Multi-principal-element iron-based medium-entropy alloy with fatigue resistance and preparation method of multi-principal-element iron-based medium-entropy alloy

Abstract

The invention discloses a multi-principal-element iron-based medium-entropy alloy with fatigue resistance and a preparation method of the multi-principal-element iron-based medium-entropy alloy, and the multi-principal-element iron-based medium-entropy alloy comprises the following components in atomic percent: 52-56% of Fe, 29-33% of Ni and 15% of Al, the multi-principal-element iron-based medium-entropy alloy is of a double-phase structure and comprises an austenite phase and a ferrite phase, the density of the multi-principal-element iron-based medium-entropy alloy is 6.43-7.03 g / cm < 3 >, the tensile strength of the multi-principal-element iron-based medium-entropy alloy is 739-835 MPa, the ductility of the multi-principal-element iron-based medium-entropy alloy is 21-55.46%, the fatigue strength of the multi-principal-element iron-based medium-entropy alloy under the room temperature environment is 180-187 MPa, and the fatigue strength of the multi-principal-element iron-based medium-entropy alloy under the 600 DEG C environment The prepared multi-principal-element iron-based medium-entropy alloy solves the problem of failure caused by high-cycle fatigue of aluminum alloy, gray cast iron and vermicular graphite cast iron used in a traditional air cylinder cover in a high-temperature environment due to strength reduction and mechanical property deterioration, has good thermal stability, hardness and strength and meanwhile has good obdurability; and the room-temperature and high-temperature fatigue performance is obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron-based medium-entropy alloys, and particularly relates to a multi-principal-element iron-based medium-entropy alloy with fatigue resistance and a preparation method thereof. Background Art

[0002] With the rapid development of high-power-density diesel engines, as a key component of diesel engines, the cylinder head works in a very complex environment and needs to serve for a long time under the conditions of high temperature (≥600 °C), high pressure and cyclic load. Research shows that under the combined action of thermal load and mechanical load, the cylinder head is prone to high-cycle fatigue and thus fails. According to statistics, under the action of random loads, the probability of fatigue failure of the cylinder head is 70%-90%. Therefore, higher requirements are put forward for the heat resistance, strength and anti-fatigue performance of the materials used for the cylinder head.

[0003] At present, the materials used for traditional cylinder heads are mostly aluminum alloys, gray cast irons and vermicular graphite cast irons, and their high-temperature stabilities are all poor. The strength of aluminum alloy materials drops sharply above 350 °C, and the mechanical properties of cast iron materials deteriorate significantly above 400 °C. The deterioration of strength and high-temperature stability will cause high-cycle fatigue of traditional cylinder heads and thus lead to failure. Summary of the Invention

[0004] The purpose of the present invention is to provide a multi-principal-element iron-based medium-entropy alloy with fatigue resistance and a preparation method thereof, so as to solve the problem of high-cycle fatigue caused by poor strength and high-temperature stability of traditional diesel engine cylinder heads mainly made of aluminum alloy and cast iron materials.

[0005] The present invention adopts the following technical solutions:

[0006] A multi-principal-element iron-based medium-entropy alloy with fatigue resistance, in atomic percentage, includes: Fe: 52-56%, Ni: 29-33%, Al: 15%;

[0007] Among them, the multi-principal-element iron-based medium-entropy alloy is a duplex structure, including an austenite phase and a ferrite phase. The density of the multi-principal-element iron-based medium-entropy alloy is 6.43-7.03 g / cm 3 , the tensile strength is 739-835 MPa, the elongation is 21-55.46%, the fatigue strength at room temperature is 180-187 MPa, and the fatigue strength at 600 °C is 239-260 MPa.

[0008] A preparation method of a multi-principal-element iron-based medium-entropy alloy with fatigue resistance, includes the following steps:

[0009] Stack an Al block, an Fe block and an Ni block in sequence from bottom to top and place them in a water-cooled crucible of a vacuum levitation melting furnace;

[0010] The Al block, Fe block and Ni block in the water-cooled crucible are melted in an argon atmosphere to obtain an ingot;

[0011] The ingot is heat-treated to obtain a multi-principal element iron-based medium-entropy alloy.

