A NiCrFe-based high-strength and high-toughness special alloy for additive manufacturing and its preparation method

Abstract

The application discloses a kind of NiCrFe base high strength and toughness special alloy for additive manufacturing and a preparation method thereof.The single-phase FCC special alloy is microstructurally designed in the application, and the precipitation of refractory element second phase at the cell boundary and the cell grain boundary is realized by the regulation and control of additive manufacturing preparation process and subsequent quenching process, and then the boundary is fixed, to obtain high strength and toughness special alloy.The reasonable selective laser melting process and scanning strategy are selected in the application, to prepare the as-built special alloy, and then the as-built special alloy is subjected to subsequent vacuum quenching treatment, so that the dispersed fine refractory element second phase is precipitated at the cell boundary and the cell grain boundary.The NiCrFe base special alloy obtained in the application has dense structure, fine grains and nanoscale second phase, and has good strength and toughness.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing special alloys, specifically relating to a NiCrFe-based high-strength and high-toughness special alloy for additive manufacturing and its preparation method. Background Technology

[0002] NiCrFe-based special alloys have a single-phase face-centered cubic matrix, exhibiting high strength, high stiffness, good toughness, and corrosion resistance, while also possessing good strength and excellent plasticity. They are widely used in rail transportation, aerospace, and nuclear power industries. However, the preparation of NiCrFe-based special alloys mainly focuses on methods such as vacuum arc melting, powder metallurgy, mechanical alloying, and plastic processing. Components prepared using these methods suffer from problems such as uniform dimensions, numerous defects, and inhomogeneous microstructure. Additive manufacturing technology, on the other hand, can meet the requirements for integrated molding of high-performance complex alloy components, achieving integrated shape and property fabrication. Examples include the integrated fabrication of complex components such as engine turbine blades and aircraft landing gear. Furthermore, the yield strength and ultimate tensile strength of additively manufactured special alloys are generally superior to those obtained using the aforementioned methods.

[0003] However, under actual service conditions, existing additive manufacturing special alloys suffer from insufficient fatigue life and impact toughness. Unmelted pre-alloyed powder particles, voids, and microcracks are typical defects commonly found in additive manufacturing alloy parts, leading to decreased density. Furthermore, the extremely rapid cooling rate during additive manufacturing results in significant undercooling and temperature gradients, causing unique multi-level structures (molten pool-columnar crystal-cellular crystal) with marked anisotropy in the special alloys. In addition, the repeated heating and cooling processes in additive manufacturing lead to the continuous accumulation of residual thermal stress in the parts, causing localized stress concentrations during service and severely impairing the toughness of the additive manufacturing special alloys. Moreover, under actual service conditions, additive manufacturing alloy parts are subjected to impact loads, leading to impact damage and failure. Therefore, there is a need for a high-toughness additive manufacturing special alloy. Summary of the Invention

[0004] The purpose of this invention is to provide a NiCrFe-based high-strength and high-toughness special alloy for additive manufacturing and its preparation method. This preparation method is rationally designed, convenient to operate, highly efficient, and can stably prepare high-strength and high-toughness special alloys.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] The NiCrFe-based high-strength and high-toughness special alloy for additive manufacturing provided by this invention is prepared from pre-alloyed powder through an additive manufacturing process and a subsequent quenching process. The pre-alloyed powder is composed of the following atomic percentages: Fe 20.93-72.93%, Ni 9.68-23.99%, Cr 15.36-25.03%, Co 0.00-22.13%, Mo 1.59-8.92%, Si 0.00-0.50%, and Mn 0.00-0.70%.

[0007] Preferably, the pre-alloyed powder is prepared by melting metal powder with a mass fraction of 99.9% or more in a vacuum induction furnace to prepare a pre-alloyed ingot, and then filling it into a gas atomization chamber for gas atomization powder preparation to obtain the pre-alloyed powder.

[0008] Preferably, the particle size of the pre-alloyed powder is 17-90 μm.

[0009] Preferably, the high-strength and high-toughness special alloy has a strength of 1500-2200 MPa under impact load and an impact absorption energy of 200-260 MJ / m. 3 .

