Preparation process of high-toughness titanium alloy by laser additive manufacturing

Abstract

The invention relates to the technical field of laser additive manufacturing, and provides a laser additive manufacturing high-toughness titanium alloy preparation process, which comprises the following steps: drying TC4 titanium alloy powder and 316L stainless steel powder at 100-140 DEG C for 1 hour, mixing the TC4 titanium alloy powder and the 316L stainless steel powder, adding the mixture into a powder feeding type metal laser 3D printer for printing, carrying out linear cutting, and finally carrying out a tensile test. The TC4 titanium alloy matrix and the 316L stainless steel powder are compounded and added, and the interface strengthening effect of 316L is utilized, so that the tensile strength and the elongation of the titanium alloy are remarkably improved, and high-toughness collaborative optimization is achieved; and the forming efficiency and quality are balanced by the laser power of 1200-1400 W, the linear speed of 1100-1400 mm / min and the powder feeding amount of 8-9 g / min, and the defects of pores, cracks and the like are reduced. The material has the light weight of titanium alloy and the corrosion resistance of 316L, and can be applied to the fields of aerospace structural parts, medical instrument implants and the like with high requirements on toughness and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of laser additive manufacturing technology, and in particular to a laser additive manufacturing process for preparing high-strength and high-toughness titanium alloys. Background Technology

[0002] While TC4 is a high-performance metallic material, technological advancements have rendered it insufficient for certain engineering requirements. To improve TC4's performance, composite alloys are employed to enhance its properties. However, traditional alloy manufacturing methods are inadequate for TC4; therefore, an advanced method—coaxial powder feeding laser additive manufacturing—is used.

[0003] TC4 titanium alloy, as an important structural material, possesses excellent strength, corrosion resistance, and low density, and is widely used in aerospace, automotive manufacturing, and other fields. However, TC4 alloy alone may not meet the performance requirements of certain engineering applications, necessitating further performance improvements. Combining different metallic materials can leverage the advantages of each material to achieve synergistic performance enhancements. Introducing 316L stainless steel powder into TC4 alloy can improve its performance and expand its application areas. Therefore, a process is needed to prepare high-strength and high-toughness titanium alloys by incorporating 316L stainless steel powder into TC4 alloy. Summary of the Invention

[0004] In view of this, the purpose of this invention is to propose a laser additive manufacturing process for high-strength and high-toughness titanium alloys, which solves the problems in the background art.

[0005] To achieve the above objectives, the present invention provides a laser additive manufacturing process for preparing high-strength and high-toughness titanium alloys, comprising the following steps:

[0006] Step 1: Prepare TC4 titanium alloy powder and 316L stainless steel powder, and dry both.

[0007] Step 2: Mix TC4 titanium alloy powder and 316L stainless steel powder in a stirrer for 4-10 hours, with 316L stainless steel powder accounting for 1-8% of the total weight.

[0008] Step 3: Add the mixed powder to the powder-feeding metal laser 3D printer. The laser power of the 3D printer is 1200W-1600W, the linear speed is 1000-1400mm / min, and the powder feeding rate is 8g / min-10g / min.

[0009] Step four: The printed parts are wire-cut, and finally, a tensile test is performed.

[0010] Preferably, the TC4 titanium alloy powder contains 6.0-6.65 wt.% Al, 3.5-4.5 wt.% V, ≤0.20 wt.% Fe, ≤0.03 wt.% C, ≤0.10 wt.% O, ≤0.01 wt.% N, ≤0.002 wt.% H, with Ti as the balance.

[0011] Preferably, the particle size of the TC4 titanium alloy powder is 53-105 μm.

[0012] Preferably, the drying time in step one is 1 hour, and the drying temperature is 100-140℃.

[0013] Preferably, the 316L stainless steel powder is 316L stainless steel powder prepared by the rotating electrode method.

[0014] Preferably, before step one, a tensile part needs to be designed based on the final tensile test, and then a printed part needs to be designed based on the tensile part.