[0012] Further, before overlapping and placing the Al block, Fe block and Ni block into the water-cooled crucible of the vacuum levitation melting furnace from bottom to top in sequence, it further includes:

[0013] The impurities and oxides on the surfaces of the Al block, Fe block and Ni block are removed respectively, and then the Al block, Fe block and Ni block are subjected to ultrasonic shock cleaning in acetone cleaning agent for 5 min.

[0014] Further, when melting the Al block, Fe block and Ni block in the water-cooled crucible in an argon atmosphere, the vacuum degree ≤ 4.5×10 -3 Pa.

[0015] Further, melting the Al block, Fe block and Ni block in the water-cooled crucible in an argon atmosphere includes:

[0016] Start the melting power supply, gradually increase the power of the power supply, adjust the power of the power supply until the Al block, Fe block and Ni block are completely and uniformly melted. After complete melting, continue melting for 5 - 10 min, and take out the ingot after cooling for 3 hours.

[0017] Further, the number of melting repetitions is 5 times.

[0018] Further, the power of the power supply ≤ 260 KW.

[0019] Further, the temperature of the heat treatment is 600 - 700 °C, and the holding time is 1 - 2 h.

[0020] A diesel engine cylinder head, the diesel engine cylinder head includes the above multi-principal element iron-based medium-entropy alloy or the multi-principal element iron-based medium-entropy alloy prepared according to the preparation method of any one of the above multi-principal element iron-based medium-entropy alloys.

[0021] The beneficial effect of the present invention is: A multi-principal element iron-based medium-entropy alloy with fatigue resistance performance of the present invention has room temperature and high temperature fatigue performance, and the density is: 6.43 - 7.03 g / cm 3, the tensile strength is 739 - 835 MPa, the elongation is 21 - 55.46%, the fatigue strength at room temperature is 180 - 187 MPa, and the fatigue strength at 600 °C is 239 - 260 MPa. It is applicable to the manufacturing of cylinder heads for high-power diesel engines and key components under high-temperature and high-load working conditions. The multi-principal element iron-based medium-entropy alloy prepared by the vacuum levitation melting process and heat treatment process of the present invention mainly consists of two structures, ferrite and austenite. Austenite provides good thermal stability, hardness and strength, and ferrite enhances strength and toughness. The combined action of the two structures can inhibit crack propagation and significantly improve the fatigue performance at room temperature and high temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the XRD pattern of the multi-principal element iron-based medium-entropy alloy prepared in Examples 1 - 4 of the present invention;

[0023] Figure 2 is the microstructural morphology diagram of the multi-principal element iron-based medium-entropy alloy prepared in Examples 1 - 4 of the present invention;

[0024] Among them, a is the microstructural morphology diagram of the multi-principal element iron-based medium-entropy alloy prepared in Example 1 under an optical microscope; b is the microstructural morphology diagram of the multi-principal element iron-based medium-entropy alloy prepared in Example 2 under an optical microscope; c is the microstructural morphology diagram of the multi-principal element iron-based medium-entropy alloy prepared in Example 3 under an optical microscope; d is the microstructural morphology diagram of the multi-principal element iron-based medium-entropy alloy prepared in Example 4 under an optical microscope;

[0025] Figure 3 is the tensile stress-strain curve diagram of the multi-principal element iron-based medium-entropy alloy prepared in Examples 1 - 4. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0027] A multi-principal element iron-based medium-entropy alloy with fatigue resistance, in atomic percentage, includes: Fe: 52 - 56%, Ni: 29 - 33%, Al: 15%;

[0028] Among them, the multi-principal element iron-based medium-entropy alloy is a duplex structure, including an austenite phase and a ferrite phase. The density of the multi-principal element iron-based medium-entropy alloy is 6.43 - 7.03 g / cm 3 , the tensile strength is 739 - 835 MPa, the elongation is 21 - 55.46%, the fatigue strength at 25 °C room temperature is 180 - 187 MPa, and the fatigue strength at 600 °C is 239 - 260 MPa.

