High-temperature wear-resistant crack-free high-entropy alloy and laser additive manufacturing method and application thereof

Abstract

The invention discloses a high-temperature wear-resistant crack-free high-entropy alloy and a preparation method and application thereof, the molecular formula of the alloy is as follows: Fe < 11.9 > Co < 23.8 > Cr < 23.8 > Ni < 35.7 > Nb < 4.8 >, and a Laves phase exists in the microstructure of the alloy. The preparation method comprises the following steps: putting weighed powder into a ball milling tank for ball milling, uniformly mixing the powder, and then drying, sieving and drying for storage; 304L stainless steel is selected as a base material, a sand mill is used for polishing the surface of the base material so as to remove surface oxide skin until a bright surface is exposed, and oil stains on the surface are cleaned; and the dried powder is placed in a powder feeding tank in a laser system, high-purity Ar gas is used for feeding the powder to a round spot laser head for melting and stacking, and the high-temperature wear-resistant crack-free high-entropy alloy without cracks is formed through layer-by-layer continuous deposition. By adding the Nb element, a Laves phase capable of improving the high-temperature performance is formed in a matrix, a high-entropy alloy sample is prepared through the laser directional energy deposition technology, subsequent heat treatment does not need to be conducted on the high-entropy alloy sample, and the deposited alloy has the excellent wear resistance at the high temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of alloys, and particularly relates to a high-temperature wear-resistant crack-free high-entropy alloy, a laser additive manufacturing method thereof, and an application thereof. Background Art

[0002] High-temperature wear-resistant materials are the core basic materials in extreme working condition fields such as aeroengines, gas turbines, and nuclear energy equipment, and their performance directly determines the service life and reliability of key components (such as turbine blades, high-temperature sealing rings, molds, etc.). Traditional high-temperature wear-resistant materials mainly include nickel-based superalloys, cobalt-based alloys, cemented carbides, and cermets. However, with the continuous improvement of the requirements of modern industry for the power density and efficiency of equipment, the limitations of traditional materials at high temperatures (>500 °C) have become increasingly prominent. Nickel-based superalloys (such as Inconel 718, Hastelloy X) rely on γ'-phase (Ni3Al) strengthening and have excellent strength and oxidation resistance below 700 °C, but face two major problems of oxidation softening and grain boundary weakening at higher temperatures (such as 800-1000 °C). Materials represented by WC-Co cemented carbides and TiC-Ni cermets, although having high hardness (>1500 HV at room temperature), their high-temperature performance is limited by the failure of the binder phase, oxidation, and thermal shock. Fe-Ni alloys (such as Fe-50Ni invar alloy) are used in high-temperature seals due to their low cost and low thermal expansion coefficient, but they have insufficient high-temperature wear resistance, insufficient hardness, and poor oxidation resistance.

[0003] Since the high-entropy alloy was proposed in 2004, a high-mixed-entropy solid solution is formed through a multi-principal element design (usually ≥5 elements, each concentration 5-35 at.%), and its "four major effects" (high-entropy effect, lattice distortion effect, sluggish diffusion effect, and "cocktail" effect) endow it with excellent high-temperature performance potential. High-entropy alloys are a class of new materials with excellent performance and have received extensive attention from the scientific community for their excellent mechanical properties, corrosion resistance, excellent thermal stability, etc. The "high entropy" of high-entropy alloys refers to chemical disorder or topological disorder at the atomic scale, that is, the atomic arrangement of the alloy has a high degree of chaos and is in a disordered state. The emergence of high-entropy alloys provides new ideas for developing new materials and applications in extreme fields. A typical system such as FeCoNiCrMn (Cantor alloy) can still maintain a hardness of 300-400 HV at 800 °C, and its oxidation resistance is better than that of traditional alloys.

[0004] Laser Additive Manufacturing (LAM) uses high-energy lasers as heat sources and breaks through the limitations of traditional manufacturing technologies through layer-by-layer stacking and forming, demonstrating significant technical advantages. Its high design freedom supports the direct forming of complex geometric structures, such as lightweight cavities, bionic topologies, or functionally integrated components, providing possibilities for innovative designs in aerospace, biomedicine, and other fields. At the same time, the material utilization rate is over 90%, significantly reducing the waste of expensive metal raw materials. Combined with the flexible production characteristics of short cycles and no molds, it effectively shortens the R & D cycle and reduces the cost of small-batch customization. With the high energy density of the laser, this technology can precisely melt difficult-to-machine materials such as titanium alloys and nickel-based superalloys, achieving densification of the microstructure and optimization of mechanical properties. At the same time, it has the potential for composite manufacturing, which can not only repair damages and strengthen the surface of key components but also reduce the use of cutting fluid and waste discharge, meeting the concept of green and sustainable development. Summary of the Invention

