Titanium-based composite material with gradient structure and preparation method thereof

Abstract

The invention discloses a titanium-based composite material with a gradient structure and a preparation method thereof.The preparation method comprises the steps that matrix powder and reinforced phase raw materials are subjected to ball milling and mixing to obtain mixed powder, and the matrix powder is titanium alloy powder; the additive manufacturing of one cycle comprises the steps that firstly, mixed powder is fed to form a composite material layer, then matrix powder is fed so that 1-2 matrix alloy layers can be formed on the composite material layer through printing, and when the current matrix alloy layer is printed, the previous layer is remelted by controlling the printing power. The titanium-based composite material prepared by the preparation method has better mechanical properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal matrix composites, and particularly relates to a titanium matrix composite with a gradient structure and a preparation method thereof. Background Art

[0002] Titanium matrix composites (TMCs) have broad application prospects in high-end equipment fields such as aerospace and national defense due to their high specific strength, excellent heat resistance, and impact resistance. Additive manufacturing technology can realize the real-time control of the microstructure during the preparation of metal materials, and this technical means has also been widely studied in the preparation of titanium matrix composites and the regulation of their microstructural properties.

[0003] During the additive manufacturing process, on the one hand, the rapid scanning of the laser results in a large temperature gradient and a high solidification rate in the molten pool, promoting the epitaxial growth of columnar grains along the deposition direction. Even during the process of repeated remelting, the columnar grains penetrate multiple deposition layers, which leads to severe anisotropy of the microstructure and mechanical properties, and also limits the mechanical properties of the additive manufacturing metal material in the Z direction. Previous studies have found that introducing heterogeneous nucleation particles into the molten pool can effectively reduce the columnar grain size by hindering the epitaxial growth of grains or forming more nucleation sites. For example, in-situ generated TiB provides more nucleation points for the β phase, hindering its epitaxial disordered growth, and at the same time provides nucleation points for the α phase during the β→α transformation, ultimately forming a fine equiaxed matrix microstructure. On the other hand, the rapid heating and cooling of the molten pool during layer-by-layer accumulation result in significantly different interlayer temperature gradients. The upper molten pool causes non-uniform reheating of the heat-affected zone of the lower layer, forming an alternating region of thick and thin microstructures, resulting in a large difference in the microstructure sizes between layers and within layers, which also severely weakens the mechanical properties in the Z direction.

[0004] Chinese invention patent CN117626031A discloses a preparation method of a high-strength and ductile titanium matrix composite with a composition gradient. This invention uses powder metallurgy to sinter a variety of β-type titanium alloy powders with different Mo equivalents and carbon nanoparticles into a bulk alloy. The prepared titanium matrix composite with a composition gradient has excellent mechanical properties, which also shows the important role of gradient design in improving the properties of titanium matrix composites. However, this invention is not based on additive manufacturing technology to regulate the gradient distribution of the reinforcement phase (ceramic compound).

[0005] Chinese invention patent CN202210685948.X discloses a method for preparing a marine titanium alloy gradient composite material based on arc additive manufacturing. In this invention, the reinforcing phase is sprayed onto the surface of the molten pool and dispersed inside the matrix as the molten pool moves and solidifies, thereby forming a ceramic particle-reinforced titanium matrix composite deposition layer. Then, by controlling the content of the reinforcing phase particles in different layers, a gradient distribution of the reinforcing phase is constructed. The purpose is to solve the technical problems of complex processes, low hardness, and low wear resistance of titanium alloys in the prior art, rather than aiming at the influence of columnar crystals and interlayer transition structures in additive manufacturing metals on mechanical properties.

[0006] Therefore, it is necessary to study a titanium matrix composite material with a gradient structure distribution of the reinforcing phase and its additive manufacturing method to solve the problem that the coarse columnar crystals in the deposition direction and the non-uniform interlayer structure weaken the mechanical properties. Summary of the Invention

[0007] The present invention provides a method for preparing a titanium matrix composite material with a gradient structure, and the titanium matrix composite material prepared by this preparation method has good mechanical properties.