[0015] Preferably, both the stretched part and the printed part are dog bone shaped, thicker at both ends and thinner in the middle.

[0016] Preferably, in step three, the laser power is 1200W-1400W, the linear speed is 1100-1400mm / min, and the powder feeding rate is 8g / min-9g / min.

[0017] Preferably, in step two, the 316L stainless steel powder accounts for 6-8% of the total weight.

[0018] The beneficial effects of this invention are as follows: First, TC4 titanium alloy powder and 316L stainless steel powder are dried at 100-140℃ for 1 hour. Then, the two are mixed and added to a powder-feed metal laser 3D printer for printing. Following wire cutting, a tensile test is performed. Through the composite addition of TC4 titanium alloy matrix and 316L stainless steel powder, the interfacial strengthening effect of 316L significantly improves the tensile strength and elongation of the titanium alloy, achieving a synergistic optimization of "high strength and toughness." The drying parameters of 100-140℃ for 1 hour ensure powder flowability and prevent powder clogging during printing. Defects such as layering are eliminated; the 316L powder prepared by the rotating electrode method has uniform particle size, further improving the consistency of mixing and printing; 4-10 hours of stirring and mixing ensures uniform powder dispersion and tight interface bonding; 1200-1400W laser power + 1100-1400mm / min linear speed + 8-9g / min powder feed balances molding efficiency and quality, reducing printing defects such as pores and cracks; the material combines the lightweight of titanium alloy with the corrosion resistance of 316L, and can be applied to aerospace structural parts, medical device implants and other fields with high requirements for strength and corrosion resistance. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 These are tensile stress-strain curves of Embodiments 1 and 2 of the present invention;

[0021] Figure 2 These are metallographic microstructure images of Embodiments 1 and 2 of the present invention;

[0022] Figure 3 These are the XRD characterization diagrams of Embodiments 1 and 2 of the present invention;

[0023] Figure 4 These are SEM characterization images of Embodiments 1 and 2 of the present invention;

[0024] Figure 5 These are EBSD characterization diagrams of Embodiments 1 and 2 of the present invention;

[0025] Figure 6 This is a characterization diagram of Embodiment 1 of the present invention;

[0026] Figure 7 This is a characterization diagram of Embodiment 2 of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0028] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0029] A laser additive manufacturing process for preparing high-strength and high-toughness titanium alloys includes the following steps:

[0030] S1, design the stretched part, and then design the printed part based on the stretched part. Both the stretched part and the printed part are dog bone shaped with thick ends and thin middle.

[0031] S2, Prepare TC4 titanium alloy powder and 316L stainless steel powder prepared by the rotating electrode method, and dry both for 1 hour at a temperature of 100-140℃.

[0032] S3, mix TC4 titanium alloy powder and 316L stainless steel powder in a stirrer for 4-10 hours;

[0033] S4. Add the mixed powder to the powder-feeding metal laser 3D printer.

[0034] S5, the printed parts are wire-cut, and finally a tensile test is performed.

[0035] S6, the TC4 titanium alloy powder contains 6.0-6.65 wt.% Al, 3.5-4.5 wt.% V, ≤0.20 wt.% Fe, ≤0.03 wt.% C, ≤0.10 wt.% O, ≤0.01 wt.% N, ≤0.002 wt.% H, with Ti as the balance.

[0036] The laser printing parameters and 316L stainless steel powder used in Example 1 are as follows:

[0037] laser power linear velocity Powder delivery volume 316L stainless steel powder W mm / mim g / min ％ 1358.7 1395.6 8.14 6.077

[0038] The laser printing parameters and 316L stainless steel powder used in Example 2 are as follows:

[0039] laser power linear velocity Powder delivery volume 316L stainless steel powder W mm / mim g / min ％ 1310.4 1370.5 8.73 6.1257

[0040] The microVickers hardness of the printed samples from Examples 1 and 2 is shown in the table below. The table shows that the average microVickers hardness of the sample printed in Example 1 is 417.4 MPa, and the average microVickers hardness of the sample printed in Example 2 is 540.5 MPa. The hardness of the sample printed in Example 2 is 123.1 MPa higher than that of the sample printed in Example 1.

