A method for improving fatigue strength of an additively manufactured titanium alloy part and a titanium alloy part

Abstract

This invention belongs to the field of metal additive manufacturing technology, specifically relating to a method for improving the fatigue strength of additively manufactured titanium alloy parts and the titanium alloy parts themselves. The method for improving the fatigue strength of additively manufactured titanium alloy parts, as described in this invention, improves the fatigue strength of the titanium alloy parts through three main processes: rigorous powder selection, optimization of the additive manufacturing process, and shot peening post-treatment. This simplifies the process, reduces costs, and facilitates quality control.

Description

Technical Field

[0001] This invention belongs to the field of metal additive manufacturing technology, specifically relating to a method for improving the fatigue strength of additively manufactured titanium alloy parts and titanium alloy parts prepared by the method. Background Technology

[0002] Titanium alloy additive manufacturing technology can achieve low-cost, low-carbon, and lightweight manufacturing of parts.

[0003] Laser melting deposition (LMD) is a crucial technology for additive manufacturing of titanium alloys. This technology involves layering a 3D model of the titanium alloy part and planning a path to achieve layer-by-layer deposition. This type of technology has been used for personalized production and large-scale automated production of precision or complex parts, with wide applications in aerospace and automotive engine fields. When using LMD for additive manufacturing, adjusting process parameters can typically result in titanium alloy parts with good tensile strength, yield strength, and elongation; however, fatigue strength is often unsatisfactory.

[0004] In the prior art, Chinese invention patent (application number CN201811319227.7) discloses a post-processing method for additively manufactured titanium and titanium alloy parts. This method involves first heat-treating the 3D-printed titanium or titanium alloy parts, then performing surface treatment, and further utilizing magnetic and electric fields for in-situ repair treatment to improve the tensile strength, yield strength, toughness, fatigue life, surface finish, and surface hardness of the 3D-printed titanium or titanium alloy parts. However, this disclosed post-processing method requires significantly more equipment, space, manufacturing processes, increased quality control complexity, and longer production cycles, leading to a substantial increase in manufacturing costs and a decrease in yield. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies, such as complex post-processing steps, high costs, and low yield rates, by providing a method to improve the fatigue strength of additively manufactured titanium alloy parts. Through three major processes—strict powder selection, process optimization of additive manufacturing, and shot peening post-processing—the fatigue strength of additively manufactured titanium alloy parts is improved, simplifying the process, reducing costs, and facilitating quality control.

[0006] The specific implementation details of this invention are as follows:

[0007] This invention provides a method for improving the fatigue strength of additively manufactured titanium alloy parts. The method mainly consists of three steps: powder screening, additive manufacturing, and shot peening.

[0008] The powder screening refers to screening out titanium alloy powders with an oxygen content of less than 300 ppm and a nitrogen content of less than 20 ppm.

[0009] The additive manufacturing process refers to the following steps: First, the titanium alloy powder that has undergone powder screening is dried in a vacuum drying furnace. During the drying process, the temperature is required to be below 1 torr and held at 80~120℃ for 30~150 minutes. Then, the dried titanium alloy powder is placed into a powder feeder, the titanium alloy substrate is fixed on the worktable in the argon-filled chamber, and the laser processing parameters are adjusted. After the laser processing parameters are adjusted, the additive manufacturing of the titanium alloy parts is carried out in the argon-filled chamber using the laser melting deposition method.

[0010] The shot peening process refers to the process of performing shot peening in an argon-filled chamber with an oxygen content of less than 100 ppm after the additive manufacturing is completed.

[0011] Furthermore, in order to better realize the present invention, the adjustment of laser processing parameters includes: a) adjusting the relative position of the laser spot of the laser head and the powder focus of the coaxial powder feeding head so that the laser spot position is 5~10mm below the powder focus position; b) adjusting the powder spot focus position so that the powder spot focus position is -1~1mm from the surface of the titanium alloy substrate; c) adjusting the laser spot diameter to 5~10mm.

[0012] Furthermore, to better realize the present invention, the adjustment of laser processing parameters also includes: d, setting the powder feeding rate of titanium alloy powder to 15~35g / min; e, setting the laser scanning speed to 600~1200mm / min, the overlap rate during the deposition process to 30~75%, and raising the laser head and coaxial powder feeding head upward by 0.4~1.0mm after each layer deposition; f, setting the laser power during the deposition process to 2000~4000W.

[0013] Furthermore, in order to better realize the present invention, the adjustment of laser processing parameters also includes: g, adjusting and controlling the oxygen content in the argon-filled chamber to be below 30 ppm and the nitrogen content to be below 20 ppm.