[0008] The present invention provides a method for preparing a titanium matrix composite material with a gradient structure, including: Step 1: Ball-mill and mix the matrix powder and the reinforcing phase raw material to obtain a mixed powder, where the matrix powder is titanium alloy powder; Step 2: Perform multi-cycle alternating additive manufacturing to obtain a titanium matrix composite material. Among them, one cycle of additive manufacturing includes: first, feed the mixed powder to form a composite material layer, and then feed the matrix powder to print 1-2 layers of matrix alloy layers on the composite material layer. When printing the current matrix alloy layer, by controlling the printing power, the previous layer is remelted.

[0009] When the present invention prints the current matrix alloy layer, the previous layer is remelted, so that the reinforcing phase in the previous layer flows upward along the heat flow direction. The temperature gradient causes the gradient diffusion of the reinforcing phase. At the same time, the gradient-diffused reinforcing phase hinders the disordered growth of β-Ti grains and pins on the grain surface, or disperses in the grains and grain boundaries. During this process, the gradient formed by the diffusion of the reinforcing phase in the deposition direction causes the β-Ti grain size to be gradientized, thereby forming a reinforcing phase with a gradient distribution structure, which preferably inhibits the formation of coarse columnar crystals and improves the mechanical properties.

[0010] At the same time, since the reinforcing phase affects the growth behavior of the matrix α phase, the size of the α phase also shows a gradient characteristic. In addition, the gradient distribution of the reinforcing phase affects the element diffusion at the solid-liquid interface of the molten pool and promotes the gradient distribution of other components.

[0011] Meanwhile, if there is too much matrix alloy layer on the composite material layer, the reinforcing phase diffuses upward too much, resulting in a partial transformation of the reinforcing phase from a network structure to a dispersed distribution, which is conducive to the formation of coarse columnar crystals and weakens the mechanical properties.

[0012] In the present invention, only the previous layer is remelted instead of remelting more layers. The purpose is to achieve a gradient change. If too many layers are remelted, due to the relatively uniform temperature of each layer, the gradient change is not obvious, and there is a risk of the appearance of coarse columnar crystals.

[0013] Preferably, 1 layer of matrix alloy layer is printed on the composite material layer. By further restricting the number of layers of the matrix alloy layer, during the remelting process, enough reinforcing phase from the previous layer moves to the current matrix alloy layer, making the gradient change of the network structure size of the reinforcing phase more obvious, and the network size smaller. The growth constraint ability of the reinforcing phase on the matrix phase is enhanced, further inhibiting the formation of coarse columnar crystals and further improving the mechanical properties.

[0014] Preferably, the continuous composite material layer does not exceed 3 layers. When there are more composite material layers, the reinforcing phase in the composite material layer is mainly in a network structure. A gradient structure cannot be constructed between multiple composite material layers, which is not conducive to inducing strain gradient distribution and its strengthening effect, and the gradient distribution structure of the reinforcing phase is the main inventive point of the present invention.

[0015] Preferably, the printing power is 600W - 1000W. By controlling the printing power, when printing the current matrix alloy layer, the previous layer is remelted by controlling the printing power.

[0016] Preferably, the additive manufacturing is laser melting deposition additive manufacturing technology. Through a multi-powder barrel feeding system, the alternating printing of the matrix alloy layer and the composite material layer is realized.

[0017] Preferably, the titanium alloy powder includes α-titanium alloy, β-titanium alloy or (α + β) dual-phase titanium alloy.

[0018] Preferably, the reinforcing phase raw materials include TiB, TiC, TiN, La 2 O 3 ,TiB 2 One or more.

[0019] Preferably, the content of the reinforcing phase raw materials in the mixed powder is 0.2 wt.% - 3 wt.%.

[0020] Further preferably, the particle size of the reinforcing phase raw materials is 1 μm - 10 μm.

[0021] By controlling the content and particle size of the reinforcing phase raw materials, a network-shaped reinforcing phase is formed, which is conducive to reducing the appearance of columnar crystals.

[0022] Using the above preparation method of the present invention, mainly based on remelting diffusion during the layer-by-layer accumulation process, titanium matrix composites with other gradient structures along the deposition direction prepared thereby also fall within the protection scope of the present invention, such as gradient distributions of metal elements, gradient distributions of phase sizes, gradient distributions of contents, or gradient distributions under any combination.

