Ni-based alloy powder for additive manufacturing, additively manufactured object, and method for manufacturing the same

Abstract

This invention provides a non-cracking Ni-based alloy powder for laminated molding, a laminated molded object, and a method for manufacturing the laminated molded object. The Ni-based alloy powder for laminated molding contains, by mass percent, 10.0% to 16.0% Cr, 4.0% to 9.0% Al, 1.0% to 6.0% Mo, 0.5% to 4.0% Nb, 0.5% to 0.5% Ti, 0.5% to 0.5% Zr, 0.06% to 0.4% C, and 0.04% to 0.04%, with the remainder being Ni and unavoidable impurities. The Ni-based alloy powder for laminated molding satisfies the following conditions: 150 ≤ 120 Nb + 650 Zr + 32 Ti - 385 C ≤ 270.

Description

Technical Field

[0001] This invention relates to a laminated structure with excellent high-temperature strength properties, a method for manufacturing the same, and a Ni-based alloy powder for laminated structures. Background Technology

[0002] For laminated components used in high-temperature applications such as aircraft gas turbine engines and power generation gas turbines, long service life is required. To address this requirement, γ' (gamma prime) precipitated Ni-based alloys, such as 713C alloy, are used. γ' refers to precipitates primarily composed of Ni3 (Al, Ti). Furthermore, to handle complex shapes, a manufacturing method using γ' precipitated Ni-based alloys for laminated structures has been proposed.

[0003] For example, Patent Document 1 discloses a stacking forming method for stacking Ni-based alloys, wherein the Ni-based alloys have 10% to 16% Cr, 4.5% to 7.5% Al, 2.8% to 6.2% Mo, 0.8% to 4% Nb+Ta, 0.01% to 2% Ti, 0.01% to 0.3% Zr, and 0.01% to 0.3% C. In the stacking forming method, when the powder is spread and a laser is irradiated along multiple parallel scanning lines on the layer, the value of the scanning interval divided by the laser spot diameter is 0.6 or more and 1.0 or less.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2020-147782 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The lamination forming method disclosed in Patent Document 1 is a method for obtaining laminations with excellent creep fracture characteristics at high temperatures. However, laminations of γ' precipitation-type alloys are prone to solidification cracking. If cracking occurs, there is a concern that it will lead to a decrease in high-temperature creep characteristics, therefore, there is a need for crack-free laminations.

[0009] Therefore, the object of the present invention is to provide a Ni-based alloy powder for laminated molding that is not prone to cracking, a laminated molding, and a method for manufacturing the laminated molding.

[0010] Technical means to solve the problem

[0011] The present invention is a Ni-based alloy powder for laminated molding, comprising, by mass %, 10.0% and 16.0% Cr, 4.0% and 9.0% Al, 1.0% and 6.0% Mo, 0.5% and 4.0% Nb, 0.5% and 0.5% Ti, 0.5% and 0.5% Zr, 0.06% and 0.4% C, and 0.04% and 0.04% B, with the remainder comprising Ni and unavoidable impurities, and the Ni-based alloy powder for laminated molding satisfies the following (Formula 1).

[0012] 150≦120Nb+650Zr+32Ti-385C≦270…(Equation 1)

[0013] In addition, the Ti content is preferably 0.002% or more and 0.2% or less.

[0014] Furthermore, the present invention is a laminated structure having the following composition: by mass % comprising 10.0% or more and 16.0% or less Cr, 4.0% or more and 9.0% or less Al, 1.0% or more and 6.0% or less Mo, 0.5% or more and 4.0% or less Nb, 0.5% or less Ti, 0.5% or less Zr, 0.06% or more and 0.4% or less C, and 0.04% or less B, with the remainder comprising Ni and unavoidable impurities, and the composition satisfies 150≦120Nb+650Zr+32Ti-385C≦270… (Equation 1), and the laminated structure having an element segregation part between dendrites and adjacent dendrites, wherein the width of the dendrites in cross-sectional microstructure observation is 5 μm or less, and the width of the element segregation part is 200 nm or less.

[0015] Here, it can also mean that at least one of Cr, Mo, Nb, and Zr is concentrated in the elemental segregation portion compared to the dendritic crystal.

[0016] In addition, the present invention is a method for manufacturing laminated shapes by irradiating the Ni-based alloy powder for laminated shaping with an electron beam or a laser beam and causing it to melt and solidify.

[0017] The effects of the invention

[0018] This invention provides a Ni-based alloy powder for laminated molding that is not prone to cracking, laminated moldings, and a method for manufacturing laminated moldings. Attached Figure Description

[0019] Figure 1 This is a diagram illustrating an example of the cracking of a layered structure.

