A method for preparing multilayer composite mesh structure titanium-based coatings by laser cladding

Abstract

This invention discloses a method for preparing a multilayer composite network structure titanium-based coating by laser cladding, belonging to the field of laser processing. The steps are as follows: using anhydrous ethanol as a binder, two different alloy powders are pre-placed in layers on the surface of a pure copper substrate, and then clad in layers. A single-pass multilayer cladding is performed on the substrate surface using laser cladding technology; a layered heterogeneous structure coating with alternating hard and soft layers is formed from the coating surface to the substrate; a continuous composite network structure is formed in the hard layer through in-situ synthesis technology, and combined with the interface between the hard and soft layers, the crack deflection is utilized to the maximum extent to enhance the elongation at break of the coating; the surface hard layer can effectively improve the shortcomings of low hardness and poor wear resistance of pure copper. By introducing layered and composite network heterogeneous structures into the cladding layer, the dual HDI strengthening and strain hardening of the layered and network heterogeneous structures are used to improve the strength and ductility of the coating.

Description

Technical Field

[0001] This invention discloses a method for preparing multilayer composite mesh structure titanium-based coatings by laser cladding, which belongs to the field of laser processing. Background Technology

[0002] Compared to conventional strengthening mechanisms such as work hardening, solid solution strengthening, grain refinement strengthening, and second-phase strengthening, which sacrifice ductility to improve strength, obtaining materials with both high strength and high ductility is currently a hot research topic. Over hundreds of years of evolution in nature, most plant and biological systems have developed various heterogeneous structures with excellent properties, combining both strength and ductility, for survival. This result has been fully validated by millions of years of natural evolution, as seen in bamboo stems, abalone shells, and seashells. This has led to extensive research on heterogeneous materials.

[0003] Heterogeneous materials are novel materials composed of heterogeneous regions with significantly different mechanical or physical properties. Compared to single or homogeneous materials, the synergistic effect generated by the coupling between heterogeneous regions in heterogeneous materials results in overall performance exceeding the predicted values ​​of the mixing rule, exhibiting an excellent combination of strength and ductility. The synergistic enhancement of strength and ductility exhibited by heterogeneous materials is mainly attributed to heterogeneous deformation-induced (HDI) strength and strain hardening. By adjusting the microstructure and size of the materials, heterogeneous materials with excellent properties, such as gradient structures, layered structures, bimodal structures, harmonic structures, and two / multiphase structures, have been successfully prepared using processes such as hot pressing sintering, rolling, and laser cladding.

[0004] However, all of the above methods have varying degrees of drawbacks. For example, the sintered body formed by hot pressing cannot be directly applied to the workpiece surface; rolling processes integrate sheet materials through heating and pressure, but the bonding effect between the layers is poor. Laser cladding, as one of the "additive manufacturing" technologies, is considered a cutting-edge and popular surface modification technology, and has achieved considerable in-depth development in the field of surface engineering. Titanium-based composite materials have broad application prospects in aerospace, medical, automotive, and military fields. To further improve the performance of titanium alloys, it is essential to prepare materials with excellent strength and plasticity. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a multilayer composite network structure titanium-based coating by laser cladding. This method utilizes laser cladding technology to clad a layered heterostructure with alternating soft and hard layers onto a copper substrate, as well as a composite network heterostructure synthesized in situ within the hard layer. The soft layer is composed of highly ductile metallic Ti, with a small amount of Ni powder added to improve the coating surface quality. The hard layer consists of a Ti-based composite coating reinforced with ZrN and TiB2. In the hard layer, the in-situ synthesis reaction of ZrN and TiB2 powders forms dispersed ZrB2 particles, with a ZrNi3 network framework and an internal composite network heterostructure of α-Ti and spherical TiN. The method combines the interface effect between the soft and hard layers with the crack-blocking effect of the composite network structure to achieve crack deflection and toughening. The HDI strengthening and strain hardening brought by the layered-network dual heterostructure improve the surface strength and ductility of the substrate material.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a multilayer composite mesh structure titanium-based coating by laser cladding includes the following steps:

[0008] S1. Prepare the cladding powder, which includes two types of first mixed powder: 95wt.%Ti and 5wt.%Ni, and second mixed powder: 80.75-90.25wt.%Ti, 4.25-4.75wt.%Ni, 2.5-10wt.%ZrN, and 0-7.5wt.%TiB2. Mix them evenly.

