High-temperature titanium alloy forming method based on stress release structure

Abstract

The invention discloses a high-temperature titanium alloy forming method based on a stress release structure, and belongs to the technical field of metal additive manufacturing. The first supporting layer, the stress releasing layer and the second supporting layer are sequentially prepared from bottom to top through a selective laser melting forming method, and then the high-temperature titanium alloy part body is formed layer by layer. The sub-densified stress release layer is prepared by controlling the SLM process parameters, the plastic deformation and controllable cracking of the sub-densified stress release layer can effectively absorb and release thermal stress, the path of transmitting the thermal stress to the part body is blocked, the residual stress of the part body can be greatly reduced, the thermal stress distribution is effectively regulated and controlled, and the buckling deformation of the part is remarkably reduced. The stress release layer can prevent cracks from expanding towards the part body, and the double supporting layers form a physical barrier to limit crack propagation, so that the high-temperature titanium alloy part maintains the original mechanical property.

Description

Technical Field

[0001] This invention belongs to the field of metal additive manufacturing technology, specifically relating to a high-temperature titanium alloy forming method based on stress relief structure. Background Technology

[0002] High-temperature titanium alloys (such as Ti-6242 and Ti-1100) are widely used in key hot-end structures such as turbine blades and combustion chamber components of aero-engines due to their excellent high-temperature strength (tensile strength ≥600 MPa at 600℃) and creep resistance. Selective laser melting (SLM) technology has made it possible to form complex structures in one piece. However, in the SLM process of high-temperature titanium alloys, the rapid melting and solidification characteristics of the high-energy laser beam cause significant thermal stress inside the part (residual stress can reach over 800 MPa), which can easily lead to warping and cracking of the part (crack incidence rate as high as 10%-20%), seriously restricting the forming quality and reliability.

[0003] Traditional technologies mainly use linear, block, or honeycomb support structures to alleviate thermal stress problems, but their functions are limited to mechanical support and heat dissipation. They cannot actively release thermal stress or prevent crack propagation, and high-rigidity support may actually exacerbate stress concentration.

[0004] Therefore, there is an urgent need for an SLM forming method that can effectively control the distribution of thermal stress and maintain the high density and mechanical properties of parts, so as to meet the high reliability requirements of the aerospace industry for complex high-temperature titanium alloy parts. Summary of the Invention

[0005] To address the problems existing in the prior art, the primary objective of this invention is to provide a high-temperature titanium alloy forming method based on a stress-relief structure.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A high-temperature titanium alloy forming method based on stress relief structure, wherein a first support layer, a stress relief layer and a second support layer are prepared sequentially from bottom to top by laser selective melting forming method, and then the high-temperature titanium alloy part body is formed layer by layer; The laser power during the processing of the first support layer and / or the second support layer is 300~500W, the scanning speed is 500~1000mm / s, and the powder layer thickness is 30~60μm; the support structure of the first support layer and / or the second support layer is at least one of linear support, tree support, lattice support or honeycomb support. The laser power for processing the stress relief layer is 180~280W, the scanning speed is 1500~2500mm / s, and the powder layer thickness is 60~80μm. The high-temperature titanium alloy is a high-temperature titanium alloy that can withstand operating temperatures of 600℃ and above.

[0007] This invention employs selective laser melting (SLM) to fabricate a "sandwich" structure consisting of a first support layer, a stress-relieving layer, and a second support layer. By controlling process parameters, the mechanical properties (such as tensile strength) of the stress-relieving layer are reduced, causing it to undergo plastic deformation or cracking during SLM, releasing the thermal stress of the part body and significantly reducing residual stress. The stress-relieving layer, through cracking, releases residual stress and prevents crack propagation into the part body. The first and second support layers undergo tensile and compressive deformation, respectively, during SLM, releasing residual stress and forming a physical barrier that restricts crack propagation.

[0008] This invention achieves directional regulation of the mechanical properties of the first support layer, stress relief layer and second support layer by controlling the process parameters of SLM, thereby controlling the cracking behavior during the part forming process and realizing thermal stress relief.

[0009] The first support layer prevents the stress relief layer from being directly and solidly connected to the substrate, thus avoiding increased forming stress. The second support layer prevents cracks in the stress relief layer from being transmitted to the component.

[0010] The first support layer, stress relief layer and second support layer of the present invention are all made of the same high-temperature titanium alloy powder as the part body, which can reduce the difference in thermal expansion coefficient at the interface between the support structure and the part.

[0011] Preferably, the laser power is 180~220W, the scanning speed is 1800~2000mm / s, and the powder layer thickness is 60~80μm during stress relief layer processing.

