3D printing high-toughness titanium alloy and preparation method thereof

Abstract

The invention belongs to the field of additive manufacturing of titanium alloys, relates to a 3D printing high-toughness titanium alloy and a preparation method thereof, and solves the problem of poor plasticity of the existing Ti-Zr alloy. The Ti-Zr-O high-toughness titanium alloy comprises the following chemical components in percentage by mass: less than or equal to 0.01% of C, 0.46-0.5% of O, 1-2% of Zr, less than or equal to 0.015% of H, less than or equal to 0.02% of N and the balance of Ti and inevitable impurities. According to the Ti-Zr-O high-toughness titanium alloy finally obtained through the method, the density reaches 99.8% or above, the tensile strength is larger than or equal to 1150 MPa, the yield strength is larger than or equal to 1050 MPa, and the ductility is larger than or equal to 21%. According to the Ti-Zr-O high-toughness titanium alloy, solid solution elements oxygen and zirconium serve as strengthening elements, common solid solution elements such as W, Mo and Nb are replaced, a Ti-Zr-O high-toughness titanium alloy product is prepared, the strength and plasticity of the Ti-Zr-O high-toughness titanium alloy product are remarkably superior to those of a traditional titanium-zirconium alloy product, the cost of the high-toughness titanium alloy is greatly reduced, and the Ti-Zr-O high-toughness titanium alloy is suitable for industrial production. The method can achieve the purposes of low cost and high performance, and is suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the field of additive manufacturing of metal materials and relates to a 3D printed high-strength and toughness titanium alloy and a preparation method thereof. Background Art

[0002] Titanium and its alloys are widely used in aerospace, biomedicine, mechanical engineering, and other fields due to their excellent corrosion resistance, low density, good biocompatibility, and high specific strength. However, the low strength of pure titanium generally fails to meet the strength requirements of structural components, thus limiting its application and development. Ti-Zr alloys, obtained by adding zirconium to titanium, are widely used in the aerospace and nuclear industries due to their excellent properties, such as high specific strength at room and high temperatures, good creep resistance, low thermal neutron absorption cross-section, and corrosion resistance. These include nuclear radiation shields, automotive and aircraft parts, bearing assemblies, ballasts, and heat exchangers, all of which are made from titanium-zirconium alloys. However, Ti-Zr alloys produced using conventional processes have poor plasticity and toughness, which has become a bottleneck restricting the development of Ti-Zr alloy powder metallurgy synthesis. In addition, parts with complex shapes (especially those with complex flow paths and shaped holes), such as blisks, pump impellers, and hot gas valves, are difficult to process using traditional cutting methods. Therefore, improving the comprehensive mechanical properties of Ti-Zr alloy, enhancing its service performance, and realizing the forming and manufacturing of complex-shaped parts are of great practical significance for its popularization in the field of aerospace key component manufacturing.

[0003] Therefore, the present invention proposes a Ti-Zr-O high-strength and toughness titanium alloy design and preparation method, which uses oxygen and zirconium as strengthening elements and combines LPBF technology to prepare a new type of high-strength and toughness titanium alloy, thereby achieving low-cost design and preparation of high-strength and toughness titanium alloy. Summary of the Invention

[0004] In order to address the deficiencies in the prior art, the purpose of the present invention is to provide a Ti-Zr-O high-strength and toughness titanium alloy design and preparation method, using oxygen and zirconium as strengthening elements and combining LPBF technology to prepare a new type of high-strength and toughness titanium alloy, thereby achieving low-cost design and preparation of high-strength and toughness titanium alloys to solve the problems of poor plasticity and toughness of existing Ti-Zr alloys.

[0005] The purpose of the present invention is mainly achieved through the following technical solutions:

[0006] The first aspect of the present invention provides a Ti-Zr-O high-strength and toughness titanium alloy, wherein the chemical composition of the titanium alloy is as follows by mass percentage: C≤0.01%, O: 0.46~0.5%, Zr: 1%~2%, H≤0.015%, N≤0.02%, and the balance is Ti and unavoidable impurities.

[0007] Furthermore, the titanium alloy is formed by forming pure titanium powder through laser powder bed melting technology, and the particle size range of the pure titanium powder used is 15 to 53 μm.