[0009] S2. Prepare the workpiece and pre-treat the surface of the pure copper substrate;

[0010] S3. Mix the two cladding powders separately with anhydrous ethanol. First, coat the first mixed powder onto the substrate and dry it. Preheat the substrate and use laser cladding technology to clad the pure copper substrate. Polish the surface oxide layer.

[0011] S4. Coat the second mixed powder onto the cladding layer obtained in step S3, dry it, preheat the substrate, use laser cladding technology to clad the second mixed powder, and polish the oxide layer on the surface.

[0012] S5. Repeat steps S3 and S4, alternating between the two cladding powders, to successfully prepare a layered heterostructure coating with alternating hard and soft layers on the surface of the copper substrate.

[0013] A further improvement of the technical solution of the present invention is that: in step S1, the average particle size of the metallic Ti powder is 100~150μm and the purity is 99.5%; the Ni is atomized Ni powder with an average particle size of 45~100μm and a purity of 99.5%; the average particle size of the ZrN powder is 3~5μm and the purity is 99.9%; and the average particle size of the TiB2 powder is 3~5μm and the purity is 99.5%.

[0014] A further improvement of the technical solution of the present invention is that the first mixed powder and the second mixed powder are prepared by mixing powders in a planetary ball mill at a speed of 300 r / min for a time of 2 h.

[0015] A further improvement to the technical solution of the present invention is that: in step S2, the copper substrate is cleaned with an angle grinder to remove surface stains and oxides, and then cleaned with anhydrous ethanol and allowed to air dry naturally.

[0016] A further improvement of the technical solution of the present invention is that: in steps S3 and S4, after the coating mixed powder is dried, the sample surface except for the pre-placed powder area is blackened with ink, and then the substrate is preheated.

[0017] A further improvement to the technical solution of the present invention is that the drying temperature in steps S3 and S4 is set to 100°C and the heat preservation time is 1 hour.

[0018] A further improvement of the technical solution of the present invention is that: an autotransformer is used to control the electric furnace plate to achieve precise temperature control of the substrate, and the copper substrate is preheated at a temperature of 750°C, with argon gas introduced during the preheating process.

[0019] A further improvement to the technical solution of this invention lies in that: the laser power P of the laser cladding is 2000W-2600W, the scanning speed V is 5-7mm / s, and the spot size D is 10×2mm. 2 The pre-set powder thickness is 1mm.

[0020] A further improvement to the technical solution of this invention is that the laser power P of the laser cladding of the first mixed powder is 2000W, the scanning speed V is 5mm / s, and the spot size D is 10×2mm. 2 The pre-set powder thickness is 1 mm; the laser power P for laser cladding of the second powder is 2400-2600 W, the scanning speed is 5-7 mm / s, and the spot size D is 10 × 2 mm. 2 The pre-set powder thickness is 1mm.

[0021] Due to the adoption of the above technical solution, the technical effects achieved by this invention are as follows:

[0022] This invention utilizes laser cladding technology to prepare a multilayered composite network structure titanium-based coating. A soft layer composed of Ti-based components and a hard layer composed of ZrN and TiB2 ceramic reinforcing phases are formed on a copper substrate, with the soft and hard layers arranged alternately. ZrN and TiB2 powders are added during the preparation of the hard layer, and dispersed ZrB2 particles are prepared through an in-situ synthesis reaction. The resulting network structure has a ZrNi3 framework and an internal composite network structure of α-Ti and spherical TiN. By combining the macroscopic layered structure with the microscopic composite network structure, HDI strengthening and strain hardening are used to improve the strength and ductility of the material. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall coating of the present invention;