[0012] Preferably, the laser power is 350~450W, the scanning speed is 800~1000mm / s, and the powder layer thickness is 30~40μm during the processing of the first support layer and / or the second support layer.

[0013] Preferably, the scanning spacing during the processing of the first support layer and / or the second support layer is 50~200μm.

[0014] More preferably, the scanning spacing during the processing of the first support layer and / or the second support layer is 80~100μm.

[0015] Preferably, the scanning spacing during the processing of the stress relief layer is 50~200μm.

[0016] More preferably, the scanning spacing during the processing of the stress relief layer is 70~150μm.

[0017] Preferably, the thickness of the first support layer, the stress relief layer, and the second support layer is 3~50mm.

[0018] Preferably, the thickness of each layer is 2 to 10% of the height of the high-temperature titanium alloy part.

[0019] The thicknesses of the first support layer, stress relief layer, and second support layer can be the same or different. The thickness of each layer is controlled within 2-10% of the height of the high-temperature titanium alloy part, allowing this "sandwich" structure to effectively relieve residual stress and support the part.

[0020] Preferably, the high-temperature titanium alloy is at least one of Ti150, Ti1100, Ti60 or Ti65.

[0021] More preferably, the high-temperature titanium alloy is Ti150 or Ti65.

[0022] More preferably, the Ti150 is Ti-5.5Al-4.0Sn-3.5Zr-Nb.

[0023] More preferably, the Ti65 is Ti-5.9Al-4Sn-3.5Zr-0.3Mo-0.4Si-0.3Nb-2.0Ta-1.0W-0.05C.

[0024] Ti150 is prone to cracking during laser selective melting and forming. However, by setting the above-mentioned "sandwich" structure at the bottom of high-temperature titanium alloy parts, cracking of high-temperature titanium alloy parts can be effectively avoided.

[0025] Preferably, the laser power for processing the high-temperature titanium alloy parts is 300~500W, the scanning speed is 500~1000mm / s, and the scanning spacing is 20~200μm. Specifically, the laser power for contour scanning is 300~500W, the scanning speed is 800~1000mm / s, the scanning spacing is 50~200μm, and the powder layer thickness is 30~60μm.

[0026] More preferably, the laser power during the processing of the high-temperature titanium alloy parts is 350~450W, the scanning speed is 800~1000mm / s, and the scanning spacing is 20~200μm. Specifically, the laser power for contour scanning is 350~450W, the scanning speed is 800~1000mm / s, the scanning spacing is 50~100μm, and the powder layer thickness is 30~50μm.

[0027] Preferably, the scanning strategy used during the machining of the high-temperature titanium alloy parts is at least one of island-shaped, long straight line, or short straight line.

[0028] Preferably, the scanning rotation angle for machining the high-temperature titanium alloy part is 66±5°.

[0029] Preferably, the support structure of the first support layer and / or the second support layer is a lattice support structure.

[0030] More preferably, the cell size of the lattice support is 2×2×2mm to 5×5×5mm.

[0031] More preferably, the diameter of the dot matrix rod is 0.5~1mm.

[0032] More preferably, the lattice-supported unit cell is at least one of diamond, body-centered cubic, or octagonal truss.

[0033] A high-temperature titanium alloy part is prepared by the above-mentioned high-temperature titanium alloy forming method.

[0034] The high-temperature titanium alloy part obtained by this invention finally needs to have its "sandwich" structure at the bottom cut off.

[0035] Compared with the prior art, the present invention has the following beneficial effects: This invention employs a selective laser melting (SLM) method to create a "sandwich" structure at the bottom of a high-temperature titanium alloy, consisting of a first support layer, a stress relief layer, and a second support layer. By controlling the SLM process parameters, a sub-densified stress relief layer is prepared. This layer effectively absorbs and releases thermal stress through plastic deformation and controllable cracking. Furthermore, acting as a "thermal stress buffer layer," it blocks the path of thermal stress transmission to the part body, significantly reducing residual stress in the part body, effectively regulating thermal stress distribution, and significantly reducing warping deformation. The stress relief layer prevents cracks from propagating into the part body. The double-layer support structure in this sandwich structure forms a physical barrier, limiting crack propagation and allowing the high-temperature titanium alloy part to maintain its original mechanical properties. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the first support layer, stress relief layer and second support layer of the present invention.

[0037] Figure 2 Metallographic images of Example 1 (left) and Comparative Example 1 (right).

[0038] Figure 3 This is a macroscopic photograph of the printed part in Comparative Example 1.