[0008] A second aspect of the present invention provides a method for preparing the above-mentioned Ti-Zr-O high-strength and toughness titanium alloy, comprising the following steps:

[0009] Step 1: heat-treating pure titanium powder with a particle size of 15 to 53 μm to obtain a titanium alloy powder with an oxygen content of 0.46 to 0.5 wt.%;

[0010] Step 2: Add 1% to 2% zirconium powder to the titanium alloy powder in step 1 to obtain Ti-Zr-O alloy powder.

[0011] Step 3: The Ti-Zr-O alloy powder obtained in step 2 is formed by laser powder bed melting technology to obtain a Ti-Zr-O high-strength and tough titanium alloy product.

[0012] Furthermore, in step 1, the chemical composition of the powder after heat treatment is as follows by mass percentage: C≤0.01%, O: 0.08-0.1%, H≤0.015%, N≤0.02%, and the remainder is Ti and unavoidable impurities.

[0013] Furthermore, in step 2, the mass of the zirconium powder accounts for 1% to 2% of the mass of the total mixture.

[0014] Furthermore, in step 2, the powder mixing process comprises weighing zirconium powder and the titanium alloy powder described in step 1 so that the weight of the zirconium powder accounts for 1% to 2% of the total weight of the mixture, and placing the mixture together with an equal weight of 5 mm diameter stainless steel balls into a mixing tank. The mixture is continuously mixed at 80 rpm for 3 hours in an argon atmosphere using a mixer.

[0015] Furthermore, in step 3, the forming parameters of the laser powder bed fusion technology are: laser power 180-200W, scanning speed 800-1000mm / s, pass spacing 100-120μm, powder thickness 30μm, and the protective atmosphere is high-purity argon.

[0016] The Ti-Zr-O high-strength and toughness titanium alloy obtained by the above preparation method has a microstructure consisting of needle-shaped α' martensite and oxygen-rich phase interlaced in primary β grains.

[0017] The Ti-Zr-O high-strength and tough titanium alloy obtained by the above preparation method has a room temperature tensile strength greater than 1150 MPa, a yield strength greater than 1050 MPa, and an elongation at break greater than 21%.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) When designing the composition of titanium alloy, oxygen was introduced as a strengthening element to replace the commonly used solid solution elements such as W, Mo, and Nb. The oxygen content of the designed Ti-Zr-O high-strength and tough titanium alloy was 0.46-0.5%, and the Zr content was 1%-2%. Expensive rare metals such as Nb, Cr, and Mo were not used. At the same time, the rapid cooling characteristics of laser powder bed melting (LPBF) technology were combined to obtain ultrafine needle-shaped α' martensite structure and oxygen-rich phase, achieving a significant enhancement in strength and plasticity.

[0020] (2) The present invention adopts the laser powder bed fusion technology (LPBF) forming process to form Ti-Zr-O high-strength and tough titanium alloy. Compared with the traditional melting and forging processes, LPBF technology has an extremely fast cooling rate and can obtain a unique solidification structure, while reducing material waste, lowering the preparation cost, and can also prepare complex shapes.

[0021] (3) The room temperature tensile strength of the Ti-Zr-O high-strength and tough titanium alloy obtained by the present invention is greater than 1150 MPa, the yield strength is greater than 1050 MPa, and the elongation at break is greater than 21%. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a photo of a Ti-Zr-O high-strength and tough titanium alloy formed part prepared by LPBF technology in Example 1 of the present invention;

[0023] Figure 2 This is a SEM photograph of the microstructure of a Ti-Zr-O high-strength and tough titanium alloy formed part prepared by LPBF technology in Example 2 of the present invention;

[0024] Figure 3 This is the room temperature tensile stress-strain curve of the Ti-Zr-O high-strength and toughness titanium alloy formed part prepared by LPBF technology in Example 3 of the present invention. DETAILED DESCRIPTION

[0025] The following describes in further detail the composition design and preparation methods of a Ti-Zr-O high-strength and toughness titanium alloy, with reference to specific examples. A detailed description of the preferred embodiments below will provide practitioners in the art with a better understanding of the advantages and benefits of the present invention. These examples are for illustrative purposes only and the present invention is not limited to these examples.