[0020] Figure 2 It is a graph showing the relationship between the solid phase ratio and temperature based on thermodynamic calculations.

[0021] Figure 3 This is a three-dimensional diagram illustrating the general structure of a laser-based lamination forming method.

[0022] Figure 4 This is a cross-sectional photograph of the layered structure of the present invention along the layering direction.

[0023] Figure 5 This is a tissue photograph of a cross-section of the layered structure of the present invention, perpendicular to the layering direction.

[0024] Figure 6 This is a micrograph showing the dendritic crystals and elemental segregation width of a stacked structure using alloy powder B (Example).

[0025] Figure 7 This is a micrograph showing the dendritic crystals and elemental segregation width of a stacked structure using alloy powder C (comparative example).

[0026] [Explanation of Symbols]

[0027] 1: Alloy powder

[0028] 2: Powder supply table

[0029] 3: Coating machine

[0030] 4: Laser Oscillator

[0031] 5: Laser

[0032] 6: Flow scanner

[0033] 7: Shapes

[0034] 8: Shaping table

[0035] 10: Dendritic crystals (primary dendritic crystals)

[0036] 11: Element Segregation

[0037] 12: Secondary dendritic crystals Detailed Implementation

[0038] First, regarding the mechanism of fracture occurrence, Figure 1 The example shown illustrates the occurrence of cracking in a layered structure. For example... Figure 1As shown, cracking tends to occur along grain boundaries in the stacking direction, and this cracking also occurs at dendritic crystal boundaries. Particularly in either Powder Bed Fusion (PBF) or Directed Energy Deposition (DED), lasers or electron beams are used to locally melt and solidify the powder, resulting in a significantly faster solidification cooling rate for stacked structures compared to cast products. Therefore, if conventionally developed γ'-precipitated Ni-based alloy powders for casting are melted and solidified, cracking easily occurs due to solidification segregation of Nb, Zr, etc. The phase transformation during solidification is entirely liquid at high temperatures, but as the temperature decreases, both liquid and solid phases coexist; if the temperature decreases further, only the solid phase remains. In this case, cracking caused by solidification segregation occurs just before the solidification process is complete. Therefore, it is believed that cracking can be prevented by selecting a composition in which the temperature difference between the state just before solidification (solid phase ratio of 0.9) and the state just after solidification (solid phase ratio of 1.0) is minimized.

[0039] Therefore, in this invention, as a composition that can reduce the temperature difference of 0.9 to 1.0 solid phase ratio, the following composition was selected: containing, by mass %, 10.0% to 16.0% Cr, 4.0% to 9.0% Al, 1.0% to 6.0% Mo, 0.5% to 4.0% Nb, 0.5% to 0.5% Ti, 0.5% to 0.5% Zr, 0.06% to 0.4% C, and 0.04% to 0.04%, with the remainder being Ni and unavoidable impurities. Furthermore, regarding the effect of elements highly correlated with fracture (fracture sensitivity index), the following (Equation 1) was found. Moreover, by using Ni-based alloy powder for laminated molding that meets these necessary conditions, a laminated molding that is less prone to fracture can be provided.

[0040] 150≦120Nb+650Zr+32Ti-385C≦270…(Equation 1)

[0041] Hereinafter, one embodiment of the present invention will be described. First, Ni-based alloy powder (hereinafter sometimes referred to as alloy powder) for laminated forming will be described, followed by a description of the laminated formed object and a laminated forming method. However, the present invention is not limited to the embodiments listed herein, and appropriate combinations or modifications can be made without departing from the technical concept of the present invention.

[0042] <Alloy Powder>

[0043] One embodiment of the alloy powder will be described. In the following description, % represents mass%. Furthermore, in this specification, the numerical range indicated by "~" refers to the range of values ​​before and after "~" as a lower and upper limit. Additionally, the upper and lower limits can be arbitrarily combined.

[0044] (Cr: 10.0%–16.0%)

[0045] Cr has the effect of improving corrosion resistance and is an important main component for obtaining good corrosion resistance at high temperatures. To improve corrosion resistance through the formation of an oxide film of Cr, a content of 10.0% or more is required. Excessive addition will form a brittle body-centered cubic (BCC) phase dominated by Cr; therefore, the content is set to 16.0% or less. Preferably, it is 11.0% to 14.0%. More preferably, it is 12.0% to 13.0%.

[0046] (A1: 4.0%–9.0%)

[0047] Al combines with Ni to precipitate the γ' phase. To improve high-temperature creep rupture strength by forming the γ' phase, a concentration of 4.0% or more is required. Excessive addition will result in the formation of brittle NiAl2 compounds; therefore, the concentration is set to 9.0% or less. Preferably, it is 6.0% to 8.0%. More preferably, it is 6.0% to 7.0%.

