A method for preparing a ta c / 316l composite

Abstract

The application discloses a method for preparing TaC / 316L composite material, and belongs to the technical field of SLM additive manufacturing composite material. In the application, micron TaC ceramic particles are used as reinforcing bodies, 316L stainless steel is used as a matrix, and the short-time high-energy ball milling method is used to mix the TaC and 316L powders, then the movable high-energy laser is used to melt the mixed uniform TaC / 316L composite powder at specific positions, so that the high-quality novel SLM formed TaC / 316L composite material is obtained. The application utilizes the SLM and short-time high-energy ball milling technology, with the addition of TaC, the grains are refined, not only the yield strength, tensile strength and hardness of the 316L are improved, but also the ductility of the TaC / 316L composite material is still good, and the problems such as the sharp decrease of plasticity of other reinforcing phase particles in reinforcing the strength of the 316L matrix can be solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of composite material preparation, and relates to a method for preparing a TaC / 316L composite material, in particular to a method for preparing a TaC / 316L composite material with different volume contents by using SLM and short-time high-energy ball milling. BACKGROUND

[0002] Additive manufacturing is a manufacturing technology that uses digital driving to print layer by layer. It can directly form high-quality parts. By melting each layer of raw materials and printing layer by layer, the manufacturing method is decomposed from three dimensions to two dimensions, which breaks away from the limitations of traditional industry and can produce more complex parts. 3D printing technology can print whole parts or multiple parts at the same time. Due to the reduction of labor, material and time costs, 3D printing technology is advancing and gradually penetrating into the medical, aviation, chip and biological industries.

[0003] The demand for technology is not stagnant. As the requirements for materials in various industries gradually increase, the pursuit of performance becomes more demanding. At this time, selective laser melting (SLM) using laser as a heat source emerges as the times require. The principle of SLM is very simple. Metal powder is uniformly laid on the powder bed. The system uses a movable high-energy laser to melt the powder at a specific location, and repeats the process until the printing is complete. Therefore, it can produce parts with high density, high performance and high precision. SLM can be used for batch or customized production of parts, and has a very wide range of applications. It can solve the problems that have plagued the aviation industry and the medical industry, such as traditional processing methods that cannot solve the problems of hollowing out, dot matrix, weight reduction, etc.

[0004] 316L stainless steel has excellent chemical properties, mechanical properties, and low cost, and is often used in medical prostheses, industrial equipment and other industries. However, due to its low yield strength, its application range is limited. In order to change this situation, researchers have gradually begun to study 316L composite materials. 316L composite materials inherit the advantages of 316L matrix and reinforcing phase, and have better mechanical properties than pure 316L. Zhai et al. found that the addition of TiC greatly reduced the ductility while improving the strength of 316. ALMangour et al. focused on the strength, wear resistance and hardness of 316L composite materials, and did not explain the plasticity. As we all know, a decrease in plasticity can cause brittle fracture, causing unpredictable damage, so the problem of sharp decline in 316L plasticity needs to be solved. SUMMARY

[0005] In view of the above problems existing in the prior art, the technical problem to be solved by the present application is to provide a method for preparing a TaC / 316L composite material, so as to solve the problem that the addition of other reinforcing phases causes the strength of 316L to be improved while the plasticity is sharply decreased.

[0006] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0007] A method for preparing a TaC / 316L composite material: micron-sized TaC ceramic particles are used as reinforcing bodies, and 316L stainless steel is used as a matrix; short-time high-energy ball milling is used to uniformly mix TaC / 316L composite powder; the mixed powder is uniformly laid on a powder bed; a movable high-energy laser is used to melt the uniformly mixed TaC / 316L composite powder at a specific position; and the process is repeated until 3D printing is completed.

[0008] Further, in the method for preparing a TaC / 316L composite material, the TaC / 316L composite powder is 0.5vol.% TaC / 316L composite powder and 1.5vol.% TaC / 316L composite powder.

[0009] Further, in the method for preparing a TaC / 316L composite material, the micron-sized TaC ceramic particle reinforcing body is TaC powder with a particle size range of less than 3μm dispersed by short-time high-energy ball milling.

[0010] Further, in the method for preparing a TaC / 316L composite material, the ball milling speed of the short-time high-energy ball milling method is 250rpm, and the ball milling time is 60min.