[0023] The present invention also provides a titanium matrix composite with a gradient structure, which is prepared by the preparation method of the titanium matrix composite with a gradient structure described above.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: Aiming at the problems of anisotropy of the additive manufacturing structure and damage to the mechanical properties of the material in the interlayer mutation tissue region, based on the layer-by-layer accumulation printing strategy of additive manufacturing, the content of the reinforcing phase in different layers is designed, and with the help of interlayer remelting diffusion, a gradient structure distribution of the reinforcing phase and the matrix phase in the Z direction is constructed, initially solving the inherent problem that the coarse columnar crystals in the deposition direction weaken the strength and plasticity of the alloy, and realizing the coordinated improvement of strength and plasticity. For example, constructing a gradient structure of the reinforcing phase significantly improves the mechanical properties of the (TiB + TiC) / Ti6Al4V composite material in the Z direction. Compared with the matrix alloy, the tensile strength of the composite material in the Z direction reaches 1.3 GPa, and the fracture elongation rate is greater than 10%, realizing the coordinated improvement of strength and plasticity and solving the inherent problem that the coarse columnar crystals in the deposition direction weaken the strength and plasticity. Therefore, constructing a gradient structure in the deposition direction effectively alleviates local stress concentration and local non-uniform strain, improves the plastic deformation ability and work hardening rate of the titanium matrix composite material, and this work innovates the method for optimizing the design and regulation of the structure and properties of the titanium matrix composite material. Description of the Drawings

[0025] Figure 1 It is the BC diagram during the EBSD test of the titanium matrix composite material prepared in Example 1, and the black line is the position pinned by the reinforcing phase; Figure 2 It is the SEM diagram of the titanium matrix composite material prepared in Comparative Example 1, wherein the white dotted line indicated by the arrow is the columnar crystal grain boundary; Figure 3 It is the SEM diagram of the titanium matrix composite material prepared in Example 2; Figure 4 It is the SEM diagram of the titanium matrix composite material prepared in Example 3; Figure 5 It is the SEM diagram of the titanium matrix composite material prepared in Comparative Example 2, wherein the white dotted line indicated by the arrow is the columnar crystal grain boundary. Detailed Embodiments

[0026] Specific embodiments are given below to further describe the present invention in detail, but the present invention is not limited in any form. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present invention.

[0027] Example 1: (1) Material selection: TC4 (Ti6Al4V) titanium alloy is used as the matrix alloy, with a particle size of 50 μm - 150 μm. B 4 C powder is used as the reinforcing phase raw material for in-situ reaction, with a particle size of 2 μm - 4 μm. The addition amount of B 4 C is 0.7 wt.%.

[0028] (2) Preparation parameters of mixed powder: The rotation speed is 200 r / min, the ball milling time is 5 h, and the ball-to-powder ratio is 3:1.

[0029] (3) Additive manufacturing parameters: The printing power is 700 W, the powder feeding rate is 5%, the scanning speed is 700 mm / min, and the layer thickness is 0.37 mm.

[0030] (4) Alternating laser forming: The matrix alloy powder and the mixed powder are respectively transported by two powder barrels, and the laser melting deposition additive manufacturing technology is used for 60 cycles of alternating additive manufacturing. One cycle is to first print a composite material layer, and then print a matrix alloy layer on the composite material layer.

[0031] Figure 1 The titanium matrix composite with a gradient structure distribution of the reinforcing phase is prepared in this example. It can be seen that the reinforcing phase obtained by in-situ reaction is TiB + TiC pinned on the grain surface, and the formed network size is the same as that of the grains. Along the deposition direction, the network size gradually increases, that is, the volume fraction of the reinforcing phase shows a gradient change. At the same time, the matrix phase size also shows the same gradient change trend, and there is no obvious interlayer mutation tissue area, and the coarse columnar crystals are eliminated.

[0032] Comparative Example 1: The difference between this comparative example and Example 1 is that the addition amount of B 4 C is 0.1 wt.%.

[0033] Figure 2 This is the SEM image of the tissue characteristics in this example. Coarse columnar crystals still exist in the matrix alloy layer, and the reinforcing phase is diffusely distributed; the network structure of the reinforcing phase in the composite material layer is not obvious, showing a mixed mode of diffusion and network; the volume fraction of the reinforcing phase in the matrix alloy is lower than that in the composite material layer.