[0026] The invention provides a high-strength and toughness Ti-Zr-O titanium alloy, whose chemical composition, calculated by mass percentage, is as follows: C≤0.01%, O: 0.46-0.5%, Zr: 1%-2%, H≤0.015%, N≤0.02%, and the balance is Ti and unavoidable impurities.

[0027] The composition design of the present invention is based on the following principles:

[0028] Oxygen: Oxygen is an interstitial solid solution element in titanium alloys, which can play a role in solid solution strengthening of titanium alloys. At the same time, the interaction between oxygen and dislocations in titanium alloys can significantly improve the strength of titanium alloys. However, most studies have reported that the addition of oxygen will lose plasticity while improving the strength of titanium alloys, resulting in a significant decrease in the elongation of titanium alloys. Excessive oxygen content will also promote the formation of brittle Ti3Al phase in titanium alloys, making titanium alloys brittle. The use of oxygen as the main strengthening element of titanium alloys in the present invention overturns the traditional perception that the oxygen content of titanium metals is inversely proportional to their plasticity, achieves a synergistic balance of strength and plasticity, and provides new ideas for the design of high-performance metal materials. The main reason is that the rapid cooling rate of LPBF technology is used to form oxygen enrichment and oxygen-rich phases in titanium alloy formed parts, so that the titanium alloy maintains a certain degree of plasticity and toughness while achieving high strength. In summary, the oxygen content of the titanium alloy of the present invention is controlled at 0.46-0.5%.

[0029] Zirconium: Because metal Zr and Ti belong to the same family, both have low density (ρ Z r =2g / cm 3 ,ρ T i =4.5g / cm 3 ), low thermal expansion coefficient (α Zr =2.36×10 -6 / K,α Ti =8.36×10 -6 / K). In the earth's crust, the reserves of Zr are higher than those of some commonly used metals, such as Cu, Ni and Zn, and the price of raw materials is close to that of Ti. In addition, studies have shown that Zr and Zr alloys have low thermal neutron cross-sections, excellent radiation resistance, and resistance to various corrosions, and have the ability to serve in complex space environments. Therefore, Zr and Zr alloys have great potential as materials for space activity components in extreme space environments. Introducing the Zr element into titanium alloys can not only lower the melting point of the alloy and reduce the amount of impurities absorbed during the alloy smelting process, but also refine the grains and play a role in fine grain strengthening of the alloy. In addition, the solid solubility in titanium alloys is extremely large, which can play a role in solid solution strengthening in titanium alloys, while reducing the martensite start transformation temperature Ms and inhibiting the formation of ω phase. In summary, the zirconium content of the titanium alloy of the present invention is controlled at 1% to 2%.

[0030] Example 1

[0031] The composition of C: 0.008%, O: 0.48%, Zr: 1%, H: 0.013%, N: 0.018%, and the balance of Ti and unavoidable impurities was LPBF formed. The printing process was carried out in a high-purity argon environment with a laser power of 180W, a scanning speed of 800mm / s, a pass spacing of 100μm, and a powder thickness of 30μm. Figure 1 The image shows an LPBF-formed part. The microstructure of the LPBF-formed titanium alloy sample was observed, and the sample was then machined into tensile bars for room-temperature mechanical property testing. The titanium alloy sample exhibited a tensile strength of 1174 MPa, a yield strength of 1072 MPa, and an elongation of 21.4%.

[0032] Example 2

[0033] A powder with a composition of 0.007% C, 0.5% O, 2% Zr, 0.012% H, and 0.002% N, with the remainder being Ti and unavoidable impurities, was subjected to LPBF forming. The printing process was carried out in a high-purity argon atmosphere with a laser power of 180W, a scanning speed of 1000mm / s, a pass spacing of 100μm, and a powder coating thickness of 30μm. The microstructure of the titanium alloy sample after LPBF forming was observed, as shown in the following figure. Figure 2 As shown. It can be seen that the microstructure of the LPBF-formed Ti-Zr-O high-strength and tough titanium alloy is needle-shaped α' martensite interlaced within the primary β grains. α' martensite is a non-equilibrium phase. Due to the rapid cooling during the LPBF process, the non-equilibrium phase transformation from the primary β phase to α' martensite occurs. The needle-shaped α' structure can effectively improve the strength of the titanium alloy formed parts. Subsequently, the formed parts were machined into tensile bars to test the room temperature mechanical properties. The titanium alloy sample had a tensile strength of 1200 MPa, a yield strength of 1090 MPa, and an elongation at break of 22.3%.