[0014] Furthermore, in order to better realize the present invention, the titanium alloy substrate is polished and then fixed to the worktable inside the argon-filled chamber.

[0015] Furthermore, in order to better realize the present invention, the powder particle size needs to be configured to meet the following conditions during the powder screening: D10 is 45±1μm and D90 is 105±1μm.

[0016] Furthermore, the titanium alloy powder is made of TC4 or Ti-6.5Al-3.5Mo-1.5Zr.

[0017] Furthermore, in order to better realize the present invention, the shot peening material used in the shot peening process is alumina ceramic shot, zirconia ceramic shot, or steel shot.

[0018] The present invention also provides a titanium alloy part, which is obtained by additive manufacturing using the above-described method for improving the fatigue strength of additively manufactured titanium alloy parts.

[0019] Furthermore, in order to better realize the present invention, the maximum pore size of the titanium alloy part is less than 200 μm; the porosity of the titanium alloy part is less than 1%; and the titanium alloy part is free from visible unfusion defects.

[0020] Furthermore, in order to better realize the present invention, the fatigue strength of the titanium alloy part is not less than 350 MPa, the tensile strength is not less than 930 MPa, and the elongation after fracture is not less than 10.0%.

[0021] The present invention has the following beneficial effects.

[0022] (1) The method for improving the fatigue strength of additively manufactured titanium alloy parts described in this invention improves the fatigue strength of additively manufactured titanium alloy parts through three major processes: strict screening of powder, optimization of additive manufacturing process, and shot peening post-treatment. It simplifies the process, reduces costs, and is conducive to quality control.

[0023] (2) The method for improving the fatigue strength of additively manufactured titanium alloy parts described in this invention can effectively reduce the porosity of laser-melted deposited titanium alloy parts.

[0024] (3) The method for improving the fatigue strength of additively manufactured titanium alloy parts described in this invention can effectively reduce the number and size of unfused defects in laser melting deposited titanium alloy parts.

[0025] (4) The titanium alloy parts prepared by the present invention have a maximum pore size of less than 200 μm, a porosity of less than 1%, and no unfused defects visible to the naked eye.

[0026] (5) The titanium alloy parts prepared by the present invention have a fatigue strength of not less than 350 MPa, a tensile strength of not less than 930 MPa, and an elongation after fracture of not less than 10.0%. Attached Figure Description

[0027] Figure 1 This is a physical image of the titanium alloy part prepared by the method described in Example 3.

[0028] Figure 2 yes Figure 1 SN curve of performance test of medium titanium alloy parts.

[0029] Figure 3 yes Figure 1 Schematic diagram of the overall fatigue fracture surface of a medium-titanium alloy component.

[0030] Figure 4 yes Figure 3 Enlarged view of the interruption point. Detailed Implementation

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments, and therefore should not be regarded as a limitation on the scope of protection. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1:

[0033] Parts manufactured using the traditional laser melting deposition additive manufacturing process often have defects such as porosity and lack of fusion, and these unique defects are directly related to the fatigue strength of the parts.

[0034] This embodiment provides a method for improving the fatigue strength of additively manufactured titanium alloy parts. It is based on laser melting deposition and optimizes the three major processes of powder screening, additive manufacturing and shot peening to improve the defects of the traditional laser melting deposition method.

[0035] The method for improving the fatigue strength of additively manufactured titanium alloy parts mainly consists of three processes: powder screening, additive manufacturing, and shot peening.

[0036] The powder screening refers to screening out titanium alloy powders with an oxygen content of less than 300 ppm and a nitrogen content of less than 20 ppm.

[0037] The additive manufacturing process refers to the following steps: First, the titanium alloy powder that has undergone powder screening is dried in a vacuum drying furnace. During the drying process, the temperature is required to be below 1 torr and held at 80~120℃ for 30~150 minutes. Then, the dried titanium alloy powder is placed into a powder feeder, the titanium alloy substrate is fixed on the worktable in the argon-filled chamber, and the laser processing parameters are adjusted. After the laser processing parameters are adjusted, the additive manufacturing of the titanium alloy parts is carried out in the argon-filled chamber using the laser melting deposition method.

[0038] The shot peening process refers to the process of performing shot peening in an argon-filled chamber with an oxygen content of less than 100 ppm after the additive manufacturing is completed.

[0039] The adjustment of laser processing parameters includes:

[0040] a. Adjust the relative position of the laser spot of the laser head and the powder focus of the coaxial powder feeding head so that the laser spot is 5-10mm below the powder focus.