[0048] (Mo: 1.0%–6.0%)

[0049] To improve high-temperature creep rupture strength and corrosion resistance based on solid solution strengthening, Mo needs to be 1.0% or more. If added excessively, it becomes impossible to increase the addition of other elements; therefore, it is set to 6.0% or less. Preferably, it is 3.0% to 5.0%. More preferably, it is 3.5% to 4.5%.

[0050] (Nb: 0.5%–4.0%)

[0051] Nb contributes to improved high-temperature creep rupture strength through solid solution strengthening. Furthermore, Nb forms carbides at grain boundaries, which also contribute to improved high-temperature creep rupture strength; therefore, the content needs to be 0.5% or more. Additionally, Nb is one of the elements related to the fracture susceptibility index. If added excessively, exceeding the solid solution limit, the added Nb will form a brittle Laffers phase, leading to fracture; therefore, the content is set to 4.0% or less. Preferably, it is 1.0% to 3.0%. More preferably, it is 1.5% to 2.5%.

[0052] (Ti: less than 0.5%)

[0053] Ti is an element that enhances high-temperature creep rupture strength by forming the γ' phase, a compound with Ni. Ti may be omitted (0%), but its presence is preferred. Ti is also one of the elements related to the fracture sensitivity index; therefore, in the case of Ti content, it is set to 0.5% or less to suppress fracture. To more reliably exert the effect of Ti, the Ti content is set to 0.002% or more, and from the viewpoint of further suppressing fracture, it is preferably set to 0.2% or less. More preferably, it is 0.002% to 0.1%.

[0054] (Zr: below 0.5%)

[0055] Zr is an element that improves high-temperature creep fracture strength by inhibiting grain boundary slip through the formation of carbides at grain boundaries. Zr may be omitted (0%), but its presence is preferred. Zr is also one of the elements related to the fracture susceptibility index; therefore, in the case of Zr presence, excessive addition will lead to fracture, so the content is set to 0.5% or less. Preferably, it is 0.01% to 0.30%. More preferably, it is 0.02% to 0.2%.

[0056] (C: below 0.06% to 0.4%)

[0057] C is one of the elements associated with the crack susceptibility index and is an element that inhibits cracking. To prevent cracking and to allow for moderate carbide segregation at grain boundaries, a content of 0.06% or higher is required. However, excessive addition will lead to excessive carbide formation, reducing high-temperature creep rupture strength; therefore, it is set to 0.4% or less. Preferably, it is 0.1% to 0.3%. More preferably, it is 0.15% to 0.25%.

[0058] (B: Below 0.04%)

[0059] Bo (B) is an element that forms compounds with Cr and Mo at grain boundaries, thereby inhibiting grain boundary slip and improving high-temperature creep rupture strength. Bo may be omitted (0%), but it is preferred to contain Bo. If excessive Bo is added, the high-temperature creep rupture strength will decrease; therefore, the content is set to 0.04% or less. Preferably, it is 0.002% to 0.03%. More preferably, it is 0.005% to 0.02%.

[0060] Furthermore, the alloy composition of this embodiment satisfies Equation 1: 150≦120Nb+650Zr+32Ti-385C≦270. In Equation 1, the element symbols directly represent the content (mass%) of each element. Hereinafter, the value calculated using the relationship in Equation 1 will be referred to as the fracture sensitivity index.

[0061] A higher fracture sensitivity index indicates a greater susceptibility to fracture. Specifically, the following relationship applies: adding large amounts of Nb, Zr, or Ti increases the fracture sensitivity index, while adding large amounts of C decreases it. Furthermore, the fracture sensitivity index exhibits the following relationship: a smaller index leads to a lower high-temperature creep fracture strength, while a larger index increases it. For example, when balancing fracture suppression and high-temperature creep fracture strength characteristics, it is sufficient to determine a compositional range that ensures the fracture sensitivity index is neither too high nor too low. Specifically, a fracture sensitivity index of 270 or less, preferably 250 or less, is preferred. Conversely, a fracture sensitivity index of 150 or more, preferably 180 or more, is also preferred.

