Gradient metal additive manufacturing method based on cross-scale collaborative interface strengthening

Abstract

The invention provides a gradient metal additive manufacturing method based on cross-scale collaborative interface strengthening. The implementation object of the additive manufacturing method is a heterogeneous interlayer interface of a gradient metal structure, corresponding cross-scale cooperative strengthening is jointly achieved based on bimetal macroscopic interface tooth-shaped meshing strengthening and microcosmic interface atom interaction diffusion strengthening, and the additive manufacturing method has the advantages of being high in reliability, wide in application system and convenient and fast to regulate and control. According to the specific means, a child-mother meshing structure is arranged on the two sides of the bimetallic interface for macroscopic strengthening, an atomic interaction diffusion layer with the specific thickness is formed on the bimetallic interface for microcosmic strengthening in combination with an additive process design, and therefore the macro-micro cross-scale cooperative strengthening effect of the heterogeneous interface is achieved. Based on the method, the heterogeneous metal structure interface can be effectively strengthened, the weak mechanical property area of the interface is eliminated, the method is particularly suitable for parts with severe and complex service loads, and the service life is prolonged.

Description

Technical Field

[0001] The invention relates to a gradient metal additive manufacturing method based on cross-scale collaborative interface strengthening, and belongs to the field of additive manufacturing methods. Background Art

[0002] Gradient metals are advanced structural materials composed of two or more metal materials. Compared with conventional homogeneous materials, they have the characteristics of gradient changes in mechanical properties and high designability of material layout, and can simultaneously exert the performance advantages of multiple metals. Gradient metals are oriented to the needs of specific service scenarios, giving parts and components differentiated performance in different positions, which not only promotes weight reduction and fatigue life improvement, but also makes the parts heat-resistant, corrosion-resistant and wear-resistant. Additive manufacturing is an important technical means for the research and development of gradient structures. Compared with traditional preparation technologies such as powder metallurgy and high-temperature self-propagation, it has the advantages of flexible and convenient design and the ability to form complex structures. By using multiple material feeding mechanisms to coordinate and control the feeding rate, various types of gradient structures can be quickly trial-produced. At present, the application of gradient metal structures in the aerospace field is concentrated in rocket engine combustion chambers, gradient wing ribs, heterogeneous radiators, etc. However, the failure of gradient structures during service mostly occurs at heterogeneous interfaces, and their promotion and use are limited by the interlayer interfaces with relatively weak mechanical properties. In addition, when there are intermetallic compounds between the constituent elements of dissimilar metals, brittle compounds are often formed at the gradient interface, further leading to the deterioration of interface performance. Therefore, in order to promote the engineering application of gradient metal materials / structures, it is urgent to develop matching heterogeneous interface strengthening technologies.

[0003] Comprehensively considering the existing gradient metal interface structure design methods, there are three main types: direct transition, composition transition and barrier layer transition. The heterogeneous metal interface with direct transition is not specially treated, and changes from a single material to another material in a natural transition manner, which is only applicable to the same type of metal materials. When selecting the composition transition, a transition layer is prepared at the interface by parameter control, and the element content gradient is completed with a transition layer of a certain thickness to alleviate the interface stress concentration caused by material mutation. The interface composition transition can be further divided into composition continuous transition and composition gradient transition. The former is a transition layer with continuously changing element content obtained by mixing multiple materials in the preparation stage, and the latter is a gradient composition transition layer obtained by adjusting the fixed composition ratio of the transition layer. The barrier layer transition method is suitable for gradient materials with intermetallic compounds, such as high-temperature alloy-titanium alloy. In order to avoid the interfacial brittle cracking caused by the cross-diffusion of elements at the interface to form brittle intermetallic compounds, an additional layer is often introduced between the heterogeneous metals to inhibit the original bimetallic cross-diffusion and harmful phase formation. At the same time, the gradient metal heterogeneous interface can also form a fine-grained zone at the interface through multi-energy field composite additive technology, and hot isostatic pressing treatment can also be used to heal local pores and unfused defects on the interface.