[0005] Aiming at the deficiencies in the existing technology, the purpose of the present invention is to provide a high-temperature wear-resistant and crack-free high-entropy alloy. The present invention also provides its laser additive manufacturing method and application. By adding Nb element, Laves phase that improves high-temperature performance is formed in the matrix. High-entropy alloy samples are prepared by laser directed energy deposition technology without subsequent heat treatment, enabling the as-deposited alloy to have excellent wear resistance at high temperatures.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: A high-temperature wear-resistant and crack-free high-entropy alloy, characterized in that: the alloy molecular formula is: Fe 11.9 Co 23.8 Cr 23.8 Ni 35.7 Nb 4.8 , and Laves phase exists in the microstructure of the alloy.

[0007] The laser additive manufacturing method of the high-temperature wear-resistant and crack-free high-entropy alloy is characterized in that it is prepared according to the following steps:

[0008] (1) Weigh medium-entropy alloy FeCoCrNi, medium-entropy alloy CoCrNi, Ni powder, and Nb powder;

[0009] (2) Put the weighed powders into a ball mill for ball milling to make the powders evenly mixed, then dry, sieve, and store them dry;

[0010] (3) Select 304L stainless steel as the substrate, use a sand mill to polish the surface of the substrate to remove the surface oxide scale until a bright surface is exposed, and clean the surface oil stain;

[0011] (4) Place the dried powder in the powder feeder of the laser system, and use high-purity Ar gas to send the powder to the round-spot laser head for melting and deposition, and continuously deposit layer by layer to form a crack-free high-temperature wear-resistant high-entropy alloy.

[0012] In the above solution: in step (1), the medium-entropy alloys FeCoCrNi, CoCrNi, and Ni powders are spherical, with a particle size of 45 - 105 μm and a purity of ≥99.5%, and the Nb powder is flaky. Since the spherical powder of Nb is expensive, flaky Nb powder is selected for the formulation.

[0013] In the above solution: in step (2), the ball milling parameters are as follows: the ball-to-material ratio is 4:1, the ball milling rotation speed is 260 - 300 rpm / min, and the forward and reverse rotations alternate.

[0014] In the above solution: rotate forward for 1 h, reverse for 1 h, with an interval of 5 min in the middle, and pass through a 50-mesh sieve after ball milling.

[0015] In the above solution: in step (4), the laser directed energy deposition parameters are as follows: the laser power P = 1000 W, the scanning rate v = 15 mm / s, the diameter of the round-spot laser beam is 3 mm, and the powder filling rotation speed is 2 r / min.

[0016] The application of the described crack-free high-temperature wear-resistant high-entropy alloy in the core basic materials in the extreme working condition fields of aero-engines, gas turbines, and nuclear energy equipment.

[0017] Beneficial effects:

[0018] The present invention uses the laser directed energy deposition technology in laser additive manufacturing to prepare a crack-free Fe 11.9 Co 23.8 Cr 23.8 Ni 35.7 Nb 4.8 high-entropy alloy. By adding the Nb element, Laves phases that improve the high-temperature performance are formed in the matrix. Currently, there are many studies on the mechanical properties of high-entropy alloys prepared by laser additive manufacturing, but few studies on the friction and wear properties at high temperatures. The present invention prepares high-entropy alloy samples through the laser directed energy deposition technology, without the need for subsequent heat treatment, enabling the as-deposited alloy to have excellent wear resistance at high temperatures. The prepared Fe 11.9 Co 23.8 Cr 23.8 Ni 35.7 Nb 4.8 high-entropy alloy exhibits excellent wear resistance at high temperatures. The average friction coefficient decreases from 0.715 at room temperature to 0.466 at 800 °C. The alloy has a shallower wear depth and a narrower wear scar width at high temperatures, and the wear rate decreases from 28.3×10 - 6mm 3 / N·m drops to 13.1×10 at 600 °C -6 mm 3 / N·m. Brief Description of the Drawings

[0019] Figure 1 Are the shapes of FeCoCrNi, CoCrNi, Ni, and Nb powders after ball milling.

[0020] Figure 2 Is Fe 11.9 Co 23.8 Cr 23.8 Ni 35.7 Nb 4.8 XRD images of the high-entropy alloy and the microstructural morphologies in the X-Z and Y-Z directions.

[0021] Figure 3 Is the surface scan distribution map of the second phase.

[0022] Figure 4 Is Fe 11.9 Co 23.8 Cr 23.8 Ni 35.7 Nb 4.8 Friction coefficients and average friction coefficients of the alloy at different temperatures.

[0023] Figure 5 Is Fe 11.9 Co 23.8 Cr 23.8 Ni 35.7 Nb 4.8 Laser confocal wear scar morphologies of the alloy at different temperatures.