[0041] b. Adjust the position of the powder spot focal point so that the focal point of the powder spot is located at -1~1mm on the surface of the titanium alloy substrate;

[0042] c. Adjust the laser spot diameter to 5~10mm;

[0043] d. Set the feeding rate of titanium alloy powder to 15~35g / min;

[0044] e. Set the laser scanning speed to 600~1200mm / min, the overlap rate during the deposition process to 30~75%, and after each layer of deposition, raise the laser head and the coaxial powder feeding head upward by 0.4~1.0mm;

[0045] f. Set the laser power to 2000~4000W during the deposition process;

[0046] g. Adjust and control the oxygen content in the argon-filled chamber to be below 30 ppm and the nitrogen content to be below 20 ppm.

[0047] The above-mentioned method for improving the fatigue strength of additively manufactured titanium alloy parts was used to prepare the parts, which reduced the size and number of defects such as porosity and lack of fusion. Combined with optimized process parameters, the fatigue strength of the titanium alloy parts was further improved.

[0048] In another specific embodiment, when screening the powder, it is also necessary to configure the powder particle size to meet the following conditions: D10 is 45±1μm, D50 is 75±1μm and D90 is 105±1μm.

[0049] D10 is the particle size corresponding to a cumulative volume distribution percentage of 10% for the sample; D50 is the particle size corresponding to a cumulative volume distribution percentage of 50% for the sample; and D90 is the particle size corresponding to a cumulative volume distribution percentage of 90% for the sample.

[0050] In another specific embodiment, the titanium alloy substrate is polished and then fixed to the worktable inside the argon-filled chamber.

[0051] In another specific embodiment, the titanium alloy powder is made of TC4 or Ti-6.5Al-3.5Mo-1.5Zr.

[0052] In another specific embodiment, the shot peening material used is alumina ceramic shot, zirconia ceramic shot, or steel shot.

[0053] Example 2:

[0054] This embodiment provides a titanium alloy part prepared using the method described in Example 1.

[0055] The maximum pore size of the titanium alloy part is less than 200 μm; the porosity of the titanium alloy part is less than 1%; the titanium alloy part is free from visible unfusion defects; and the fatigue limit of the titanium alloy part is not less than 350 MPa, the tensile strength is not less than 930 MPa, and the elongation after fracture is not less than 10.0%.

[0056] Example 3:

[0057] This embodiment, based on the method described in Example 1, uses TC4 titanium alloy powder as raw material to prepare... Figure 1 The titanium alloy part shown is manufactured using the following specific method.

[0058] A method for improving the fatigue strength of additively manufactured titanium alloy parts includes the following three main steps.

[0059] Step 1: Powder screening.

[0060] The powder screening refers to screening out titanium alloy powder with an oxygen content of less than 300 ppm and a nitrogen content of less than 20 ppm; and configuring the powder particle size to meet the following conditions: D10 is 45±1 μm, D50 is 75±1 μm and D90 is 105±1 μm.

[0061] Step 2, Additive Manufacturing.

[0062] The additive manufacturing process refers to the following steps: First, the titanium alloy powder that has undergone powder screening is dried in a vacuum drying furnace. During the drying process, the powder is held at a vacuum of 0.9 ± 0.1 torr and a temperature of 120°C for 100 minutes. Then, the dried titanium alloy powder is placed into a powder feeder, the titanium alloy substrate is fixed onto the worktable inside the argon-filled chamber, and the laser processing parameters are adjusted. After the laser processing parameters are adjusted, the titanium alloy parts are additively manufactured using a laser melting deposition method inside the argon-filled chamber.

[0063] The adjustment of laser processing parameters includes:

[0064] a. Adjust the relative position of the laser spot of the laser head and the powder focus of the coaxial powder feeding head so that the laser spot is 5mm below the powder focus.

[0065] b. Adjust the position of the powder spot focal point to 0.2 mm below the surface of the titanium alloy substrate;

[0066] c. Adjust the laser spot diameter to 5 mm;

[0067] d. Set the powder feeding rate of titanium alloy powder to 20.25 g / min;

[0068] e. Set the laser scanning speed to 800 mm / min, the overlap rate during the deposition process to 50%, and after each layer of deposition, raise the laser head and the coaxial powder feeding head upward by 0.5 mm;

[0069] f. Set the laser power to 4000 W during the deposition process;

[0070] g. Adjust and control the oxygen content in the argon-filled chamber to be 20±5 ppm and the nitrogen content to be 10±5 ppm.