[0029] A multi-principal element iron-based medium entropy alloy with fatigue resistance has room temperature and high temperature fatigue properties, and its density is 6.43 - 7.03 g / cm 3 , its tensile strength is 739 - 835 MPa, its elongation is 21 - 55.46%, its fatigue strength at room temperature is 180 - 187 MPa, and its fatigue strength at 600 °C is 239 - 260 MPa. It is suitable for the manufacture of high-power diesel engine cylinder heads and key components under high-temperature and high-load working conditions.

[0030] A preparation method of a multi-principal element iron-based medium entropy alloy with fatigue resistance includes the following steps:

[0031] S110, Weigh metal single-element Al blocks, Fe blocks and Ni blocks with a purity ≥ 99.99% according to the proportion, remove the impurities and oxides on the surfaces of the Al blocks, Fe blocks and Ni blocks respectively, and then use acetone cleaning agent to oscillate and clean the Al blocks, Fe blocks and Ni blocks in ultrasonic waves for 5 minutes.

[0032] Utilizing the cavitation effect generated by high-frequency sound waves in the liquid can effectively remove the grease, dust, oxides and other pollutants on the surfaces of the Al blocks, Fe blocks and Ni blocks, ensuring the purity of the materials during the melting process.

[0033] S120, Stack the Al blocks, Fe blocks and Ni blocks in order from bottom to top according to the density gradient and place them in the water-cooled crucible of the vacuum levitation melting furnace;

[0034] S130, Melting the Al blocks, Fe blocks and Ni blocks in the water-cooled crucible under an argon atmosphere to obtain an ingot. Specifically:

[0035] Start the mechanical pump, roughing valve and Roots pump of the vacuum levitation furnace to extract low vacuum. When the low vacuum degree is 5 Pa, open the fore valve and diffusion pump, and wait for 55 minutes, then close the roughing valve and open the main pumping valve. When the vacuum degree meets the requirement (4.5×10 -3 Pa), close the main pumping valve and vacuum gauge, and finally open the argon filling valve to fill the furnace cavity with argon.

[0036] Start the melting power supply, gradually increase the power of the power supply, observe the situation of the water-cooled crucible in the furnace through the furnace door and furnace cover, adjust the power of the power supply until the Al blocks, Fe blocks and Ni blocks are completely and evenly melted. After complete melting, continue melting for 5 - 10 minutes, and take out the ingot after cooling for 3 hours.

[0037] The vacuum degree during melting ≤ 4.5×10 -3 Pa.

[0038] The power of the power supply ≤ 260 KW.

[0039] The number of melting repetitions is 5 times.

[0040] Melting the Al block, Fe block and Ni block under an argon atmosphere can prevent oxygen in the air from reacting with the molten metal, avoid the formation of metal oxides, and ensure the purity of the alloy.

[0041] Melting is carried out in an environment with a vacuum degree ≤ 4.5×10 -3 Pa, which can significantly reduce the chance of oxygen, nitrogen and other gases that may react with the molten metal in the air from entering the ingot, contribute to reducing the formation of oxides and other non-metallic inclusions, and thus improve the purity of the multi-principal-element iron-based medium-entropy alloy.

[0042] A power supply power ≤ 260KW can improve the energy utilization efficiency, reduce unnecessary energy consumption, lower the production cost, and is beneficial to environmental protection. Setting a suitable upper limit of the power supply power can protect the melting equipment from being damaged by excessive current or heat, extend the service life of the equipment, and also ensure the safety of the operators.

[0043] Repeating the melting 5 times helps to ensure the uniform distribution of each element in the multi-principal-element iron-based medium-entropy alloy. In addition, repeated melting can remove non-metallic inclusions such as oxides and nitrides in the metal and dissolved gases, thereby improving the purity of the multi-principal-element iron-based medium-entropy alloy.