[0024] Figure 6 Are the wear scar depths, widths, wear areas, and wear rates of the alloy at different temperatures.

[0025] Figure 7 Is the model of the high-temperature friction and wear testing machine and the SEM images and oxygen content distributions of the wear scars at different temperatures. Detailed Description of the Invention

[0026] The present invention will be further described in detail through specific embodiments as follows:

[0027] Example 1

[0028] A preparation method of a high-temperature wear-resistant and crack-free high-entropy alloy is prepared according to the following steps:

[0029] (1) Weigh accurately medium-entropy alloy FeCoCrNi, medium-entropy alloy CoCrNi, Ni powder and Nb powder; FeCoCrNi, CoCrNi, Ni, and Nb powders are all purchased from Changsha Tianjiu Metal Materials Co., Ltd. The FeCoCrNi, CoCrNi, and Ni alloy powders are spherical with a size of 45 - 105 μm.

[0030] (2) Put the weighed powders into a ball mill for ball milling to make the powders mix evenly. The ball milling parameters are: the ball-to-material ratio is 4:1, the ball milling speed is 260 - 300 rpm / min, the ball mill rotates forward for 1 h, rotates backward for 1 h, and pauses for 5 min between forward and backward rotations. After ball milling, dry the powders, and then dry, sieve through a 50-mesh sieve, and store them dry. It can be seen from Figure 1 that the spherical powders that are evenly mixed by ball milling become elliptical after long-term ball milling, and the Nb powder remains flaky.

[0031] (3) Select a magnetic 304L stainless steel with dimensions of 100 mm in length, 100 mm in width, and 10 mm in height as the substrate. The substrate has little dilution effect on the high-entropy alloy composition during the laser direct energy deposition process. Use a sand mill to remove the oxide scale on the surface of the substrate to prevent holes from forming at the lower part of the sample during the deposition process. Clean the surface oil stain with alcohol and dry it with a hair dryer for standby.

[0032] (4) Put the dried powders into the powder feeding tank of the laser powder feeding system, use high-purity argon with a purity of 99.999% to transport the powder raw materials to the substrate, and at the same time focus the laser beam to form a small molten pool, and gradually deposit it into a crack-free wall-shaped sample through a Z-shaped path. During the whole deposition process, high-purity argon is filled to prevent the sample from oxidizing during deposition. The laser direct energy deposition process parameters are: laser power P = 1000 W, scanning speed v = 15 mm / s, circular spot diameter 3 mm, and powder filling rotation speed 2 r / min.

[0033] High-temperature wear test: Cut the as-deposited Fe 11.9 Co 23.8 Cr 23.8 Ni 35.7 Nb 4.8 high-entropy alloy samples into friction and wear specimens with dimensions of 20 mm × 10 mm × 2 mm by wire cutting, and use an HT-1000 high-temperature friction and wear testing machine for experiments. Use a heating furnace to raise the temperature to 200 °C, 400 °C, 600 °C, and 800 °C for friction and wear experiments. The load is 10 N, and the rotation speed is 1000 rpm to study the friction and wear properties of the laser additive manufacturing high-entropy alloy at room temperature, 200 °C, 400 °C, 600 °C, and 800 °C.

[0034] From Figure 2 it can be seen that the Fe prepared by laser direct energy deposition11.9 Co 23.8 Cr 23.8 Ni 35.7 Nb 4.8 The main phase of the high-entropy alloy is the FCC phase. The SEM image shows that there are a large number of Laves phases in the microstructure of the alloy. The X-Z direction is dendritic, while the Y-Z direction is cellular.

[0035] From Figure 3 it can be clearly found that the second phase is the product of Nb element enrichment, that is, the Laves phase mentioned above. The Laves phase is an intermetallic compound, which has a complex and crucial influence on the material properties in a high-temperature environment. Its high-temperature strengthening effect is mainly reflected in pinning the grain boundaries through the precipitated phase and hindering the movement of dislocations, significantly improving the high-temperature strength and creep resistance.

[0036] As Figure 4 shown, the experimental load is 10 N and the rotational speed is 1000 rpm. From the change of the friction coefficient with time in Figure (a), it can be found that at the beginning, there will be a "running-in" stage, where the change range of the friction coefficient is large and it will gradually tend to be stable. As the temperature increases, the friction coefficient gradually decreases. Through calculation, the average friction coefficients are 0.715 (room temperature), 0.722 (200 °C), 0.621 (400 °C), 0.484 (600 °C), and 0.466 (800 °C) respectively.