[0041] Group Hardness 1 Hardness 2 Hardness 3 Hardness 4 Hardness 5 average value Example 1 432.5 393.4 430.3 420.9 410.1 417.4 Example 2 547.2 535.3 548.4 546.2 525.2 540.5

[0042] The two sets of samples prepared in Examples 1 and 2 were cut into metallographic and tensile specimens, and then polished to prepare metallographic samples. For the tensile tests, randomly selected specimens were numbered 1, 3, 7, 8, and 9 for Example 1, and 1-1, 3-1, 7-1, 8-1, and 9-1 for Example 2. For each set of process parameters, five samples were taken for mechanical property testing. The tensile stress-strain curves are shown below. Figure 1 As shown.

[0043] The mechanical properties of Examples 1 and 2 are shown in the table below.

[0044]

[0045] As shown in the figure and table above, positions 7 and 9, and 7-1 and 9-1 of the additively manufactured samples with the two sets of parameters exhibit excellent mechanical properties. The yield strength of the samples in Example 2 all exceeded 1.1 GPa, demonstrating good ductility and meeting the technical requirements.

[0046] Further characterization and testing were performed on samples at positions 7 and 9, 7-1 and 9-1 after additive manufacturing with parameters from Examples 1 and 2. Figure 2 Metallographic microstructure images of two sets of samples are shown. Figure 2 The results show that the grains of the two sets of samples are uniform and fine equiaxed grains, and also confirm that the samples printed with the two sets of process parameters exhibit excellent mechanical properties.

[0047] Samples numbered 9 and 9-1 from the two examples were selected for XRD characterization, and the results are as follows: Figure 3 As shown, the sample printed in Example 1 has peaks of the α and α' phases and a β phase peak. At the same time, the sample printed in Example 22 also has peaks of the α and α' phases and a β phase peak. Further detailed and in-depth analysis is needed through characterization and testing methods such as SEM.

[0048] Then, SEM characterization and analysis were performed on samples numbered 9 and 9-1 in the two examples, and the results are as follows. Figure 4 As shown, the deposited sample mainly consists of short rod-shaped α′ phases. During SLM forming, the high volume energy density of the laser instantly melts the TC4 powder, forming a molten pool. The cooling rate then rapidly decreases the temperature, resulting in α / α′ phase grains. The results are consistent with the XRD results. The study indicates that the alloy in the printed state is not a simple mixture of the two original alloys; that is, there are no pure Ti64 alloy or 316 stainless steel regions in the alloy. On the contrary, during the melting and mixing of the two powders, all alloying elements undergo effective diffusion and fusion. Elements such as Fe, Cr, Ni, and Mo in the stainless steel are completely dissolved in the Ti64 alloy matrix, achieving in-situ alloying. More importantly, the specially selected printing parameters can effectively control the concentration gradient and spatial distribution of elements such as Fe and Cr.

[0049] EBSD characterization was performed on samples numbered 9 and 9-1 in the two examples, as follows: Figure 5 As shown, the results indicate that the main phase is equiaxed β phase, and the large grains are β phase grains. The secondary α′ phase may not have been characterized because it is small.

[0050] The fracture surfaces of the tensile specimens at positions 7 and 9, 7-1 and 9-1, which exhibited excellent mechanical properties in the two embodiments, were characterized and analyzed, as follows: Figure 6 and 7 As shown.

[0051] For sample No. 7 in Example 1, some micropores were observed in the fracture morphology, which showed ductile fracture. For sample No. 9 in Example 1, some shear fracture was observed in the fracture morphology, and the dimples were relatively shallow under high magnification. The comparison showed that the dimples of sample No. 7 were deeper than those of sample No. 9, which indicates that the mechanical properties of sample No. 7 have a higher elongation than those of sample No. 9.