[0044] S140, performing heat treatment on the ingot to obtain a multi-principal-element iron-based medium-entropy alloy, specifically:

[0045] Put the ingot into a muffle furnace for heat treatment. The heat treatment temperature is 600 - 700 °C, and the holding time is 1 - 2 h.

[0046] Within this temperature and time range, it can promote the diffusion of elements in the multi-principal-element iron-based medium-entropy alloy, make the composition of the multi-principal-element iron-based medium-entropy alloy more uniform, and can also promote the precipitation of nano-phases, improving the comprehensive mechanical properties of the multi-principal-element iron-based medium-entropy alloy.

[0047] Through the coordinated regulation of vacuum melting - heat treatment, the present invention realizes the efficient dispersion and interface strengthening of the dual-phase structure. The multi-principal-element iron-based medium-entropy alloy prepared by the vacuum levitation melting process and the heat treatment process is mainly composed of two structures, austenite and ferrite, has good thermal stability, hardness and strength, and at the same time has good strength and toughness, significantly improving the fatigue performance at room temperature and high temperature.

[0048] A diesel engine cylinder head, and the diesel engine cylinder head includes the above multi-principal-element iron-based medium-entropy alloy or a multi-principal-element iron-based medium-entropy alloy prepared according to the preparation method of any one of the above multi-principal-element iron-based medium-entropy alloys.

[0049] Example 1

[0050] Prepare Fe52 Ni 33 Al 15 The specific process of the fatigue-resistant medium-entropy alloy includes:

[0051] Step 1: Prepare metal elements Fe 52%, Ni 33%, and Al 15% with a purity of ≥99.99% according to atomic percentages. Remove the impurities and oxides on the surfaces of the Al block, Fe block, and Ni block respectively, and then use acetone cleaning agent to oscillate and clean the Al block, Fe block, and Ni block in ultrasonic waves for 5 minutes for later use.

[0052] Step 2: Stack the Al block, Fe block, and Ni block in order from bottom to top according to the density gradient and place them in the water-cooled crucible of the vacuum levitation melting furnace.

[0053] Step 3: Start the mechanical pump, roughing valve, and Roots pump of the vacuum levitation furnace to extract low vacuum. When the low vacuum degree reaches 5 Pa, open the fore-vacuum valve and diffusion pump, and wait for 55 minutes. Then close the roughing valve and open the main pumping valve. When the vacuum degree meets the requirement (4.5×10-3 Pa), close the main pumping valve and vacuum gauge, and finally open the argon filling valve to fill the furnace cavity with argon.

[0054] Start the melting power supply, gradually increase the power of the power supply, observe the situation of the water-cooled crucible in the furnace through the furnace door and furnace cover, adjust the power of the power supply until the Al block, Fe block, and Ni block are completely and evenly melted (the maximum power is 260 KW). After complete melting, continue melting for 5 - 10 minutes, take out the ingot after cooling for 3 hours, repeat the above operation 5 times to completely and evenly melt the alloy, and obtain the ingot.

[0055] Step 4: Put the ingot into a muffle furnace for heat treatment. Control the heat treatment temperature at 600 °C, keep the temperature for 1 h, and then stop heating and cool it to room temperature with the furnace.

[0056] Example 2

[0057] This example prepares Fe 54 Ni 31 Al 15 , and the specific steps are the same as those in Example 1, except that:

[0058] In Step 1, prepare metal elements Fe 54%, Ni 31%, and Al 15% with a purity of ≥99.99% according to atomic percentages;

[0059] In Step 4, control the heat treatment temperature at 600 °C and keep the temperature for 2 h.

[0060] Example 3

[0061] This example prepares Fe 56 Ni 29 Al15 , which is the same as the specific steps of Example 1, except that:

[0062] In Step 1, metallic elements Fe 56%, Ni 29%, and Al 15% with a purity of ≥99.99% are prepared according to atomic percentages;

[0063] In Step 4, the heat treatment temperature is controlled at 700 °C and the holding time is 1 h.

