Laser additive manufacturing method for high-density low-defect molybdenum-rhenium alloy part

Abstract

The invention discloses a laser additive manufacturing method for a high-density low-defect molybdenum-rhenium alloy part. The method comprises the steps that firstly, molybdenum-rhenium alloy spherical powder is prepared from a molybdenum-rhenium alloy raw material bar prepared through a powder metallurgy method through a plasma rotating electrode atomization method; secondly, laser additive manufacturing equipment with a high-temperature platform and a beam shaping system is used, the molybdenum-rhenium alloy spherical powder serves as a raw material, laser powder bed melting additive manufacturing is conducted, and a molybdenum-rhenium alloy printed piece is obtained; and thirdly, the molybdenum-rhenium alloy part is obtained through hot isostatic pressing treatment. Molybdenum-rhenium alloy spherical powder high in sphericity degree and low in oxygen content is prepared through a plasma rotating electrode atomization method, a powder laying base plate is preheated through a high-temperature platform, an annular laser beam is adopted for replacing a Gaussian laser beam, a heat management partition scanning strategy and heat treatment after hot isostatic pressing are adopted, and the spherical molybdenum-rhenium alloy powder is obtained. Cracking and cracking phenomena in the laser additive manufacturing process are reduced, the high-density and low-defect molybdenum-rhenium alloy part is obtained, and the molybdenum-rhenium alloy part is suitable for a reactor core structure material and a cladding material in a space reactor.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of additive manufacturing, and particularly relates to a laser additive manufacturing method for a high-density low-defect molybdenum-rhenium alloy part. BACKGROUND

[0002] The molybdenum-rhenium alloy significantly improves the intrinsic brittleness and irradiation brittleness of molybdenum due to the "rhenium effect", and improves the processing and welding performance of the alloy, and is a very promising advanced reactor candidate cladding, heat pipe and structural material. Due to the high hardness, high melting point and serious work hardening of the molybdenum-rhenium alloy, it is difficult to prepare complex parts by traditional casting or forging process. The rapidly developing metal additive manufacturing technology can solve the problems faced by the traditional molybdenum alloy processing technology in complex shape.

[0003] Laser powder bed melting is one of the fastest growing and most widely used additive manufacturing technologies, and has been widely used in rapid preparation of iron-copper-aluminum-based alloys, stainless steel, titanium-based alloys, nickel-based high-temperature alloys and other materials, but there are still many challenges in the forming of refractory metals, such as pores and cracks which are still difficult to control defects.

[0004] The laser power required in the preparation process of refractory metals by laser powder bed melting is large, so it is inevitable to bring a large cooling rate and temperature gradient, which will produce a large thermal stress in the cooling process. Similar to other molybdenum alloys, the grain boundary of the molybdenum-rhenium alloy is very weak, and the cracking phenomenon is particularly serious under a large thermal stress. In the preparation process, the method of preheating the substrate is usually used to reduce and improve the temperature gradient. However, in the traditional laser powder bed melting process, considering the temperature resistance of various parts and seals, the preheating temperature of the substrate is generally not more than 200 DEG C, which is not obvious for refractory metals.

[0005] On the other hand, the traditional laser powder bed melting process generally uses Gaussian laser, but the peak energy of the Gaussian laser focused spot center and the edge is very different, and the width-depth ratio of the molten pool is small when it acts on the metal powder, and has a large temperature gradient and cooling rate. The instability caused by the complex melt flow dynamics and the cumulative effect of repeated heating and cooling cycles, and the anisotropic microstructure, can easily produce pores, spatter, spheroidization, cracks and other metallurgical defects, which seriously affect the strength, toughness and fatigue resistance of the formed parts.

[0006] Therefore, for the additive manufacturing of molybdenum-rhenium alloy, a preparation method is needed which can effectively improve the thermal stress cracking and defects and improve the density. SUMMARY

[0007] The technical problem solved by the present application is to provide a high-density low-defect molybdenum-rhenium alloy piece laser additive manufacturing method to solve the problems of the prior art.

