Titanium alloy metal powder and structural part laser melting deposition additive manufacturing method

Abstract

The invention provides titanium alloy metal powder and a laser melting deposition additive manufacturing method for a structural part. According to the method, a + beta double-phase titanium alloy metal powder strengthened by elements such as oxygen and iron is firstly prepared, and then deposition forming of a large-size component is completed according to a laser melting deposition additive manufacturing process. According to the method, the technological characteristics that during laser additive manufacturing, the molten metal cooling speed is high, and the element segregation degree is low are utilized, the problem that during titanium alloy component system design, the content of oxygen, iron and other elements is too high, and consequently brittleness is sharply increased is solved, and the purpose that the element O serves as an alpha-phase stable element is achieved; and designing a component system by taking Fe element as a main beta-phase stable element. The prepared large-size titanium alloy component shows good strength and toughness, the tensile strength is larger than or equal to 930 Mpa, the yield strength is larger than or equal to 850 Mpa, the percentage elongation after fracture is larger than or equal to 10%, and the percentage reduction of area is larger than or equal to 20%.

Description

Technical Field

[0001] The invention relates to the field of laser additive manufacturing, and in particular to a titanium alloy metal powder with high oxygen and iron content and a laser melting deposition additive manufacturing method for a structural part. Background Art

[0002] Titanium alloy is an alloy formed by adding other alloy elements to titanium. Titanium alloy has good corrosion resistance, fatigue resistance and high specific strength, and plays an irreplaceable role in reducing the weight of aerospace equipment. Therefore, it is widely used in aero engines, aircraft, missiles and other fields.

[0003] Titanium has two allotropic structures, the close-packed hexagonal α phase and the body-centered cubic β phase. Taking advantage of the allotropic characteristics of titanium, different phase-stabilizing elements are added to the titanium alloy to make the phase transition temperature and phase component content show differences. According to the different matrix structures obtained under room temperature conditions, titanium alloys can be divided into the following three categories: α titanium alloy, β titanium alloy and a+β titanium alloy. Among them, a+β titanium alloy is the most widely used. It has good comprehensive properties, good organizational stability, good toughness, plasticity and high-temperature deformation properties, can be well processed by hot pressure, and can be quenched and aged to strengthen the alloy.

[0004] The laser generates a molten pool on the surface of the substrate and moves at high speed. The material is directly fed into the high-temperature melting zone in the form of powder or filaments. After melting, it is deposited layer by layer. This is called laser melting deposition (LMD) additive manufacturing technology. The use of this technology to complete the near-net forming of titanium alloy structural parts greatly improves the production and processing efficiency, and has a high degree of freedom in forming. With the multi-axis motion platform, it can realize the unsupported additive manufacturing of complex components. In addition, due to its own process characteristics, the microstructure and composition distribution of the titanium alloy prepared by laser melting deposition additive manufacturing are different from traditional production and processing methods such as casting, showing more excellent comprehensive mechanical properties, providing more possibilities for the design of titanium alloy components.

[0005] The α-phase stabilizing elements of titanium alloy mainly include Al, O, N, C, etc., and the β-phase stabilizing elements mainly include Mo, Nb, V, Cr, Fe, Mn, Cu, etc. O and Fe elements are abundant in nature and have low material costs. The development of O and Fe-strengthened a+β titanium alloys with stable performance has great market value. However, in the traditional material preparation process, higher O and Fe contents will lead to increased brittleness and poor mechanical properties of titanium alloys. When designing the titanium alloy material composition system, O, Fe and other elements are often regarded as harmful elements and their content is controlled at a low level. It is necessary to reduce or eliminate the embrittlement effect caused by O, Fe, etc. in the process of titanium alloy parts indicators by adopting new preparation technologies, reduce the cost of titanium alloy use, and increase the freedom of titanium alloy composition design. Summary of the invention

[0006] In order to make up for the deficiencies of the prior art, the present invention provides a titanium alloy metal powder and a laser melting deposition additive manufacturing method for structural parts. The present invention first prepares a+β dual-phase titanium alloy metal powder reinforced with elements such as oxygen and iron, and then completes the deposition molding of large-size components according to the laser melting deposition additive manufacturing process. The present invention utilizes the process characteristics of fast cooling speed of molten metal and low degree of element segregation during laser additive manufacturing, solves the problem that high levels of oxygen, iron and other elements can easily lead to a sharp increase in brittleness when designing the titanium alloy component system, and realizes the component system design with O element as the α-phase stabilizing element and Fe element as the main β-phase stabilizing element.