[0052] The fracture surfaces of tensile specimens 7-1 and 9-1, manufactured by additive manufacturing in Example 2, were characterized and analyzed. Specimen 7-1 exhibited ductile fracture morphology; specimen 9-1 showed partial shear fracture morphology, with shallow dimples observed under high magnification. Comparison revealed that specimen 7-1 had deeper dimples, indicating that specimen 7-1 possessed a higher elongation than specimen 9-1.

[0053] In summary, when the process parameters are the same, the mechanical properties of the samples manufactured by additive manufacturing in sequence are slightly different, indicating that the temperature field in the initial state of the forming process has a relatively large influence on the microstructure and properties after forming.

[0054] A neural network modeling optimization high-entropy design method was adopted. The composition of TC4 titanium alloy was controlled by adding 316L. Titanium alloy was prepared by laser-directed energy deposition. Characterization methods such as metallographic microscopy, scanning electron microscopy, and electron backscattering, as well as mechanical property testing, were used to clarify the correlation between microstructure and mechanical properties. Process parameters were optimized to achieve the mechanical property indicators. A four-in-one model for preparing high-strength and high-toughness titanium alloys can be established to integrate composition, process, microstructure, and properties.

[0055] The average hardness of the printed specimens in Example 1 was 417.4 HV, and the average hardness of the printed specimens in Example 2 was 540.5 HV. Tensile tests showed that the average yield strength of both specimens exceeded 1.1 GPa, exhibiting good ductility and meeting the technical requirements.

[0056] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and many other variations of different aspects of the invention as described above exist, which are not provided in detail for the sake of brevity. Any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A laser additive manufacturing process for preparing high-strength and high-toughness titanium alloys, characterized in that, It includes the following steps: Step 1: Prepare TC4 titanium alloy powder and 316L stainless steel powder, and dry both. Step 2: Mix TC4 titanium alloy powder and 316L stainless steel powder in a stirrer for 4-10 hours, with 316L stainless steel powder accounting for 1-8% of the total weight. Step 3: Add the mixed powder to the powder-feeding metal laser 3D printer. The laser power of the 3D printer is 1200W-1600W, the linear speed is 1000-1400mm / min, and the powder feeding rate is 8g / min-10g / min. Step four: The printed parts are wire-cut, and finally, a tensile test is performed.

2. The laser additive manufacturing process for high-strength and high-toughness titanium alloys according to claim 1, characterized in that, The TC4 titanium alloy powder contains 6.0-6.65 wt.% Al, 3.5-4.5 wt.% V, ≤0.20 wt.% Fe, ≤0.03 wt.% C, ≤0.10 wt.% O, ≤0.01 wt.% N, ≤0.002 wt.% H, with Ti as the balance.

3. The laser additive manufacturing process for high-strength and high-toughness titanium alloys according to claim 2, characterized in that, The particle size of the TC4 titanium alloy powder is 53-105 μm.

4. The laser additive manufacturing process for high-strength and high-toughness titanium alloys according to claim 1, characterized in that, The drying time in step one is 1 hour, and the drying temperature is 100-140℃.

5. The laser additive manufacturing process for high-strength and high-toughness titanium alloys according to claim 1, characterized in that, The 316L stainless steel powder is 316L stainless steel powder prepared by the rotating electrode method.

6. The laser additive manufacturing process for high-strength and high-toughness titanium alloys according to claim 1, characterized in that, Before step one, a tensile part needs to be designed based on the final tensile test, and then a printed part needs to be designed based on the tensile part.

7. The laser additive manufacturing process for high-strength and high-toughness titanium alloys according to claim 6, characterized in that, Both the stretched and printed parts are dog bone shaped, thicker at both ends and thinner in the middle.

8. The laser additive manufacturing process for high-strength and high-toughness titanium alloys according to claim 1, characterized in that, In step three, the laser power is 1200W-1400W, the linear speed is 1100-1400mm / min, and the powder feeding rate is 8g / min-9g / min.

9. The laser additive manufacturing process for high-strength and high-toughness titanium alloys according to claim 8, characterized in that, In step two, the 316L stainless steel powder accounts for 6-8% of the total weight.

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