[0062] Regarding the lower limit of the fracture sensitivity index, considering compositions selected from the preferred range described above, for example, in the case of a composition of 12.0% Cr, 7.0% Al, 4.0% Mo, 1.5% Nb, 0.1% Ti, 0.1% Zr, 0.18% C, 0.02% B, with the remainder being Ni and unavoidable impurities, the fracture sensitivity index is approximately 180, effectively preventing fracture. On the other hand, in the case of a composition of 12.0% Cr, 7.0% Al, 4.0% Mo, 1.2% Nb, 0.002% Ti, 0.01% Zr, 0.1% C, 0.02% B, with the remainder being Ni and unavoidable impurities, the fracture sensitivity index is approximately 110%. In this case, although each element is within the preferred value range, it is considered a composition where the effect of simultaneously reducing Nb and C, and consequently Zr and Ti, is also limited. As a result, the balance of Nb, Zr, Ti, and C is disrupted, and (Equation 1) cannot be satisfied, thus resulting in a value with low high-temperature creep fracture strength. Due to this situation, a lower limit value of 150 or higher is set. An example of a fracture sensitivity index of 150 can be listed as follows: Cr 12.0%, Al 7.0%, Mo 4.0%, Nb 1.99%, Ti 0%, Zr 0.1%, C 0.4%, B 0.02%, with the remainder being Ni and unavoidable impurities.

[0063] The derivation process of the fracture sensitivity index (Equation 1) is also explained. Thermodynamic calculations were used to derive the fracture sensitivity index. The thermodynamic calculation method is explained. During solidification, as the temperature decreases from the liquid phase, the liquid and solid phases coexist; if the temperature decreases further, only the solid phase remains. Regarding fracture occurring during the solidification process, the relationship between the solid phase proportion and temperature is calculated. Figure 2The graph shows the relationship between the solid phase ratio and temperature based on thermodynamic calculations. The horizontal axis represents the solid phase ratio, and the vertical axis represents temperature (°C). Here, the calculations are performed with a composition of 12.1% Cr, 5.69% Al, 4.53% Mo, 2.03% Nb, 0.65% Ti, 0.10% Zr, 0.014% C, and the remainder being Ni. The dashed line represents the values ​​obtained from thermodynamic calculations on the equilibrium diagram, with a liquidus temperature of 1348°C and a solidus temperature of 1382°C. The difference between the liquidus and solidus temperatures is 34°C. In contrast, the rapid cooling and solidification of the stacked structure is simulated, and thermodynamic calculations are performed using Scheil's solidification model.

[0064] Thermodynamic calculations show that the liquidus temperature is the same at 1382℃, but the solidus temperature is 1108℃, resulting in a temperature difference of 274℃, which is greater than the equilibrium value. This is because, in slow solidification processes like precision casting, the process is close to equilibrium and less prone to cracking. However, in laminated molding, due to the rapid solidification rate, the solidification segregation caused by sudden cooling leads to a decrease in the solidus temperature of the segregated portion, which is the final solidified part. Considering this temperature difference, if cracking occurs just before solidification, then... Figure 2 The gradient shown is large just before solidification is about to end; specifically, the slope (gradient) is steep when the solid phase ratio is 0.9 or higher. Furthermore, the steeper the slope, the longer the time until solidification, and the longer the solidification time before cracking occurs (between solid phase ratios of 0.9 and 1). Therefore, cracking can be considered to have occurred.

[0065] Therefore, it is believed that cracking can be suppressed by mitigating the inclination when the solid proportion is above 0.9. To support this idea, a thorough study of alloy composition was conducted. The results showed that the change in temperature difference between a solid proportion of 0.9 and a solid proportion of 1, divided by the change in composition (unit: °C / mass%), was calculated using the respective elemental amounts. The results indicated that Nb, Zr, Ti, and C are the elements that significantly contribute to mitigating the gradient just before solidification ends (elements highly correlated with cracking). For example, in the case of Nb, if the composition is reduced by 0.5% by mass, the temperature difference between a solid proportion of 0.9 and a solid proportion of 1 changes from 190 °C to 130 °C, a change of 60 °C. Therefore, 60 is divided by 0.5, and the coefficient is set to 120. Similarly, in the case of Zr, if the composition decreases by 0.06% by mass, the temperature difference between the solid-phase ratio of 0.9 and the solid-phase ratio of 1 changes from 190°C to 151°C, a change of 39°C. Therefore, 39 is divided by 0.06, and the coefficient is set to 650. In the case of Ti, if the composition decreases by 0.25% by mass, the temperature difference between the solid-phase ratio of 0.9 and the solid-phase ratio of 1 changes from 190°C to 182°C, a change of 8°C. Therefore, 8 is divided by 0.25, and the coefficient is set to 32. In the case of C, if the composition increases by 0.096% by mass, the temperature difference between the solid-phase ratio of 0.9 and the solid-phase ratio of 1 changes from 190°C to 153°C, a change of 37°C. Therefore, 37 is divided by 0.096, and the coefficient is set to 385.

[0066] The above results show that, according to Equation 1, if the amount of Nb, Zr, and Ti (with positive coefficients) increases, the fracture sensitivity index increases, making fracture more likely; conversely, if the amount of C (with negative coefficients) increases, the fracture sensitivity index decreases, making fracture less likely. Furthermore, Equation 1 confirms this relationship. Specific examples are shown in the embodiments described later, but these are consistent with experimental values.