[0004] However, most of the existing interface structure design methods and strengthening technologies are based solely on the interface morphology, composition and structure. Although gradient materials can be prepared for homogeneous metals such as titanium alloy-titanium alloy, for systems with intermetallic compounds or material systems with large differences in physical and chemical properties such as ceramic-metal, interface cracking failure is still the main factor limiting the promotion and application of gradient structures. Although the composition transition and barrier layer transition interface design can release the stress concentration caused by interface thermal mismatch to a certain extent, the heterogeneous interface still has a composition mutation layer at the microscale. What is more serious is that the interface between transition layers with different composition ratios introduces a new weak interface in the gradient structure. Although the interface fine grain area and dislocation-dense area based on multi-energy field composite manufacturing can improve the mechanical properties of the interface in situ, the interface microstructure cannot be stably present under the action of concentrated heating and melting of high-energy beams, and the multi-energy field interaction mechanism is complex. When promoting it between different gradient metal systems, it is necessary to re-explore the process parameters, which is not universal. Therefore, the existing technical means cannot fundamentally strengthen the heterogeneous interface of gradient metals. Summary of the invention

[0005] The purpose of the present invention is to provide a gradient metal additive manufacturing method based on cross-scale collaborative interface strengthening. The interface morphology design method is adopted to design a tooth-shaped meshing structure at the bimetallic interface to achieve macroscopic strengthening, and the additive process is controlled to form a fixed thickness atomic interdiffusion layer at the bimetallic interface to achieve microscopic strengthening, thereby achieving cross-scale collaborative strengthening of the gradient structure heterogeneous interface. Through a series of steps of interface macroscopic meshing structure design-laser precision additive manufacturing of base metal-parameter control manufacturing of interface atomic diffusion layer-secondary additive manufacturing of gradient metal structure, the gradient material heterogeneous interface is strengthened.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A gradient metal additive manufacturing method based on cross-scale collaborative interface strengthening, wherein the cross-scale collaborative strengthening is achieved through a macro-scale interface meshing structure and a micro-scale interface atomic interdiffusion layer. The specific method is divided into heterogeneous material interface tooth-shaped meshing structure design and precise additive forming and moderate composition gradient atomic interdiffusion layer additive manufacturing. The overall manufacturing process of the gradient metal involved in the present invention is: gradient metal interface meshing structure design - base metal laser additive manufacturing - interface atomic interdiffusion layer design and manufacturing - gradient metal overall additive manufacturing.

[0008] A gradient metal additive manufacturing method based on cross-scale synergistic interface strengthening comprises the following steps:

[0009] Step 1: Design of gradient metal interface meshing structure. The design criteria of the meshing structure mainly refer to the specific material type. For homogeneous metals with similar physical and chemical properties, the interface meshing structure is a uniform geometry; for metals with large differences in physical and chemical properties, such as high-temperature alloys-titanium alloys, the interface structure is a variable-size staggered structure.

[0010] Step 2: Laser additive manufacturing of the base metal. For the base A alloy, laser additive manufacturing is performed with preset process parameters. When forming to the upper surface, the laser power and scanning rate are reduced to control the precise shape control manufacturing of the tooth meshing structure.

[0011] Step 3: Design and manufacture of the interfacial atomic interdiffusion layer. Based on the additively manufactured matrix A alloy, the additive surface is moderately polished to remove local undulations such as surface adhesion particles. Around the A / B gradient metal interface atomic interdiffusion layer, the laser power is moderately increased, the working distance and the scanning rate are reduced to enhance the remelting and melt stirring of the tooth meshing surface of the A alloy, promote atomic interdiffusion, and solidify to form an interfacial atomic interdiffusion layer of a certain thickness.

[0012] Step 4: Gradient metal integral additive manufacturing. Based on the cross-scale synergistic strengthening of heterogeneous metal interfaces obtained in steps 1 to 3, high-efficiency additive manufacturing of B alloy is performed to obtain A / B gradient titanium alloy parts.

[0013] Furthermore, the gradient metal additive manufacturing method may involve homogeneous metals, such as titanium alloy-titanium alloy, or heterogeneous metals, such as titanium alloy-copper alloy, titanium alloy-high temperature alloy. When adding heterogeneous metals, it is necessary to add barrier layer screening and manufacturing links between step two and step three based on the compound formation between the materials. In addition, the interface strengthening technology of the gradient additive can be further extended to the metal surface cladding corrosion-resistant, wear-resistant, and high-temperature resistant ceramic systems.