[0007] The present invention is achieved through the following technical scheme: a titanium alloy metal powder used in a laser melting deposition additive manufacturing method, characterized in that the titanium alloy metal powder is composed of spherical metal powder particles with a particle size of 53~150 microns; its composition and content are: O: 0.16~0.26wt.%, Fe: 3~3.5wt.%, Mo: 1.5~2.0wt.%, Ti: balance.

[0008] The preparation method of the above-mentioned titanium alloy metal powder is: select suitable alloy raw materials, mix them according to the above-mentioned alloy components, and then place them in a vacuum furnace to complete vacuum smelting; then use a gas atomization powder making process to prepare spherical titanium alloy metal powder, and sieve out powder particles with a particle size of 53-150 microns, and then dry them at a high temperature of 100~120℃ to obtain titanium alloy metal powder.

[0009] The above-mentioned suitable alloy raw materials are industrial pure titanium and ferromolybdenum, and can also be other alloy raw materials containing titanium, iron or molybdenum to achieve the above-mentioned alloy composition requirements.

[0010] Furthermore, the gas atomization powder making process uses argon as the gas flow, with a pressure of 6-9 MPa and a speed of 200-300 m / s.

[0011] The laser melting deposition additive manufacturing method for a structure of the titanium alloy metal powder is characterized in that the titanium alloy metal powder is deposited and formed into a large-size component according to the laser melting deposition additive manufacturing process, specifically: 1) Build a printing model and use path planning software to generate a machine tool program; 2) Fix the printed substrate on the machine tool work surface and polish and clean the surface of the printed substrate as necessary; 3) Close the equipment cabin door and replace the air in the cabin with inert gas; 4) Run the processing program. The laser generated by the laser forms a moving molten pool on the surface of the substrate through the laser head. The powder delivery airflow continuously delivers the metal powder from the powder delivery copper nozzle to the molten pool and melts and deposits on the surface of the substrate under the action of the laser. The laser melting deposition molding additive manufacturing of large components is completed by layer-by-layer deposition. Figure 3 ); 5) After printing is completed, wait for the workpiece to cool down to room temperature along with the equipment, open the equipment door, and take the printed blank out of the equipment together with the substrate; 6) Heat-treat the printed blank and substrate simultaneously to eliminate or reduce internal thermal stress; 7) Use machining equipment to process the printed blank according to the part size and tolerance requirements to obtain the finished part, and conduct various performance index tests.

[0012] Furthermore, during the laser melting deposition molding additive manufacturing process of large components, the oxygen content in the working chamber is less than 500ppm, the laser spot diameter is 4~6mm, the laser power is 4~8kw, the scanning speed is 25~40mm / s, the powder feeding rate is 20~35g / min, and the overlap rate is 40~60%.

[0013] Furthermore, the establishment of the printing model requires the establishment of an additive model based on the original model. This includes adding a 1-3 mm milling compensation amount to the surface that needs to be machined (see Figure 2 ), add solid support for surfaces with an inclination angle greater than 45°, add process tables required for subsequent machining, etc.

[0014] Further, a vacuum heat treatment furnace or an inert atmosphere furnace is used for heat treatment, with a heating rate of 3-5°C / min, the temperature is raised to 600±50°C and kept at that temperature for 2-4h, and then the product is cooled to room temperature and taken out of the furnace.

[0015] This method has a small laser spot diameter and a fast scanning speed. The molten metal cools down very quickly during the additive manufacturing process. The additive manufacturing printed blank has a series of advantages such as dense internal structure, fine grain size, and weak component segregation.

[0016] The technical effect of the present invention is as follows: compared with the prior art, the present invention utilizes the process characteristics of fast cooling speed of molten metal and low degree of element segregation during laser additive manufacturing, solves the problem that high oxygen, iron and other elements easily lead to a sharp increase in brittleness when designing the titanium alloy component system, and realizes the component system design with O element as α-phase stabilizing element and Fe element as the main β-phase stabilizing element. The prepared large-size titanium alloy components show good strength and toughness, with tensile strength ≥930Mpa, yield strength ≥850Mpa, elongation after fracture ≥10%, and cross-sectional shrinkage ≥20%, which greatly improves the freedom of design of titanium alloy component system and reduces the cost of titanium alloy raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The microscopic morphology of the titanium alloy metal powder of the present invention; Figure 2 Add milling compensation to the part surface; (a) initial model; (b) printed model; Figure 3 It is a schematic diagram of the laser melting deposition process of the present invention; Figure 4 A path planning strategy for laser melting deposition additive manufacturing of the present invention; Figure 5 The microstructure of the deposited titanium alloy component; (a) transverse - 200X; (b) longitudinal - 200X; (c) transverse - 500X; (d) longitudinal - 500x. DETAILED DESCRIPTION

[0018] The effects are described below in conjunction with the embodiments and drawings.

