Wear-resistant high-entropy alloy coating prepared by laser cladding

Abstract

The invention discloses a wear-resistant high-entropy alloy coating prepared by laser cladding, which comprises the following components in percentage by atom: 14-15% of Co, 13-15% of Cr, 13-15% of Fe, 28-30% of Ni, 13-15% of Mo, 3-5% of W and 10-12% of Ti, and is prepared by a laser cladding process with the scanning speed of 3-5 mm / s. And an intermetallic compound strengthening phase is generated in situ in the cladding process, so that the technical problems that a high-entropy alloy coating is easy to crack, air holes are easy to generate and high wear resistance is difficult to consider are effectively solved. The obtained coating is compact in structure and free of macroscopic defects, forms excellent metallurgical bonding with a matrix, has high hardness and excellent wear resistance, is stable, simple and convenient in preparation process, and is suitable for surface strengthening and life prolonging of mechanical parts under the working condition of strong wear.

Description

Technical Field

[0001] This invention relates to the field of surface engineering of metallic materials, and specifically to a wear-resistant high-entropy alloy coating prepared by laser cladding. Background Technology

[0002] Laser cladding technology, due to its advantages such as high energy density, controllable heat input, and good bonding strength, has become one of the mainstream technologies for preparing high-performance wear-resistant coatings. Currently, there are two main technical approaches aimed at improving the wear resistance of laser cladding coatings: The first is the introduction of external hard ceramic phases such as WC and TiC. While this method can significantly improve the macroscopic hardness of the coating, the ceramic phase and the metal matrix have significant differences in thermophysical properties. During rapid cooling after cladding, large residual stresses are easily generated at the interface, becoming the initiation source of microcracks and even macroscopic cracks, and may also produce defects such as porosity. This not only weakens the bonding strength between the coating and the substrate but may also become the failure starting point during service, reducing the long-term protective reliability of the coating. The second approach is pure high-entropy alloy coatings without external ceramic phases. This method obtains high-hardness multi-principal element alloy coatings through solid solution strengthening, ordered precipitation, or in-situ self-generated intermetallic compounds. While avoiding heterogeneous interface problems, a prominent "performance-process-quality" triangle contradiction arises: to achieve high wear resistance, alloy composition tends to promote the in-situ formation of a large number of hard phases, but this usually exacerbates the brittleness and solidification shrinkage stress of the coating, leading to a sharp increase in crack sensitivity during laser cladding and deteriorating the coating forming quality. To suppress cracking, it is often necessary to resort to auxiliary methods such as ultra-high-speed laser cladding, adding a tough transition layer, or complex preheating / post-heat treatment, which generally have problems such as high equipment requirements and complicated production processes, affecting the universality and economy of the technology.

[0003] Therefore, how to achieve the controllable formation and distribution of high-strength in-situ reinforcing phases inside the coating under conventional laser cladding process conditions, without relying on external ceramic phases or complex auxiliary processes, while simultaneously ensuring extremely low crack sensitivity, excellent metallurgical bonding quality, and outstanding wear resistance of the coating, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] The present invention aims to solve the above-mentioned technical problems existing in the prior art by providing a wear-resistant high-entropy alloy coating prepared by laser cladding.

[0005] The technical solution of the present invention is: a wear-resistant high-entropy alloy coating prepared by laser cladding, which is composed of Co, Cr, Fe, Ni, Mo, W and Ti elements, with the following composition in atomic percentage: Co 14~15%, Cr 13~15%, Fe 13~15%, Ni 28~30%, Mo 13~15%, W 3~5%, Ti 10~12%.

[0006] The preferred composition, in atomic percentage, is Co 14%, Cr 14%, Fe 14%, Ni 29%, Mo 14%, W 4%, and Ti 11%.

[0007] Preferably, a pre-alloyed powder prepared by mixing various elements is uniformly spread on the surface of a substrate to form a pre-layer, and a coating is formed by cladding the pre-layer with a laser beam with a scanning speed of 3~5 mm / s under a protective atmosphere, thus forming a metallurgically bonded coating with the surface of the substrate.

[0008] Preferably, the output power of the laser beam is 1400~1700 W, the spot diameter is 2~5 mm, and the thickness of the pre-placed layer is 0.8~1.2 mm.

[0009] The preferred microstructure includes a face-centered cubic solid solution phase, a body-centered cubic solid solution phase, and a W-Mo-rich intermetallic compound phase.

[0010] The preferred average microhardness is not less than 930 HV.

[0011] The preferred base material is Q235 steel.

