A method for laser surface coating of refractory metals and applications thereof

Abstract

The present application provides a refractory metal laser surface coating method, comprising the following steps: first, the refractory metal powder to be coated is pre-deposited on the surface of the substrate; second, a pulsed laser is used to irradiate the substrate with the refractory metal powder layer, forming a base layer with a small-size molten pool between the refractory metal powder layer and the substrate; finally, laser surface coating or additive manufacturing of the refractory metal powder is carried out on the base layer. The coating method provided by the present application can achieve the following two effects: first, the surrounding refractory metal powder particles are fixed by the advantage of rapid cooling of the small-size molten pool; second, the surrounding refractory metal powder particles are avoided to be adsorbed by the advantage of low surface tension of the small-size molten pool. The combined effect of the above two effects can effectively solve the defects such as spheroidization and porosity that occur during the preparation of refractory metal alloys, improve the quality and appearance of the products in additive manufacturing, and has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of laser processing, specifically relating to a method for laser surface coating of refractory metals, and also to the application of a method for laser surface coating of refractory metals. Background Technology

[0002] Refractory metals are metals with melting points above 2000 degrees Celsius and abundant reserves, such as tungsten, molybdenum, niobium and zirconium. More and more researchers are using these metals as the main body and adding some common elements to form alloys called refractory metal alloys.

[0003] The most significant advantage of refractory metals lies in their excellent high-temperature strength and corrosion resistance, making refractory metal alloys frequently used as structural materials in industry and research. However, their high melting point and poor oxidation resistance have limited their widespread application. Laser irradiation of material surfaces can generate ultra-high temperature fields, making it a very suitable technique for melting and preparing refractory metal alloys. However, the properties of refractory metals also bring many problems during the preparation process; they are difficult to melt and bond with common metals and tend to spheroidize and become unformable.

[0004] Therefore, developing an effective method to address defects such as spheroidization and porosity in the preparation of refractory metal alloys is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] One of the objectives of this invention is to provide a laser surface coating method for refractory metals that can effectively solve defects such as spheroidization and porosity in the process of refractory metal alloying.

[0006] The second objective of this invention is to provide an application of a laser surface coating method for refractory metals in the preparation of composite materials with low spheroidization defects and low porosity defects.

[0007] One of the technical solutions adopted to achieve the objective of this invention is: to provide a method for laser surface coating of refractory metals, comprising the following steps:

[0008] S1. The refractory metal powder to be coated is pre-laid in a small amount on the surface of the substrate;

[0009] S2. Irradiate a substrate with a refractory metal powder layer using a pulsed laser to form a base layer with several molten pools in the refractory metal powder layer or between the refractory metal powder layer and the substrate; the width and / or length of the molten pools is less than 0.5 mm and the depth is greater than 0.05 mm.

[0010] S3. Perform laser surface coating and / or additive manufacturing of refractory metal powder on the substrate.

[0011] The general idea of ​​the laser surface coating method for refractory metals provided by this invention is as follows: Research has found that a thick refractory metal powder layer combined with a high-energy continuous laser easily forms a large molten pool (3-5 mm), which has two characteristics: high surface tension and temperature field. On the one hand, the high surface tension makes it easy to adsorb refractory metal powder particles around the molten pool; on the other hand, the high temperature field is non-uniformly distributed and exhibits a Gaussian distribution along the center of the continuous laser. Therefore, the temperature around the molten pool is too low to melt the adsorbed refractory metal powder particles. The above two characteristics lead to spheroidization defects that are easy to occur in conventional laser surface coating or additive manufacturing processes of refractory metals.

[0012] To effectively address the aforementioned problems, the laser surface coating method for refractory metals provided by this invention first involves pre-laying a small amount of the refractory metal powder to be coated onto the surface of a substrate to form a refractory metal powder layer. Then, a pulsed laser is used, with its pulse width, pulse energy, and repetition frequency adjusted to act on the pre-laid refractory metal powder layer along a defined scanning path. This pre-melts the refractory metal powder rapidly before formal coating to create a "base layer" and reduce accumulated defects, thereby avoiding spheroidization defects caused by large molten pools generated by high-energy continuous lasers. Compared to continuous lasers, this invention reduces the size and surface tension of the molten pool by decreasing the laser's radiation range, controlling the molten pool diameter (maximum width) to below 1 mm. This achieves two effects: firstly, the rapid cooling of the smaller molten pool helps to fix the surrounding refractory metal powder particles; secondly, the low surface tension of the smaller molten pool prevents the adsorption of surrounding refractory metal powder particles. Subsequently, laser surface coating and / or additive manufacturing of the refractory metal powder are performed on the base layer surface, thereby effectively suppressing spheroidization and porosity defects.