[0039] Appendix Figure 1 Markings: 1. First support layer; 2. Stress relief layer; 3. Second support layer; 4. Rear bearing housing component. Detailed Implementation

[0040] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0041] Example 1 This embodiment discloses a Ti150 high-temperature titanium alloy rear bearing housing formed by laser selective melting, the forming method of which includes the following steps: (1) A first support structure layer with a thickness of 30 mm, representing 8% of the part height, was prepared on a TC4 titanium alloy substrate by selective laser melting. The support structure adopted a lattice support, with a body-centered cubic structure for the lattice cells, each cell measuring 3×3×3 mm, and the diameter of the lattice rods being 0.8 mm. The selective laser melting process for the support structure used the optimal process parameters for high-temperature titanium alloys: a laser power of 400 W, a scanning speed of 900 mm / s, a powder layer thickness of 40 μm, and a scanning spacing of 80 μm.

[0042] (2) A stress relief layer is prepared on the first support layer by selective laser melting, with a thickness of 20 mm, which is 5.3% of the height of the part. The selective laser melting process of the stress relief layer is a process parameter that deviates from the optimal process parameters of high temperature titanium alloy. The preferred laser power is 200W, the scanning speed is 1800 mm / s, the powder layer thickness is 80μm, and the scanning spacing is 80μm.

[0043] (3) A second support layer with a thickness of 30 mm, representing 8% of the part height, is prepared on the stress relief plate by selective laser melting. The support structure also adopts a lattice support, with the lattice cell being a body-centered cubic structure with a cell size of 3×3×3 mm and a lattice rod diameter of 0.8 mm. The selective laser melting process uses the optimal process parameters for high-temperature titanium alloys: laser power 400 W, scanning speed 900 mm / s, powder layer thickness 40 μm, and scanning spacing 80 μm.

[0044] (4) The high-temperature titanium alloy part body is formed layer by layer on the second support layer. The laser selective melting forming process is the optimal process parameter for high-temperature titanium alloy. The preferred laser power is 400 W, the scanning speed is 900 mm / s, the scanning interval is 80 μm, the contour scanning laser power is 400 W, the contour scanning speed is 900 mm / s, the layer thickness is 40 μm, the scanning interval is 80 μm, the island scanning strategy is adopted, and the scanning rotation angle is 66°±5°.

[0045] (5) After molding is completed, wait for the temperature inside the molding chamber to drop to room temperature of 25°C, then take out the part and remove excess powder.

[0046] Example 2 This embodiment discloses a method for laser selective melting to form Ti65 high-temperature titanium alloy blades, with a total part height of 80mm. The forming method includes the following steps: (1) A first support structure layer with a thickness of 8 mm, representing 10% of the part height, was prepared on a TA15 titanium alloy substrate by selective laser melting. The support structure adopted a lattice support with diamond lattice cells of 3×3×3 mm in size and 0.6 mm in diameter for the lattice rods. The laser selective melting process for the support structure used the optimal process parameters for high-temperature titanium alloys: laser power of 350 W, scanning speed of 1000 mm / s, powder layer thickness of 30 μm, and scanning spacing of 70 μm.

[0047] (2) A stress relief layer with a thickness of 3 mm, which is 3.75% of the part height, is prepared on the first support layer by selective laser melting. The laser selective melting process of the stress relief layer deviates from the optimal process parameters of Ti65 high-temperature titanium alloy in order to reduce residual stress: the laser power is 180W, the scanning speed is 2000mm / s, the powder layer thickness is 60 μm, and the scanning spacing is 70μm.

[0048] (3) A second support layer with a thickness of 5 mm, representing 6.25% of the part height, is prepared on the stress relief layer by selective laser melting. The support structure also adopts a lattice support, with diamond lattice cells of 3×3×3 mm in size and 0.6 mm in diameter for the lattice rods. The optimal process parameters for the selective laser melting process of Ti65 high-temperature titanium alloy are as follows: laser power of 350 W, scanning speed of 1000 mm / s, powder layer thickness of 30 μm, and scanning spacing of 70 μm.

[0049] (4) The high-temperature titanium alloy part body is formed layer by layer on the second support layer. The optimal process parameters for the laser selective melting forming process of Ti65 high-temperature titanium alloy are: laser power of 350W, scanning speed of 1000mm / s, contour scanning laser power of 350W, contour scanning speed of 1000mm / s, powder layer thickness of 30μm, and scanning spacing of 70μm. An island scanning strategy is adopted, and the scanning rotation angle is 66°±5°.

[0050] (5) After molding is completed, wait for the temperature inside the molding chamber to drop to room temperature of 25°C, then take out the part and remove excess powder.

