25-0.0004×[T]) ~ [CoA]+(0.84×[Nb]-4.269×[C]+0.1)/(0.25-0.0004×[T])+0.5%
Co, along with the aforementioned Ni, is an important element that determines α. It compensates for the increase in α that accompanies the addition of alloys to prevent cracking during welding and is an essential element for making α equivalent to the target thermal expansion coefficient of the alloy. That is, the Co/Ni ratio in the Ni equivalent (described later) is increased depending on the type and amount of alloy added to prevent cracking, thereby achieving a low α value for the alloy. However, the Co content of the alloy is related to the Co content of the target α alloy and the temperature range in which the alloy exhibits low thermal expansion. The Co content (mass%) of the target α alloy is [CoA] (when the target α alloy is Invar, [CoA] = 0.00 mass% as shown in No. 31 in Table 1 below, and when the target α alloy is Super Invar, [CoA] = 5.17 mass% as shown in No. 32 in Table 1 below) , the C content is [C], the Nb content is [Nb], and the upper limit temperature T (°C) of the thermal expansion measurement temperature range of the target α alloy is [°C]. When [T] is used to represent the temperature (40°C when the target α alloy is Invar or Super Invar) , if the Co content of the alloy is less than [CoA] + (0.84 × [Nb] - 4.269 × [C] + 0.1)/(0.25 - 0.0004 × [T])%, or more than [CoA] + (0.84 × [Nb] - 4.269 × [C] + 0.1)/(0.25 - 0.0004 × [T]) + 0.5%, it will not be possible to make α equivalent to the target α alloy. Therefore, the Co content is set in the range of [CoA] + (0.84 × [Nb] - 4.269 × [C] + 0.1) / (0.25 - 0.0004 × [T]) to [CoA] + (0.84 × [Nb] - 4.269 × [C] + 0.1) / (0.25 - 0.0004 × [T]) + 0.5%.

・Ni equivalent: 35.945-0.00025×[T]+0.0000375×[T] ^2.026 -0.5 to 35.945-0.00025×[T]+0.0000375×[T] ^2.026 +0.5%
When the Ni content (mass%) is expressed as [Ni] and the Co content (mass%) as [Co], the Ni equivalent is expressed as [Ni] + 0.8 × [Co], and has a certain relationship with the temperature range in which the alloy exhibits low thermal expansion. Adjusting the Ni equivalent reduces the α of the alloy. When the Ni equivalent is in the range of 35.945 - 0.00025 × [T] + 0.0000375 × [T] ^2.026 -0.5 to 35.945 - 0.00025 × [T] + 0.0000375 × [T] ^2.026 + 0.5% (where [T] is the upper limit temperature T (°C) of the thermal expansion measurement temperature range of the target α alloy), the α between 10 and T°C is significantly reduced. However, if the Ni equivalent is outside this range, it becomes difficult to achieve the desired low thermal expansion. Therefore, the Ni equivalent is set to a range of 35.945-0.00025×[T]+0.0000375×[T] ^2.026 −0.5 to 35.945-0.00025×[T]+0.0000375×[T] ^2.026 +0.5%.

In the present invention, the balance other than C, Si, Mn, Ni, Co, and Nb is Fe and unavoidable impurities.

The method for manufacturing a low-thermal expansion additive manufacturing alloy according to the present invention enables stable operation during wire-type DED by adjusting the alloy composition as described above, and the resulting low-thermal expansion additive manufacturing alloy prevents cracking because the alloy elements added are required to prevent cracking. Furthermore, by adjusting the alloy composition based on a certain relationship depending on the type and amount of alloy elements added to prevent cracking, a low thermal expansion coefficient equivalent to that of an alloy with a target thermal expansion coefficient can be obtained.

Examples of the present invention will be described below.
Alloys with the chemical compositions of Nos. 1 , 3 to 5 , 11 to 18 , and 31 and 32 shown in Table 1 were air-melted in a high-frequency induction furnace and cast at 1600°C into a _CO2 silica sand mold to produce ingots measuring φ127 mm x 270 mm. Note that Nos. 31 and 32 are existing Fe-Ni low-thermal expansion alloys that serve as the target α alloys having the α value targeted by the present invention materials, with No. 31 being Invar and No. 32 being Super Invar.

Ingots No. 1 , 3-5 , and No. 11-18 were heated in a heating furnace at 1200°C and then hot forged with an air drop hammer to produce blanks measuring approximately 40 mm square x 1400 mm. The blanks were heated in a heating furnace at 1150°C and subjected to primary rolling to approximately 22 mm square, followed by secondary rolling to produce wires measuring 9.6 mm in diameter. The wires were then cold drawn to produce wires measuring 1.2 mm in diameter.
For the target α alloys Nos. 31 and 32 , the ingots were used as they were.