[0034] Example 2: The difference between this example and Example 1 is that the addition amount of B 4 C is 2 wt.%.

[0035] Figure 3 This is the SEM image of the tissue characteristics under this embodiment. The columnar crystals are eliminated. Due to the increase in the volume fraction of the reinforcement phase, the reticulated reinforcement phase formed is small and dense. Due to the effect of interlayer diffusion, a gradient distribution of reticulated sizes is formed between the matrix alloy layer and the composite material layer.

[0036] Example 3: The difference between this example and Example 1 is that in one cycle, a composite material layer is printed first, and then two matrix alloy layers are printed successively on the composite material layer, and the printing is carried out in an alternating cycle.

[0037] Figure 4 This is the SEM image of the tissue characteristics under this embodiment. At the junction of the matrix alloy layer and the composite material layer, the volume fraction of the reinforcement phase along the deposition direction shows a significant gradient distribution. The reinforcement phase pins on the grain surface, and the reticulated size formed is equal to the grain size.

[0038] Comparative Example 2: The difference between this example and Example 1 is that in one cycle, a composite material layer is printed first, and then three matrix alloy layers are printed successively on the composite material layer, and the printing is carried out in an alternating cycle.

[0039] Figure 5 This is the SEM image of the tissue characteristics under this embodiment. Inside the matrix alloy layer adjacent to the composite material layer, the reinforcement phase shows a mixed mode of dispersion and reticulation. The main reason is that in the process of layer-by-layer accumulation, the second matrix alloy layer dilutes the reinforcement phase in the first matrix alloy layer, forming a gradient distribution of the volume fraction of the reinforcement phase in the upper section of the composite material layer, and large columnar crystals are formed. It can be seen that in combination with Example 4, under this total volume fraction of the reinforcement phase, the matrix alloy layer is not recommended to exceed 2 layers.

[0040] As described above, by designing the ratio of the matrix alloy layer and the composite material layer, the gradient distribution of the volume fraction of the reinforcement phase and the adjustable and controllable structure of the reinforcement phase are realized. In particular, Example 1 realizes a continuous gradient distribution along the deposition direction. The described embodiments do not impose any form of limitation on the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, any simple modification, equivalent replacement, and improvement made to the above embodiments all fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a titanium-based composite material with a gradient structure, characterized in that: include: Step 1, ball-milling a matrix powder and a reinforcement phase raw material to obtain a mixed powder, wherein the matrix powder is a titanium alloy powder; Step 2: Perform multiple cycles of alternating additive manufacturing to obtain a titanium-based composite material, wherein one cycle of additive manufacturing includes: first feeding mixed powder to form a composite material layer, and then feeding matrix powder to print on the composite material layer to form 1-2 matrix alloy layers, and when printing the current matrix alloy layer, the previous layer is remelted by controlling the printing power.

2. The method for preparing a titanium-based composite material having a gradient structure according to claim 1, characterized in that: A base alloy layer is printed on the composite material layer.

3. The method for preparing a titanium-based composite material having a gradient structure according to claim 1, characterized in that: The number of continuous composite material layers is no more than 3.

4. The method for preparing a titanium-based composite material having a gradient structure according to claim 1, characterized in that: The printing power is 600 W - 1000 W.

5. The method for preparing a titanium-based composite material with a gradient structure according to claim 1, characterized in that: The additive manufacturing is a laser molten deposition additive manufacturing technology.

6. The method for preparing a titanium-based composite material with a gradient structure according to claim 1, characterized in that: The reinforcing phase raw material includes one or more of TiB, TiC, TiN, La2O3, and TiB2.

7. The method for preparing a titanium-based composite material with a gradient structure according to claim 1, characterized in that: The content of the reinforcing phase raw material in the mixed powder is 0.2 wt.% - 3 wt.%.

8. The method for preparing a titanium-based composite material with a gradient structure according to claim 7, characterized in that: The particle size of the reinforcing phase raw material is 1 μm - 10 μm.

9. A titanium-based composite material with a gradient structure, characterized in that: It is prepared by the preparation method of the titanium-based composite material with a gradient structure according to any one of claims 1 to 8.

Images