[0067] (Unavoidable impurities)

[0068] Furthermore, the remaining portion contains unavoidable impurities. Unavoidable impurities refer to trace impurities that are technically difficult to remove due to trace elements mixed in with the raw materials or reactions with various components that come into contact with the manufacturing process. Among these impurities, impurities such as P, S, O, and N should be particularly limited. P is preferably less than 0.02%, S is preferably less than 0.005%, O is preferably less than 0.02%, and N is preferably less than 0.04%. Of course, the lower the content of these unavoidable impurities, the better; 0% is even better.

[0069] Furthermore, the remaining portion may also contain trace elements such as Mn and Si that have a deacidifying effect. These trace elements are preferably 1.0% or less, and more preferably 0.5% or less. In addition, the composition of the alloy powder can be analyzed, for example, using high-frequency inductively coupled plasma (ICP) luminescence analysis.

[0070] As the raw material for the laminated structure of this embodiment, an alloy powder having the aforementioned composition is prepared. The chemical composition of the laminated structure (laminated structure) is substantially the same as that of the alloy powder.

[0071] [Particle size]

[0072] As a method for manufacturing the alloy powder in this embodiment, gas atomization, water atomization, jet atomization, etc., can be used, but it is preferable to use gas atomization, which easily produces spherical powder, to manufacture the alloy powder. In addition, regarding the size of the alloy powder, if the particle size is too small, the flowability will be poor; conversely, if the particle size is too large, the precision of the formed product will be poor and the defect rate will be high. Therefore, for example, it is preferable to set the average particle size (D50) to 5 μm to 200 μm.

[0073] <Layered Forms>

[0074] Next, the layered shapes will be explained.

[0075] The laminated structure formed by laminating powder based on the alloy composition of the present invention is characterized by having a microstructure comprising elemental segregation portions between dendritic crystals and adjacent dendritic crystals, wherein the width of the dendritic crystals in cross-sectional microstructure observation is 5 μm or less, and the width of the elemental segregation portions is 200 nm or less. Furthermore, it is characterized by the thickening of Cr, Mo, Nb, and Zr in the elemental segregation portions compared to the dendritic crystals. Because the laminated structure is formed using powder based on the alloy composition, the width of the elemental segregation portions can be narrowed, thereby suppressing fracture. That is, not only does it possess the fracture suppression effect provided by the alloy powder, but it also has the effect of suppressing fracture by narrowing the width of the dendritic crystals and the elemental segregation width through rapid cooling.

[0076] Furthermore, dendritic crystals are preferably as follows: Figure 6The diagram shows the formation of only primary dendritic crystals. "Only primary dendritic crystals" refers to a situation where elemental segregation portions may exist between adjacent dendritic crystals, but secondary dendritic crystals do not form. Furthermore, if, as described above, the temperature difference between a solid-phase ratio of 0.9 and a solid-phase ratio of 1 is large and the gradient is steep, the solidification time is prolonged, promoting the formation of secondary dendritic crystals and increasing the width of the elemental segregation portions. Conversely, by reducing the temperature difference between a solid-phase ratio of 0.9 and a solid-phase ratio of 1, the formation of secondary dendritic crystals can be suppressed, resulting in a structure with only primary dendritic crystals. However, even when secondary dendritic crystals are formed, as long as the width of the elemental segregation portions is less than 200 nm, a crack-suppressing effect is achieved. Based on the above description, if the Ni-based alloy powder of the present invention is used for lamination molding, a laminated structure that is not easily cracked can be obtained.

[0077] <Methods for Manufacturing Layered Shapes>

[0078] An embodiment of the method for manufacturing a laminated object using the alloy powder described above will be described. The method for manufacturing a laminated object according to the present invention is a method for manufacturing a laminated object by irradiating the Ni-based alloy powder described above with an electron beam or a laser beam to melt and solidify it. One of its features is that the shaping is performed by irradiating the Ni-based alloy powder with an electron beam or a laser beam to melt and solidify it.

[0079] As an embodiment of shaping by melting and solidifying an object by irradiating it with an electron beam or a laser beam, it is applicable to either the additive manufacturing method (referred to as the stacking shaping method in this invention) for metal materials, namely powder bed fusion (PBF) and directed energy deposition (DED).

[0080] Figure 3 The diagram illustrates a schematic structure of a laser lamination method that uses a laser as a heat source for lamination shaping in a powder bed fusion bonding manner. For example... Figure 3 As shown, it includes: alloy powder as raw material 1, powder supply stage 2, coating machine 3, laser oscillator 4, laser 5, galvano scanner 6, shaping object (layered shaping object) 7, shaping stage 8.