[0037] As Figure 5 shown, as the temperature rises from 200 °C to 800 °C, the wear scar characteristics and wear mechanisms show significant changes: at low temperature (200 °C), the wear scar is shallow and the surface roughness is low, showing abrasive wear, and the high hardness of the alloy inhibits plastic deformation; when the temperature rises to 400 °C, the material softens, resulting in a wider and deeper wear scar, and the local adhesive wear increases, and the frictional heat promotes surface micro-area adhesion; when the temperature reaches 600 °C, oxide layer spalling and cracks appear at the edge of the wear scar, and the dynamic recrystallization and the rupture of the discontinuous oxide film trigger a mixed mechanism of oxidative wear and fatigue wear; while at 800 °C high temperature, the wear scar tends to be flat, and the continuous coverage of the dense oxide film significantly reduces the wear rate, dominating the oxidative wear mechanism.

[0038] As Figure 6 , Figure (a) shows the depth and width of the wear scar at different temperatures. As the temperature increases, the wear depth at high temperatures (600 °C and 800 °C) is relatively shallow and the wear width is relatively narrow. Figure (b) shows the wear volume and wear rate at different temperatures. The wear volumes are 5663.4 μm 2 (room temperature), 5411.8 μm 2 (200 °C), 4798.0 μm 2 (400 °C), 2662.7 μm 2(600 °C) and 2684.0 μm 2 (800 °C). The wear rates are 28.3×10 -6 mm 3 / N·m (room temperature), 27.1×10 -6 mm 3 / N·m (200 °C), 24.0×10 -6 mm 3 / N·m (400 °C), 13.1×10 -6 mm 3 / N·m (600 °C) and 13.4×10 -6 mm 3 / N·m (800 °C). Compared with the room temperature environment, the alloy has better wear resistance at high temperatures.

[0039] As Figure 7 shown, in the Fe 11.9 Co 23.8 Cr 23.8 Ni 35.7 Nb 4.8 alloy, the high Cr and Ni contents improve the high-temperature oxidation resistance. The Nb element enhances the matrix's anti-softening ability by refining the grains and forming strengthening phases, enabling it to exhibit excellent wear resistance in high-temperature environments (such as 800 °C). Generally speaking, the increase in temperature promotes the wear mechanism to shift from mechanically dominated to oxidation protection dominated. Optimizing the stability of the oxide film is the key to further improving the high-temperature wear resistance of the alloy.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A high-temperature wear-resistant and crack-free high-entropy alloy, characterized in that: The alloy molecular formula is: Fe 11.9 Co 23.8 Cr 23.8 Ni 35.7 Nb 4.8 , and there is a Laves phase in the microstructure of the alloy.

2. The laser additive manufacturing method of the high-temperature wear-resistant and crack-free high-entropy alloy according to claim 1, characterized in that, It is prepared according to the following steps: (1) Weigh accurately medium-entropy alloy FeCoCrNi, medium-entropy alloy CoCrNi, Ni powder and Nb powder; (2) Put the weighed powders into a ball milling jar for ball milling to make the powders evenly mixed, then dry, sieve, and store them after drying; (3) Select 304L stainless steel as the substrate, and use a sand mill to polish the surface of the substrate to remove the surface oxide scale until a bright surface is exposed, and clean the surface oil; (4) Place the dried powders in the powder feeding tank in the laser system, and use high-purity Ar gas to send the powders to the round spot laser head for melting and deposition, and continuously deposit layer by layer into a high-temperature wear-resistant crack-free high-entropy alloy.

3. The laser additive manufacturing method of the high-temperature wear-resistant and crack-free high-entropy alloy according to claim 2, characterized in that: In step (1), the medium-entropy alloy FeCoCrNi, medium-entropy alloy CoCrNi, and Ni powders are spherical, with a particle size of 45-105 μm and a purity of ≥99.5%, and the Nb powder is flaky.

4. The laser additive manufacturing method of the high-temperature wear-resistant and crack-free high-entropy alloy according to claim 3, wherein: In step (2), the ball milling parameters are: the ball-to-material ratio is 4:1, the ball milling rotation speed is 260-300 rpm / min, and the forward and reverse rotations are alternated.

5. The laser additive manufacturing method of the high-temperature wear-resistant and crack-free high-entropy alloy according to any one of claims 2-4, characterized in that: The forward rotation is for 1 h, the reverse rotation is for 1 h, with an interval of 5 min in the middle, and after ball milling, it is sieved through a 50-mesh sieve.

6. The laser additive manufacturing method of the high-temperature wear-resistant and crack-free high-entropy alloy according to claim 5, characterized in that: In step (4), the laser directed energy deposition parameters are: laser power P = 1000 W, scanning speed v = 15 mm / s, round spot diameter 3 mm, and powder filling rotation speed 2 r / min.

7. Application of the high-temperature wear-resistant crack-free high-entropy alloy as claimed in claim 1 in the core basic materials in the extreme working condition fields of aeroengines, gas turbines, and nuclear energy equipment.

Images