Preparation method of gradient-structure titanium-based composite material

Abstract

The invention discloses a gradient structure titanium-based composite material and a preparation method thereof. The preparation method comprises the following steps: performing high-energy ball milling and mixing on titanium powder and reinforced phase powder (at least one of TiB, TiC or TiB with the particle size of 0.5-5 microns) according to different mass fractions (5-30 wt%); preparing a core wire with low content (5-10 wt%) of composite powder through cold isostatic pressing and hot extrusion; a double-barrel powder feeding system (respectively loaded with high-content composite powder and pure titanium powder) is adopted for coaxial laser cladding, and the powder feeding speed is dynamically regulated and controlled to realize gradient distribution of a reinforced phase; and then hot isostatic pressing interface strengthening, multi-pass equal-channel angular pressing refining and high-energy shot peening surface strengthening are carried out. Optionally, laser shock peening and chemical vapor deposition of a TiN coating can also be carried out. The obtained material has a gradient structure of a core part (low-content reinforced phase), a transition layer (gradient change) and a surface layer (high-content reinforced phase), and the microstructure has the characteristics of nanocrystalline (surface layer), ultra-fine crystal (transition layer) and isometric crystal (core part). The room-temperature tensile strength of the material is not less than 1200 MPa, the ductility is not less than 8%, and the surface hardness is not less than 600 HV; the tensile strength at the high temperature of 600 DEG C is larger than or equal to 800 MPa, the creep life is larger than or equal to 500 h (under the load of 300 MPa), the interface bonding strength is high (larger than or equal to 350 MPa), and the alloy is suitable for the fields of aero-engine blades, spacecraft structural parts, biomedical implants and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal matrix composite material preparation, in particular to a titanium-based composite material with composition and structure gradient and a preparation method thereof. BACKGROUND

[0002] Titanium and its alloys are widely used in aerospace, biomedical and other fields due to their high specific strength, excellent corrosion resistance and good biocompatibility. However, their low hardness, wear resistance and high temperature performance limit their application in key load-bearing components. Introducing ceramic reinforcing phases (such as TiB, TiC, TiB2) into the titanium matrix to form titanium matrix composites (TMCs) is an effective means to improve their strength, hardness and wear resistance. However, high content of reinforcing phases can significantly improve the surface performance (such as hardness and wear resistance) of the material, but can also cause a sharp decrease in the overall toughness and plasticity of the material, and may introduce stress concentration, causing early failure. In order to balance the high performance of the surface and the high toughness of the interior, the concept of gradient structure composite material is proposed. The existing methods for preparing gradient materials include powder metallurgy, laser cladding, thermal spraying, etc., but these methods usually have the following problems: the interface bonding strength of the gradient layer and the substrate is insufficient, which is easy to peel off during service; the gradient composition change is discontinuous or difficult to control accurately; the preparation process is complex, making it difficult to achieve near-net shaping of complex components; the reinforcing phase distribution is uneven, the grain structure is coarse, and the overall performance of the material is affected. Therefore, it is of great significance to develop a gradient structure titanium-based composite material with high interface bonding strength, continuous and controllable composition gradient, and fine and uniform structure, and an efficient preparation method thereof. SUMMARY

[0003] The present application aims to overcome the shortcomings of the prior art and provide a gradient structure titanium-based composite material with firm interface bonding, fine structure and excellent performance, and a preparation method thereof. The method realizes continuous gradient change of the reinforcing phase content from the core to the surface by combining wire and double-powder laser cladding, and significantly improves the overall mechanical properties of the material by combining subsequent thermal mechanical treatment and surface strengthening.

[0004] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: In a first aspect, the present application provides a preparation method of a gradient structure titanium-based composite material, comprising the following steps: (1) Composite powder preparation: titanium powder and reinforcing phase powder are mixed by high-energy ball milling according to different mass fractions (5-30wt%). The ball milling parameters are as follows: ball-to-material ratio 10:1-15:1, rotation speed 300-400 rpm, and time 4-8 h.

[0005] (2) Core wire preparation: low content (5-10wt%) composite powder is formed by cold isostatic pressing, and then a hot extrusion process is used to prepare a wire with a diameter of 1-3 mm, and the extrusion ratio is 10:1-15:1.