[0019] Embodiment 1-3: 1. Preparation of high-oxygen and high-iron titanium alloy metal powder Composition design of Example 1-3: O: 0.16~0.26wt.%, Fe: 3~3.5wt.%, Mo: 1.5~2.0wt.%, Ti: balance; 1) Select appropriate alloy raw materials, mix them according to the alloy composition, and then place them in a vacuum furnace to complete vacuum melting. The vacuum degree is less than 0.1Pa, the melting temperature is 1700±50℃, and the holding time is not less than 60min; 2) Prepare spherical titanium alloy metal powder by gas atomization powder making process; wherein, the gas atomization powder making process uses argon as the gas flow, the pressure is 6-9MPa, and the speed is 200-300m / s. Powder particles with a particle size of 53-150 microns are screened from the collected powder, dried, and stored for later use; 3) The sieved metal powder with a particle size of 53-150 microns is dried at a high temperature of 100-120° C., cooled to room temperature with the drying equipment, taken out and sealed for storage to obtain a high-oxygen and high-iron titanium alloy metal powder.

[0020] After testing, the composition of the titanium alloy metal powder of each embodiment is shown in Table 1, and the microscopic morphology of the titanium alloy metal powder prepared in Example 1 is shown in Figure 1 As shown, the titanium alloy metal powder has high sphericity and uniform particle size distribution.

[0021] Table 1 Titanium alloy metal powder composition of each example

[0022] 2. A method for laser melting deposition additive manufacturing of titanium alloy structural parts, comprising the following steps: 1) Create an additive model based on the original model. This includes adding 1~3mm milling compensation to the surface that needs to be machined (see Figure 2 ), add physical support to the surface with an inclination angle greater than 45°, add process tables required for subsequent machining, etc. Use path planning software to generate machining programs for machine tools based on the printed model; 2) Fix the printed substrate on the machine tool work surface with a pressing plate, and polish and clean the substrate surface as necessary; 3) Close the equipment cabin door, and gradually replace the air in the cabin with argon gas by cyclically evacuating and replenishing argon gas; 4) Run the processing program, the laser generated by the laser forms a moving molten pool on the surface of the substrate through the laser head, the powder delivery airflow continuously delivers the metal powder from the powder delivery copper nozzle to the molten pool and melts and deposits on the surface of the substrate under the action of the laser, and completes the laser melting deposition molding additive manufacturing of large components by layer-by-layer deposition. The schematic diagram of the laser melting deposition process of the present invention is shown in Figure 3 As shown in the figure, the direction of the laser movement changes layer by layer during the deposition process. Figure 4 The oxygen content in the working chamber is less than 500ppm, the laser spot diameter is 4-6mm, the laser power is 4-8kw, the scanning line speed is 25-40mm / s, the powder feeding rate is 20-35g / min, and the overlap rate is 40-60%. The laser melting deposition process parameters of each embodiment are shown in Table 2.

[0023] Table 2 Laser melting deposition process parameters of various embodiments

[0024] 5) After printing is completed, wait for the workpiece to cool down to room temperature along with the equipment, open the equipment door, and take the printed blank out of the equipment together with the substrate; 6) Heat-treat the printed blank and the substrate at the same time to eliminate or reduce internal thermal stress; wherein, use a vacuum heat treatment furnace or an inert atmosphere furnace to heat-treat the printed blank, with a heating rate of 3~5℃ / min, heating to 600±50℃ and keeping the temperature for 2~4h, and then cool to room temperature and take out of the furnace; 7) Use machining equipment to process the printed blank according to the part size and tolerance requirements to obtain the finished part, and conduct various performance index tests.

[0025] Product structure Figure 5 As shown in the figure, the deposited microstructure and properties of titanium alloy components are anisotropic. The columnar crystals grow along the deposition direction, resulting in the observation of coarse columnar crystals in the longitudinal direction, while equiaxed crystals are mainly present in the transverse direction, and a+β two-phase lamellar structures are distributed inside the grains.