[0081] In the layering process, the powder supply stage 2 is raised a predetermined distance, and the shaping stage 8 is lowered a predetermined distance. The coating machine 3 moves along the X direction, thereby supplying alloy powder 1 onto the shaping stage 8. In the supplied area, a laser 5 from a laser oscillator 4 is controlled by a current detector 6 to irradiate the alloy powder, thereby selectively melting and solidifying it to form a layered solidified structure. By repeating this process, a three-dimensional object 7 is shaped.

[0082] For the conditions of layered shaping, it is sufficient to set the layer thickness to 10μm~200μm, the laser output power to 50W~1000W, the scanning speed to 100mm / s~5000mm / s, and the scanning interval to 0.05mm~0.5mm. To improve shaping accuracy or prevent molten residue of Ni-based alloy powder, it is preferable to set the layer thickness to 20μm~50μm, the laser output power to 100W~200W, the scanning speed to 600mm / s~1200mm / s, and the scanning interval to 0.05mm~0.12mm.

[0083] Example

[0084] The embodiments of the present invention will be described below. However, the present invention is not limited to the embodiments described below.

[0085] As an example, laminated shapes (hereinafter, also simply referred to as shapes) are created for each of the eight types of powders, from alloy powder A to alloy powder H, as shown in Table 1. The laminated shaping method is achieved through... Figure 3 The PBF (Physical Shape Frame) shaping device (Mlab-200R manufactured by Conceptlaser) was used to create 10mm × 10mm × 10mm shapes. The stacking conditions were set as follows: each layer thickness was 30μm; the laser output power was appropriately selected from 140W, 160W, 180W, and 200W; the scanning speed was appropriately selected from 600mm / s, 800mm / s, 1000mm / s, 1200mm / s, 1400mm / s, and 1600mm / s; and the scanning interval was 0.07mm. The cross-sections of each shape created in this manner were polished to a mirror finish. Photographs of areas measuring 8mm in length and 8mm in width were taken, and the area ratio (porosity) of pores with a maximum diameter of 5μm or larger was measured using binarized image processing. As a result, for shapes with a porosity of less than 0.1%, optical microscopy and scanning electron microscopy (SEM) were used to determine the presence and rate of fractures. This is because, under conditions of high porosity, the determination of fractures is prone to error. In this case, in the binarized image, defects with a roundness of less than 0.3 and a maximum diameter of more than 5 μm are considered fractures, and half the circumference is taken as the fracture length. Each 1 mm... 2 The total fracture length (μm) was defined as the fracture rate and calculated. The evaluation results of fracture and fracture rate are shown in Table 1. The values ​​of each element are by mass%. In addition, the fracture sensitivity index was calculated based on the composition of each powder using Equation 1.

[0086] The alloy powder used was a powder with an average particle size (D50) of 34 μm obtained by classifying spherical powder obtained by gas atomization.

[0087] [Table 1]

[0088] powder Ni C Al Mo Nb Ti Zr B C index rupture Fracturing rate A 801 12.1 5.69 4.53 2.03 0.65 0.10 0.00 0.014 324 have 7.20 B 801 12.6 6.27 4.08 1.91 0.04 0.11 0.010 0.170 237 none 0 C 803 12.6 6.45 4.09 1.95 0.64 0.15 0.012 0.167 288 have 5.85 D 803 12.2 6.46 3.98 1.96 0.20 0.16 0.010 0.164 282 have 0.27 E 801 13.0 6.00 4.50 2.30 0.75 0.11 0.00 0.104 332 have 3.55 F 801 12.5 5.50 4.51 2.31 0.74 0.01 0.00 0.100 295 have 3.33 G 801 13.5 6.4 4.00 1.91 0.50 0.01 0.011 0.15 284 have 2.11 H 801 12.6 6.44 4.12 1.95 0.00 0.12 0.010 0.183 241 none 0

[0089] Alloy powders A, C, D, E, F, and G exhibited fracture rates exceeding 0, indicating fracture. However, alloy powders B and H showed a fracture rate of 0, indicating no fracture. The fracture sensitivity indices of fractured alloy powders A, C, D, E, F, and G all exceeded 270. Powders A, C, E, and F, containing significant amounts of Ti, also had high fracture sensitivity indices exceeding 300. Furthermore, powder A, with its high Ti and low C content, had the highest fracture rate. Conversely, the fracture sensitivity indices of unfractured alloy powders B and H were 237 and 241, respectively, both below 270. No Ti was added to alloy powder H. Based on the above, it is effective to select an alloy composition that satisfies (Equation 1) and has a fracture sensitivity index below 270. Additionally, maintaining the elemental balance of (Equation 1) while reducing the Ti content is also effective.