[0006] (3) Laser cladding system configuration: a double-cylinder powder feeding system is set up, one of which is loaded with high content (20-30wt%) titanium-based composite powder, and the other is loaded with pure titanium powder (purity ≥99.9%).

[0007] (4) Gradient cladding forming: the wire prepared in step (2) is used as the substrate for coaxial laser cladding, and the powder feeding speed of the double powder feeding system is dynamically controlled during the cladding process: the powder feeding speed of the high content powder cylinder is gradually increased from 5-10g / min to 15-20g / min; the powder feeding speed of the pure titanium powder cylinder is gradually reduced from 15-20g / min to 5-10g / min, in this way, a gradient transition layer and a surface layer with gradually increasing reinforcement phase content from inside to outside are formed on the outside of the wire core.

[0008] (5) Interface strengthening treatment: the cladded component is subjected to hot isostatic pressing treatment, the treatment parameters are: temperature 800-900℃, pressure 100-150MPa, holding time 1-2h, this process can eliminate internal defects and promote interface metallurgical bonding.

[0009] (6) Multi-directional extrusion refinement: the component treated by hot isostatic pressing is subjected to multi-pass equal channel angular pressing (ECAP), the specific process is: first pass: along the extrusion direction A, temperature 700-750℃; second pass: along the extrusion direction B, 90° to the direction A, temperature 650-700℃; third pass: along the extrusion direction C, 45° to the directions A and B, temperature 600-650℃, this process can significantly refine the grains of each gradient layer.

[0010] (7) Surface strengthening treatment: the component treated by ECAP is subjected to high-energy shot peening treatment, the parameters are: the projectile material is ZrO2, the diameter is 0.2-0.5mm, the jet speed is 80-120m / s, the coverage is ≥2000%, this process can further refine the surface layer grains and introduce residual compressive stress.

[0011] Preferably, the reinforcing phase in step (1) is at least one of TiB, TiC or TiB2, and the particle size is 0.5-5μm.

[0012] Preferably, the laser cladding parameters in step (4) are: laser power 1500-2000W, scanning speed 5-15mm / s, spot diameter 1-2mm, protective gas argon, flow rate 15-25L / min.

[0013] Preferably, after each pass of ECAP processing in step (6), an intermediate annealing treatment is performed: the annealing temperature is 50-100℃ higher than the extrusion temperature of the pass, the time is 20-30min, and the atmosphere is vacuum or argon protection.

[0014] Preferably, after the high-energy shot peening treatment in step (7), the following subsequent treatments are further included: Laser shock peening: energy density is 5-10J / cm², and the number of impacts is 3-5 times.

[0015] Chemical vapor deposition TiN coating: the deposition thickness is 2-5μm, and the coating hardness is ≥2000HV.

[0016] In a second aspect, the present application provides a gradient structure titanium-based composite material prepared by the above method, characterized in that: Structural composition: from inside to outside, it includes three parts: the core is a low-content (5-10wt%) reinforced phase titanium-based composite material, with a diameter of about 1-3mm; the middle is a transition layer with a gradient change (10-25wt%) in the content of the reinforced phase; and the surface layer is a high-content (25-30wt%) reinforced phase titanium-based composite material, with a thickness of about 0.5-1mm.

[0017] Microstructure: the surface layer is a nanocrystalline structure with a grain size of 50-100nm; the transition layer is a ultra-fine grain structure with a grain size of 100-300nm; and the core is an equiaxed grain structure with a grain size of 1-3μm.

[0018] Preferably, the room temperature mechanical properties of the material are: tensile strength ≥1200MPa, elongation ≥8%, and surface layer hardness ≥600HV.

[0019] Preferably, the high-temperature performance of the material at 600℃ is: tensile strength ≥800MPa, and creep life under a load of 300MPa ≥500h.

[0020] Preferably, the interfacial bonding strength of the material is: the interfacial bonding strength between the core and the transition layer ≥400MPa, and the interfacial bonding strength between the transition layer and the surface layer ≥350MPa.

[0021] Preferably, the gradient structure titanium-based composite material is suitable for manufacturing aircraft engine blades, spacecraft structural parts, and biomedical implants.

[0022] Compared with the prior art, the present application has the following beneficial effects: (1) The gradient design is reasonable and the performance is excellent: through the structural design of "low reinforced phase core + gradient transition layer + high reinforced phase surface layer", the toughness and plasticity of the core and the hardness, strength and wear resistance of the surface layer are perfectly balanced, and the best match of strength and toughness is achieved.