[0024] Figure 2 This is a macroscopic morphology diagram of the first Ti-based coating obtained in Example 1 of the present invention;

[0025] Figure 3 This is a macroscopic morphology diagram of the coating containing ZrN and TiB2 reinforced phases obtained in Example 1 of the present invention;

[0026] Figure 4 This is a cross-sectional view of the coating obtained in Embodiment 1 of the present invention;

[0027] Figure 5 This is a cross-sectional microstructure diagram of the layers obtained in Embodiment 1 of the present invention;

[0028] Figure 6 This is the XRD pattern of the first Ti-based coating obtained in Example 1 of the present invention;

[0029] Figure 7 This is the XRD pattern of the ZrN and TiB2 reinforced phase coating obtained in Example 1 of the present invention;

[0030] Figure 8 This is an EDS image of the coating containing ZrN and TiB2 reinforced phases obtained in Example 1 of the present invention;

[0031] Figure 9 This is a fracture toughness diagram of the coating containing ZrN and TiB2 reinforced phases obtained in Example 1 of the present invention;

[0032] Figure 10 This is a tensile test dimension diagram obtained in Embodiment 1 of the present invention;

[0033] Figure 11 This is a stress-strain curve diagram of the overall coating tensile test obtained in Embodiment 1 of the present invention;

[0034] Figure 12 This is a hardness distribution diagram of the overall coating obtained in Embodiment 1 of the present invention;

[0035] Figure 13 This is an EDS image of the ZrN-reinforced phase coating obtained in Example 4 of the present invention. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and the base embodiment.

[0037] Example 1:

[0038] A method for preparing a multilayer composite mesh structure titanium-based coating by laser cladding, using a pure copper block with dimensions of 50×15×5mm. 3 (Length × Width × Height), first use an angle grinder to remove surface stains and oxides to improve surface roughness;

[0039] Next, clean the surface with anhydrous ethanol and allow it to air dry. Mix the first mixed powder (metallic Ti powder with an average particle size of 100-150 μm and a purity of 99.5%) and atomized Ni powder with an average particle size of 45-100 μm and a purity of 99.5% with anhydrous ethanol into a paste, and pre-coat it onto the surface of the copper substrate. The powder layer should be 1 mm thick, 10 mm wide, and 40 mm long. Then, keep it in a drying oven at 100°C for 1 hour.

[0040] The dried sample surface (excluding the pre-placed powder area) is coated with ink to perform a "blackening" treatment. The purpose is to increase the absorption rate of the copper substrate to the laser, making it easier to heat and melt, and reducing the power of the laser.

[0041] The "blackened" sample was preheated on an electric furnace plate equipped with an autotransformer, positioned below the laser head. The furnace plate had a diameter of 180mm and used nichrome wire with a maximum power of 1500W. The furnace plate was surrounded by sheet metal, resulting in an overall height of 300mm. A cylindrical container (without a top) with a diameter of 220mm was formed. The inner wall of the container was insulated with asbestos, with a layer thickness of 40mm, secured with wire. The voltage was 200V, and the heating time was 9 minutes. Asbestos was used to cover the top of the container to accelerate the temperature rise. Thermocouples were used for temperature measurement. When the temperature reached 750℃, the cover was removed, and the sample was placed on the furnace plate. The cover was quickly replaced, and argon gas was introduced to prevent oxidation of the pre-placed powder during preheating. The surface temperature of the sample was monitored using thermocouples. When the temperature reached 750℃, a laser cladding experiment was performed.

[0042] The laser head is fixed on a six-axis robotic arm. The laser beam wavelength is 1.064 μm, the laser processing power is 2000 W, the scanning speed is 5 mm / s, and the spot size is 10 × 2 mm. 2The pre-formed powder layer thickness is 1 mm, and the processing is carried out under argon protection. After laser cladding the first mixed powder (95 wt.% Ti + 5 wt.% Ni) onto the copper substrate surface, it is placed in an asbestos box for heat preservation and cooled to room temperature. The surface oxide layer is then polished with an angle grinder, thus completing the preparation of the first coating layer.