[0064] Example 4

[0065] In this example, Fe 56 Ni 29 Al 15 is prepared, which is the same as the specific steps of Example 3, except that:

[0066] In Step 4, the heat treatment temperature is controlled at 700 °C and the holding time is 2 h.

[0067] As can be seen from Table 1, the density of the multi-principal element iron-based medium entropy alloy prepared in Examples 1-4 is 6.43-7.03 g / cm 3 .

[0068] Table 1 Density comparison table of different materials and heat treatment processes

[0069]

[0070]

[0071] As can be seen from Table 2, the tensile strength of the multi-principal element iron-based medium entropy alloy prepared in Examples 1-4 is 739-835 MPa, the elongation is 21-55.46%, the fatigue strength at 25 °C is 180-187 MPa, and the fatigue strength at 600 °C is 239-260 MPa.

[0072] Table 2 Performance comparison table of different materials and heat treatment processes

[0073]

[0074] Table 3 shows the performance comparison between the multi-principal element iron-based medium entropy alloy of the present invention and the traditional diesel engine cylinder head material. It can be seen from the table that the multi-principal element iron-based medium entropy alloy of the present invention has a lower density while ensuring excellent performance in various aspects, meeting the current lightweight requirements and significantly improving the fuel economy of vehicles. While ensuring lightweight, the multi-principal element iron-based medium entropy alloy of the present invention also has excellent comprehensive mechanical properties. The fatigue performance of the traditional diesel engine cylinder head material gradually decreases with the increase of temperature, while the fatigue performance of the multi-principal element iron-based medium entropy alloy of the present invention is significantly improved at a service temperature of 600 °C.

[0075] Table 3 Performance Comparison Table of the Cylinder Head Materials of the Present Invention and Traditional Diesel Engines

[0076]

[0077] As Figure 1 shown, the horizontal axis in the figure represents the diffraction angle, and the vertical axis represents the diffraction intensity. It can be seen from the figure that the multi-principal element Fe-based medium-entropy alloy prepared in Examples 1-4 is an alloy composed of a ferrite phase and an austenite phase. By changing the heat treatment process and alloy composition, there is no obvious change in the phase composition of the material.

[0078] As Figure 2 shown, the microstructures of the multi-principal element Fe-based medium-entropy alloys prepared in Examples 1-4 are ferrite phase and austenite phase. Among them, the light-colored regions in a, b, c, and d are austenite phases, and the dark-colored regions are ferrite phases.

[0079] Figure 3 is the tensile stress-strain curve of the multi-principal element Fe-based medium-entropy alloy prepared in Examples 1-4. The abscissa in the figure represents the strain of the alloy, and the ordinate represents the stress. It can be seen from the figure that the multi-principal element Fe-based medium-entropy alloys prepared by different processes all have good strength and toughness.

[0080] The strength of aluminum alloy drops sharply above 350 °C. High temperature can promote the dislocation climb and dynamic recovery of aluminum alloy, resulting in the disappearance of the work-hardening effect, material softening, and reduced fatigue life.

[0081] The mechanical properties of gray cast iron and vermicular graphite cast iron deteriorate significantly above 400 °C, resulting in a substantial reduction in their fatigue strength. The fatigue strength of typical vermicular graphite cast iron at 600 °C is usually lower than 150 MPa. The matrix of gray cast iron is mainly pearlite and ferrite, with low plastic deformation ability. It is difficult to dissipate energy through plastic deformation, and the interfacial bonding force between graphite and ferrite and pearlite matrix is poor, easy to debond and form microcracks, which rapidly expand under alternating stress, leading to brittle fracture. If the matrix of vermicular graphite cast iron is ferrite, the strength is low; if it is pearlite, although the strength is high, the toughness decreases, which is not conducive to fatigue performance. At high temperatures, the matrix may undergo pearlite decomposition or graphitization, resulting in material softening.