[0013] Furthermore, in this invention, in the base layer formed by pulsed laser irradiation, the width and / or length of the molten pool is less than 0.5 mm, which can effectively reduce the effect of the molten pool surface tension on the transport of powder; at the same time, the depth of the molten pool needs to be greater than 0.05 mm to ensure sufficient melting depth and to generate a surface with mechanical positioning function to fix the surface powder.

[0014] Furthermore, in step S1, the thickness of the metal powder is 0.05 to 10 mm; preferably, the thickness of the metal powder is 0.1 to 0.5 mm.

[0015] Preferably, the metal powder comprises a refractory metal and its alloy, wherein the refractory metal comprises one or more of titanium, tungsten, molybdenum, niobium and zirconium.

[0016] Preferably, the substrate includes iron, non-ferrous metals and their alloys; the alloy can be common materials such as 304 stainless steel, 45 steel, nickel-based alloys, etc.

[0017] Furthermore, in step S2, the parameters of the pulsed laser include: pulse width 2ns to 100ms, pulse energy 0.05mJ to 500J, and repetition frequency 1Hz to 3000kHz.

[0018] Furthermore, the pulsed laser includes one of a nanosecond laser, a microsecond laser, or a millisecond laser. Preferably, the pulsed laser is a nanosecond laser, and in step S2, its irradiation parameters include: pulse width 2–20 ns, pulse energy 0.25–500 mJ, and repetition frequency 100 kHz–300 kHz.

[0019] Furthermore, in step S2, the scanning path of the pulsed laser is either continuous or skip-scan. Preferably, the scanning speed of the pulsed laser is 2–5 mm / s and the scanning interval is 0.2–0.5 mm.

[0020] Furthermore, in step S3, the power of the laser surface coating is higher than 20W, the scanning speed is greater than 0.1mm / s, and the scanning interval is greater than 0.005mm. In some preferred embodiments, the power of the laser surface coating is 950-2000W, the scanning speed is 4-10mm / s, and the scanning interval is 1-2mm.

[0021] Furthermore, the power of the laser surface coating is sufficient to melt refractory metals of coating thickness, but the melting depth does not exceed 5 times the coating thickness.

[0022] Furthermore, in step S3, additive manufacturing includes one of selective laser melting (SLM) and selective laser sintering.

[0023] Furthermore, during the preparation of additive manufacturing multilayer structures, a base layer with a small-sized molten pool can be formed only between the initial matrix and the first refractory metal layer; preferably, the method of the present invention is used to form a base layer with a small-sized molten pool between each new refractory metal layer and the metal layer coated below it, so as to improve the overall quality of the composite material.

[0024] The second objective of this invention is achieved by providing a composite material, comprising a matrix and a refractory metal layer disposed on the surface of the matrix, wherein the refractory metal layer of the composite material is prepared by the refractory metal laser surface coating method according to one objective of this invention.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The present invention provides a laser surface coating method for refractory metals, in which a small amount of refractory metal powder to be coated is pre-laid on the surface of a substrate, and a small-sized molten pool is formed between the refractory metal powder and the substrate by scanning with a pulsed laser. On the one hand, the rapid cooling of the small-sized molten pool fixes the surrounding refractory metal powder particles; on the other hand, the low surface tension of the small-sized molten pool avoids the adsorption of surrounding refractory metal powder particles. The combined effect of the above two aspects can effectively eliminate defects such as spheroidization and porosity that occur during the preparation of refractory metal alloys.