[0008] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a high-density low-defect molybdenum-rhenium alloy piece laser additive manufacturing method, characterized in that the method comprises the following steps: Step one: according to the composition of the target product molybdenum-rhenium alloy piece, a powder metallurgy method is used to prepare a molybdenum-rhenium alloy raw material rod, and then a plasma rotating electrode atomization method is used to make the molybdenum-rhenium alloy raw material rod into powder, and a molybdenum-rhenium alloy spherical powder suitable for laser additive manufacturing is screened out; Step two: using a laser additive manufacturing equipment with a high-temperature platform and a beam shaping system, laser powder bed fusion additive manufacturing is carried out with the molybdenum-rhenium alloy spherical powder suitable for laser additive manufacturing obtained in step one as raw material, and a molybdenum-rhenium alloy printed piece is obtained after layer-by-layer printing; Step three: the molybdenum-rhenium alloy printed piece obtained in step two is subjected to hot isostatic pressing treatment to obtain a molybdenum-rhenium alloy piece.

[0009] The high-density low-defect molybdenum-rhenium alloy piece laser additive manufacturing method, characterized in that the molybdenum-rhenium alloy spherical powder suitable for laser additive manufacturing in step one meets the following indexes: Re mass content is 5%~45%, O mass content is not more than 0.01%, sphericity is not less than 0.9, and particle size range is 15μm~53μm.

[0010] The high-density low-defect molybdenum-rhenium alloy piece laser additive manufacturing method, characterized in that the high-temperature platform in step two can heat the powder laying substrate in the laser additive manufacturing equipment to above 350℃.

[0011] The high-density low-defect molybdenum-rhenium alloy piece laser additive manufacturing method, characterized in that the beam shaping system in step two can convert the Gaussian laser beam in the laser additive manufacturing equipment into a ring-shaped laser beam.

[0012] The high-density low-defect molybdenum-rhenium alloy piece laser additive manufacturing method, characterized in that in step two, the powder laying substrate is preheated to 350℃~450℃ before laser powder bed fusion additive manufacturing.

[0013] The aforementioned laser additive manufacturing method for high-density, low-defect molybdenum-rhenium alloy parts is characterized in that the laser process parameters for laser powder bed melting additive manufacturing in step two include: using a ring laser beam, and the outer diameter D of the ring spot. outer =150μm~350μm, inner diameter D of the annular light spot inner =80μm~200μm, laser power is 200W~500W.

[0014] The above-mentioned laser additive manufacturing method for high-density, low-defect molybdenum-rhenium alloy parts is characterized in that the scanning process parameters of the laser powder bed melting additive manufacturing in step two include: a scanning speed of 400 mm / s to 800 mm / s, a scanning spacing of 50 μm to 150 μm, a layer thickness of 30 μm to 80 μm, and an interlayer deflection angle of 67° or 90°.

[0015] The aforementioned laser additive manufacturing method for high-density, low-defect molybdenum-rhenium alloy parts is characterized by employing a thermal management zoned scanning strategy in step two: based on the size and quantity of the target molybdenum-rhenium alloy parts, each printing layer is divided into several sub-regions. Skip scanning and alternating printing are performed in different sub-regions, and laser power is reduced in high-heat areas. High-heat areas are those regions within each printing layer where heat easily accumulates. Typically, the four corners of a square molybdenum-rhenium alloy part are high-heat areas.

[0016] The above-mentioned laser additive manufacturing method for high-density, low-defect molybdenum-rhenium alloy parts is characterized in that the process parameters of the hot isostatic pressing treatment in step three include: temperature of 1300℃~1600℃, pressure of 100MPa~150MPa, holding time of 2h~4h, and protective gas of argon.

[0017] Compared with the prior art, the present invention has the following advantages: 1. This invention uses a plasma rotating electrode atomization method to prepare spherical molybdenum-rhenium alloy powder with high sphericity and low oxygen content as a raw material for subsequent laser additive manufacturing. During the laser additive manufacturing process, the grain boundaries of this powder are less affected by oxygen elements and are less prone to cracking, which greatly reduces the defects of molybdenum-rhenium alloy parts.

