High compressive strength high plasticity iron-based alloy and preparation method and application thereof

Abstract

The application discloses a high-compression-strength high-plasticity iron-based alloy and a preparation method and application thereof, and relates to the technical field of high-performance metal structural materials.The application provides an element composition of the high-compression-strength high-plasticity iron-based alloy; the microstructure of the alloy comprises a Fe2Nb Laves phase network structure distributed along grain boundaries and an intracrystalline nanometer-scale composition modulation structure; the room-temperature compression yield strength of the high-compression-strength high-plasticity iron-based alloy is not less than 2000 MPa, and the compression fracture strain is not less than 30%. The application further provides a preparation method and application of the alloy. The application forms a multi-level micro-nano strengthening structure in-situ in an alloy block through a specific non-equilibrium solidification process, so that the alloy simultaneously has ultrahigh strength and high plasticity under compression load, and can be applied to high-pressure-resistant structural parts, and effectively solves problems of a complicated preparation process of traditional high-strength materials, high strength necessarily accompanied by low plasticity and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-performance metal structural materials, and in particular to a high-compressive-strength high-plasticity iron-based alloy and a preparation method and application thereof. BACKGROUND

[0002] Metal structural materials have long been faced with the challenge of being difficult to achieve both strength and plasticity / toughness, which is known as the "strength-plasticity inversion relationship". When the strength is improved by traditional means such as fine-grain strengthening and precipitation strengthening, the plasticity is often significantly reduced. In recent years, the preparation of heterogeneous structural materials such as gradient structures and layered structures through severe plastic deformation (such as high-pressure torsion and equal channel angular extrusion) or complex thermal mechanical treatment processes has become a way to solve this problem. However, such methods have problems such as complex process, high cost, and limited sample size, making it difficult to achieve large-scale industrial application. Rapid solidification technology can achieve non-equilibrium solidification and obtain high-performance structures such as amorphous and nanocrystalline, but its main product forms are low-dimensional materials such as thin strips and powders, which are difficult to use directly as load-bearing structural parts. In addition, the existing technology mainly pursues the comprehensive performance of materials under tensile load, and the study of microstructure design of materials for compression performance is relatively less.

[0003] Therefore, it is of great scientific significance and engineering value to develop a process that is simple and can directly prepare a bulk material with ultra-high performance under compression load, and to clarify its specific application direction in the high-tech field. SUMMARY

[0004] The purpose of the present application is to provide a high-compressive-strength high-plasticity iron-based alloy and a preparation method and application thereof. Through a specific non-equilibrium solidification process, a multi-level micro-nano strengthening structure is formed in situ in the alloy bulk, thereby simultaneously achieving ultra-high strength and high plasticity under compression load, and the alloy is applied to high-pressure-resistant structural parts, effectively solving the problems of complex preparation process and low plasticity accompanying high strength of traditional high-strength materials.

[0005] The technical solution of the present application to solve the above technical problems is as follows: a high-compressive-strength high-plasticity iron-based alloy is provided, which comprises the following atomic percentage components: copper 3.0-9.0%, niobium 1.0-7.0%, and the balance being iron and unavoidable impurities.

[0006] The microstructure of the high-compressive-strength high-plasticity iron-based alloy comprises a network structure of Fe2Nb Laves phase distributed along the grain boundaries and an intragranular nanoscale composition modulation structure. The high-compressive-strength high-plasticity iron-based alloy has a room-temperature compression yield strength of not less than 2000 MPa and a compression fracture strain of not less than 30%.

[0007] Further, the high compressive strength and high ductility iron-based alloy comprises the following atomic percentage components: copper 4.0-8.0%, niobium 2.0-6.0%, and the balance of iron and inevitable impurities.

[0008] Further, the atomic percentage of the inevitable impurities is not more than 1.5%.

[0009] Further, the atomic percentage of the inevitable impurities is not more than 0.5%.

[0010] Further, the inevitable impurities are at least one of C, O, N, B, S, P, Si, Mn and Al.

