A crack-free high-entropy alloy and its laser additive manufacturing method

Abstract

The present invention discloses a crack-free high-entropy alloy and a laser additive manufacturing method, which are prepared according to the following method: 1) Weigh and mix atomic powders according to the molar ratio of the molecular formula; 2) Put the mixed metal powders into a stainless steel ball milling tank for ball milling; 3) Select stainless steel as the substrate; Remove the oxide scale and surface stains on the cladding surface of the substrate, and use the laser additive manufacturing method to lap and melt deposit the alloy powders layer by layer from bottom to top on the surface of the substrate to obtain a as-deposited high-entropy alloy sample; 4) Perform aging heat treatment on the as-deposited high-entropy alloy at 700 °C. It solves the typical crack problem existing in the preparation of high-entropy alloys containing Al elements by the laser additive manufacturing process, and achieves the effect of strengthening the properties of the high-entropy alloy through direct aging heat treatment, so as to obtain a high-entropy alloy with both high strength and high plasticity.

Description

Technical Field

[0001] The present invention relates to a high-entropy alloy, and more particularly to a crack-free high-entropy alloy and a laser additive manufacturing method thereof. Background Art

[0002] With the rapid innovation of technology, traditional materials can no longer meet the demanding environment, so the development of new materials has become an inevitable requirement. High-entropy alloys have emerged under this trend, greatly solving the problems existing in traditional alloys. The so-called high-entropy alloy is composed of five or more main elements mixed in an equimolar ratio or a near-equimolar ratio. Due to its unique four major effects, it has the characteristic of a single solid-solution structure, thus obtaining excellent comprehensive properties. However, in recent years, the composition design of high-entropy alloys has become a major difficulty, and many researchers hope to design a composition system that can meet higher usage requirements.

[0003] Samples obtained by traditional methods for preparing high-entropy alloys often have defects such as pores, inclusions, and inter-dendritic segregation, which will directly affect the properties of the alloy. Laser additive manufacturing, as an advanced rapid prototyping technology for materials, can directly eliminate the defects that are prone to occur in traditional preparation due to its characteristics of fast heating and fast cooling. The innovative forming method of "from top to bottom, layer by layer deposition" makes the alloy generate multiple melt pools, further improving the density inside the metal. In addition, with its highly flexible and integrated system, it greatly saves the manufacturing cycle and can design lightweight shapes.

[0004] Although the research on laser additive manufacturing of high-entropy alloys is a hot topic, there are still some problems, that is, high-Al high-entropy alloys are prone to cracking. For the commonly studied FeCoCrNi-based high-entropy alloys, adding Al elements is extremely prone to cracking. This is because the melting point of Al element is relatively low, with a large difference from that of other elements. During the process of fast heating and fast cooling, a mushy zone will be generated between grains, and the cracks will extend along the grain boundaries. Some studies have also found that with the increase of Al content, the FCC structure gradually transforms into the BCC structure, resulting in a sharp increase in the brittleness of the material, thus causing cracking. It has to be said that designing high-quality high-entropy alloy compositions has become a huge challenge.

[0005] In addition, most of the methods for improving the mechanical properties of high-entropy alloys often use solution heat treatment followed by aging heat treatment first. This not only increases the complexity of production and prolongs the production cycle, but is not conducive to actual industrial production. Therefore, exploring new heat treatment processes to achieve good strengthening effects has also become a major challenge. Summary of the Invention

[0006] Aiming at the problems of the existing technology, the first object of the present invention is to provide two crack-free high-entropy alloys, and the second object is to provide a laser additive manufacturing method for crack-free high-entropy alloys, which solves the typical crack problem in the preparation of high-entropy alloys containing Al element by laser additive manufacturing process, and achieves the strengthening effect of the high-entropy alloy performance through direct aging heat treatment, so as to obtain a high-entropy alloy with both high strength and high plasticity.