[0018] 2. This invention effectively reduces the cooling rate and temperature gradient during the laser additive manufacturing process by configuring a high-temperature platform in the laser additive manufacturing equipment to preheat the powder-coated substrate, thereby reducing cracking caused by thermal stress and further reducing defects in molybdenum-rhenium alloy parts.

[0019] 3、The present application effectively reduces the thermal stress cracks caused by excessive temperature gradient during the solidification process of molybdenum-rhenium alloy, avoids the molten pool splashing and spoon hole defects caused by the excessive concentration of Gaussian laser beam spot energy, improves the uniformity and stability of the molten pool spreading and cooling process, and improves the overall quality of the molybdenum-rhenium alloy parts.

[0020] 4、The present application adopts a thermal management partition scanning strategy, which significantly prolongs the heat dissipation time, thereby indirectly reducing the cooling rate and temperature gradient, and further inhibiting the generation of defects and cracks in the molybdenum-rhenium alloy parts.

[0021] 5、The present application adopts a hot isostatic pressing and heat treatment, which further improves the density of the molybdenum-rhenium alloy parts and reduces defects and cracks.

[0022] The technical solutions of the present application will be further described in detail below with the help of the accompanying drawings and examples. DRAWINGS

[0023] Figure 1 It is a schematic diagram of the Gaussian spot and radial temperature distribution generated by the Gaussian laser beam in the prior art laser additive manufacturing equipment.

[0024] Figure 2 It is a schematic diagram of the ring-shaped spot and radial temperature distribution generated by the ring-shaped laser beam in the additive manufacturing equipment of the present application.

[0025] Figure 3 It is a schematic diagram of the thermal management partition scanning strategy adopted in the laser powder bed melting additive manufacturing of Example 1 of the present application.

[0026] Figure 4 It is a schematic diagram of the high-heat zone division and determination in the thermal management partition scanning strategy of Example 1 of the present application.

[0027] Figure 5 It is a scanning electron microscope image of the surface morphology of the molybdenum-rhenium alloy part prepared in Example 1 of the present application.

[0028] Figure 6 It is a metallographic micrograph of the build direction section of the molybdenum-rhenium alloy part prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0029] Figure 1 It is a schematic diagram of the Gaussian spot and radial temperature distribution generated by the Gaussian laser beam in the prior art laser additive manufacturing equipment, wherein Figure a is the shape of the Gaussian spot, and Figure b is a schematic diagram of the radial temperature distribution of the Gaussian spot, Figure 2 It is a schematic diagram of the ring-shaped spot and radial temperature distribution generated by the ring-shaped laser beam in the additive manufacturing equipment of the present application, wherein Figure a is the shape of the Gaussian spot, and Figure b is a schematic diagram of the radial temperature distribution of the Gaussian spot,Figure 1 Compared with Figure 2 , it can be seen that the Gaussian light spot has higher center energy and higher temperature, and the instantaneous melt depth is large and the molten pool width is narrow, and the molten pool stability is poor, and splashes and spoon holes are easy to occur. The double-peak temperature distribution of the annular light spot has a wider energy distribution under the same power, the center temperature is lower, the melt depth is shallow but the molten pool is wide, so the molten pool stability is better, the splashes are less, and the spoon holes are not easy to occur.