[0011] Further, the content of the inevitable impurities does not substantially damage the microstructure and compression mechanical properties of the alloy. Specifically, "substantially damaging the microstructure and / or mechanical properties" is a functional definition, and the judgment criteria include but are not limited to: causing the compression strength of the alloy to decrease by more than 20%, or the compression fracture strain to decrease by more than 50%, or the characteristic multi-level micro-nano structure to completely disappear and be replaced by coarse equilibrium phase. The "inevitable impurities" of the present application refer to trace impurity elements that may be introduced by raw materials, smelting environment or equipment during the preparation of the alloy from industrial-grade raw materials and conventional metallurgical processes, which are common elements such as carbon (C), oxygen (O), nitrogen (N), boron (B), sulfur (S), phosphorus (P), silicon (Si), manganese (Mn), aluminum (Al) and the like.

[0012] The present application also provides a preparation method of the high compressive strength and high ductility iron-based alloy, comprising the following steps: smelting iron source, copper source and niobium source under inert or reducing protective atmosphere until the components are uniform, then contacting with a high thermal conductivity cooling body, and solidifying at a cooling rate of not less than 10 2 K / s to obtain the high compressive strength and high ductility iron-based alloy.

[0013] Further, during solidification, the cooling rate is 10 3 -10 4 K / s.

[0014] Further, the high thermal conductivity cooling body refers to any device or element that can achieve the required cooling rate (greater than 10 2 K / s) of the present application.

[0015] Further, the high thermal conductivity cooling body is a water-cooled copper crucible, a water-cooled copper mold, a cooling roll or a water-cooled copper substrate.

[0016] Further, the iron source, copper source and niobium source are independently selected from pure metals, metal powders or alloys.

[0017] Further, the niobium source is pure niobium or niobium-iron alloy.

[0018] In the preparation of the alloy, the iron source, the copper source and the niobium source are smelted under an inert or reducing protective atmosphere until the composition is uniform, then contacted with a high thermal conductivity cooling body, and solidified at a cooling rate sufficient to promote the formation of the nanoscale composition modulation structure, thereby obtaining the target alloy bulk, without the need for any subsequent heat treatment.

[0019] The application also provides the use of the high-compressive-strength high-plasticity iron-based alloy in the preparation of high-pressure-resistant structural components.

[0020] Further, the high-pressure-resistant structural components are armored protective components, spacecraft load-bearing components, deep-sea probe pressure-resistant cabin bodies, high-performance mold cavities or super-high-pressure system components.

[0021] The application of the application is to utilize the high-compressive-strength and high-compressive-fracture-strain of the high-compressive-strength high-plasticity iron-based alloy, and the excellent compression mechanical properties are the key to the application.

[0022] The application has the following beneficial effects:

[0023] 1. The high-compressive-strength high-plasticity iron-based alloy has excellent compression performance, and successfully realizes the excellent combination of a compression strength not less than 2000 MPa and a compression fracture strain not less than 30%; the preparation process is simple, the required multi-level micro-nano structure can be obtained in situ in the bulk material through only one step of rapid solidification process, the subsequent complicated heat treatment or processing steps are saved, the process flow is short, the cost is low, the efficiency is high, and the process is easy to scale up; the application is clear and reasonable, based on the proven and excellent intrinsic compression performance, the key application in high-end equipment mainly bearing compression load is reasonably predicted and protected, and the commercial orientation is clear.

[0024] 2. The high-compressive-strength high-plasticity iron-based alloy breaks the traditional cognition that high strength must be accompanied by low plasticity, and the mechanism is novel. The strength is derived from the "skeleton" (Fe2Nb network) + "vein" (composition modulation) which jointly constitutes a hard bearing system; the plasticity is derived from the ductile Fe matrix which plays a key role as "adhesive" and "energy absorber" under compression load.