[0010] The present invention provides a method for preparing a NiCrFe-based high-strength and high-toughness special alloy for additive manufacturing, comprising: designing an additive manufacturing process and a subsequent quenching process to achieve the precipitation of a second phase of refractory elements at the molten pool boundary and the cellular grain boundary, thereby consolidating the boundary and obtaining the high-strength and high-toughness special alloy; the preparation method specifically includes the following steps:

[0011] S1. Add the pre-alloyed powder into the powder feeding box of the selective laser melting equipment, install the pre-treated base plate into the forming box of the selective laser melting equipment, then fill the forming box with inert gas to keep the volume fraction of oxygen in the forming box within a set range, set the printing parameters and start the selective laser melting equipment to print the pre-alloyed powder layer by layer onto the base plate.

[0012] S2. Separate the printed part from the base material, then protect the printed part with inert gas and vacuum seal it to obtain the sealed sample;

[0013] S3. The sealed sample is subjected to vacuum quenching to obtain the high-strength and high-toughness special alloy.

[0014] Preferably, in step S1, the base plate is a 304L stainless steel plate; the pretreatment of the base plate includes surface grinding to remove rust, degreasing treatment and cleaning with alcohol, and then preheat treatment.

[0015] More preferably, the temperature for preheating the base plate is 200–350°C and the time is 0.5–1.5 h.

[0016] Preferably, in step S1, argon gas is introduced into the molding chamber to maintain the oxygen volume fraction within the molding chamber at 100 × 10⁻⁶. -6 the following.

[0017] Preferably, in step S1, the printing parameters are as follows: the diameter of the laser spot for selective laser melting is 90-100μm, the laser power is 300-450W, the scanning speed is 500-1300mm / s, the powder thickness is 0.04-0.15mm, the scanning interval is 0.05-0.15mm, and the scanning strategy adopts strip scanning or orthogonal scanning.

[0018] In a further preferred embodiment, if the scanning strategy employs strip scanning, the rotation angle between adjacent powder layers is 67-70°.

[0019] Preferably, in step S2, the method for separating the printed part from the base plate is wire electrical discharge machining (EDM).

[0020] Preferably, the specific process of step S3 is as follows: first, the sealed sample is placed in a vacuum resistance furnace and heated to 700-850°C at a rate of 10-20°C / min, and held at that temperature for 8-10 hours. Then, oil quenching or water quenching is performed to rapidly cool the sample and obtain the high-strength and high-toughness special alloy.

[0021] The principle and beneficial effects of this invention:

[0022] The pre-alloyed powder of NiCrFe-based high-strength and high-toughness special alloy provided by the present invention has the following characteristics: 1) The powder has good flowability and is not prone to cracks and pores during additive manufacturing; 2) The high Cr content gives the alloy powder good corrosion resistance; 3) After the alloy is printed, it has a single-phase face-centered cubic FCC structure with good plasticity and toughness, which is suitable for the development of impact-resistant parts.

[0023] This invention utilizes additive manufacturing and subsequent quenching processes to prepare high-strength and high-toughness special alloys from pre-alloyed powders. The resulting special alloys exhibit high density, uniform microstructure, low residual thermal stress, and fine grains. Furthermore, they achieve a finely dispersed distribution of refractory element second phases at the interface, stabilizing the interface and balancing good strength and toughness. Attached Figure Description

[0024] Figure 1 The image shows a metallographic photograph of the NiCrFe-based special alloy in the constructed state as described in Example 1.

[0025] Figure 2 This is a scanning electron microscope image of the NiCrFe-based high-strength and high-toughness special alloy prepared in Example 1.

[0026] Figure 3 This is a transmission electron microscope (TEM) image of the NiCrFe-based high-strength and high-toughness special alloy prepared in Example 1. Detailed Implementation

[0027] The following methods for testing the relative density of samples prepared in the examples and comparative examples are as follows: the mass of the sample is weighed using a balance, its volume is measured by Archimedes' displacement method, the actual density is calculated, and the relative density of the sample is obtained by dividing the actual density by the theoretical density.

[0028] Example 1

[0029] The pre-alloyed powder of the special alloy in this embodiment is composed of the following atomic percentages: Fe 22.93%, Co 21.13%, Ni 23.99%, Cr 24.03%, Mo 7.92%.

[0030] The preparation of the special alloy in this embodiment includes the following steps:

[0031] Step 1:

[0032] Pre-alloyed powder with a particle size of 40-90μm was screened five times for additive manufacturing. The pre-alloyed powder weighed 10kg and was then vacuum-packed.