[0014] Furthermore, the gradient metal interface meshing structure is designed. The meshing tooth shapes include triangles, rectangles and trapezoids. The size of a single meshing structure is 3 to 10 mm, and it is divided into uniform type and variable size staggered type according to the uniform distribution type. The smaller the size of the meshing structure, the greater the interface bite area, and the stronger the corresponding strengthening effect, but the difficulty of controlling the unfused defects in the secondary laser additive process of the corresponding surface increases. The variable size staggered meshing teeth specifically refer to the regular change of a single structure size (such as from small to high) or the coupling of multiple types of structures (such as triangle-rectangle).

[0015] Furthermore, the design criteria of the interface macro-meshing structure are that for materials with similar physical and chemical properties, the uniform distribution of a single meshing tooth shape is given priority, such as a triangular meshing interface with a side length of 4 mm. For materials with large differences in properties such as thermal expansion performance, priority is given to adjusting the structural dimensions of the meshing teeth, such as a triangular meshing interface with a side length of 3 to 8 mm. If simply changing the structural dimensions cannot strengthen the interface, multiple types of meshing tooth coupling are introduced.

[0016] Furthermore, the design and manufacture of the interfacial atomic interdiffusion layer aims to form an element interdiffusion layer of a certain thickness (200 to 500 μm) at the heterogeneous metal interface, so that the element content at the microscopic scale changes gently along the interface, thereby reducing stress concentration caused by sudden changes in element content across the interface.

[0017] Furthermore, the preparation of the interfacial atomic inter-diffusion layer is achieved by regulating the stirring of the molten pool based on the additive process. The parameter combination of high laser power, low scanning rate and working distance promotes the remelting of the upper surface of the A alloy meshing structure on the one hand, and on the other hand, intensifies the stirring and mixing of the molten pool to promote the inter-mixing between elements, thereby forming an inter-diffusion layer of a specific thickness at the heterogeneous metal interface to complete the microscale interface strengthening.

[0018] Furthermore, the specific method for adjusting the parameters of the interface atomic interdiffusion layer is to use the high-quality additive forming parameter combination of B alloy as α. When preparing the interface atomic interdiffusion layer, the laser power is increased by 10-20% compared with the parameter combination α, the scanning rate is reduced by 5-10%, and the working distance is reduced by 1-2 mm.

[0019] Furthermore, when the forming accuracy requirements for specific gradient parts are high, the A metal forming process of the present invention can adopt laser selective melting forming to accurately manufacture the required interface tooth structure. When the specific part size is large and the deposition efficiency needs to reach a certain level, laser melting deposition, laser fuse deposition and arc fuse deposition technology can be adopted.

[0020] Compared with the existing gradient metal interface control technology, the present invention has the following advantages:

[0021] 1) Multi-scale synergistic strengthening, high reliability. The interface preset tooth meshing not only macroscopically strengthens the interface, but also effectively blocks crack propagation by the meshing structure. Combined with the interface atomic inter-diffusion layer to eliminate the composition mutation layer, the gradient interface is strengthened at the micro scale. Compared with the gradient interface control technology that simply relies on composition transition and barrier layer transition, it has higher reliability.

[0022] 2) Widely applicable systems. The macro-micro cross-scale interface strengthening technology based on the present invention is universal and not only applicable to the additive forming of homogeneous metals and heterogeneous metals, but also can be transferred to scenes such as functional gradient ceramics, ceramic-metal heterostructure additive forming and metal surface ceramic layer cladding.