[0051] Example 3 This embodiment discloses a large, thin-walled aero-engine casing part with an overall height of 300mm. Such parts are highly susceptible to deformation or cracking due to significant residual stress during SLM forming. The high-temperature titanium alloy forming method based on a stress-relief structure of this invention is employed, with the following specific steps: (1) Substrate and material preparation: TC4 titanium alloy was used as the forming substrate, and Ti150 high-temperature titanium alloy spherical powder prepared by gas atomization was used as the forming raw material.

[0052] (2) Forming a "sandwich" support structure: (2-1) Forming of the first support layer: The first support layer is formed by selective laser melting on the substrate, with a thickness of 12mm (approximately 4% of the part height). A lattice support structure is used, with an octagonal truss structure as the lattice cell, a cell size of 3×3×3mm, and a lattice rod diameter of 0.7mm. The optimal process parameters for high-temperature titanium alloy are used for forming: laser power of 450W, scanning speed of 800mm / s, powder layer thickness of 40μm, and scanning spacing of 100μm.

[0053] (2-2) Stress Relief Layer Forming: A stress relief layer with a thickness of 9 mm (approximately 3% of the part height) is formed by selective laser melting on the first support layer. Deviating from optimal process parameters is used to reduce its mechanical properties: laser power of 220 W, scanning speed of 2000 mm / s, powder layer thickness of 70 μm, and scanning spacing of 150 μm. During the forming process, this layer undergoes microscopic plastic deformation and microcracks due to thermal stress, effectively releasing the stress transmitted from the upper part during forming.

[0054] (2-3) Forming of the second support layer: A second support layer with a thickness of 12 mm (approximately 4% of the part height) is formed by selective laser melting on the stress relief layer. Its support structure, lattice parameters, and selective laser melting process are completely consistent with those of the first support layer. This layer acts as a physical barrier, effectively preventing microcracks generated in the stress relief layer from propagating upwards to the part body.

[0055] (3) Part Body Forming: The Ti150 high-temperature titanium alloy casing part body is formed layer by layer on the second support layer. An optimized body forming process is adopted: the laser power is 450W and the scanning speed is 800mm / s. The contour scanning uses a laser power of 450W, a scanning speed of 900mm / s, a powder layer thickness of 40μm, and a scanning spacing of 100μm. The scanning strategy adopts island scanning with a scanning rotation angle of 66°.

[0056] (4) Post-processing: After the molding is completed, wait for the temperature of the molding chamber to cool to 25°C room temperature, take out the part with the "sandwich" support structure, use wire cutting to separate the support structure from the part body, and remove the residual powder.

[0057] The engine casing formed by this method, as measured, has a residual stress that is more than 60% lower than that of the traditional direct forming method, and there are no macroscopic cracks or obvious deformation.

[0058] Comparative Example 1 This comparative example discloses a Ti150 high-temperature titanium alloy rear bearing housing formed by laser selective melting, the forming method of which includes the following steps: (1) A support structure layer with a thickness of 30 mm, representing 8% of the part height, was prepared on a TC4 titanium alloy substrate by selective laser melting. The support structure adopted a lattice support, with cubic lattice cells of 3×3×3 mm in size and 0.8 mm in diameter for the lattice rods. The selective laser melting process for the support structure used the optimal process parameters for high-temperature titanium alloys: laser power of 400 W, scanning speed of 900 mm / s, powder layer thickness of 40 μm, and scanning spacing of 80 μm.

[0059] (2) The high-temperature titanium alloy part body is formed layer by layer on the support layer. The laser selective melting forming process is the optimal process parameter for high-temperature titanium alloy. The preferred laser power is 400 W, the scanning speed is 900 mm / s, and the scanning interval is 80 μm. The contour scanning laser power is 400 W, the contour scanning speed is 900 mm / s, the layer thickness is 40 μm, the scanning interval is 80 μm, the island scanning strategy is adopted, and the scanning rotation angle is 66°±5°.

[0060] (3) After the molding is completed, wait for the temperature inside the molding chamber to drop to room temperature of 25°C, then take out the part and remove excess powder.

[0061] Comparative Example 2 This comparative example discloses a Ti150 high-temperature titanium alloy rear bearing seat formed by laser selective melting. The difference between its forming method and that of Example 1 is only in step (2). The laser selective melting forming process of the stress relief layer adopts the same optimal process parameters for high-temperature titanium alloy as the main body of the part, namely, laser power of 400W, scanning speed of 900mm / s, powder layer thickness of 40μm, and scanning spacing of 80μm. The rest is the same as that of Example 1.