[0043] The preparation method of the second coating layer differs from that of the first coating layer in that the second layer is a direct cladding of the second mixed powder (90.25wt.%Ti+4.75wt.%Ni+2.5wt.%ZrN+2.5wt.%TiB2) onto the first layer; the laser power is 2400W and the scanning speed is 5mm / s; after the laser processing is completed, the surface oxide layer is polished with an angle grinder, thus completing the preparation of the second coating layer.

[0044] Repeat the preparation steps of the first and second layers to finally complete the laser cladding of four heterogeneous structure coatings on the surface of the copper substrate.

[0045] Figure 1 This is a schematic diagram of the overall coating model in an embodiment of the present invention. Figure 2 The image shows the surface morphology of the first Ti-based coating after laser cladding and polishing. The coating is evenly spread and free of defects such as cracks and pores, indicating good surface quality. Figure 3 This is a surface morphology image after polishing the second layer of laser cladding. The surface is smooth, clean, and free of cracks, and the coating has good formability. Figure 4 This is a cross-sectional view of a multilayer titanium-based coating. The coating and the substrate, as well as the layers, are well bonded together, with no obvious pores or cracks. Figure 5 It forms the interface between the soft and hard layers, with a flat surface and good adhesion. Figure 6 The XRD pattern of the first coating layer shows the presence of α-Ti and β-Ti at 38–40°. In addition, the CuTi3 phase is also present. This is mainly due to the simultaneous melting of the powder and matrix caused by the high-energy laser beam, which promotes the reaction between Cu and Ti to form CuTi3 and Cu3Ti phases. Figure 7 The XRD pattern of the second layer containing the ceramic reinforcing phase coating shows that the coating is composed of TiB, α-Ti, and ZrB2. TiB2 undergoes an in-situ synthesis reaction with Ti to form the TiB phase. However, after comparing with the standard PDF card, it was found that the diffraction peaks are shifted to a smaller angle. This is mainly because a large amount of residual tensile stress is generated during the cooling process of the coating, and the tensile stress leads to an increase in the interplanar spacing. Figure 8 The image shows the EDS diagram of the second layer coating containing ZrN and TiB2 ceramic reinforcing phases. The interior of the composite network structure is composed of spherical TiN particles, and the boundary is ZrNi3. ZrB2 particles are uniformly distributed throughout the coating. Figure 9The fracture toughness diagram shows the coating containing ZrN and TiB2 ceramic reinforcing phases, where cracks are deflected by the network structure. Figure 10 This is a dimensional diagram of the tensile specimen. Figure 11 The stress-strain curve of the coating shows an ultimate tensile strength of 610 MPa and an elongation of 5.7%. Figure 12 The hardness distribution diagram from the surface to the substrate shows that the coating hardness values ​​exhibit a high-low-high-low trend from the surface to the substrate, with a maximum hardness of 976.45 HV. 0.5 The hardness of the copper matrix (63HV) 0.5 15.5 times that of ).

[0046] Example 2

[0047] The difference between this embodiment and Embodiment 1 is that the second mixed powder consists of Ti powder, Ni powder, ZrN powder, and TiB2 powder, with a weight percentage of 85.5%:4.5%:5%:5%. The laser power P is set to 2500W and the scanning speed V to 6mm / s. Everything else is the same as in Embodiment 1, thus obtaining a Ti-based heterostructure coating.

[0048] Example 3

[0049] The difference between this example and Example 1 is that the second mixed powder consists of Ti powder, Ni powder, ZrN powder, and TiB2 powder, with a weight percentage of 80.75%: 4.25%: 7.5%: 7.5%. The laser power P is set to 2600W and the scanning speed V to 7mm / s. Everything else is the same as in Example 1, thus obtaining a Ti-based heterostructure coating.