[0007] To achieve the above first object, the present invention is realized through the following technical solutions: A crack-free high-entropy alloy, characterized in that the molecular formula is Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Ti 1.25 。

[0008] The second object of the present invention is realized as follows: A laser additive manufacturing method for a crack-free high-entropy alloy, characterized in that it is prepared according to the following method:

[0009] 1) Weigh the atomic powders of Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Ti 1.25 or Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Nb 1.25 in molar ratio and mix the Fe, Co, Ni, Cr, Al, Ti, Nb atomic powders;

[0010] 2) Put the mixed metal powders into a stainless steel ball milling tank for ball milling;

[0011] 3) Select stainless steel as the substrate; remove the oxide scale and surface stains on the cladding surface of the substrate, and deposit the alloy powders layer by layer from bottom to top by laser additive manufacturing method on the surface of the substrate to obtain a deposited high-entropy alloy sample;

[0012] 4) Perform aging heat treatment on the deposited high-entropy alloy at 700 °C to obtain Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Ti 1.25 or Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Nb 1.25 。

[0013] In the above solution: the purity of the raw materials of Fe, Co, Ni, Cr, Al, Ti, and Nb is not less than 99.95 wt.%.

[0014] In the above solution: during the preparation process, it works in an argon-protected environment, the pressure rate of the protector is 5 L / min, and the oxygen content in the argon-filled environment is not higher than 50 ppm.

[0015] In the above solution: the laser power is 1000 w, the moving rate is 15 mm / s, the powder feeding rate is 2 r / min, the layer height is 0.35 mm, and the spot diameter is 3 mm.

[0016] In the above solution: the thickness of the as-deposited high-entropy alloy is 0.3 - 0.4 mm.

[0017] In the above solution: the aging treatment time is 20 h.

[0018] Another crack-free high-entropy alloy of the present invention is: a crack-free high-entropy alloy Fe prepared by a laser additive manufacturing method of a crack-free high-entropy alloy 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Nb 1.25 .

[0019] Through exploration, we found that adding high melting point elements such as Ti, Nb, and Ta can effectively solve the problem of cracks in Al-containing high-entropy alloys. Based on the cluster plus connecting atom model, the present invention adopts the high-entropy alloy strategy to design [Al-(FeCoNi) 12 Cr 2.8 Ti 0.2 , [Al-(FeCoNi) 12 Cr 2.8 Nb 0.2 Two excellent high-entropy alloy compositions. It well coordinates the molar ratios of the contents of Al and Ti, and Al and Nb elements, controls the average melting point of the alloying elements, directly and fundamentally solves the crack problem, and makes it have extremely high ductility. In addition, directly adopting an appropriate aging heat treatment process can further eliminate micro-defects, precipitate the second phase, make the formability and density of the alloy higher, and thus obtain more excellent strength and hardness.

[0020] Beneficial effects: After aging heat treatment of the high-entropy alloy of the present invention, it is found that the sample structure is more uniform and the density is higher. Almost no microvoids can be seen, and no microcracks can be seen at all under high magnification. The as-deposited state has higher ductility. When aging heat treatment is carried out at 700 °C for 20 h, the second phase precipitates, and the yield strength and tensile strength are both significantly improved, and the elongation is good. It exceeds the comprehensive performance of traditional high-entropy alloy preparation, not only solves the problem of easy cracking of high-entropy alloy containing Al element, but also has excellent strength-plasticity combination. Description of the drawings

[0021] Figure 1 Macrograph of the as-deposited state of the Fe 25 Co 25 Ni 25 Cr 18.75 Al 6.25 high-entropy alloy.

[0022] Figure 2 Macrograph of the as-deposited state of the Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Ti 1.25 high-entropy alloy.

[0023] Figure 3 Macrograph of the as-deposited state of the Fe 25 Co 25 Ni 25 Cr 18.75 Al 6.25 Microstructure morphology diagram of the as-deposited state of the high-entropy alloy, with obvious cracks on the surface.

[0024] Figure 4 Microstructure morphology diagram of the as-deposited state of the Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Ti 1.25 Microstructure morphology diagram of the as-deposited state of the high-entropy alloy, with obvious surface cracks eliminated.

[0025] Figure 5 Microstructure morphology diagram of the aged state of the high-entropy alloy at 700 °C / 20 h, and obvious grain boundaries can be observed. 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Ti 1.25 high-entropy alloy.

[0026] Figure 6For laser additive manufacturing of Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Ti 1.25 XRD patterns of as-deposited and aged high-entropy alloys.