[0062] Performance testing Metallographic testing method for high-temperature titanium alloys: First, a representative sample is cut from the target part and heat-mounted with thermosetting plastic for easy handling. Then, a series of wet abrasive tests are performed using metallographic sandpaper with grits ranging from 180# to 2000#, rotating the sample 90° each time a new grit is applied, until all old scratches are completely removed. Next, diamond polishing compound is used on a polishing cloth for rough and fine polishing to obtain a scratch-free mirror finish. Finally, the microstructure is observed using an optical microscope.

[0063] Representative samples were taken from the target part, and the density of the part and stress-relief layer in Example 1 was tested using the water displacement method. The density of the part was above 99.9%, while that of the stress-relief layer was approximately 96%. This indicates that the stress-relief layer has a sub-dense structure.

[0064] Figure 2 Metallographic images of Example 1 (left) and Comparative Example 1 (right), by Figure 2 Metallographic analysis revealed that no obvious cracks were observed in the microstructure of the part with the added "sandwich" stress relief structure; in contrast, the part without this stress relief structure showed clearly visible cracks.

[0065] Figure 3 Macroscopic photographs of the printed parts of Example 1 (top) and Comparative Example 1 (bottom). (By...) Figure 3 It is evident that parts without stress relief structures developed cracks, while parts with the added "sandwich" stress relief structure remained intact. This demonstrates that the "sandwich" structure of the first support layer-stress relief layer-second support layer in this invention can effectively absorb and release thermal stress, blocking the path of thermal stress transmission to the part body. This significantly reduces the residual stress in the part body, effectively controls the distribution of thermal stress, and significantly reduces warping deformation. The stress relief layer can prevent cracks from propagating into the part body. The double-layer support in this sandwich structure forms a physical barrier, limiting crack propagation and maintaining the high density and mechanical properties of the high-temperature titanium alloy parts.

[0066] The part obtained using the forming method of Comparative Example 2 cracked. This indicates that using the same optimal process as the main body to manufacture the stress relief layer cannot effectively alleviate or release the residual stress accumulated during the forming process, ultimately leading to cracking of the part during or after manufacturing. In contrast, in Example 1, a sub-densified stress relief layer was obtained by controlling the SLM process parameters. By using low laser power and high scanning speed to reduce the energy input and bonding strength of the stress relief layer, it was able to effectively release or buffer stress during the forming process, successfully preventing the part from cracking.

[0067] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A stress relief structure based forming method for high temperature titanium alloys, characterized in that, The first support layer, the stress release layer and the second support layer are sequentially prepared from bottom to top by using a laser selective melting forming method, and then the high-temperature titanium alloy part body is formed layer by layer. The laser power is 300-500 W, the scanning speed is 500-1000 mm / s, and the powder layer thickness is 30-60 μm during the processing of the first support layer and / or the second support layer; the support structure of the first support layer and / or the second support layer is at least one of linear support, tree support, dot matrix support or honeycomb support. The laser power is 180-280 W, the scanning speed is 1500-2500 mm / s, and the powder layer thickness is 30-60 μm during the processing of the stress release layer. The high-temperature titanium alloy is a high-temperature titanium alloy resistant to a working temperature of 600 ℃ and above.

2. The method of claim 1, wherein The laser power is 180-220 W, the scanning speed is 1800-2000 mm / s, and the powder layer thickness is 60-80 μm during the processing of the stress release layer.

3. The method of claim 1, wherein The laser power is 350-450 W, the scanning speed is 800-1000 mm / s, and the powder layer thickness is 30-40 μm during the processing of the first support layer and / or the second support layer.

4. The method of claim 1, wherein The scanning interval is 50-200 μm during the processing of the first support layer and / or the second support layer.

5. The method of claim 1, wherein The scanning interval is 50-200 μm during the processing of the stress release layer.

6. The method of claim 1, wherein The thickness of each layer is 2-10% of the height of the high-temperature titanium alloy part.

7. The method of claim 1, wherein The high-temperature titanium alloy is a high-temperature titanium alloy resistant to a working temperature of 600 ℃ and above.

8. The method of claim 6, wherein the forming is performed at a temperature of 1200°C or higher. The high-temperature titanium alloy is at least one of Ti150, Ti1100, Ti60 or Ti65.

9. The method of claim 1, wherein The laser power is 300-500 W, the scanning speed is 500-1000 mm / s, and the scanning interval is 20-200 μm during the processing of the high-temperature titanium alloy part, wherein the laser power for contour scanning is 300-500 W, the scanning speed is 800-1000 mm / s, the scanning interval is 50-200 μm, and the powder layer thickness is 30-60 μm.

10. A high temperature titanium alloy part characterized by, The high-temperature titanium alloy is prepared by using the forming method of any one of claims 1-9.

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