[0023] (2) High interface bonding strength: The wire is used as the cladding matrix, and the hot isostatic pressing process is combined to ensure that a firm metallurgical bond is formed between the core and the cladding layer, the interface bonding strength is much higher than that of mechanical bonding method, and delamination failure is avoided.

[0024] (3) Fine and uniform structure: Through the multi-pass and multi-directional ECAP process, the entire cross section from the core to the surface is subjected to strong plastic deformation, effectively refining the grain size of each region, especially obtaining a nanocrystalline surface layer and a ultra-fine grain transition layer, greatly improving the material strength.

[0025] (4) Strong process controllability: The double-powder laser cladding technology is adopted, and the powder feeding rate of the two kinds of powders is accurately controlled by program, which can realize continuous and smooth gradient change of the reinforcing phase content, and avoid the performance step and stress concentration caused by composition mutation.

[0026] (5) Comprehensive performance is comprehensively improved: The finally prepared material not only has high super room temperature strength, hardness and plasticity matching, but also has excellent high temperature strength and creep resistance, which meets the harsh requirements of high-end fields on the comprehensive performance of the material. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The core microstructure diagram obtained in Example 1 of the present application. DETAILED DESCRIPTION

[0028] The present application will be described in detail below through specific examples, but the protection scope of the present application is not limited to the following examples. Example 1

[0029] Step one: composite powder preparation Pure titanium powder with an average particle size of 45 μm (purity 99.95%) and TiB2 powder with an average particle size of 1.8 μm were selected as raw materials, and three kinds of composite powders with reinforcing phase mass fractions of 6wt%, 25wt% and 30wt% were prepared. A planetary ball mill was used for high-energy ball milling under argon protection, and the parameters were set as follows: ball-to-material ratio 12:1, rotation speed 350 rpm, and time 6 h.

[0030] Step two: core wire preparation The 6wt% TiB2 low-content composite powder was taken and loaded into a rubber mold, and cold isostatic pressing was carried out under a pressure of 200 MPa, and the pressure was maintained for 5 minutes. The compact was preheated at 850℃, and then a hot extrusion process was used to prepare a wire with a diameter of 2.0 mm, and the extrusion ratio was 12:1.

[0031] Step three: laser cladding system configuration Two powder feeding systems were set up, one for high content composite powder with 30wt% TiB2, and the other for pure titanium powder (purity 99.9%).

[0032] Step four: gradient cladding forming The wire was used as the substrate for coaxial laser cladding. The laser power was 1800 W, the scanning speed was 10 mm / s, the spot diameter was 1.5 mm, the protective gas was argon, the flow rate was 20 L / min, and the powder feeding speed was dynamically controlled: the high content powder cylinder was gradually increased from 6 g / min to 18 g / min, and the pure titanium powder cylinder was gradually reduced from 18 g / min to 6 g / min.

[0033] Step five: interface strengthening treatment The hot isostatic pressing process was used, with a temperature of 860℃, a pressure of 130 MPa, and a holding time of 1.5 h.

[0034] Step six: multi-directional extrusion refinement Three passes of equal channel angular pressing were performed: First pass: extrusion direction A, temperature 720℃; Second pass: extrusion direction B (90° to A), temperature 680℃; Third pass: extrusion direction C (45° to A and B), temperature 630℃.

[0035] After each pass of extrusion, intermediate annealing was performed: the temperature was 60℃ higher than the extrusion temperature, the time was 25 min, and the protective gas was argon.

[0036] Step seven: surface strengthening treatment High-energy shot peening process was used: the projectile material was ZrO2, the diameter was 0.3 mm, the speed was 100 m / s, the coverage rate was 2500%, and then laser shock peening was performed: the energy density was 8 J / cm², and the impact was 4 times; finally, TiN coating was deposited by chemical vapor deposition: the thickness was 3 μm, and the hardness was 2200 HV.