[0033] Step Two:

[0034] Pre-treatment of the base plate. The base plate is made of 304L stainless steel, with a size of 300mm×300mm. The surface is polished with 600# metallographic sandpaper to remove rust, degreased with acetone, and cleaned with alcohol. Then, it is pre-heat treated at 200℃ for 1 hour.

[0035] Step 3:

[0036] The pre-alloyed powder from step one is added to the powder feeding box of the selective laser melting equipment. The pre-treated base plate from step two is then installed in the forming box of the selective laser melting equipment. Argon gas is then introduced into the forming box to maintain the oxygen volume fraction at 100 × 10⁻⁶. -6 the following.

[0037] Step Four:

[0038] The specific printing parameters are set as follows: laser power 330-360W, scanning speed 800-1000mm / s, powder thickness 0.06-0.08mm, scanning spacing 0.08-0.1mm, strip scanning strategy, and 67° rotation angle between adjacent powder layers. The selective laser melting equipment is then started to print the pre-alloyed powder layer by layer onto the base plate.

[0039] Step 5:

[0040] The printed part is separated from the substrate using wire electrical discharge machining (EDM), followed by vacuum sealing of the printed part and protection with argon gas. The printed part is a constructed NiCrFe-based special alloy.

[0041] Step Six:

[0042] The sealed NiCrFe-based special alloy was placed in a resistance furnace and heated to 700-750℃ at a heating rate of 15-20℃ / min, and held for 8-10 hours.

[0043] Step Seven:

[0044] The sample from step six was removed and subjected to oil quenching to obtain a NiCrFe-based high-strength and high-toughness special alloy.

[0045] Figure 1 This is a metallographic photograph of the printed part, i.e., the constructed NiCrFe-based special alloy, obtained in step 5 of this embodiment. The typical molten pool structure characteristic of additive manufacturing of special alloys can be clearly observed in the image.

[0046] Figure 2 This is a scanning electron microscope (SEM) image of the NiCrFe-based high-strength and high-toughness special alloy prepared in this embodiment. The image clearly shows a hexagonal cellular crystal structure inside the molten pool of the special alloy, with a size of 650–700 nm.

[0047] Figure 3 This is a transmission electron microscope (TEM) image of the NiCrFe-based high-strength and high-toughness special alloy prepared in this embodiment. The image shows the morphology of the refractory element second phase, which is approximately spherical and distributed at the boundaries of the cellular crystal structure. Its size is 60–80 nm, and it is a Mo-rich precipitate phase.

[0048] The special alloy prepared in this embodiment has a relative density of 99.36%, an impact compressive strength of 1872 MPa, and an impact absorption energy of 210 MJ / m. 3 .

[0049] Comparative Example 1

[0050] Compared with Example 1, the only difference in this comparative example is that the laser power is 260-290W, while other conditions remain unchanged.

[0051] The special alloy prepared in this comparative example has an impact compressive strength of 1350.2 MPa and an impact absorption energy of 175 MJ / m. 3 .

[0052] Comparative Example 2

[0053] Compared with Example 1, the only difference in this comparative example is that the laser power is 460-480W, while other conditions remain unchanged.

[0054] The special alloy prepared in this comparative example has a relative density of 98.26%, an impact compressive strength of 1425.5 MPa, and an impact absorption energy of 136 MJ / m. 3 .

[0055] Comparative Example 3

[0056] Compared with Example 1, the only difference in this comparative example is that the scanning speed is 400-480 mm / s, while other conditions remain unchanged.

[0057] The special alloy prepared in this comparative example has a relative density of 97.83%, an impact compressive strength of 1585.5 MPa, and an impact absorption energy of 166 MJ / m. 3 .

[0058] Comparative Example 4

[0059] Compared with Example 1, the only difference in this comparative example is that the scanning speed is 1350-1400 mm / s, while other conditions remain unchanged.

[0060] The special alloy prepared in this comparative example has a relative density of 97.35%, an impact compressive strength of 1661 MPa, and an impact absorption energy of 173 MJ / m. 3 .

[0061] Comparative Example 5

[0062] Compared with Example 1, the only difference in this comparative example is that the heat preservation temperature is 600-690℃, while other conditions remain unchanged.