[0030] Example 1 This example includes the following steps: Step 1: According to the composition of the target product molybdenum-rhenium alloy part (Re mass content is 14%), a molybdenum-rhenium alloy raw material rod with a diameter of φ50mm and a Re mass content of 14% is prepared by a powder metallurgy method, processed into an electrode rod, and then an electric plasma rotating electrode atomization method is used to prepare a powder, and a molybdenum-rhenium alloy spherical powder suitable for laser additive manufacturing is screened out. The molybdenum-rhenium alloy spherical powder meets the following indicators: Re mass content is 14%, O mass content is 0.005%, sphericity is 0.93, and particle size range is 15μm~53μm; Step 2: Using a laser additive manufacturing equipment with a high-temperature platform and a beam shaping system, the molybdenum-rhenium alloy spherical powder suitable for laser additive manufacturing in step 1 is used as raw material for laser powder bed fusion additive manufacturing: first, the powder laying substrate is preheated to 350℃ using the high-temperature platform, and argon is introduced. When the oxygen content in the chamber is reduced to 0.002%, the powder laying and printing are started. The beam shaping system emits an annular laser beam during printing, and the outer diameter D outer of the annular light spot is 350μm, the inner diameter D inner of the annular light spot is 200μm, the laser power is 500W, the scanning speed is 600mm / s, the scanning interval is 150μm, the layer thickness is 30μm, the layer deflection angle is 67°, and the laser powder bed fusion additive manufacturing adopts a heat management zoning scanning strategy as shown in Figure 3 : the substrate size is 80mm×80mm, the target product molybdenum-rhenium alloy part size is 10mm×10mm×10mm, a total of 9 pieces are printed, so each layer is divided into 9 subintervals, each subinterval corresponds to one molybdenum-rhenium alloy part, and the adjacent subintervals in the direction of 45° are rows. The 9 different subintervals are sequentially scanned and printed alternately in rows, and the scanning order is shown in Figure 3 Fig. a, since the scanning speed is 600mm / s, when the scanning line length is less than 3mm, the scanning line time interval is less than 5ms, and all the regions with scanning line time interval less than 5ms are divided into high heat zones, as shown in Figure 4 Fig. a, the laser power is reduced to 70% for printing in the high heat zone, and the molybdenum-rhenium alloy printed part is obtained after layer-by-layer printing; Step three, the molybdenum-rhenium alloy printing piece obtained in step two is subjected to hot isostatic pressing treatment, the temperature is 1400℃, the pressure is 120 MPa, the holding time is 3h, the protective gas is argon, and a molybdenum-rhenium alloy piece is obtained, the surface of the molybdenum-rhenium alloy piece is smooth and flat, and the density reaches 10.95g / cm 3 (theoretical density 11.03 g / cm 3 , and the relative density reaches 99%).

[0031] Figure 5 The scanning electron microscope image of the surface morphology of the molybdenum-rhenium alloy piece prepared in this embodiment is shown in Figure 5 It can be seen that the molten pool of this embodiment is relatively stable by emitting a ring-shaped laser beam and using a ring-shaped spot for printing, which can effectively spread and overlap each other, and no obvious cracks occur after solidification.

[0032] Figure 6 The metallographic micrograph of the build direction section of the molybdenum-rhenium alloy piece prepared in this embodiment is shown in Figure 6 It can be seen that the structure along the build direction section is uniform, the crystallization form is regular, the grain boundary is clear, and there is no obvious visible defect or crack.