[0011] Further, in the method for preparing a TaC / 316L composite material, the ball-to-material ratio used in the short-time high-energy ball milling method is 2:1.

[0012] Further, in the method for preparing a TaC / 316L composite material, the ball milling beads used in the short-time high-energy ball milling method are zirconia ball milling beads, and the ball milling tank used is a polytetrafluoroethylene ball milling tank.

[0013] Further, in the method for preparing a TaC / 316L composite material, the forming equipment of SLM is YLM-150.

[0014] Further, in the method for preparing a TaC / 316L composite material, the scanning strategy of SLM uses Zigzag, each layer rotates 67°, the laser power is 240W, the scanning interval is 85μm, the scanning speed is 1200mm / s, and the layer thickness is 30μm.

[0015] Further, the method for preparing the TaC / 316L composite material, after short-time high-energy ball milling, the TaC ceramic particles are uniformly distributed on the surface of the 316L powder ball.

[0016] Compared with the prior art, the application has the following beneficial effects:

[0017] (1) After the 316L-based composite material is prepared by SLM and short-time high-energy ball milling forming technology, the density of all samples exceeds 99.0%;

[0018] (2) After the micron-sized TaC is added, the number of epitaxial subgrains is significantly reduced, while the number of equiaxed subgrains is significantly increased, a large number of small-angle grain boundaries generated by the interaction between the TaC particles and the 316L matrix hinder the deformation dislocations of the matrix, thereby improving the yield strength, tensile strength and microhardness;

[0019] (3) 1.5 vol.% TaC significantly enhances the SLM-316L matrix, and the obtained composite material not only has improved strength, but also maintains a high level of ductility. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 (a): SEM image of 316L powder; Figure 1 (b): SEM image of TaC powder; Figure 1 (c): SEM image of 0.5 vol.% TaC / 316L composite powder; Figure 1 (d): SEM image of 1.5 vol.% TaC / 316L composite powder;

[0021] Figure 2 (a): Optical metallography of SLM-316L; Figure 2 (b): Optical metallography of SLM-0.5% TaC / 316L; Figure 2 (c): Optical metallography of SLM-1.5% TaC / 316L;

[0022] Figure 3 : SEM image of longitudinal section of the sample under low magnification; Fig. (a) is the SEM image of the longitudinal section of SLM-316L after etching; Fig. (b) is the SEM image of the longitudinal section of SLM-0.5% TaC / 316L after etching; Fig. (c) is the SEM image of the longitudinal section of SLM-1.5% TaC / 316L after etching;

[0023] Figure 4 (a): EBSD pole figure of SLM-316L; Figure 4 (b): EBSD pole figure of SLM-0.5% TaC / 316L; Figure 4(c): EBSD pole figure of SLM-1.5%TaC / 316L;

[0024] Figure 5 (a): EBSD grain orientation distribution map of SLM-316L; Figure 5 (b): EBSD grain orientation distribution map of SLM-0.5%TaC / 316L; Figure 5 (c): EBSD grain orientation distribution map of SLM-1.5%TaC / 316L;

[0025] Figure 6 (a): KAM map of SLM-316L; Figure 6 (b): KAM map of SLM-0.5%TaC / 316L; Figure 6 (c): KAM map of SLM-1.5%TaC / 316L;

[0026] Figure 7 : Mechanical properties; Figure 7 (a): Stress-strain curve; Figure 7 (b): Microhardness map. DETAILED DESCRIPTION

[0027] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described below in combination with specific examples. In the following examples, the technical means used are all conventional means well known to those skilled in the art, unless otherwise specified.

[0028] Example 1

[0029] The substrate used in the experiment is 316L powder with high sphericity, good fluidity, and a particle size range of 15-53 μm, which is prepared by gas atomization; the reinforcing phase is TaC powder with a particle size range of less than 3 μm, which is dispersed by high-energy ball milling, and the morphology is as shown in Figure 1 (a, b). The above-mentioned TaC and 316L powders are mixed in proportions of SLM-316L, SLM-0.5%TaC / 316L and SLM-1.5%TaC / 316L respectively by using short-time high-energy ball milling, and the ball milling parameters are as follows: rotation speed 250 rpm, ball-to-powder ratio 2:1, time 60 min, zirconia ball milling beads, and polytetrafluoroethylene ball milling tank. The morphology of the TaC / 316L composite powder after short-time high-energy ball milling is shown in Figure 1 (c, d), and the TaC ceramic particles are uniformly distributed on the surface of the 316L powder balls.