[0027] (2) The laser surface coating method for refractory metal provided by the present invention is applied to the additive manufacturing of composite materials. The refractory metal and the substrate in the resulting composite material form a good bond, which effectively suppresses defects such as spheroidization and porosity on the surface of the product substrate, improves the product quality and appearance, and has broad prospects for promotion and application. Attached Figure Description

[0028] Figure 1 A comparison diagram of the laser surface coating method for refractory metals provided by the present invention and the process of conventional laser surface coating is shown; wherein, (a) is the conventional laser surface coating method that is prone to spheroidization defects; (b) is a schematic diagram of preparing a base layer with a small-sized molten pool using the coating method of the present invention;

[0029] Figure 2 The images show a comparison of the appearance of titanium carbide (TiC) refractory metal powder additively manufactured on the surface of 45# steel substrate in Example 1 and Comparative Example 1, respectively; wherein, (a) is the product obtained in Comparative Example 1; and (b) is the product obtained in Example 1.

[0030] Among them, 1-metal substrate; 2-scanning path; 3-high-energy continuous laser beam; 4-scraper pneumatic powder feeder; 5-refractory metal powder; 6-nanosecond laser beam. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0033] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0034] The main raw materials and parameters involved in Examples 1-3 of this invention are shown in Table 1 below.

[0035] Table 1

[0036]

[0037] Example 1

[0038] In this embodiment, the refractory metal powder used is the widely used titanium carbide (TiC) refractory metal powder, which has a particle size of 20-50 μm and good flowability. The experimental substrate is the common No. 45 steel.

[0039] This embodiment employs a laser surface coating method for refractory metals, including the following steps:

[0040] Step 1: The titanium carbide (TiC) refractory metal powder to be additively manufactured is pre-laid in a small amount on the surface of the 45# steel substrate. The thickness of the titanium carbide (TiC) refractory metal powder layer is about 0.5mm.

[0041] Step 2: Fix the No. 45 steel substrate coated with titanium carbide (TiC) refractory metal powder layer on the processing platform. Set the pulse width of the nanosecond laser to 2ns, the pulse energy to 0.25mJ, and the repetition frequency to 100kHz. Follow the S-shaped scanning path, set the scanning speed to 2mm / s and the scanning interval to 0.2mm, and apply the nanosecond laser to the pre-laid metal powder layer to create a base layer with a small molten pool.

[0042] Step 3: Using a 1kW fiber continuous laser, set the continuous laser power to 950W, the scanning speed to 4mm / s and the scanning spacing to 1mm, coat the surface of the 45# steel substrate with titanium carbide (TiC) refractory metal.

[0043] Example 2

[0044] In this embodiment, the refractory metal powder used is niobium alloy 5BMⅡ (Nb-5W-2Mo-1Zr) powder, which has a particle size of 15-53μm and good flowability. The substrate is 304 stainless steel.

[0045] This embodiment employs a laser surface coating method for refractory metals, including the following steps:

[0046] Step 1: The niobium alloy 5BMⅡ refractory metal powder to be additively manufactured is pre-laid in a small amount on the surface of the 304 stainless steel substrate. The thickness of the niobium alloy 5BMⅡ refractory metal powder layer is about 0.1 mm.

[0047] Step 2: Fix the 304 stainless steel substrate coated with niobium alloy 5BMⅡ refractory metal powder layer on the processing platform, set the pulse width of the nanosecond laser to 10ns, the pulse energy to 50mJ, the repetition frequency to 200kHz, and follow the S-shaped scanning path. Set the scanning speed to 3mm / s and the scanning interval to 0.3mm, and apply the nanosecond laser to the pre-laid metal powder layer to create a base layer with a small molten pool.

[0048] Step 3: Using a 2kW fiber continuous laser, set the continuous laser power to 1500W, the scanning speed to 7mm / s and the scanning spacing to 1.5mm, coat the surface of the 304 stainless steel substrate with 5BMⅡ niobium alloy.

[0049] Example 3

[0050] In this embodiment, the refractory metal powder used is tantalum alloy Ta-10W powder, which has a particle size of 30-70 μm and good flowability. The substrate is nickel-based 718 alloy.

[0051] This embodiment employs a laser surface coating method for refractory metals, including the following steps:

[0052] Step 1: The tantalum alloy Ta-10W refractory metal powder to be additively manufactured is pre-laid in a small amount on the surface of the nickel-based alloy substrate. The thickness of the tantalum alloy Ta-10W refractory metal powder layer is about 0.5 mm.