[0027] Figure 7 For laser additive manufacturing of Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Ti 1.25 Room temperature tensile engineering stress-strain curves of as-deposited and aged heat-treated at 700 °C / 20 h specimens of high-entropy alloys.

[0028] Figure 8 For laser additive manufacturing of Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Nb 1.25 Macromorphology of as-deposited high-entropy alloys.

[0029] Figure 9 For laser additive manufacturing of Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Nb 1.25 Microstructure morphology of as-deposited high-entropy alloys, with obvious elimination of surface cracks.

[0030] Figure 10 For laser additive manufacturing of Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Nb 1.25 Microstructure morphology of aged high-entropy alloys at 700 °C / 20 h, where large and small grain boundaries can be clearly observed.

[0031] Figure 11 For laser additive manufacturing of Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Nb 1.25 XRD patterns of as-deposited and aged high-entropy alloys.

[0032] Figure 12 For laser additive manufacturing of Fe 25 Co25 Ni 25 Cr 17.5 Al 6.25 Nb 1.25 Engineering stress-strain curve of as-deposited and solution heat-treated high-entropy alloy samples at 700 °C for 20 h at room temperature. Detailed implementation manners

[0033] The present invention will be further described below in conjunction with embodiments and the accompanying drawings.

[0034] Example 1 Preparation of Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Ti 1.25 Preparation

[0035] 1) Powder preparation: Fe, Co, Cr, Ni, Al, and Ti in the alloy raw materials are all spherical powders with a purity greater than 99.5 wt.%. Weigh them on an electronic balance according to the molar ratio of 25:25:25:17.5:6.25:1.25.

[0036] 2) Powder mixing: Put the prepared powders into a stainless-steel ball-milling tank and ball-mill them in a planetary ball mill at a rotation speed of 260 rpm / s for 1 h. After sieving through a 100-mesh sieve, place the sample in a vacuum drying oven at 100 °C - 120 °C for at least 2 h.

[0037] 3) Substrate grinding: Use a grinding wheel to remove the surface oxide scale of the 304L stainless-steel substrate, and then clean the surface oil stain with alcohol.

[0038] Under an argon atmosphere, the protective gas pressure rate is 5 L / min, and the oxygen content in the argon-filled environment is not higher than 50 ppm. Use 304L stainless steel with dimensions of 100 × 100 × 10 mm 3 as the substrate material to prepare the as-deposited high-entropy alloy. Laser power: 1000 W, powder feeding rate: 10 g / min, powder feeding speed: 2 r / min, scanning speed: 15 mm / s, layer height: 0.35 mm, and laser spot diameter: 3 mm. The thickness of the as-deposited high-entropy alloy is 0.35 mm.

[0039] 4) Place the as-deposited high-entropy alloy sample in a box furnace for solution heat treatment at 700 °C for 20 h. After the holding time is reached, immediately quench it in water to obtain a uniform single-phase solid solution sample.

[0040] After solution heat treatment of the high-entropy alloy, it is found that the microstructure of the sample is more uniform and has a higher density. Almost no microvoids can be seen, and no microcracks can be seen at high magnification. The ductility of the as-deposited state is as high as 43.05%. When solution heat treatment is carried out at 700 °C for 20 h, the second phase precipitates, the yield strength is 627 MPa, an increase of about 126%. The tensile strength is increased from 632 MPa to 1040 MPa, an increase of about 65% compared with the as-deposited state. The elongation rate reaches 20.42%. It exceeds the comprehensive performance of the traditional high-entropy alloy preparation, not only solves the problem of easy cracking of the high-entropy alloy containing Al element, but also has excellent strength-plasticity matching.

[0041] Example 2 Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Nb 1.25 Preparation

[0042] 1) Powder preparation: Fe, Co, Cr, Ni, Al, and Nb in the alloy raw materials are all spherical powders with a purity greater than 99.5 wt.%. Weigh them on an electronic balance according to the molar ratio of 25:25:25:17.5:6.25:1.25.

[0043] 2) Powder mixing: Put the prepared powder into a stainless steel ball milling tank and ball mill it for 1 h in a planetary ball mill with a rotation speed of 260 rpm / s. After sieving through a 100-mesh sieve, place the sample in a vacuum drying oven at 100 °C - 120 °C for at least 2 h.