[0030] The three kinds of 316L-based composite materials SLM-316L, SLM-0.5%TaC / 316L and SLM-1.5%TaC / 316L mixed by short-time high-energy ball milling respectively were uniformly laid on the powder bed, and the mixed uniform 316L-based composite powder in a specific position was melted by a movable high-energy laser, and the process was repeated until the 3D printing was completed. The SLM forming equipment used YLM-150, and the oxygen content of the forming bin was controlled below 100 ppm in consideration of the safety of the machine and raw materials. The scanning strategy adopted Zigzag, the rotation of each layer was 67°, the laser power was 240 W, the scanning interval was 85 μm, the scanning speed was 1200 mm / s, and the layer thickness was 30 μm.

[0031] The micro-characterization samples were polished by an automatic grinding and polishing machine, and the grit sizes of sandpaper were 240#, 320#, 400#, 600#, 800#, 1000#, 1200#, 1500#, 2000#, 2500# in turn, and finally 2.5 μm spray polishing agent was used for polishing. The optical metallography (OM), scanning electron microscopy (SEM) and micro-morphology characterization of the corroded samples (corrosion solution HF:HNO3:H2O=3:1:5) were carried out. The polished samples were electrolytically polished, and analyzed by electron backscatter diffraction (EBSD) with a step size of 0.5 μm, and the EBSD test results were analyzed by AZtecCrystal software.

[0032] The polished samples were subjected to micro Vickers hardness detection, the pressure was 200 g, the residence time was 15 s, and three samples of each material were tested. The SLM formed tensile samples were subjected to room temperature tensile test, the pre-load was 50 N, and the running rate was 1 mm / min.

[0033] The longitudinal cross-sectional morphologies of SLM-316L, SLM-0.5%TaC / 316L and SLM-1.5%TaC / 316L after corrosion are shown in Figure 2 The OM images show that the densities of SLM-316L, SLM-0.5%TaC / 316L and SLM-1.5%TaC / 316L samples are all more than 99.0%, which indicates that the process parameters have reached the optimum, and the wettability of 316L and TaC ceramic is good. The Marangoni effect and the laser scanning trajectory together cause the fish-scale-shaped molten pool in the cross-section of the sample.

[0034] As shown in Figure 3 Honeycomb-shaped equiaxed subgrains and epitaxial subgrains can be observed in the molten pool, and subgrains with the same misorientation together constitute a complete grain. Figure 3It can be seen that the number of epitaxial grains in 1.5%TaC / 316L is much less than that in SLM-316L and SLM-0.5%TaC / 316L, which indicates that the TaC particles hinder the growth of epitaxial grains during the solidification of 316L and lead to the increase of subgrains.

[0035] As shown in Figure 4 , SLM-316L with different TaC contents exhibit strong random-oriented texture and anisotropy caused by the epitaxial growth of grains. In addition, the preferred orientation changes from <101> of SLM-316L to <001> of 0.5%TaC / 316L due to the change of rotation angle between different powder layers. The texture of 316L is weakened and the preferred orientation disappears after adding 1.5%TaC. However, the weakening effect of TaC on the texture is not obvious for 0.5%TaC / 316L, which indicates that the lower content of TaC has little effect on the texture.

[0036] Figure 5 The grain size and orientation in SLM-316L, SLM-0.5%TaC / 316L and SLM-1.5%TaC / 316L are shown. The microstructure inside the melt pool consists of columnar grains grown along the maximum temperature gradient and a small amount of equiaxed grains. The local average dislocation distribution (KAM) is shown in Figure 6 , where the sheet green fluorescence appears in the area containing obvious color fluctuation. The color fluctuation can be attributed to the existence of low-angle grain boundaries caused by the slight twist of the orientation in columnar grains.

[0037] It can be seen that the grain size decreases dramatically due to the addition of TaC. With the increase of TaC content, the grain size becomes finer and shorter. This can be attributed to the fact that the added TaC particles act as heterogeneous nucleation sites during the solidification of 316L, which increases the nucleation rate and the number of grains during the solidification of the melt pool, leading to the tendency of fine grain growth. In addition, it can be seen from Figure 6 that the strip green fluorescence gradually increases with the increase of TaC content, and the number of strip green fluorescence in 1.5%TaC / 316L is the largest. Since this strip green fluorescence is essentially a low-angle grain boundary, TaC increases the number of low-angle grain boundaries in 316L, thereby increasing the dislocation density.