[0023] 3) Flexible and convenient process control. The macroscopic interface tooth meshing corresponding to the present invention is introduced for the purpose of increasing the heterogeneous interface bonding area. The corresponding preparation process window is wide, and there is no excessively high precision requirement for the structural size, type and distribution uniformity of the meshing teeth. Similarly, the realization of the microscopic atomic interdiffusion layer only requires its thickness, so that the operator can design the interface structure and implementation method according to the needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the gradient metal laser additive manufacturing process based on cross-scale synergistic interface strengthening;

[0025] FIG2( a ) is a schematic diagram of a gradient metal interface tooth meshing structure of a single meshing structure;

[0026] FIG2( b ) is a schematic diagram of a tooth meshing structure of a variable-size staggered gradient metal interface;

[0027] Figure 2(c) is a schematic diagram of the meshing structure of the gradient metal interface tooth profile from small to high;

[0028] Figure 2(d) is a schematic diagram of the tooth meshing structure of the gradient metal interface with multi-type structural coupling;

[0029] Figure 3 This is a schematic diagram of the gradual change of the composition of the atomic interdiffusion layer at the gradient metal interface;

[0030] Figure 4 (a) is an optical metallographic photograph of a gradient metal cross section;

[0031] Figure 4 (b) is a macroscopic tooth meshing photo of the surface of the additively formed copper alloy and niobium alloy;

[0032] Figure 5 This is an optical metallographic photograph of a gradient metal interface with only the interface composition transition.

[0033] In the figure: 1-base A alloy, 2-tooth meshing structure, 3-laser cladding head, 4-gradient metal interface atomic interdiffusion layer, 5-illustration of element content change, 6-B alloy, 7-copper alloy, 8-niobium alloy, 9-zirconium alloy, 10-primitive coarse dendrites, 11-interface spherical pores. DETAILED DESCRIPTION

[0034] Figure 1Figure 2 is a schematic diagram of the gradient metal laser additive manufacturing process based on cross-scale collaborative interface strengthening. Figure 3 is a schematic diagram of various types of gradient metal interface tooth meshing structures. Figure 3 This is a schematic diagram of the gradual change of the composition of the atomic interdiffusion layer at the gradient metal interface. Figure 4 This is a metallographic photograph of the gradient structure of zirconium alloy-niobium alloy-copper alloy after cross-scale synergistic interface strengthening. Figure 5 This is an optical metallographic photograph of a gradient metal interface with only the interface composition transition.

[0035] Gradient metal interface meshing structure design. Referring to the material types contained in the specific gradient metal, for homogeneous metals with similar physical and chemical properties, such as titanium alloy-titanium alloy, the corresponding interface meshing structure is preferentially considered to be a uniform geometry; for metals with large differences in physical and chemical properties, such as high-temperature alloy-titanium alloy, the interface structure is a variable-size staggered shape.

[0036] Laser additive manufacturing of matrix metals. Figure 1 As shown in a, for the matrix A alloy 1, the laser additive manufacturing of the matrix is ​​performed with preset process parameters such as laser power, scanning rate, overlap rate, etc. When forming to the upper surface, the laser power, scanning rate, etc. of the forming process are reduced to control the relatively precise shape control manufacturing of the tooth meshing structure 2, such as Figure 1 b. In order to strengthen the gradient metal heterogeneous interface and avoid the formation of coarse dendrites growing along the deposition direction across the interface, when depositing the tooth-shaped meshing structure, the scanning direction of the laser cladding head 3 is perpendicular to the original scanning direction of the base metal. Based on the adjusted laser additive process parameters, a preset tooth-shaped fitting structure is made on the surface of alloy A.

[0037] Design and manufacture of atomic interdiffusion layer at the interface. Based on the matrix A alloy of additive manufacturing, the surface of the additive is moderately polished to remove local undulations such as surface adhesion particles. Around the A / B gradient metal interface atomic interdiffusion layer 4, such as Figure 1 As shown in Figure c, the laser power is moderately increased, the working distance and the scanning rate are reduced to enhance the remelting and melt stirring of the tooth meshing surface of alloy A, promote atomic cross-diffusion, and thus solidify to form an interfacial atomic cross-diffusion layer of a certain thickness. In the atomic cross-diffusion layer, the content of the constituent elements of alloy A and alloy B changes almost continuously along the deposition direction.