[0044] 3) Substrate grinding: Use a grinding wheel to remove the surface oxide scale of the 304L stainless steel substrate, and then clean the surface oil stain with alcohol.

[0045] Under an argon atmosphere, use 304L stainless steel with a size of 100×100×10 mm3 as the substrate material to prepare the as-deposited high-entropy alloy. Laser power: 1000 W, powder feeding amount 10 g / min, powder feeding rate 2 r / min, scanning rate: 15 mm / s, layer height: 0.35 mm, and laser spot diameter 3 mm. The thickness of the as-deposited high-entropy alloy is 0.35 mm.

[0046] Put the as-deposited high-entropy alloy sample in a box furnace for solution heat treatment at 700 °C for 20 h. After the holding time is reached, immediately quench it in water to obtain a uniform single-phase solid solution state sample.

[0047] Figure 9 For laser additive manufacturing of Fe 25 Co 25 Ni 25 Cr 17.5 Al6.25 Nb 1.25 Microstructure morphology diagram of as-deposited high-entropy alloy, with surface cracks significantly eliminated. Figure 10 Microstructure morphology diagram of the aged high-entropy alloy by laser additive manufacturing at 700 °C for 20 h, where large and small grain boundaries can be clearly observed.

[0048] After aging heat treatment of the high-entropy alloy, it is found that the sample structure is more uniform and has a higher density. Almost no microvoids can be seen, and no microcracks can be seen at high magnification. The ductility of the as-deposited state is as high as 37.82%. When aged at 700 °C for 20 h, the second phase precipitates, and the yield strength increases from 292 Mpa to 601 MPa, an increase of about 106%. The tensile strength increases from 633 MPa to 914 MPa, an increase of about 44% compared to the as-deposited state. The elongation rate reaches 14.66%. It exceeds the comprehensive performance of traditional high-entropy alloys, not only solves the problem of easy cracking of high-entropy alloys containing Al elements, but also has excellent strength-plasticity matching.

[0049] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A laser additive manufacturing method for crack-free high-entropy alloy, characterized in that, it is prepared according to the following method: 1) According to the molecular formula Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Ti 1.25 or Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Nb 1.25 weigh the metal powders of Fe, Co, Ni, Cr, Al, Ti, and Nb according to the molar ratio and mix them; 2) Put the mixed metal powder into a stainless steel ball milling jar for ball milling; 3) Select stainless steel as the substrate; remove the oxide scale and surface stains on the cladding surface of the substrate, and layer by layer lap and melt deposit the ball-milled alloy powder on the substrate surface from bottom to top through the laser additive manufacturing method to obtain a as-deposited high-entropy alloy sample; 4) The as-deposited high-entropy alloy is subjected to aging heat treatment at 700 °C to obtain Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Ti 1.25 or Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Nb 1.25 a crack-free high-entropy alloy.

2. The laser additive manufacturing method for crack-free high-entropy alloy according to claim 1, characterized in that: The purity of Fe, Co, Ni, Cr, Al, Ti, Nb metal powder is not less than 99.95wt.%.

3. The laser additive manufacturing method for crack-free high-entropy alloy according to claim 2, characterized in that: The laser additive manufacturing works in an argon-protected environment, the protector pressure rate is 5L / min, and the oxygen content in the argon-filled environment is not higher than 50ppm.

4. The laser additive manufacturing method for crack-free high-entropy alloy according to claim 3, characterized in that: In the laser additive manufacturing, the laser power is 1000W, the moving rate is 15mm / s, the powder feeding rate is 2r / min, the layer height is 0.35mm, and the spot diameter is 3mm.

5. The laser additive manufacturing method for crack-free high-entropy alloy according to claim 4, characterized in that: The thickness of the as-deposited high-entropy alloy is 0.3 - 0.4mm.

6. The laser additive manufacturing method for crack-free high-entropy alloy according to any one of claims 1-5, characterized in that: The aging treatment time is 20h.

7. An Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Nb 1.25 or Fe 25 Co 25 Ni 25 Cr 17.5 Al 6.25 Ti 1.25 crack-free high-entropy alloy prepared by the laser additive manufacturing method of the high-entropy alloy according to any one of claims 1-6.

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