[0063] The special alloy prepared in this comparative example has a relative density of 98.31%, an impact compressive strength of 1653 MPa, and an impact absorption energy of 171 MJ / m. 3 .

[0064] Comparative Example 6

[0065] Compared with Example 1, the only difference in this comparative example is that the heat preservation temperature is 860-900℃, while other conditions remain unchanged.

[0066] The special alloy prepared in this comparative example has a relative density of 98.55%, an impact compressive strength of 1626 MPa, and an impact absorption energy of 173 MJ / m. 3 .

[0067] Comparative Example 7

[0068] The composition of the pre-alloyed powder of the special alloy used in this comparative example is the same as that in Example 1.

[0069] This comparative example uses existing conventional methods, namely powder metallurgy (plasma sintering + hot extrusion), to prepare special alloys.

[0070] The special alloy prepared in this comparative example has a relative density of 98.37%, an impact compressive strength of 1026 MPa, and an impact absorption energy of 123.5 MJ / m. 3 .

[0071] By comparing Example 1 and Comparative Example 7, it can be seen that the method of the present invention can significantly improve the impact compressive strength and impact absorption energy of special alloys.

[0072] Example 2

[0073] The pre-alloyed powder of the special alloy in this embodiment is composed of the following atomic percentages: Fe 38.99%, Co 21.12%, Ni 15.96%, Cr 21.04%, Mo 2.89%.

[0074] The preparation of the special alloy in this embodiment includes the following steps:

[0075] Step 1: Same as Step 1 in Example 1.

[0076] Step Two:

[0077] Pre-treatment of the base plate. The base plate is made of 304L stainless steel, with a size of 300mm*300mm. The surface is polished with 400# metallographic sandpaper to remove rust, degreased with acetone, and cleaned with alcohol. Then, it is pre-heat treated at a temperature of 300-350℃ for 1 hour.

[0078] Step 3: Same as Step 3 in Example 1.

[0079] Step Four:

[0080] Set the printing parameters as follows: laser power 330-340W, scanning speed 1200-1300mm / s, powder thickness 0.06-0.07mm, scanning spacing 0.1-0.12mm, strip scanning strategy, and 70° rotation angle between adjacent powder layers. Start the selective laser melting equipment to print the pre-alloyed powder layer by layer onto the base plate.

[0081] Step 5: Same as Step 5 in Example 1.

[0082] Step Six:

[0083] The sealed printed part is placed in a resistance furnace and heated to 800-850℃ at a heating rate of 15-20℃ / min, and held at that temperature for 8-10 hours.

[0084] Step 7: Same as Step 7 in Example 1.

[0085] The special alloy prepared in this embodiment has a relative density of 99.17%, an impact compressive strength of 1970 MPa, and an impact absorption energy of 217 MJ / m. 3 .

[0086] Comparative Example 8

[0087] Compared with Example 2, the only difference in this comparative example is that the laser power is 240-280W, while other conditions remain unchanged.

[0088] The special alloy prepared in this comparative example has a relative density of 98.37%, an impact compressive strength of 1431 MPa, and an impact absorption energy of 176 MJ / m. 3 .

[0089] Comparative Example 9

[0090] Compared with Example 2, the only difference in this comparative example is that the laser power is 460-500W, while other conditions remain unchanged.

[0091] The special alloy prepared in this comparative example has a relative density of 98.39%, an impact compressive strength of 1611 MPa, and an impact absorption energy of 173 MJ / m. 3 .

[0092] Comparative Example 10

[0093] Compared with Example 2, the only difference in this comparative example is that the scanning speed is 480-490 mm / s, while other conditions remain unchanged.

[0094] The special alloy prepared in this comparative example has a relative density of 97.26%, an impact compressive strength of 1512 MPa, and an impact absorption energy of 170 MJ / m. 3 .

[0095] Comparative Example 11

[0096] Compared with Example 2, the only difference in this comparative example is that the scanning speed is 1320-1400 mm / s, while other conditions remain unchanged.

[0097] The special alloy prepared in this comparative example has a relative density of 97.59%, an impact compressive strength of 1673 MPa, and an impact absorption energy of 176 MJ / m. 3 .