[0053] Step 2: Fix the nickel-based alloy coated with tantalum alloy Ta-10W refractory metal powder layer on the processing platform, set the pulse width of the nanosecond laser to 20ns, the pulse energy to 500mJ, and the repetition frequency to 300kHz, and follow the S-shaped scanning path, setting the scanning speed to 4mm / s and the scanning interval to 0.4mm, and apply the nanosecond laser to the pre-laid metal powder layer to create a base layer with a small molten pool;

[0054] Step 3: Using a 2kW fiber continuous laser, with a continuous laser power of 2000W, a scanning speed of 10mm / s and a scanning spacing of 2mm, tantalum alloy Ta-10W is coated on the surface of a nickel-based 718 alloy substrate.

[0055] Comparative Example 1

[0056] The materials used in this comparative example are the same as those in Example 1, namely, the refractory metal powder used is titanium carbide (TiC) metal powder (particle size of 20-50 μm and good flowability), and the substrate is common No. 45 steel.

[0057] The specific preparation method is as follows: using the same parameters as step 3 of Example 1, titanium carbide (TiC) metal is additively manufactured on the surface of a No. 45 steel substrate with a continuous laser power of 950W, a scanning speed of 4mm / s and a scanning spacing of 1mm.

[0058] Figure 2 These are comparative images of the appearance of titanium carbide (TiC) refractory metal powder additively manufactured on the surface of a steel substrate in Example 1 and Comparative Example 1 of the present invention. In particular, 2(a) is the product obtained in Comparative Example 1; 2(b) is the product obtained in Example 1.

[0059] Comparison shows that the substrate surface of the product prepared in Comparative Example 1 exhibits large-area spheroidization defects, which will prevent the parts from meeting usage requirements. In contrast, the substrate surface of the product prepared in Example 1 does not show spheroidization defects and has a good appearance. This indicates that the composite material prepared by the refractory metal laser surface coating method provided by this invention can effectively suppress spheroidization and improve product quality.

[0060] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for laser surface coating of refractory metals, characterized in that, Includes the following steps: S1. The refractory metal powder to be coated is pre-laid on the surface of the substrate, and the thickness of the metal powder is 0.05-0.5 mm. S2. Irradiate a substrate with a refractory metal powder layer using a pulsed laser to form a base layer with several molten pools in the refractory metal powder layer or between the refractory metal powder layer and the substrate; the scanning speed of the pulsed laser is 2-5 mm / s; the width and / or length of the molten pool is less than 0.5 mm and the depth is greater than 0.05 mm. S3. Perform laser surface coating and / or additive manufacturing of refractory metal powder on the substrate.

2. The laser surface coating method for refractory metals according to claim 1, characterized in that, The metal powder contains refractory metals and their alloys, and the refractory metals include one or more of titanium, tungsten, molybdenum, niobium and zirconium.

3. The laser surface coating method for refractory metals according to claim 2, characterized in that, The substrate includes one or more of iron, non-ferrous metals, and alloys containing iron or non-ferrous metals.

4. The laser surface coating method for refractory metals according to claim 1, characterized in that, In step S2, the parameters of the pulsed laser include: pulse width 2 ns-100 ms, pulse energy 0.05 mJ-500 J, and repetition frequency 1 Hz-3000 kHz.

5. The laser surface coating method for refractory metals according to claim 4, characterized in that, The pulsed laser includes one of a nanosecond laser, a microsecond laser, or a millisecond laser.

6. The laser surface coating method for refractory metals according to claim 5, characterized in that, The scanning path of the pulsed laser is either continuous or skip scanning, with a scanning interval of 0.2-0.5 mm.

7. The laser surface coating method for refractory metals according to claim 1, characterized in that, In step S3, the power of the laser surface coating is higher than 20 W, the scanning speed is greater than 0.1 mm / s, and the scanning spacing is greater than 0.005 mm.

8. The laser surface coating method for refractory metals according to claim 7, characterized in that, The power of the laser surface coating is sufficient to melt refractory metals of coating thickness, but the melting depth does not exceed 5 times the coating thickness.

9. A composite material, comprising a matrix and a refractory metal layer disposed on the surface of the matrix, characterized in that: The refractory metal layer of the composite material is prepared by the refractory metal laser surface coating method according to any one of claims 1-8.

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