[0038] Gradient metal integral additive manufacturing. Based on the cross-scale synergistic strengthening of heterogeneous metal interfaces obtained in steps 1 to 3, high-efficiency additive manufacturing of B alloy 6 is performed, such as Figure 1 As shown in (d), an A / B gradient titanium alloy product is obtained, and the heterogeneous interface shows a tight metallurgical bonding as a whole.

[0039] In the design stage of the macro-scale tooth meshing structure of the gradient metal interface, the meshing tooth shapes that can be selected include triangle, trapezoid and rectangle, etc. As shown in Figure 2, the size of a single meshing structure is 3 to 10 mm, and it can be divided into uniform type according to the uniform distribution type. Figure 2a and 2b and variable size staggered type. The smaller the size of the meshing structure, the larger the interface bite area, and the stronger the corresponding strengthening effect, but the difficulty of controlling the unfused defects in the corresponding surface secondary laser additive process increases. In addition, variable size staggered meshing teeth specifically refer to the regular change of a single structure size, such as from small to high, such as Figure 2c or multi-type structural coupling Figure 2d .

[0040] For the gradient metal interface micro-scale element inter-diffusion layer, its preparation is realized by controlling the molten pool stirring based on the additive process, such as Figure 3 As shown in FIG. 1 , when the meshing tooth surface is subjected to secondary laser additive manufacturing of alloy B, the laser power is appropriately adjusted to increase by 10-20%, the scanning rate is reduced by 5-10%, and the working distance is lowered by 1-2 mm to form a composition gradient layer at the interface, such as Figure 3 As shown in the local enlarged image, micro-scale interface strengthening is achieved.

[0041] In this embodiment, copper alloy 7, niobium alloy 8 and zirconium alloy 9 are selected as gradient additive objects, and copper alloy-niobium alloy-zirconium alloy are sequentially laser additively formed. The metal powder used has high sphericity and high purity> 99.9%, and is produced by radio frequency plasma spheroidization. The additive equipment is an infrared fiber laser based on a wavelength of 1040nm and a maximum power of 5000W. Gradient metal interface meshing structure design. The copper alloy-niobium alloy interface selects a triangular tooth meshing structure, and the niobium alloy-zirconium alloy interface selects a wavy meshing structure.

[0042] Laser additive manufacturing of gradient metal structures in the deposition sequence of copper alloy-niobium alloy-zirconium alloy. When forming to the upper surface of copper alloy and niobium alloy, the laser power and scanning rate of the forming process are reduced to control the relatively precise shape control manufacturing of triangular and wavy meshing structures. The optical metallographic photos of the gradient metal cross section are shown in Figure 2. Figure 4 As shown in a.

[0043] Design and fabrication of interfacial atomic interdiffusion layer. After the macroscopic tooth-shaped meshing structure of the copper alloy and niobium alloy surface is formed by additive manufacturing, the laser additive manufacturing process parameters are adjusted to prepare the heterogeneous interfacial atomic interdiffusion layer, such as Figure 4 As shown in b, after the formation of the interfacial atomic interdiffusion layer, the primary coarse dendrite 10 is suppressed near the heterogeneous interface, thereby avoiding coarse structure across the interface. In the atomic interdiffusion layer, the element content changes almost continuously along the deposition direction. The heterogeneous interface of the zirconium alloy / niobium alloy / copper alloy gradient metal structure after integrated forming is closely metallurgically bonded, with no obvious defects inside, showing high forming quality.

[0044] Comparative Example 1

[0045] The gradient alloy system of this comparative example is zirconium alloy and niobium alloy, and the additive manufacturing equipment and laser additive parameters of each layer remain unchanged. The heterogeneous alloy interface is transitioned in the form of composition transition, and the metal powder used is high sphericity and high purity> 99.9%, which is prepared by radio frequency plasma spheroidization. The additive equipment is based on an infrared fiber laser with a wavelength of 1040nm and a maximum power of 5000W.

[0046] When designing the heterogeneous metal interface structure, the process parameters are adjusted to make the element content in the transition layer gradually change layer by layer, thereby completing the interlayer transition from niobium alloy to zirconium alloy. Figure 5 As shown in the figure, spherical pores 11 with a diameter of 40 μm appear at the interlayer interface, and microcracks are formed along the horizontal direction of the interface. Only the composition transition method cannot fully release the thermal stress of the heterogeneous metal additive manufacturing process.