[0012] This invention employs a seven-element system of Co-Cr-Fe-Ni-Mo-W-Ti and precisely controls the Ti content to 10-12%. This process promotes the in-situ formation of a W-Mo-rich intermetallic compound hard phase during laser cladding, exhibiting good compatibility with the BCC / FCC solid solution matrix and completely avoiding defects such as interfacial stress caused by the addition of ceramic phases. Furthermore, addressing the characteristics of this seven-element high-entropy alloy system—large differences in elemental properties and poor molten pool fluidity—this invention employs low-speed scanning laser cladding at 3-5 mm / s, effectively extending the molten pool's existence time, promoting uniform element diffusion, smoothing the temperature gradient, and reducing solidification shrinkage stress. This fundamentally solves the technical challenges of easy cracking and porosity in high-entropy alloy laser cladding layers. Experimental results show that the coating prepared by this invention has a dense structure, no macroscopic defects, forms an excellent metallurgical bond with the matrix, and possesses high hardness and excellent wear resistance, with a hardness reaching 900 HV and a wear rate of 9.20 × 10⁻⁶. -6 mm 3 / (N·m). This invention does not require ultra-high-speed laser cladding equipment, the addition of a tough transition layer, or complex preheating / post-heat treatment and other auxiliary means. Its preparation process is stable and simple, reducing production costs and improving production efficiency. It is suitable for surface strengthening and life extension of mechanical parts under strong wear conditions. Attached Figure Description

[0013] Figure 1 This is a cross-sectional topography diagram of the high-entropy alloy coating in an embodiment of the present invention.

[0014] Figure 2 These are the X-ray diffraction (XRD) patterns of the high-entropy alloy coatings of the embodiments and comparative examples 1-4 of this invention.

[0015] Figure 3 This is a scanning electron microscope (SEM) image of the high-entropy alloy coating according to an embodiment of the present invention.

[0016] Figure 4 These are microhardness diagrams of the high-entropy alloy coatings in the embodiments and comparative examples 1-4 of this invention.

[0017] Figure 5 This is a wear rate diagram of the Q235 steel used in the embodiments of the present invention, and the high-entropy alloy coatings of the embodiments and comparative examples 1 to 4. Detailed Implementation Example

[0018] (1) Coating composition design (atomic percentage): Co (cobalt) 14%, Cr (chromium) 14%, Fe (iron) 14%, Ni (nickel) 29%, Mo (molybdenum) 14%, W (tungsten) 4%, Ti (titanium) 11%.

[0019] (2) Preparation process: a) Batching and Ball Milling: Select pure metal spherical powder with a particle size of 50-100 μm and weigh it precisely according to the designed ratio. Mix the metal powder and place it in a planetary ball mill using alumina grinding balls. Set the ball-to-powder mass ratio to 10:1 and the rotation speed to 100 rpm. The ball milling mode is: forward rotation for 45 min → pause for 20 min → reverse rotation for 45 min, repeating this cycle for a total duration of 4 h to obtain a uniform pre-alloyed powder.

[0020] b) Substrate pretreatment: The substrate is made of Q235 steel plate, which is ground, degreased, ultrasonically cleaned with alcohol and dried.

[0021] c) Powder pre-laying: The pre-alloyed powder is evenly laid on the surface of the substrate, and the pre-laying layer size is 50mm×5mm×1.1mm.

[0022] d) Laser cladding: The sample is placed in a laser processing chamber and protected with argon gas. A fiber laser is used with a power of 1600 W, a spot diameter of 3 mm, and a scanning speed of 4 mm / s for single-pass cladding. After cladding, the sample is slowly cooled to room temperature.

[0023] The preparation processes of Comparative Examples 1-4 are exactly the same as those of the embodiments of the present invention, except that the atomic percentage of Ti element in the coating is changed: Comparative Example 1: Ti 0%, Comparative Example 2: Ti 4%, Comparative Example 3: Ti 7%, Comparative Example 4: Ti 14%.

[0024] The specific composition of the atomic percentage meter is as follows: Comparative Example 1: The raw materials of this comparative example coating, by atomic percentage, include: Co 16%, Cr 16%, Fe 16%, Ni 31%, Mo 16%, W 5%.

[0025] Comparative Example 2: The raw materials of this comparative example coating, by atomic percentage, include: Co 15%, Cr 15%, Fe 15%, Ni 31%, Mo 15%, W 5%, Ti 4%.

[0026] Comparative Example 3: The raw materials of this comparative example coating, by atomic percentage, include: Co 14%, Cr 15%, Fe 15%, Ni 30%, Mo 15%, W 4%, and Ti 7%.

[0027] Comparative Example 4: The raw materials of this comparative example coating, by atomic percentage, include: Co 14%, Cr 13%, Fe 14%, Ni 27%, Mo 14%, W 4%, and Ti 14%.

[0028] 1. The cross-sectional morphology of the high-entropy alloy coating prepared in the embodiments of the present invention is shown in the figure below. Figure 1 As shown. From Figure 1 As can be seen, there are no cracks or pores inside the coating, and a straight and dense metallurgical interface is formed between the coating and the Q235 steel substrate, with no incomplete fusion defects. This indicates that the specific components described in this invention, combined with the low-speed cladding process, effectively overcome the problem of easy cracking, ensuring the integrity and reliability of the coating.