[0037] Performance test results: Microstructure: nanocrystalline size 80 nm in the surface layer, ultra-fine grain size 200 nm in the transition layer, and equiaxed grain size 2.0 μm in the core. Room temperature mechanical properties: tensile strength 1280 MPa, elongation 9.5%, surface layer hardness 625 HV. High temperature performance (600℃): tensile strength 820 MPa, creep life 580 h (300 MPa load). Interface bonding strength: core to transition layer 420 MPa, transition layer to surface layer 365 MPa. Example 2

[0038] Step one: composite powder preparation The pure titanium powder with an average particle size of 38 μm and the TiC powder with an average particle size of 2.2 μm were selected to prepare three kinds of composite powders with the reinforcing phase mass fraction of 8wt%, 22wt% and 28wt% respectively. The ball milling parameters were as follows: ball-to-powder ratio 14:1, rotation speed 380 rpm, and time 5 h.

[0039] Step two: core wire preparation The 8wt% TiC composite powder was cold isostatic pressed at a pressure of 180 MPa and hot extruded at a temperature of 830 °C to prepare a wire with a diameter of 1.5 mm and an extrusion ratio of 14:1.

[0040] Step three: laser cladding system configuration The 28wt% TiC composite powder was loaded in a high-content powder cartridge, and the pure titanium powder was loaded in a pure titanium powder cartridge.

[0041] Step four: gradient cladding forming The laser power was 1700 W, the scanning speed was 8 mm / s, and the spot diameter was 1.2 mm; the powder feeding control was as follows: the high-content powder cartridge was increased from 7 g / min to 17 g / min, and the pure titanium powder cartridge was decreased from 17 g / min to 7 g / min.

[0042] Step five: interface strengthening treatment The temperature was 840 °C, the pressure was 120 MPa, and the holding time was 2 h.

[0043] Step six: multi-directional extrusion refinement The first pass was at 700 °C, the second pass was at 670 °C, and the third pass was at 620 °C. The intermediate annealing temperature was 70 °C higher than the extrusion temperature, and the time was 20 min.

[0044] Step seven: surface strengthening treatment The high-energy shot peening was performed using ZrO2 pellets with a diameter of 0.4 mm at a speed of 90 m / s and a coverage rate of 2200%. The laser shock peening was performed at an energy density of 6 J / cm² with 3 impacts.

[0045] Performance test results: Microstructure: the nanocrystalline size of the surface layer was 70 nm, the ultrafine grain size of the transition layer was 180 nm, and the equiaxed grain size of the core was 1.8 μm. Room temperature mechanical properties: tensile strength 1320 MPa, elongation 10.2%, and surface hardness 638 HV. High temperature performance (600 °C): tensile strength 835 MPa, and creep life 550 h. Interface bonding strength: core to transition layer 435 MPa, and transition layer to surface layer 370 MPa.

[0046] Comparative example 1 (traditional powder metallurgy method) The powder with the same composition as in Example 1 (6wt%, 25wt%, 30wt% TiB2) was used to prepare the gradient material by layering and hot-pressing sintering. Process parameters: sintering temperature 950℃, pressure 30MPa, time 1h.

[0047] Performance test results: The material presents obvious layered structure, and composition mutation exists at the interface. The tensile strength at room temperature is 950MPa, and the elongation is 4.5%. The surface hardness is 580HV. The high-temperature performance (600℃): the tensile strength is 720MPa, and the creep life is 320h. The interface bonding strength test shows that the interlayer bonding strength is only 185MPa, and the fracture occurs at the interface in the mechanical test.

[0048] Comparative Example 2 (without ECAP processing) After the material is prepared according to steps one to five of Example 1, the multi-directional extrusion refinement step is omitted, and the surface strengthening treatment is directly performed.

[0049] Performance test results: The material has gradient composition, but the grain is coarse: the grain size of the surface layer is 300nm, the transition layer is 500nm, and the core is 5μm. The tensile strength at room temperature is 980MPa, and the elongation is 6.8%. The surface hardness is 590HV. The high-temperature performance (600℃): the tensile strength is 740MPa, and the creep life is 350h. The interface bonding strength: 300MPa (core and transition layer), 280MPa (transition layer and surface layer).

[0050] Comparative Example 3 (without gradient design) The composite powder with a single composition (20wt% TiB2) is used to prepare the overall uniform composite material by traditional hot extrusion process.

[0051] Performance test results: The material has uniform composition and no gradient structure. The tensile strength at room temperature is 1050MPa, and the elongation is 3.5%. The hardness is 580HV. The high-temperature performance (600℃): the tensile strength is 750MPa, and the creep life is 380h. The material shows typical high strength and low plasticity characteristics.