[0082] The multi-principal element Fe-based medium-entropy alloy prepared in the present invention has a fatigue strength of 239-260 MPa at 600 °C, which is significantly higher than that of traditional materials. This improvement is due to the synergistic effect of the austenite and ferrite dual-phase structure. Austenite provides high-temperature stability, and ferrite enhances toughness, jointly inhibiting crack propagation, thereby improving the fatigue resistance.

[0083] In summary, the diesel engine cylinder head needs to work under high temperature, high pressure and cyclic loads above 600 °C for a long time. Due to insufficient high temperature performance, traditional materials are prone to high-cycle fatigue failure (probability 70%-90%). The multi-principal element iron-based medium entropy alloy prepared by the present invention has a fatigue strength more than 1.5 times that of traditional materials in an environment of 600 °C, significantly extending the life of components. At the same time, the synergistic effect of austenite and ferrite inhibits high temperature phase transformation and oxidation, ensuring the stability of long-term service.

Claims

1. A multi-principal element iron-based medium entropy alloy with fatigue resistance, characterized in that By atomic percentage, it includes: Fe: 52 - 56%, Ni: 29 - 33%, Al: 15%; Among them, the multi-principal element Fe-based medium entropy alloy has a duplex structure, including an austenite phase and a ferrite phase. The density of the multi-principal element Fe-based medium entropy alloy is 6.43 - 7.03 g / cm 3 , the tensile strength is 739 - 835 MPa, the elongation is 21 - 55.46%, the fatigue strength at room temperature is 180 - 187 MPa, and the fatigue strength at 600 °C is 239 - 260 MPa.

2. A preparation method of a multi-principal element iron-based medium-entropy alloy with fatigue resistance as described in claim 1, characterized in that, It includes the following steps: Overlap and place the Al block, Fe block and Ni block into the water-cooled crucible of the vacuum levitation melting furnace from bottom to top in sequence; Under an argon atmosphere, melt the Al block, Fe block and Ni block in the water-cooled crucible to obtain an ingot; Perform heat treatment on the ingot to obtain a multi-principal element iron-based medium entropy alloy.

3. The preparation method of the multi-principal element iron-based medium entropy alloy with fatigue resistance according to claim 2, characterized in that, Before overlapping and placing the Al block, Fe block and Ni block into the water-cooled crucible of the vacuum levitation melting furnace from bottom to top, it further includes: Remove the impurities and oxides on the surfaces of the Al block, Fe block and Ni block respectively, and then use acetone cleaning agent to oscillate and clean the Al block, Fe block and Ni block in ultrasonic wave for 5 min.

4. The preparation method of the multi-principal element iron-based medium entropy alloy with fatigue resistance according to claim 3, characterized in that When melting the Al block, Fe block and Ni block in the water-cooled crucible under an argon atmosphere, the vacuum degree ≤ 4.5×10 -3 Pa.

5. The preparation method of the multi-principal element iron-based medium entropy alloy with fatigue resistance according to claim 4, characterized in that, Melting the Al block, Fe block and Ni block in the water-cooled crucible under an argon atmosphere includes: Start the melting power supply, gradually increase the power of the power supply, adjust the power of the power supply until the Al block, Fe block and Ni block are completely and evenly melted. After complete melting, continue melting for 5 - 10 min, and take out the ingot after cooling for 3 hours.

6. The preparation method of the multi-principal element iron-based medium entropy alloy with fatigue resistance according to claim 5, characterized in that, The number of melting repetitions is 5 times.

7. The preparation method of the multi-principal element iron-based medium entropy alloy with fatigue resistance according to claim 6, characterized in that, The power of the power supply ≤ 260 KW.

8. The preparation method of the multi-principal element iron-based medium entropy alloy with fatigue resistance according to claim 7, characterized in that, The temperature of the heat treatment is 600 - 700 °C, and the holding time is 1 - 2 h.

9. A cylinder head of a diesel engine, characterized in that, The diesel engine cylinder head includes the multi-principal element iron-based medium entropy alloy described in Claim 1 or the multi-principal element iron-based medium entropy alloy prepared by the preparation method of the multi-principal element iron-based medium entropy alloy described in any one of Claims 2 - 8.

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