[0029] 2. The X-ray diffraction (XRD) patterns of the high-entropy alloy coatings of the embodiments and comparative examples 1-4 of the present invention are as follows: Figure 2 As shown. Figure 2 The Ti0, Ti0.25, Ti0.5, Ti0.75, and Ti1.0 in the figures are the X-ray diffraction patterns of Comparative Example 1, Comparative Example 2, Comparative Example 3, the embodiment of the present invention, and Comparative Example 4, respectively. From... Figure 2 It can be seen that the XRD diffraction peak intensity of the W-Mo rich intermetallic compound phase in the embodiments of the present invention is significantly higher than that of the coatings in comparative examples 1-4. Scanning electron microscope (SEM) images of the high-entropy alloy coatings in the embodiments of the present invention are shown below. Figure 3 As shown, from Figure 3 It can be seen that the coating forms a three-phase composite structure consisting of the FCC phase, the BCC phase, and the intermetallic compound phase. Figure 2 , Figure 3 The results show that within the Ti content range of 10-12% defined in this invention, the formation degree and structural stability of the hard phase of the intermetallic compound reach the optimal state, and the same effect cannot be achieved if the Ti content is lower or higher than this range.

[0030] 3. The microhardness diagrams of the high-entropy alloy coatings of the embodiments of the present invention and comparative examples 1-4 are shown below. Figure 4 As shown. Figure 4 The Ti0, Ti0.25, Ti0.5, Ti0.75, and Ti1.0 values ​​in the diagram represent the microhardness images of Comparative Example 1, Comparative Example 2, Comparative Example 3, the embodiment of the present invention, and Comparative Example 4, respectively. From... Figure 4 As can be seen, the coating hardness changes non-linearly with Ti content. The coating in the embodiment of the present invention has the highest average hardness, approximately 930 HV. The hardness of Comparative Example 3 is approximately 850 HV, while the hardness of Comparative Example 4 decreases to approximately 890 HV. The results show that the peak hardness can only be achieved when the Ti content is within the range of 10-12% specified in this invention. Deviations from this range fail to achieve the optimal strengthening effect, fully demonstrating the non-obviousness of the composition design and the unexpected technical effect.

[0031] 4. The wear rate diagrams of the Q235 steel used in the embodiments of the present invention, and the high-entropy alloy coatings of Examples 1-4 are shown below. Figure 5 As shown. Figure 5 The wear rates of Q235, Ti0, Ti0.25, Ti0.5, Ti0.75, and Ti1.0 used in the embodiments of the invention, comparative examples 1, 2, and 3, and the embodiments of the present invention and comparative example 4 are respectively. Figure 5 It can be seen that the coating in the embodiment of the present invention has the lowest wear rate, which is 9.20 × 10⁻⁶. -6 mm 3 The wear resistance (N·m) is only about 17.2% of that of Q235 steel substrate. The wear rates of Comparative Examples 1, 2, 3, and 4 are all higher than those of the embodiment of the present invention. The wear resistance variation trend is highly positively correlated with hardness, and the embodiment of the present invention has the best wear resistance performance. The results show that the specific multiphase microstructure obtained by controlling the Ti content at 10-12% is the fundamental reason for the excellent wear resistance of the present invention. Moreover, the improvement in wear resistance (>80%) is significant, bringing unexpected technical effects.

[0032] In summary, this invention provides a specific Co-Cr-Fe-Ni-Mo-W-Ti seven-element high-entropy alloy (Ti content strictly limited to 10-12 at.%), and matches it with a low-speed laser cladding process with a scanning speed of 3-5 mm / s, successfully and stably preparing a high-quality coating with no cracks, high hardness, good wear resistance and strong adhesion on conventional laser cladding equipment.

Claims

1. A wear-resistant high-entropy alloy coating prepared by laser cladding, characterized in that: It is composed of elements Co, Cr, Fe, Ni, Mo, W and Ti, with an atomic percentage composition of Co 14~15%, Cr 13~15%, Fe 13~15%, Ni 28~30%, Mo 13~15%, W 3~5%, and Ti 10~12%.

2. The wear-resistant high-entropy alloy coating prepared by laser cladding according to claim 1, characterized in that: The composition, by atomic percentage, is Co 14%, Cr 14%, Fe 14%, Ni 29%, Mo 14%, W 4%, and Ti 11%.

3. The wear-resistant high-entropy alloy coating prepared by laser cladding according to claim 1 or 2, characterized in that: The process involves uniformly spreading a pre-alloyed powder prepared by mixing various elements onto the surface of a substrate to form a pre-layer. Under a protective atmosphere, a laser beam with a scanning speed of 3~5 mm / s is used to clad the pre-layer, forming a coating that is metallurgically bonded to the surface of the substrate.

4. The wear-resistant high-entropy alloy coating prepared by laser cladding according to claim 3, characterized in that: The laser beam has an output power of 1400~1700 W and a spot diameter of 2~5 mm. The thickness of the pre-placed layer is 0.8~1.2 mm.

5. The wear-resistant high-entropy alloy coating prepared by laser cladding according to claim 4, characterized in that: The microstructure includes face-centered cubic solid solution phase, body-centered cubic solid solution phase, and W-Mo rich intermetallic compound phase.

6. The wear-resistant high-entropy alloy coating prepared by laser cladding according to claim 5, characterized in that: The average microhardness is not less than 930 HV.

7. The wear-resistant high-entropy alloy coating prepared by laser cladding according to claim 6, characterized in that: The base material is Q235 steel.

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