JP7702236B2 - FORMED BODY MANUFACTURING METHOD AND FORMED BODY - Google Patents

Description

The present invention relates to a method for producing a shaped body and a shaped body obtained by the method.

A method for producing a shaped body by powder bed fusion using powder made of a Ni-based alloy has been known for some time. A shaped body made of a Ni-based alloy produced by this method is used as a high-temperature part for a gas turbine engine, for example.

The Ni-based alloy constituting the powder may be a gamma prime precipitation strengthened Ni-based alloy, which is an Ni-based alloy whose composition is adjusted so that a strength-strengthening gamma prime ( _Ni3 (Al,Ti)) phase precipitates when the manufactured shaped body is heat-treated.

It is known that Ni-based alloys containing Al and Ti are prone to cracking during welding if the sum of twice the Al content and the Ti content (2Al + Ti) is 6% or more. In powder bed fusion, for example, microcracks measuring several micrometers to several hundred micrometers in length can form in the manufactured shaped body.

As a technique for suppressing the occurrence of cracks during welding of gamma prime precipitation strengthened Ni-based alloys, for example, Patent Document 1 describes limiting the Si content and Zr content to less than 0.03% by mass percentage.

Special table 2017-508877 publication

In response to this, it is desirable to suppress the occurrence of cracks during welding of gamma prime precipitation strengthened Ni-based alloys, regardless of whether the Si and Zr contents in the Ni-based alloy are limited, and in particular to reduce cracks formed in shaped bodies produced by powder bed fusion.

The present invention aims to provide a method for manufacturing a shaped body that can reduce cracks formed in a shaped body manufactured by powder bed fusion using powder made of a gamma prime precipitation strengthened Ni-based alloy, and a shaped body obtained by this method.

In order to solve the above problems, the inventors of the present invention conducted extensive research and discovered that in powder bed fusion, in which a laser is irradiated onto a layer of powder along multiple parallel scanning lines, there is a correlation between the value obtained by dividing the distance between the scanning lines by the laser spot diameter and the formation of cracks in a shaped body. The present invention was made from this perspective.

That is, the method for producing a shaped body of the present invention is a method for producing a shaped body by powder bed fusion using a powder made of a gamma prime precipitation strengthened Ni-based alloy, the method comprising the steps of:
The Ni-based alloy contains, by mass percentage, 7.0 to 17.0% Cr, 7.0 to 12.0% Co, 5.0 to 8.0% Al + Ti, 2.0 to 12.0% W, 1.5 to 4.4% Nb + Ta, 2.3% or less Mo, 0.3% or less C, 2.0% or less Hf, and 0.2% or less Zr, and is characterized in that when a laser is irradiated along a plurality of parallel scanning lines on a layer made of the powder, a value obtained by dividing the interval between the plurality of scanning lines by a laser spot diameter is 0.2 to 1.1.

The above configuration can reduce cracks that form in the molded body.

The shaped body of the present invention is a shaped body made of a Ni-based alloy and containing a dendritic crystal structure, characterized in that the Ni-based alloy contains, by mass percentage, 7.0 to 17.0% Cr, 7.0 to 12.0% Co, 5.0 to 8.0% Al + Ti, 2.0 to 12.0% W, 1.5 to 4.4% Nb + Ta, 2.3% or less Mo, 0.3% or less C, 2.0% or less Hf, and 0.2% or less Zr, the spacing between the branches of the primary dendrites of the dendritic crystal structure is less than 3 μm, and the maximum pole density of the pole figure measured by the EBSD method is 5 or more.

Here, the "pole density of the pole figure" is found by calculating how frequently each crystal orientation in the measurement surface occurs, when all crystal orientations appear in uniform density (i.e., a structure with completely random orientation) is used as the standard, and is calculated as MUD (Multiples of a Uniform Density) through analysis using software provided with the EBSD device. The larger the MUD, the more the crystal orientation of the measurement surface is biased toward a specific crystal direction.