[0034] Example 3

[0035] The powder with the composition of C: 0.005%, O: 0.46%, Zr: 1%, H: 0.010%, N: 0.019%, and the balance of Ti and inevitable impurities was LPBF formed. The printing process was carried out in a high-purity argon environment. The printing process was as follows: laser power 200W, scanning speed 866mm / s, pass spacing 120μm, and powder thickness 30μm. The microstructure of the titanium alloy sample after LPBF forming was observed, and then it was machined into tensile bars to test the room temperature mechanical properties. Figure 3 As shown, the tensile strength of the titanium alloy sample is 1150 MPa, the yield strength is 1050 MPa, and the elongation after fracture is 21%.

[0036] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A Ti-Zr-O high-strength and tough titanium alloy, characterized in that: The chemical composition of the titanium alloy is as follows by mass percentage: C≤0.01%, O: 0.46-0.5%, Zr: 1%-2%, H≤0.015%, N≤0.02%, and the remainder is Ti and unavoidable impurities.

2. The Ti-Zr-O high-strength and toughness titanium alloy according to claim 1, characterized in that: The titanium alloy is formed by using a laser powder bed melting technology to form titanium alloy powder, and the particle size range of the titanium alloy powder used is 15 to 53 μm.

3. A method for preparing the Ti-Zr-O high-strength and toughness titanium alloy according to claim 2, characterized in that: The steps include: Step 1: heat-treating pure titanium powder with a particle size of 15 to 53 μm to obtain a titanium alloy powder with an oxygen content of 0.46 to 0.5 wt.%; Step 2: Add zirconium powder to the titanium alloy powder described in step 1 to mix the powders to obtain Ti-Zr-O alloy powder; Step 3: The Ti-Zr-O alloy powder obtained in step 2 is formed by laser powder bed melting technology to obtain a Ti-Zr-O high-strength and tough titanium alloy product.

4. The method for preparing a Ti-Zr-O high-strength and tough titanium alloy according to claim 3, wherein: In step 1, the chemical composition of the powder after heat treatment is as follows by mass percentage: C≤0.01%, O: 0.08-0.1%, H≤0.015%, N≤0.02%, and the remainder is Ti and unavoidable impurities.

5. The method for preparing a Ti-Zr-O high-strength and tough titanium alloy according to claim 3, wherein: In step 2, the mass of the zirconium powder accounts for 1% to 2% of the total mass of the mixture.

6. The method for preparing a Ti-Zr-O high-strength and tough titanium alloy according to claim 3, wherein: In step 2, the powder mixing process is to weigh the zirconium powder and the titanium alloy powder described in step 1 according to the percentage of the mass of the zirconium powder to the mass of the total mixture being 1% to 2%, and put them into a mixing tank together with stainless steel metal balls of the same mass and a diameter of 5 mm. Under an argon protective atmosphere, the mixing is continued for 3 hours by a mixer at a speed of 80 r / min.

7. The method for preparing a Ti-Zr-O high-strength and tough titanium alloy according to claim 3, wherein: In step 3, the forming parameters of the laser powder bed fusion technology are: laser power 180-200W, scanning speed 800-1000mm / s, pass spacing 100-120μm, powder thickness 30μm, and the protective atmosphere is high-purity argon.

8. The Ti-Zr-O high-strength and toughness titanium alloy obtained by the preparation method according to any one of claims 3 to 7, characterized in that: The microstructure of the titanium alloy is needle-shaped α' martensite and oxygen-rich phase interlaced in primary β grains.

9. The Ti-Zr-O high-strength and toughness titanium alloy obtained by the preparation method according to any one of claims 3 to 7, characterized in that: The room temperature tensile strength of the titanium alloy is ≥1150 MPa, the yield strength is ≥1050 MPa, and the elongation at break is ≥21%.

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