[0090] [The organization of layered structures]

[0091] For the specimen formed by lamination using alloy powder B (Example) from Table 1, a microstructure photograph (magnification: 20000x) taken from the lamination direction is shown. Figure 4 . Figure 4 The images were observed using a scanning electron microscope (manufactured by Nippon Electronics Co., Ltd., model JSM-7900F). The surface direction on the paper is the stacking direction. Parallel dendritic crystals (primary dendritic crystals) 10 were formed. Furthermore, the dendritic crystals referred to in this invention are a different structure from the dendritic crystals seen in casting structures, etc., and refer to a morphology of solidified structure extending parallel to the stacking direction. Figure 4 In this case, the spacing (interval) between adjacent dendrites 10, i.e. the width of the dendrites 10, is approximately 1 μm. The scanning speed during the stacking process is fast, and the cooling speed for melting and solidification is also fast. The width of the dendrites 10 becomes narrower and more prone to breakage due to rapid cooling. However, it is known that if the alloy powder of the present invention is used, breakage can be effectively prevented even if the width of the dendrites 10 is less than 5 μm.

[0092] Similarly, for the specimens shaped using alloy powder B from Table 1, microstructure photographs (magnification: 20000x) obtained by taking pictures from a plane perpendicular to the stacking direction are shown. Figure 5 . Figure 5 These photographs were taken using a scanning electron microscope (manufactured by Nippon Electronics Corporation, model JSM-7900F). The vertical direction of the paper indicates the stacking direction. For example... Figure 5 As shown, an aggregate of roughly circular structures with a diameter of approximately 1 μm was observed. According to... Figure 4 and Figure 5 The tissue photographs suggest the formation of cylindrical dendritic crystals 10.

[0093] Next, in Figure 6 The image shows a microstructure photograph (magnification: 80,000x) of a layered structure obtained by molding with alloy powder B, which is a molded object of alloy powder that has not cracked in the molded object. Figure 6 These photographs were taken using a transmission electron microscope (manufactured by Nippon Electronics Corporation, model ARM-200F). Figure 6 As shown, only primary dendrites are formed in dendritic crystal 10, and secondary dendrites 12 are not observed (see reference). Figure 7 The white lines between adjacent dendrites 10 are elemental segregation portions 11. They appear white because their electron beam transmittance differs from that of dendrites 10, and they have a different composition (indicating elemental segregation) than dendrites 10. The width of dendrites 10 is approximately 1 μm, and the width of elemental segregation portions 11 is approximately 40 nm. In the example described, since secondary dendrites 12 are not formed, the width of elemental segregation portions 11 can be considered as simply the width of elemental segregation portions located at the boundaries of primary dendrites.

[0094] Table 2 shows Figure 6 The compositional analysis results of the tissue based on energy-dispersive X-ray diffraction (EDXRD) show that Cr, Mo, Nb, and Zr are segregated in elemental segregation zone 11 compared to dendritic crystal 10. Specifically, Mo segregates to more than four times the amount found in dendritic crystal 10, Nb to more than ten times the amount, and Zr, which was not detected in dendritic crystal 10, segregates in elemental segregation zone 11. Thus, although elemental segregation zone 11 is formed in alloy powder b, its narrow width suggests that no fracture has occurred.

[0095] [Table 2]

[0096]

[0097] Next, in Figure 7The image shows a microstructure photograph (magnification: 40,000x) of a layered structure obtained by molding with alloy powder C (comparative example) as a fractured structure, showing the width of the dendritic crystals 10 and the elemental segregation portion 11. Figure 7 This photograph was taken using a transmission electron microscope (manufactured by Nippon Electronics Corporation, model ARM-200F). The dendrite 10 is approximately 1.2 μm wide, and secondary dendrites 12 are formed perpendicular to the growth direction of the dendrite 10. Between the secondary dendrites 12... Figure 7 The image shows a white elemental segregation portion 11, and the width of the elemental segregation portion 11 with the addition of secondary dendritic crystals 12 is approximately 300 nm.

[0098] Table 3 shows Figure 7 The results of component analysis of the tissue based on energy-dispersive X-ray diffraction (EDXD) analysis. Segregated elements and Figure 6 Similarly, it can be considered that the width of the elemental segregation portion 11 in the fractured structure exceeds 200 nm even in other alloy powders. Therefore, if the width of the elemental segregation portion 11 is wide, the solidification time becomes longer, making it easier for fracture to occur. Therefore, it is known that the width of the elemental segregation portion 11 is preferably 200 nm or less. In addition, it is also known that the width of the elemental segregation portion 11 becomes wider due to the formation of secondary dendrites 12. Therefore, it is preferable to have a structure with only primary dendrites 10 without the formation of secondary dendrites 12.