Directional solidification casting and single crystal casting are known methods for producing castings with large MUD by casting, but in these castings, the spacing between the branches of the primary dendrites in the dendritic crystal structure is large, exceeding approximately 40 μm. In contrast, in a shaped body produced by powder bed fusion using a laser as a heat source, the spacing between the branches of the primary dendrites in the dendritic crystal structure is small, less than 3 μm. Also, as described above, if the value obtained by dividing the spacing between multiple scanning lines by the laser spot diameter in powder bed fusion is 0.2 to 1.1, the maximum pole density (i.e., MUD) of the pole figure measured by the EBSD method will be 5 or more. Therefore, a shaped body having the above configuration has few cracks.

According to the present invention, it is possible to reduce cracks that form in a shaped body produced by powder bed fusion using powder made of a gamma prime precipitation strengthened Ni-based alloy.

1A to 1C are diagrams for explaining a method for manufacturing a shaped body by powder bed fusion. 1 is a graph showing maximum MUD values and crack amounts for Examples 1 to 7 and Comparative Examples 1 and 2. 1 is a micrograph of Example 5. 1 is a micrograph of Comparative Example 1.

The method for manufacturing a shaped body according to one embodiment of the present invention is a method for manufacturing a shaped body by powder bed fusion using powder made of a gamma prime precipitation strengthened Ni-based alloy. In powder bed fusion, the heat source for melting the powder can be an electron beam, but in this embodiment, the heat source is a laser.

In powder bed fusion, as shown in FIG. 1, a layer 3 of powder is formed on a platform 1, and a laser is irradiated onto the layer 3 along multiple parallel scanning lines 4. The laser is irradiated so as to be focused near the surface of the layer 3. The position, shape, and length of each scanning line 4 are determined by the cross-sectional shape of the object to be manufactured. For example, the scanning lines 4 may be straight or curved.

Figure 1 shows an example of manufacturing a rectangular prism-shaped object. In Figure 1, the laser scanning directions are opposite to each other for adjacent scanning lines 4, but the laser scanning direction may be the same for all scanning lines 4.

The laser irradiation onto layer 3 melts and solidifies part or all of that layer 3. After that, the platform 1 is lowered by the thickness of layer 3, a new layer (hereinafter, top layer) 3 made of powder is formed on the layer previously formed (hereinafter, previous layer) 3, and the laser is irradiated onto the top layer 3 along multiple scanning lines 4 that are parallel to each other. The bed 2 includes the previously formed portion on top of the previous layer 3, where the top layer 3 is formed, and the unmelted powder.

The orientation of the scanning lines 4 may be the same or different between the top layer 3 and the immediately preceding layer 3. When the orientation of the scanning lines 4 differs between the top layer 3 and the immediately preceding layer 3, the angle of the scanning lines 4 of the top layer 3 relative to the scanning lines 4 of the immediately preceding layer 3 (hereinafter, the scanning rotation angle) can be appropriately determined. For example, in FIG. 1, the scanning rotation angle is 90 degrees.

The above process is repeated, and finally the unmelted powder is removed from bed 2 to produce a shaped body. In such a shaped body, the spacing between the branches of the primary dendrites in the dendritic crystal structure is small, less than 3 μm.

The particle size distribution of the powder used in powder bed fusion is, for example, 5 to 75 μm, but preferably 15 to 63 μm. The thickness of each layer 3 is, for example, 20 to 60 μm.

The Ni-based alloy constituting the powder contains, as essential components other than Ni, the following mass percentages (same below): 7.0-17.0% Cr, 7.0-12.0% Co, 5.0-8.0% Al+Ti, 2.0-12.0% W, and 1.5-4.4% Nb+Ta. Examples of such Ni-based alloys include IN738C (IN is an abbreviation for Inconel (registered trademark), same below), IN738LC, CM247LC, and Mar-M247. Note that with regard to Nb and Ta, the Ni-based alloy does not necessarily need to contain either Nb or Ta.

The more desirable contents of each essential component are Cr: 7.0-10.0%, Co: 8.0-11.0%, Al+Ti: 5.0-7.5%, W: 8.0-11.0%, Nb+Ta: 2.0-4.0%.