Claims

1. A gradient metal additive manufacturing method based on cross-scale synergistic interface strengthening, characterized in that: The following steps are involved: Step 1: Design of gradient metal interface meshing structure; Design criteria for meshing structure: For homogeneous metals with similar physical and chemical properties, the interface meshing structure is uniform in geometry; for metals with greatly different physical and chemical properties, the interface structure is variable-size staggered; Step 2: Laser additive manufacturing of base metal; For the matrix A alloy, laser additive manufacturing is performed with preset process parameters. When forming to the upper surface, the laser power and scanning rate are reduced to control the precise shape control manufacturing of the tooth meshing structure; Step 3: Design and manufacture of interface atomic interdiffusion layer; Based on the additively manufactured matrix A alloy, the additive surface is moderately ground and polished to remove the local undulations of the surface adhering particles; Around the atomic interdiffusion layer of the A / B gradient metal interface, the laser power is appropriately increased, the working distance and the scanning rate are reduced to enhance the remelting and melt stirring of the tooth meshing surface of the A alloy, promote atomic interdiffusion, and thus solidify to form an interface atomic interdiffusion layer of a certain thickness; Step 4: Gradient metal overall additive manufacturing; Based on the cross-scale synergistically strengthened heterogeneous metal interface obtained in steps one to three, high-efficiency additive manufacturing of B alloy is carried out to obtain A / B gradient titanium alloy parts.

2. A gradient metal additive manufacturing method based on cross-scale synergistic interface strengthening as claimed in claim 1, characterized in that: The meshing tooth shapes of the gradient metal interface meshing structure include triangle, rectangle and trapezoid, the size of a single meshing structure is 3-10 mm, and it is divided into uniform type and variable size staggered type according to the uniform distribution type.

3. A gradient metal additive manufacturing method based on cross-scale synergistic interface strengthening as claimed in claim 2, characterized in that: The variable-size staggered meshing teeth refer to the regular change of the size of a single structure or the coupling of multiple types of structures.

4. A gradient metal additive manufacturing method based on cross-scale synergistic interface strengthening as claimed in claim 3, characterized in that: The variable-size staggered meshing teeth adopt a single structure or a triangular-rectangular structure that changes from small to high.

5. A gradient metal additive manufacturing method based on cross-scale synergistic interface strengthening as described in claim 1, 2, 3 or 4, characterized in that: The specific method for adjusting the parameters of the interface atomic interdiffusion layer is as follows: taking the high-quality additive forming parameter combination of B alloy as α, when preparing the interface atomic interdiffusion layer, the laser power is increased by 10-20% compared with the parameter combination α, the scanning rate is reduced by 5-10%, and the working distance is reduced by 1-2 mm.

6. A gradient metal additive manufacturing method based on cross-scale synergistic interface strengthening as described in claim 1, 2, 3 or 4, characterized in that: The preparation of the interfacial atomic inter-diffusion layer uses a combination of high laser power, low scanning rate and working distance parameters, which, on the one hand, promotes the remelting of the upper surface of the A alloy meshing structure, and on the other hand, intensifies the stirring and mixing of the molten pool to promote the inter-mixing between elements, thereby forming an inter-diffusion layer of a specific thickness at the heterogeneous metal interface to complete micro-scale interface strengthening.

7. The gradient metal additive manufacturing method based on cross-scale synergistic interface strengthening according to claim 1, characterized in that: The design criteria of the interface meshing structure are: for materials with similar physical and chemical properties, a uniform distribution of a single meshing tooth shape is selected.

8. The gradient metal additive manufacturing method based on cross-scale synergistic interface strengthening according to claim 1, characterized in that: The design principle of the interface meshing structure is: for materials with greatly different properties such as thermal expansion performance, the structural dimensions of the meshing teeth are selected and regulated.

9. The gradient metal additive manufacturing method based on cross-scale synergistic interface strengthening according to claim 1, characterized in that: The design principle of the interface meshing structure is as follows: simply changing the structural dimensions cannot strengthen the interface, and multiple types of meshing tooth coupling are used.

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