[0026] According to "GB / T228.1-2021 Tensile Test of Metal Materials Part 1: Room Temperature Test Method", the mechanical properties of deposited titanium alloy structural parts were characterized. The results are shown in Table 3. The transverse and longitudinal tensile strengths of each embodiment are all above 930 MPa, the yield strength is all above 850 MPa, the elongation after fracture is all above 10%, and the cross-sectional shrinkage rate is all above 20%, showing good comprehensive mechanical properties.

[0027] Table 3 Mechanical properties of titanium alloy components manufactured by laser melting deposition additive manufacturing in various examples

Claims

1. A titanium alloy metal powder used in a laser melting deposition additive manufacturing method, characterized in that: The titanium alloy metal powder is composed of spherical metal powder particles with a particle size of 53 to 150 microns; its composition and content are: O: 0.16 to 0.26 wt.%, Fe: 3 to 3.5 wt.%, Mo: 1.5 to 2.0 wt.%, Ti: balance; The laser melting deposition additive manufacturing method is as follows: the laser generated by the laser forms a moving molten pool on the surface of the substrate through the laser head, the powder feeding airflow continuously delivers the metal powder from the powder feeding copper nozzle to the molten pool and melts and deposits on the surface of the substrate under the action of the laser, and the laser melting deposition molding additive manufacturing of large components is completed by layer-by-layer deposition. After completion, the workpiece is cooled to room temperature along with the equipment.

2. The method for preparing the titanium alloy metal powder according to claim 1, characterized in that: Select appropriate alloy raw materials, mix them according to the alloy composition described in claim 1, and then place them in a vacuum furnace to complete vacuum smelting; then use a gas atomization powder making process to prepare spherical titanium alloy metal powder, and sieve out powder particles with a particle size of 53-150 microns, and then dry them at high temperature to obtain titanium alloy metal powder; the suitable alloy raw materials are industrial pure titanium and ferromolybdenum.

3. The method for preparing titanium alloy metal powder according to claim 2, characterized in that: The gas atomization powder making process uses argon as the gas flow, with a pressure of 6-9 MPa and a speed of 200-300 m / s.

4. The method for manufacturing a structure of titanium alloy metal powder by laser melting deposition additive manufacturing according to claim 1, characterized in that: 1) Build a printing model and use path planning software to generate a machine tool processing program; 2) Fix the printed substrate on the machine tool work surface and polish and clean the surface of the printed substrate as necessary; 3) Close the equipment cabin door and replace the air in the cabin with inert gas; 4) Run the processing program. The laser generated by the laser forms a moving molten pool on the surface of the substrate through the laser head. The powder feeding airflow continuously delivers the metal powder from the powder feeding copper nozzle to the molten pool and melts and deposits on the surface of the substrate under the action of the laser. The laser melting deposition molding additive manufacturing of large components is completed by layer-by-layer deposition. 5) After printing is completed, wait for the workpiece to cool down to room temperature along with the equipment, open the equipment door, and take the printed blank out of the equipment together with the substrate; 6) Heat treat the printed blank and the substrate at the same time to eliminate or reduce internal thermal stress; 7) Use machining equipment to process the printed blank according to the part size and tolerance requirements to obtain the finished part.

5. The laser melting deposition additive manufacturing method for a structural component according to claim 4, characterized in that: In the step 4) of the large-scale component laser melting deposition molding additive manufacturing process, the oxygen content in the working chamber is less than 500ppm, the laser spot diameter is 4-6mm, the laser power is 4-8kw, the scanning speed is 25-40mm / s, the powder feeding rate is 20-35g / min, and the overlap rate is 40-60%.

6. The laser melting deposition additive manufacturing method for a structural component according to claim 4, characterized in that: The establishment of the printing model requires establishing an additive model based on the original model.

7. The laser melting deposition additive manufacturing method for a structural component according to claim 6, characterized in that: For surfaces that need to be machined, add 0.5~2mm milling compensation, and for surfaces with an inclination angle greater than 45°, add solid support.

8. The laser melting deposition additive manufacturing method for a structural component according to claim 4, characterized in that: In step 6), a vacuum heat treatment furnace or an inert atmosphere furnace is used for heat treatment, with a heating rate of 3-5°C / min, the temperature is raised to 600±50°C and kept at that temperature for 2-4h, and then the mixture is cooled to room temperature and taken out of the furnace.

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