[0033] Example 2 This embodiment includes the following steps: Step one, according to the composition of the target product molybdenum-rhenium alloy piece (Re mass content is 5%), a molybdenum-rhenium alloy raw material rod with a diameter of φ50mm and a Re mass content of 5% is prepared by a powder metallurgy method, and is processed into an electrode rod, then is made into a powder by a plasma rotating electrode atomization method, and a molybdenum-rhenium alloy spherical powder suitable for laser additive manufacturing is screened out, which meets the following indexes: Re mass content is 5%, O mass content is 0.01%, sphericity is 0.9, and particle size range is 15μm~53μm; Step two, using a laser additive manufacturing equipment with a high-temperature platform and a beam shaping system, laser powder bed melting additive manufacturing is carried out with the molybdenum-rhenium alloy spherical powder suitable for laser additive manufacturing in step one as raw material: first, the powder laying substrate is preheated to 450℃ by using the high-temperature platform, and argon is introduced, and when the oxygen content in the chamber is reduced to 0.002%, the powder laying printing is started, and a ring-shaped laser beam is emitted by using the beam shaping system during printing, and the outer diameter D outer of the ring-shaped spot is 150μm, the inner diameter D inner of the ring-shaped spot is 80μm, the laser power is 200W, the scanning speed is 400mm / s, the scanning interval is 50μm, the layer thickness is 50μm, the layer deflection angle is 90°, and the laser powder bed melting additive manufacturing adopts the following parameters: Figure 3The heat management partition scanning strategy is shown: the substrate size is 80 mm x 80 mm, the target product molybdenum-rhenium alloy part size is 10 mm x 10 mm x 10 mm, a total of 4 parts are printed, so each layer printing area is divided into 4 sub-intervals, each sub-interval corresponds to one molybdenum-rhenium alloy part, the adjacent sub-intervals in the direction of 45° are rows, and the 4 different sub-intervals are sequentially scanned and printed in turn, the scanning order is as follows Figure 3 As shown in FIG. b, when the scanning line length is less than 2 mm, the scanning line time interval is less than 5 ms, and the scanning speed is 400 mm / s, the regions with all scanning line time intervals less than 5 ms are divided into high heat areas, as shown in FIG. b Figure 4 As shown in FIG. b, the laser power is reduced to 70% in the high heat area for printing, and the molybdenum-rhenium alloy printed part is obtained after layer-by-layer printing; Step three, the molybdenum-rhenium alloy printed part obtained in step two is subjected to hot isostatic pressing treatment, the temperature is 1300℃, the pressure is 100MPa, the holding time is 2h, and the protective gas is argon, to obtain a molybdenum-rhenium alloy part, the surface of the molybdenum-rhenium alloy part is smooth and flat, and the density reaches 10.99g / cm 3 (theoretical density 11.03 g / cm 3 , relative density reaches 99%).

[0034] Example 3 This example includes the following steps: Step one, according to the composition of the target product molybdenum-rhenium alloy part (Re mass content is 45%), a molybdenum-rhenium alloy raw material rod with a diameter of φ50mm and a Re mass content of 45% is prepared by a powder metallurgy method, processed into an electrode rod, and then made into a powder by a plasma rotating electrode atomization method, and a molybdenum-rhenium alloy spherical powder suitable for laser additive manufacturing is screened out, which meets the following indexes: Re mass content is 45%, O mass content is 0.004%, sphericity is 0.95, and particle size range is 15μm~53μm; Step two, using a laser additive manufacturing equipment with a high-temperature platform and a beam shaping system, laser powder bed melting additive manufacturing is carried out with the molybdenum-rhenium alloy spherical powder suitable for laser additive manufacturing in step one as raw material: first, the powder laying substrate is preheated to 400℃ by using the high-temperature platform, and argon is introduced, and when the oxygen content in the chamber is reduced to 0.002%, the powder laying printing is started, and a ring-shaped laser beam is emitted by using the beam shaping system during printing, and the ring-shaped spot outer diameter D outer =200μm, the ring-shaped spot inner diameter D inner =100μm, the laser power is 300W, the scanning speed is 800mm / s, the scanning interval is 100μm, the layer thickness is 80μm, the layer deflection angle is 90°, and the laser powder bed melting additive manufacturing adopts the heat management partition scanning strategy as shown in FIG. a Figure 3The heat management partition scanning strategy shown: the substrate size is 80mm*80mm, the target product molybdenum rhenium alloy part size is 10mm*10mm*10mm, a total of 16 parts are printed, so each layer printing area is divided into 16 subintervals, each subinterval corresponds to a molybdenum rhenium alloy part, the adjacent subintervals in the direction of 45° are rows, and the 16 different subintervals are sequentially jumped and printed in turn, the scanning order is as follows Figure 3 As shown in FIG. c, when the scanning line length is less than 4mm, the scanning line time interval is less than 5ms, and the area with all scanning line time intervals less than 5ms is divided into a high heat area, as shown in FIG. Figure 4 As shown in FIG. c, the laser power is reduced to 70% in the high heat area for printing, and the molybdenum rhenium alloy printed part is obtained after layer-by-layer printing. Step three: the molybdenum rhenium alloy printed part obtained in step two is subjected to hot isostatic pressing treatment, the temperature is 1600℃, the pressure is 150MPa, the holding time is 4h, the protective gas is argon, and the molybdenum rhenium alloy part is obtained, the surface of the molybdenum rhenium alloy part is smooth and flat, and the density reaches 11.01g / cm 3 (the theoretical density is 11.03 g / cm 3 , and the relative density reaches 99%).