[0098] Comparative Example 12

[0099] Compared with Example 2, the only difference in this comparative example is that the heat preservation temperature is 600-650℃, while other conditions remain unchanged.

[0100] The special alloy prepared in this comparative example has a relative density of 98.28%, an impact compressive strength of 1753 MPa, and an impact absorption energy of 193 MJ / m. 3 .

[0101] Comparative Example 13

[0102] Compared with Example 2, the only difference in this comparative example is that the heat preservation temperature is 900-1000℃, while other conditions remain unchanged.

[0103] The special alloy prepared in this comparative example has a relative density of 98.56%, an impact compressive strength of 1516 MPa, and an impact absorption energy of 153 MJ / m. 3 .

[0104] Example 3

[0105] The pre-alloyed powder of the special alloy in this embodiment is composed of the following atomic percentages: Fe 70.41%, Cr 16.36%, Ni 10.68%, Mo 1.59%, Si 0.36%, Mn 0.60%.

[0106] The preparation of the special alloy in this embodiment includes the following steps:

[0107] Step 1: The pre-alloyed powder with a particle size of 17-70μm is screened out for additive manufacturing. The screening is performed 5 times and the weight of the pre-alloyed powder is 10kg. Then it is vacuum packaged.

[0108] Step Two:

[0109] Pre-treatment of the base plate. The base plate is made of 304L stainless steel, with a size of 300mm*300mm. The surface is polished with 400# metallographic sandpaper to remove rust, degreased with acetone, and cleaned with alcohol. Then, it is pre-heat treated at 300℃ for 1 hour.

[0110] Step 3: Same as Step 3 in Example 1.

[0111] Step Four:

[0112] Set the printing parameters as follows: laser power 350-360W, scanning speed 500-550mm / s, powder thickness 0.04-0.05mm, scanning spacing 0.12-0.15mm, and orthogonal scanning strategy. Start the selective laser melting equipment to print the pre-alloyed powder layer by layer onto the base plate.

[0113] Step 5: Same as Step 5 in Example 1.

[0114] Step Six:

[0115] The sealed printed part is placed in a resistance furnace and heated to 800-850℃ at a heating rate of 15-20℃ / min, and held at that temperature for 8-10 hours.

[0116] Step 7: Same as Step 7 in Example 1.

[0117] The special alloy prepared in this embodiment has a relative density of 99.77%, an impact compressive strength of 1699 MPa, and an impact absorption energy of 210.2 MJ / m. 3 .

[0118] Comparative Example 14

[0119] Compared with Example 3, the only difference in this comparative example is that the laser power is 250-290W, while other conditions remain unchanged.

[0120] The special alloy prepared in this comparative example has a relative density of 98.29%, an impact compressive strength of 1212 MPa, and an impact absorption energy of 135.2 MJ / m. 3 .

[0121] Comparative Example 15

[0122] Compared with Example 3, the only difference in this comparative example is that the laser power is 460-480W, while other conditions remain unchanged.

[0123] The special alloy prepared in this comparative example has a relative density of 98.68%, an impact compressive strength of 1325 MPa, and an impact absorption energy of 143.1 MJ / m. 3 .

[0124] Comparative Example 16

[0125] Compared with Example 3, the only difference in this comparative example is that the scanning speed is 450-490 mm / s, while other conditions remain unchanged.

[0126] The special alloy prepared in this comparative example has a relative density of 98.77%, an impact compressive strength of 1369 MPa, and an impact absorption energy of 145.2 MJ / m. 3 .

[0127] Comparative Example 17

[0128] Compared with Example 3, the only difference in this comparative example is that the scanning speed is 400-430 mm / s, while other conditions remain unchanged.

[0129] The special alloy prepared in this comparative example has a relative density of 97.56%, an impact compressive strength of 1369 MPa, and an impact absorption energy of 159.6 MJ / m. 3 .

[0130] Comparative Example 18

[0131] Compared with Example 3, the only difference in this comparative example is that the scanning interval is 0.03-0.04 mm, while other conditions remain unchanged.

[0132] The special alloy prepared in this comparative example has a relative density of 96.38%, an impact compressive strength of 1256 MPa, and an impact absorption energy of 146.3 MJ / m. 3 .

[0133] Comparative Example 19

[0134] Compared with Example 3, the only difference in this comparative example is that the scanning interval is 0.16-0.20 mm, while other conditions remain unchanged.