The Ni-based alloy may contain at least one of the following optional components: 2.3% or less (preferably 0.2-1.0%) Mo, 0.3% or less (preferably 0.01-0.2%) C, 2.0% or less (preferably 0.5-2.0%) Hf, and 0.2% or less Zr. The balance of the Ni-based alloy other than the above-mentioned components is Ni and unavoidable impurities.

In this embodiment, when irradiating each layer 3 with a laser, the value (L/D) obtained by dividing the interval L of the scanning lines 4 by the laser spot diameter D is set to be 0.2 or more and 1.1 or less. The laser spot diameter D is the beam diameter at the position where the laser intensity has dropped to 1/ ^e2 from the peak value (in other words, the position where it is about 13.5% of the peak value). Some powder bed fusion devices that use a laser allow the user to set the laser spot diameter, while others do not.

The laser spot diameter D is, for example, 0.02 to 0.20 mm, but is preferably 0.05 to 0.15 mm. The spacing L between the scanning lines 4 is, for example, 0.03 mm to 0.08 mm.

The laser scanning speed is, for example, 500 to 3000 mm/s, preferably 600 to 2000 mm/s, and more preferably 700 to 1500 mm/s. The laser output is, for example, 100 to 400 W, preferably 130 to 350 W, and more preferably 150 to 300 W.

As described above, by setting the value (L/D) obtained by dividing the distance L of the scanning lines 4 by the laser spot diameter D when irradiating each layer 3 with a laser to 0.2 or more and 1.1 or less, it is possible to reduce the cracks that form in the molded body. In addition, in a molded body with few cracks produced in this way, the maximum value of MUD (pole density of a pole figure measured by the EBSD method) is 5 or more (10 or more under some conditions).

The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

Example 1
A cubic object with a side length of 10 mm was manufactured by powder bed fusion using a powder having an alloy composition equivalent to CM247LC. The particle size distribution of the powder was 16 to 45 μm. In addition, when the alloy composition of the powder was analyzed, the contents of components other than Ni were Cr: 8.0%, Co: 9.1%, Al: 5.5%, Ti: 0.7%, W: 9.5%, Nb: 0%, Ta: 3.1%, Mo: 0.5%, C: 0.06%, Hf: 1.5%, and Zr: 0.01% (the contents of inevitable impurities are omitted).

The powder bed fusion device used was an EOS M290 manufactured by EOS. In this device, the laser spot diameter D was set by the manufacturer to 0.08 mm. The thickness of each layer when manufacturing the molded object was 40 μm, the spacing between the scanning lines when irradiating each layer with the laser was 0.03 mm, the laser scanning speed was 1000 mm/s, the laser output was 180 W, and the scanning rotation angle was 90 degrees.

Example 2
A shaped body was manufactured in the same manner as in Example 1, except that the interval between scanning lines when irradiating each layer with a laser was set to 0.04 mm.

Example 3
A shaped body was manufactured in the same manner as in Example 1, except that the interval between scanning lines when irradiating each layer with a laser was set to 0.05 mm.

Example 4
A shaped body was manufactured in the same manner as in Example 1, except that the interval between scanning lines when irradiating each layer with a laser was set to 0.06 mm.

(Example 5)
A shaped body was manufactured in the same manner as in Example 4, except that the scanning rotation angle was set to 67 degrees.

Example 6
A shaped body was manufactured in the same manner as in Example 1, except that the interval between scanning lines when irradiating each layer with a laser was set to 0.07 mm.

(Example 7)
A shaped body was manufactured in the same manner as in Example 1, except that the interval between scanning lines when irradiating each layer with a laser was set to 0.08 mm.

(Comparative Example 1)
A shaped body was manufactured in the same manner as in Example 1, except that the interval between scanning lines when irradiating each layer with a laser was set to 0.09 mm.

(Comparative Example 2)
A shaped body was manufactured in the same manner as in Example 1, except that the interval between scanning lines when irradiating each layer with a laser was set to 0.10 mm.

The manufacturing conditions for the shaped bodies of Examples 1 to 7 and Comparative Examples 1 and 2 are shown in Table 1. Table 1 also shows the value (L/D) obtained by dividing the distance L between the scanning lines by the laser spot diameter D.