[0099] [Table 3]

[0100]

[0101] [Strength Evaluation of Layered Forms]

[0102] Laminated specimens were fabricated using alloy powder B. Regarding the laminated fabrication method, similar to specimens used for fracture evaluation or microstructure observation, PBF (Plasma-Based Fraction) was employed using a Mlab-200R fabrication apparatus manufactured by Conceptlaser. The lamination conditions were: lamination thickness 30 μm, laser output power 200 W, scanning speed 1000 mm / s, and scanning interval 0.1 mm. Cross-sectional observation of the specimens confirmed the absence of fracture. Furthermore, the cross-section of the specimens was polished to a mirror finish, and photographs were taken of an area measuring 8 mm in length and 8 mm in width. Binarized image processing was used to determine the area ratio of pores with a maximum diameter of 5 μm or more. The porosity was found to be a good 0.02%. Following fabrication, a solution heat treatment at 1177 °C for 2 hours was performed, followed by an aging heat treatment at 927 °C for 16 hours. A high-temperature creep fracture test was then conducted on the specimens at 980 °C and 150 MPa. As a result, since the specimen did not break, a good value was obtained with a fracture time of 46 hours and an elongation of 25% after fracture. That is, it can be confirmed that a non-fracture specimen with the characteristics of a fracture time of more than 40 hours and an elongation of more than 20% in a high-temperature creep fracture test at 980°C and 150MPa can be obtained.

[0103] Similarly, alloy powder H was used to prepare the model. Regarding the stacking modeling method, the same PBF method was used as for the specimens used for fracture evaluation or microstructure observation, employing a Mlab-200R modeling device manufactured by Conceptlaser. The stacking conditions were: stack thickness 30 μm, laser output power 190 W, scanning speed 1000 mm / s, and scanning interval 0.08 mm. Cross-sectional observation of the model confirmed the absence of fracture. Furthermore, the cross-section of the model was polished to a mirror finish, and photographs were taken of an area measuring 8 mm in length and 8 mm in width. The area ratio of the pores was measured using binarized image processing. The porosity was found to be good at 0.01%. After modeling, a solution heat treatment at 1250 °C for 10 hours was performed, followed by an aging heat treatment at 927 °C for 16 hours. A high-temperature creep fracture test was then conducted on the model at 980 °C and 150 MPa. As a result, the specimen did not crack, and achieved an excellent value of 4% elongation after fracture and a fracture time of 62 hours. That is, it can be confirmed that the porosity or high-temperature creep fracture characteristics are excellent even in the absence of Ti.

[0104] Furthermore, since alloy powders A, C, D, E, F, and G have fractured, creep rupture tests are not performed on them.

Claims

1. A Ni-based alloy powder for layered shaping, characterized in that... Included by weight %: Cr content between 10.0% and 16.0% Al content above 4.0% and below 9.0% Mo content of 1.0% or more and 6.0% or less Nb content above 0.5% and below 4.0% Ti content below 0.5% Zr content below 0.5% C, which is above 0.06% and below 0.4%, and B below 0.04%, The remainder contains Ni and unavoidable impurities, and The Ni-based alloy powder used for the layered molding process satisfies the following conditions: 150 ≤ 120Nb + 650Zr + 32Ti - 385C ≤ 270, and the element symbols directly represent the mass of each element.

2. The Ni-based alloy powder for layered shaping according to claim 1, characterized in that, The Ti content is above 0.002% and below 0.2%.

3. A layered structure, characterized in that... It has the following composition, that is, it contains, by mass%: Cr content between 10.0% and 16.0% Al content above 4.0% and below 9.0% Mo content of 1.0% or more and 6.0% or less Nb content above 0.5% and below 4.0% Ti content below 0.5% Zr content below 0.5% C, which is above 0.06% and below 0.4%, and B below 0.04%, The remainder contains Ni and unavoidable impurities, and The composition satisfies 150≤120Nb+650Zr+32Ti-385C≤270, and the symbols of each element directly represent the mass percentage of each element. Furthermore, the stacked structure has an organization that includes elemental segregation portions between dendritic crystals and adjacent dendritic crystals. The width of the dendritic crystals observed in the cross-section is less than 5 μm, and the width of the elemental segregation portion is less than 200 nm.

4. The layered structure according to claim 3, characterized in that, The elemental segregation portion is thickened with at least one of Cr, Mo, Nb, and Zr compared to the dendritic crystal.

5. A method for manufacturing a laminated object, wherein the object is shaped by irradiating Ni-based alloy powder for laminated shaping according to claim 1 or 2 with an electron beam or laser beam and causing it to melt and solidify.

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