Using wires Nos. 1 and 3 to 5 of the alloys of the present invention corresponding to each target α alloy in Table 1 and wires Nos. 11 to 18 of the comparative alloys as raw materials, additive manufacturing was performed under the following additive manufacturing conditions to produce the shaped object shown in Figure 1.

<Additive manufacturing conditions>
(1) Power supply: Fronius TPS5000CMT
(2) Robot: KUKA KR20
(3) Detailed modeling conditions ・Movement speed: 300mm/min
Wire feed speed: 9 m/min
・Current: 200A
Voltage: 25V

From the manufactured object, a φ6 mm x 50 mm thermal expansion measurement test piece and a 10 mm x 3 mm □ AM defect observation test piece were cut out as shown in Figure 2 and subjected to evaluation tests. The evaluation method was as follows. The thermal expansion coefficient was measured using a thermal dilatometer (NETZSCH DIL402C) between 10 and T°C to determine the average thermal expansion coefficient α. When the target α alloy was Invar , the absolute value of the difference between [α of the object] and [α of the target α alloy] was ±10% or less of [α of the target α alloy], making it a pass. When the target α alloy was Super Invar alloy, the α was extremely small and there was also negative expansion, so the absolute value of [α of the object] was 0.15 ppm/°C or less, making it a pass. For AM defects, the test pieces were observed at 50x magnification using an optical stereo microscope to check for the presence or absence of cracks. The evaluation criteria were: no cracks at all (pass), and even one crack (fail).

As shown in Table 1, the average thermal expansion coefficients α between 10°C and T°C of the alloys No. 1 , 3 to 5 of the present invention were all comparable to those of the corresponding target α alloys No. 31 and 32 , and no defects were observed in the additively manufactured articles.

On the other hand, comparative alloys Nos. 11, 12, and 15 to 17 , like the alloys of the present invention, contained the necessary amounts of C and Nb to prevent additive manufacturing defects, and no welding defects were observed. However, Nos. 11 and 16 had Ni equivalents above the upper limit and Co below the lower limit, No. 12 had Ni equivalents below the lower limit and Co above the upper limit, No. 15 had Si and Mn above the upper limit, and No. 17 had Ni below the lower limit, resulting in an increased α and none of them meeting the evaluation criteria. Furthermore, comparative alloys Nos. 13 and 18 had Ni above the upper limit and C and Nb below the lower limit, and No. 14 had C and Nb above the upper limit, resulting in additive manufacturing cracking.

Claims (1)

A method for manufacturing a low thermal expansion alloy using Invar or Super Invar, an existing Fe-Ni based low thermal expansion alloy, as a target thermal expansion coefficient alloy , and manufacturing a low thermal expansion additive manufacturing alloy using a wire-type DED with the target thermal expansion coefficient.
The low thermal expansion laminate alloy is
In mass%,
C: 0.05-0.20%,
Si: 0.3% or less,
Mn: 0.2 to 0.4%,
Ni: 29.5-40%,
Nb: 7.74 x [C] ~ 1.6%,
Co: [CoA] + (0.84 × [Nb] - 4.269 × [C] + 0.1) / (0.25 - 0.0004 × [T]) ~ [CoA] + (0.84 × [Nb] - 4.269 × [C] + 0.1) / (0.25 - 0.0004 × [T]) + 0.5%,
Contains
Furthermore, the Ni equivalent expressed by [Ni] + 0.8 × [Co] is in the range of 35.945 − 0.00025 × [T] + 0.0000375 × [T] ^2.026 −0.5 to 35.945 − 0.00025 × [T] + 0.0000375 × [T] ^2.026 + 0.5%,
A method for producing a low thermal expansion additive manufacturing alloy, characterized in that the balance consists of Fe and unavoidable impurities.
where [C], [Nb], and [Co] are the C content, Nb content, and Co content (all in mass %), respectively; [CoA] is the Co content (mass %) of the alloy with the target thermal expansion coefficient , and when the alloy with the target thermal expansion coefficient is Invar, [CoA] = 0.00 mass %; when the alloy with the target thermal expansion coefficient is Super Invar, [CoA] = 5.17 mass %; and [T] is the upper limit temperature T (°C) of the thermal expansion measurement temperature range of the alloy with the target thermal expansion coefficient, and when the alloy with the target thermal expansion coefficient is Invar or Super Invar, [T] = 40°C.