(test)
The shaped bodies of Examples 1 to 7 and Comparative Examples 1 and 2 were cut along a plane perpendicular to the stacking direction (the vertical direction in FIG. 1), and micrographs of the cut surfaces were taken. Figure 3 is a micrograph of Example 5, and Figure 4 is a micrograph of Comparative Example 1. Then, the length of cracks per unit area observed on the cut surfaces in each of Examples 1 to 7 and Comparative Examples 1 and 2 was calculated as the amount of cracks.

In addition, for each of Examples 1 to 7 and Comparative Examples 1 and 2, the pole density of the pole figures was measured by EBSD on the cut surfaces of the molded bodies cut along a plane perpendicular to the lamination direction. For this measurement, Hitachi's SEM-SU5000 and EDAX/TSL's Pegasus Digiview5 were used as EBSD devices.

Regarding the measurement of the pole density of the pole figure, more specifically, the cut surface was mechanically polished using waterproof abrasive paper and diamond abrasive grains as a preliminary preparation, and then polished using colloidal silica. This preliminary preparation is for reducing measurement failures and ensuring measurement accuracy, and is generally used for EBSD measurement. Next, the Kikuchi line was measured with a step size of 3 μm for a 900 μm x 900 μm area on the cut surface, and the {100} pole figure was obtained by projecting the {100} pole using analysis software (EDAX/TSL OIM Data Collection/OIM Analysis ver.8). The MUD was calculated from the pole figure. The spherical harmonic method was used to calculate the MUD, with the expansion order set to 16 and the half-width set to 5 degrees.

The maximum MUD values and crack amounts for Examples 1 to 7 and Comparative Examples 1 and 2 are shown in Table 2. The maximum MUD values and crack amounts for Examples 1 to 7 and Comparative Examples 1 and 2 are also shown in a graph in Figure 2.

As is clear from Table 2 and Figure 2, the amount of cracking was large in Comparative Examples 1 and 2, in which the spacing between the scanning lines when irradiating each layer with a laser was set to greater than 0.09 mm, i.e., L/D was set to greater than 1.1. In contrast, the amount of cracking was small in Examples 1 to 7, in which the spacing between the scanning lines when irradiating each layer with a laser was adjusted to set L/D to 0.2 or more and 1.1 or less.

In addition, in Comparative Examples 1 and 2, the maximum MUD value was less than 5, whereas in Examples 1 to 7, the maximum MUD value was 5 or more. Therefore, a molded body with a maximum MUD value of 5 or more is a molded body with few cracks.

1 Platform 2 Bed 3 Layer 4 Scanning line

Claims (2)

1. A method for producing a shaped body by powder bed fusion using a powder made of a gamma prime precipitation strengthened Ni-based alloy, comprising:
The Ni-based alloy contains, by mass percentage, 7.0 to 10.0% Cr, 8.0 to 11.0% Co, 5.0 to 7.5% Al + Ti, 8.0 to 11.0% W, 2.0 to 4.0% Nb + Ta, 0.2 to 1.0% Mo, 0.01 to 0.2% C, 0.5 to 2.0% Hf, and 0.2% or less Zr, with the balance being Ni and unavoidable impurities;
when irradiating the layer made of the powder with a laser along a plurality of parallel scanning lines, a value obtained by dividing an interval between the plurality of scanning lines by a laser spot diameter is set to be 0.2 or more and 1.1 or less.
Modeled object manufacturing method. A shaped body including a dendritic crystal structure and made of a Ni-based alloy,
The Ni-based alloy contains, by mass percentage, 7.0 to 10.0% Cr, 8.0 to 11.0% Co, 5.0 to 7.5% Al + Ti, 8.0 to 11.0% W, 2.0 to 4.0% Nb + Ta, 0.2 to 1.0% Mo, 0.01 to 0.2% C, 0.5 to 2.0% Hf, and 0.2% or less Zr, with the balance being Ni and unavoidable impurities;
The spacing of the branches of the primary dendrites of the dendritic crystal structure is less than 3 μm;
A molded body having a maximum pole density of 5 or more in a pole figure measured by an EBSD method.

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