[0035] The above is only a preferred embodiment of the present application, and does not limit the present application. Any simple modification, change and equivalent change of the above embodiment according to the technical essence of the present application still belongs to the protection scope of the technical solution of the present application.

Claims

1. A method for laser additive manufacturing of high density low defect molybdenum rhenium alloy components, characterized by, The method comprises the following steps: Step one, according to the composition of the target product molybdenum-rhenium alloy part, a molybdenum-rhenium alloy raw rod is prepared by a powder metallurgy method, and then the molybdenum-rhenium alloy raw rod is made into powder by a plasma rotating electrode atomization method, and a molybdenum-rhenium alloy spherical powder suitable for laser additive manufacturing is screened out; Step two, using a laser additive manufacturing equipment with a high-temperature platform and a beam shaping system, laser powder bed fusion additive manufacturing is carried out with the molybdenum-rhenium alloy spherical powder suitable for laser additive manufacturing in step one as raw material, and a molybdenum-rhenium alloy printed part is obtained after layer-by-layer printing; Step three, the molybdenum-rhenium alloy printed part obtained in step two is subjected to hot isostatic pressing treatment to obtain a molybdenum-rhenium alloy part.

2. A method of laser additive manufacturing of high density low defect molybdenum rhenium alloy parts according to claim 1, characterized in that, The molybdenum-rhenium alloy spherical powder suitable for laser additive manufacturing in step one meets the following indexes: Re mass content is 5%~45%, O mass content is not more than 0.01%, sphericity is not less than 0.9, and particle size range is 15μm~53μm.

3. The method of claim 1, wherein the method is characterized by: The high-temperature platform in step two can heat the powder laying substrate in the laser additive manufacturing equipment to above 350℃.

4. The method of claim 1, wherein the method is a laser additive manufacturing method of a high-density low-defect molybdenum-rhenium alloy part, characterized in that, The beam shaping system in step two can convert the Gaussian laser beam in the laser additive manufacturing equipment into a ring-shaped laser beam.

5. The method of claim 1, wherein the method is a laser additive manufacturing method of a high-density low-defect molybdenum-rhenium alloy part, characterized in that, In the laser powder bed fusion additive manufacturing in step two, the powder laying substrate is preheated to 350℃~450℃.

6. The method of claim 1, wherein the method is a laser additive manufacturing method of a high-density low-defect molybdenum-rhenium alloy component, characterized by, The laser process parameters of the laser powder bed fusion additive manufacturing in step two include: adopting a ring laser beam, and the outer diameter D outer of the ring-shaped spot is 150 μm ~ 350 μm, the inner diameter D inner of the ring-shaped spot is 80 μm ~ 200 μm, and the laser power is 200 W ~ 500 W.

7. The method of claim 1, wherein the method is a laser additive manufacturing method of a high-density low-defect molybdenum-rhenium alloy part, characterized in that, The scanning process parameters of the laser powder bed fusion additive manufacturing in step two include: scanning speed is 400mm / s~800mm / s, scanning interval is 50μm~150μm, layer thickness is 30μm~80μm, and layer deflection angle is 67° or 90°.

8. The method of claim 1, wherein the method is a laser additive manufacturing method of a high-density low-defect molybdenum-rhenium alloy part, characterized in that, The laser powder bed fusion additive manufacturing in step two adopts a thermal management partition scanning strategy: according to the size and quantity of the target product molybdenum-rhenium alloy part, each layer printing area is divided into several sub-areas, and jump scanning and alternate printing are carried out in different sub-areas, and printing is carried out in the high heat area with reduced laser power.

9. The method of claim 1, wherein the method is a laser additive manufacturing method of a high-density low-defect molybdenum-rhenium alloy part, characterized in that, The process parameters of the hot isostatic pressing treatment in step three include: temperature is 1300℃~1600℃, pressure is 100MPa~150MPa, holding time is 2h~4h, and protective gas is argon.

Images