[0135] The special alloy prepared in this comparative example has a relative density of 96.55%, an impact compressive strength of 1326 MPa, and an impact absorption energy of 147.2 MJ / m. 3 .

[0136] Comparative Example 20

[0137] Compared with Example 3, the only difference in this comparative example is that the heat preservation temperature is 600-650℃, while other conditions remain unchanged.

[0138] The special alloy prepared in this comparative example has a relative density of 97.59%, an impact compressive strength of 1487 MPa, and an impact absorption energy of 173.5 MJ / m. 3 .

[0139] Comparative Example 21

[0140] Compared with Example 3, the only difference in this comparative example is that the heat preservation temperature is 900-1000℃, while other conditions remain unchanged.

[0141] The special alloy prepared in this comparative example has a relative density of 98.11%, an impact compressive strength of 1326 MPa, and an impact absorption energy of 153.6 MJ / m. 3 .

Claims

1. A NiCrFe-based high strength and toughness special alloy for additive manufacturing, characterized in that, The high-toughness special alloy is prepared from pre-alloyed powder through an additive manufacturing preparation process and a subsequent quenching process; the pre-alloyed powder is composed of the following atomic percentage components: Fe 20.93%-72.93%, Ni 9.68%-23.99%, Cr 15.36%-25.03%, Co 0.00%-22.13%, Mo 1.59%-8.92%, Si 0.00%-0.50%, and Mn 0.00%-0.70%; The high-toughness special alloy is prepared by the following preparation method: Through the additive manufacturing preparation process and the subsequent quenching process, the precipitation of the refractory element second phase at the melt pool boundary and the cellular crystal grain boundary is realized, and then the boundary is pinned, so that the high-toughness special alloy is obtained; The preparation method specifically comprises the following steps: S1. The pre-alloyed powder is added into a powder feeding box of a selective laser melting device, a pretreated substrate material is installed in a forming box of the selective laser melting device, then inert gas is filled into the forming box to keep the volume fraction of oxygen in the forming box within a set range, printing parameters are set and the selective laser melting device is started, and the pre-alloyed powder is printed and formed on the substrate material layer by layer; S2. The printed and formed piece is separated from the substrate material, then the printed and formed piece is protected by inert gas and vacuum tube sealing is performed to obtain a sealed sample; S3. The sealed sample is subjected to vacuum quenching treatment to obtain the high-toughness special alloy; In step S1, argon is filled into the molding box to keep the volume fraction of oxygen in the molding box at 100 x 10 -6 The printing parameters are as follows: the laser spot diameter of selective laser melting is 90-100 μm, the laser power is 300-450 W, the scanning speed is 500-1300 mm / s, the powder laying thickness is 0.04-0.15 mm, the scanning interval is 0.05-0.15 mm, and the scanning strategy adopts strip scanning or orthogonal scanning; the substrate material is 304L stainless steel plate; the pretreatment of the substrate material includes surface polishing, rust removal, oil removal treatment and alcohol cleaning, and then pre-heat treatment; the temperature of the pre-heat treatment is 200-350 ℃, and the time is 0.5-1.5 h; The specific process of step S3 is that the sealed sample is first placed in a vacuum resistance furnace, heated to 700-850 ℃ at a rate of 10-20 ℃ / min, and then kept for 8-10 h, and then oil quenching or water quenching treatment is performed to rapidly cool the sample to obtain the high-toughness special alloy.

2. The high toughness specialty alloy of claim 1, wherein, The preparation method of the pre-alloyed powder is that metal powder with a mass fraction of 99.9% or more is melted in a vacuum induction furnace to prepare a pre-alloyed ingot, which is then filled into an air atomization chamber for air atomization powdering to obtain the pre-alloyed powder.

3. The high toughness specialty alloy of claim 1 wherein, The particle size of the pre-alloyed powder is 17-90 μm.

4. The high toughness specialty alloy of claim 1 wherein, The high-toughness special alloy has a density of ≥ 99%, a strength under impact load of 1500-2200 MPa, and an impact absorption of 200-260 MJ / m 3 .

5. The high toughness specialty alloy of claim 1 wherein, If the scanning strategy adopts strip scanning, the scanning rotation angle of adjacent powder layers is 67-70°.

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