[0071] Step 3: Shot peening.

[0072] The shot peening process refers to the process of shot peening with alumina ceramic shot in an argon-filled chamber with an oxygen content of 50±10 ppm after the additive manufacturing is completed.

[0073] right Figure 1 The titanium alloy parts shown were subjected to fatigue testing using a GP-100 high-frequency fatigue tester according to GB / T3075-2008 "Methods for Controlling Axial Force in Fatigue Testing of Metallic Materials". The SN curves and fatigue limits of the titanium alloy parts were obtained, as shown in the figure. Figure 2 As shown. From Figure 2 It can be seen that the fatigue strength of this titanium alloy part is 358 MPa. The overall fatigue fracture surface of the specimen is as follows: Figure 3 As shown, no non-fusion defects were observed on the fracture surface, the porosity of the fracture surface was less than 1%, and the maximum pore size was 105 μm. Figure 4 The image shows a magnified view of the fracture surface, revealing numerous tear ridges, indicating excellent toughness and strong resistance to crack propagation.

[0074] The other parts of this embodiment are the same as those in Embodiment 1 or Embodiment 2, so they will not be described again.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for improving the fatigue strength of additively manufactured titanium alloy parts, characterized in that, It mainly consists of three processes: powder screening, additive manufacturing, and shot peening, and the additive manufacturing method is optimized. The powder screening refers to screening out titanium alloy powders with an oxygen content of less than 300 ppm and a nitrogen content of less than 20 ppm. The additive manufacturing process refers to the following steps: First, the titanium alloy powder that has undergone powder screening is dried in a vacuum drying furnace. During the drying process, the temperature is required to be below 1 torr and held at 80~120℃ for 30~150 minutes. Then, the dried titanium alloy powder is placed into a powder feeder, the titanium alloy substrate is fixed on the worktable in the argon-filled chamber, and the laser processing parameters are adjusted. After the laser processing parameters are adjusted, the additive manufacturing of the titanium alloy parts is carried out in the argon-filled chamber using the laser melting deposition method. The adjustment of laser processing parameters includes: a) adjusting the relative position of the laser spot of the laser head and the powder focus of the coaxial powder feeding head, so that the laser spot position is 5~10mm below the powder focus position; b) adjusting the powder focus position, so that the powder focus position is -1~1mm from the surface of the titanium alloy substrate; c) adjusting the laser spot diameter to 5~10mm; d) setting the titanium alloy powder feeding rate to 15~35g / min; e) setting the laser scanning speed to 600~1200mm / min, the overlap rate during the deposition process to 30~75%, and raising the laser head and coaxial powder feeding head upward by 0.4~1.0mm after each layer deposition; f) setting the laser power during the deposition process to 2000~4000W. g. Adjust and control the oxygen content in the argon-filled chamber to be below 30 ppm and the nitrogen content to be below 20 ppm; The shot peening process refers to the process of performing shot peening in an argon-filled chamber with an oxygen content of less than 100 ppm after the additive manufacturing is completed.

2. The method for improving the fatigue strength of additively manufactured titanium alloy parts according to claim 1, characterized in that, The titanium alloy substrate is polished and then fixed onto the worktable inside the argon-filled chamber.

3. The method for improving the fatigue strength of additively manufactured titanium alloy parts according to claim 1, characterized in that, During the powder screening process, the powder particle size also needs to be configured to meet the following conditions: D10 is 45±1μm, D50 is 75±1μm and D90 is 105±1μm.

4. A method for improving the fatigue strength of additively manufactured titanium alloy parts according to any one of claims 1-3, characterized in that, The titanium alloy powder is made of TC4 or Ti-6.5Al-3.5Mo-1.5Zr.

5. A method for improving the fatigue strength of additively manufactured titanium alloy parts according to any one of claims 1-3, characterized in that, The shot peening process uses alumina ceramic shot, zirconia ceramic shot, or steel shot.

6. A titanium alloy part, characterized in that, The titanium alloy part is obtained by additive manufacturing using the method for improving the fatigue strength of additively manufactured titanium alloy parts as described in any one of claims 1-5.

7. A titanium alloy part according to claim 6, characterized in that, The maximum pore size is less than 200 μm; the porosity is less than 1%; and there are no visible non-fusion defects.

8. A titanium alloy part according to claim 7, characterized in that, Fatigue strength not less than 350 MPa, tensile strength not less than 930 MPa, and elongation after fracture not less than 10.0%.

Images