[0052] The above examples show that the gradient structure titanium-based composite material with excellent comprehensive performance is successfully prepared by the unique process combination of the application. The results of the comparative examples fully prove the necessity and synergistic effect of each process step of the application, especially the key role of the gradient structure design and multi-directional extrusion refinement in improving the performance of the material.

[0053] The above embodiments are preferred embodiments of the present application, but the present application is not limited to the above embodiments, and any obvious improvement, replacement or modification made by those skilled in the art without departing from the spirit of the present application shall fall within the protection scope of the present application.

Claims

1. A method for producing a gradient structure titanium-based composite material, characterized by, The method comprises the following steps: (1) composite powder preparation: titanium powder and reinforcing phase powder are mixed by high-energy ball milling at different mass fractions (5-30wt%); ball milling parameters: ball-to-material ratio 10:1-15:1, rotation speed 300-400 rpm, time 4-8 h; (2) core wire preparation: low-content (5-10wt%) composite powder is formed by cold isostatic pressing, and then a wire with a diameter of 1-3 mm is prepared by hot extrusion process, with an extrusion ratio of 10:1-15:1; (3) laser cladding system configuration: a double-cylinder powder feeding system is set up, and high-content (20-30wt%) titanium-based composite powder and pure titanium powder (purity ≥99.9%) are loaded respectively; (4) gradient cladding forming: the wire is used as a substrate for coaxial laser cladding, and the powder feeding speed is dynamically controlled: the initial speed of the high-content powder cylinder is 5-10 g / min, and gradually increases to 15-20 g / min; the initial speed of the pure titanium powder cylinder is 15-20 g / min, and gradually decreases to 5-10 g / min; (5) interface strengthening treatment: hot isostatic pressing process is adopted, with a temperature of 800-900℃, a pressure of 100-150 MPa, and a holding time of 1-2 h; (6) multi-directional extrusion refinement: multi-pass equal-channel angular pressing (ECAP) is implemented: first pass: extrusion direction A, temperature 700-750℃; second pass: extrusion direction B, 90° to A, temperature 650-700℃; third pass: extrusion direction C, 45° to A and B, temperature 600-650℃; (7) surface strengthening treatment: high-energy shot peening process is adopted: projectile material: ZrO2, diameter: 0.2-0.5 mm, speed: 80-120 m / s, coverage: ≥2000%.

2. The method of claim 1, wherein: The reinforcing phase in step (1) is at least one of TiB, TiC or TiB2, with a particle size of 0.5-5 μm.

3. The method of claim 1, wherein: In step (4), the laser cladding parameters are: laser power 1500-2000 W, scanning speed 5-15 mm / s, spot diameter 1-2 mm, protective gas argon, flow rate 15-25 L / min.

4. The method of claim 1, wherein: In step (6), intermediate annealing is performed after each pass of ECAP treatment: temperature: 50-100℃ higher than the extrusion temperature, time: 20-30 min, atmosphere: vacuum or argon protection.

5. The method of claim 1, wherein: After step (7), it further comprises: laser shock peening: energy density: 5-10 J / cm², impact times: 3-5 times, chemical vapor deposition TiN coating: thickness: 2-5 μm, hardness: ≥2000 HV.

6. A gradient structure titanium-based composite material prepared by any one of the methods of claims 1-5, characterized in that: structural composition: core: low-content (5-10wt%) reinforcing phase, diameter 1-3 mm; transition layer: reinforcing phase content gradient change (10-25wt%); surface layer: high-content (25-30wt%) reinforcing phase, thickness 0.5-1 mm; microstructure: surface layer: nanocrystalline, grain size 50-100 nm; transition layer: ultra-fine grain, 100-300 nm; core: equiaxed grain, 1-3 μm.

7. The titanium-based composite of claim 6, wherein: Room temperature mechanical properties: tensile strength: ≥ 1200 MPa, elongation: ≥ 8%, surface hardness: ≥ 600 HV.

8. The titanium-based composite of claim 6, wherein: High temperature properties (600°C): tensile strength: ≥ 800 MPa, creep life: ≥ 500 h (300 MPa load).

9. The titanium-based composite of claim 6, wherein: Interfacial bonding strength: core and transition layer: ≥ 400 MPa, transition layer and surface layer: ≥ 350 MPa.

10. The titanium matrix composite of claim 6, wherein: Suitable for aero-engine blades, spacecraft structural parts and biomedical implants.

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