[0038] The tensile test data at room temperature are converted into engineering stress-strain curves and quantitative data, respectively, by Figure 7(a) and Table 1. The yield strength (yield strength) and ultimate tensile strength (tensile strength) of SLM-316L are 603.3 MPa and 716.5 MPa, respectively. In addition, the strength of SLM-316L is superior to conventional 316L because of its higher cooling rate than conventional 316L. The yield strength of SLM-0.5%TaC / 316L increases from 603.3 MPa to 648.2 MPa, an increase of 7.4%, the tensile strength increases from 716.5 MPa to 756.5 MPa, an increase of 5.6%, and the ductility decreases from 46.3% to 35.6%, a decrease of 23.1%. In addition, the yield strength of SLM-1.5%TaC / 316L increases from 603.3 MPa to 789.7 MPa, an increase of 30.9%, the tensile strength increases from 716.5 MPa to 910.5 MPa, an increase of 27.1%, and the ductility decreases from 46.3% to 28.0%, a decrease of 39.5%. It can be concluded that the yield strength and tensile strength of 316L composites treated by SLM and high-energy ball milling increase significantly with the addition of TaC, and linearly with the content of TaC.

[0039] Table 1 Tensile property test

[0040] Material Yield Strength (MPa) Tensile Strength (MPa) Elongation (%) 316L 603.3 716.5 46.3 0.5% TaC / 316L 648.2 756.5 35.6 1.5% TaC / 316L 789.7 910.5 28.0

[0041] The microhardness of the samples, including SLM-316L, SLM-0.5%TaC / 316L, and SLM-1.5%TaC / 316L, is shown in Figure 7 (b). Compared with SLM-316L, the microhardness of SLM-0.5%TaC / 316L increases from 206.4 HV to 226.8 HV, an increase of 9.9%. Similarly, the microhardness of SLM-1.5%TaC / 316L is higher than that of SLM-316L, increasing from 206.4 HV to 253.2 HV, an increase of 22.7%. Therefore, after the addition of TaC and treatment by SLM and high-energy ball milling, a large number of small-angle grain boundaries generated by the interaction between TaC particles and the 316L matrix hinder the matrix deformation dislocations, increasing the yield strength, tensile strength, and microhardness. By SLM-316L (603.3 MPa, 716.5 MPa, and 46.3%), SLM-0.5%TaC / 316L (648.2 MPa, 756.5 MPa, 35.6%), and SLM-1.5%TaC / 316L (789.7 MPa, 910.5 MPa, 28.0%), it can be seen that only 1.5 vol.% TaC significantly strengthens the SLM-316L matrix, and the ductility remains good.

[0042] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A method of preparing a TaC / 316L composite material, characterized by, The steps are as follows: 1) Short-time high-energy ball milling of TaC / 316L composite powder Micron TaC ceramic particles are used as the reinforcing body, and 316L stainless steel is used as the matrix. The TaC / 316L composite powder is uniformly mixed by short-time high-energy ball milling. After short-time high-energy ball milling, the TaC ceramic particles are uniformly distributed on the surface of the 316L powder ball; The ball milling speed of the short-time high-energy ball milling method is 250 rpm, the ball milling time is 60 min, the ball-to-material ratio is 2:1, the ball milling beads are zirconia ball milling beads, and the ball milling tank used is a polytetrafluoroethylene ball milling tank; The micron TaC ceramic reinforcing body is TaC powder with a particle size range of less than 3 μm dispersed by short-time high-energy ball milling. The content of TaC in the TaC / 316L composite powder is 1.5 vol.%; 2) SLM laser consolidation to prepare TaC / 316L composite material The mixed powder is uniformly laid on the powder bed, and the movable YLM-150 forming equipment is used to melt the uniformly mixed TaC / 316L composite powder in a Zigzag scanning strategy. Each layer is rotated by 67°, the laser power is 240 W, the scanning interval is 85 μm, the scanning speed is 1200 mm / s, the layer thickness is 30 μm, and the process is repeated until the 3D printing is completed.

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