[0050] Example 4

[0051] The difference between this embodiment and Embodiment 1 is that the second mixed powder is Ti powder, Ni powder, and ZrN powder, with a weight percentage of 90.25%:4.75%:5%. Everything else is the same as in Embodiment 1, thus obtaining a Ti-based heterostructure coating that forms a continuous network structure.

[0052] Figure 13 The image shows the EDS diagram of the coating with 5 wt.% ZrN added. The network boundary is the segregation of Ni and Zr elements, and the interior of the composite network structure is spherical TiN.

[0053] Example 5

[0054] The difference between this embodiment and Embodiment 1 is that the second mixed powder is Ti powder, Ni powder, and ZrN powder, with a weight percentage of 85.5%:4.5%:10%. Everything else is the same as in Embodiment 1, thus obtaining a Ti-based heterostructure coating that forms a continuous network structure.

[0055] This application utilizes laser cladding technology to perform single-pass multi-layer cladding on the substrate surface; a layered heterogeneous coating with alternating hard and soft layers is formed from the coating surface to the substrate; a continuous composite network structure is formed in the hard layer through in-situ synthesis technology, and combined with the interface between the hard and soft layers, the crack deflection is utilized to the maximum extent to enhance the elongation at break of the coating; the surface hard layer can effectively improve the shortcomings of low hardness and poor wear resistance of pure copper. By introducing layered and composite network heterogeneous structures into the cladding layer, the dual HDI strengthening and strain hardening of the layered and network heterogeneous structures are used to improve the strength and ductility of the coating.

[0056] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for producing a multilayer composite net-shape structure titanium-based coating by laser cladding, characterized in that The method comprises the following steps: S1, preparing cladding powder, the cladding powder comprising a first mixed powder of 95wt.% Ti and 5wt.% Ni and a second mixed powder of 80.75-90.25wt.% Ti, 4.25-4.75wt.% Ni, 2.5-10wt.% ZrN and 0-7.5wt.% TiB2; S2, preparing a workpiece and pre-treating the surface of a pure copper base; S3, mixing the two kinds of cladding powder with anhydrous ethanol respectively, first coating the first mixed powder on the base, drying, pre-heating the base, cladding on the pure copper base by laser cladding technology and polishing the surface oxide layer; S4, coating the second mixed powder on the cladding layer obtained in step S3, drying, pre-heating the base, cladding the second mixed powder by laser cladding technology and polishing the surface oxide layer; S5, repeating steps S3 and S4, alternately cladding the two kinds of cladding powder to prepare a layered heterogeneous structure coating with hard / soft layers alternately distributed on the surface of the pure copper base; In step S1, the average particle size of the metal Ti powder is 100-150μm, the purity is 99.5%; the average particle size of the atomized Ni powder is 45-100μm, the purity is 99.5%; the average particle size of the ZrN powder is 3-5μm, the purity is 99.9%; and the average particle size of the TiB2 powder is 3-5μm, the purity is 99.5%; The first mixed powder and the second mixed powder are prepared by mixing powder through a planetary ball mill, the rotating speed is 300r / min and the powder mixing time is 2h; In step S2, the surface stains and oxides of the pure copper base are removed by an angle grinder, the surface is cleaned with anhydrous ethanol and naturally air-dried; In steps S3 and S4, after coating the mixed powder and drying, the surface of the sample is blackened except the preset powder area, and then the base is pre-heated; In steps S3 and S4, the drying temperature is set to 100℃ and the holding time is 1h; The base is pre-heated by using a self-coupled transformer to control the electric furnace disc, the pre-heating temperature is 750℃ and argon is introduced during the pre-heating process; The laser power P of the laser cladding is 2000W-2600W, the scanning speed V is 5-7mm / s, the spot size D is 10×2mm2 and the preset powder thickness is 1mm; The laser power P of the laser cladding of the first mixed powder is 2000W, the scanning speed V is 5mm / s, the spot size D is 10×2mm2 and the preset powder thickness is 1mm; the laser power P of the laser cladding of the second powder is 2400-2600W, the scanning speed is 5-7mm / s, the spot size D is 10×2mm2 and the preset powder thickness is 1mm.

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