[0025] 3. The high-compressive-strength high-plasticity iron-based alloy is applied to the preparation of high-pressure-resistant structural components, specifically including armored protective components, spacecraft load-bearing components, deep-sea probe pressure-resistant cabin bodies, high-performance mold cavities or super-high-pressure system components; for example, the armored protective layer absorbs impact energy by utilizing the high compression strength and deformation capacity, the deep-sea probe pressure-resistant cabin body resists hydrostatic pressure by utilizing the ultra-high strength, and the spacecraft load-bearing frame and high-performance mold utilize the high compression yield strength and stability.

[0026] 4、The high compressive strength high plasticity iron-based alloy of the present application is mainly composed of iron, Cu and Fe are difficult to be mutually soluble at room temperature, Cu and Nb are also difficult to be mutually soluble, only by combining with rapid cooling, the unique micro-nano multi-level structure can be formed, and each component is indispensable. The alloy selects the Fe-Cu-Nb system which is difficult to be mutually soluble in thermodynamics, and utilizes the kinetic constraint of rapid solidification to force the elements to be redistributed in the micro-nano scale under the condition that macroscopic segregation is impossible, thereby guiding the formation of the unique multi-level structure from bottom to top. The alloy naturally forms a stable structure cooperated by two scales; micron scale: the reticular Fe2Nb Laves phase is formed at the grain boundary. The hard and brittle phase as the "skeleton" of the material is the primary contributor to provide ultra-high strength; nano scale: the parallel arranged light and dark stripes are formed in the grain, which is derived from the periodic composition modulation frozen by rapid solidification, that is, the matrix is still a single phase, but the Cu and Nb element concentration in the matrix fluctuates in a wave form (rich and poor areas are alternated), and the nano composition fluctuation itself is a powerful strengthening mechanism.

[0027] 5、The high compressive strength high plasticity iron-based alloy of the present application is mainly composed of iron, Cu and Fe are difficult to be mutually soluble at room temperature, Cu and Nb are also difficult to be mutually soluble, only by combining with rapid cooling, the unique micro-nano multi-level structure can be formed, and each component is indispensable. The alloy selects the Fe-Cu-Nb system which is difficult to be mutually soluble in thermodynamics, and utilizes the kinetic constraint of rapid solidification to force the elements to be redistributed in the micro-nano scale under the condition that macroscopic segregation is impossible, thereby guiding the formation of the unique multi-level structure from bottom to top. The alloy naturally forms a stable structure cooperated by two scales; micron scale: the reticular Fe2Nb Laves phase is formed at the grain boundary. The hard and brittle phase as the "skeleton" of the material is the primary contributor to provide ultra-high strength; nano scale: the parallel arranged light and dark stripes are formed in the grain, which is derived from the periodic composition modulation frozen by rapid solidification, that is, the matrix is still a single phase, but the Cu and Nb element concentration in the matrix fluctuates in a wave form (rich and poor areas are alternated), and the nano composition fluctuation itself is a powerful strengthening mechanism. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1Low-magnification SEM photograph of the alloy obtained in Example 1;

[0029] Figure 2 High-magnification SEM photograph of the alloy obtained in Example 1;

[0030] Figure 3 EDS line scanning result of the Fe element in the alloy obtained in Example 1;

[0031] Figure 4 EDS line scanning result of the Cu element in the alloy obtained in Example 1;

[0032] Figure 5 EDS line scanning result of the Nb element in the alloy obtained in Example 1;

[0033] Figure 6 X-ray diffraction pattern of the alloy obtained in Example 1;

[0034] Figure 7 SEM photograph of the alloy obtained in Comparative Example 1;

[0035] Figure 8 SEM photograph of the alloy obtained in Comparative Example 2;

[0036] Figure 9 Comparison chart of room-temperature compression engineering stress-strain curves of the alloys obtained in Examples 1-2 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0037] The present application will be further described in conjunction with specific embodiments, but the embodiments do not limit the present application in any form. Unless otherwise specified, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field.

[0038] Example 1:

[0039] A high-compressive-strength high-plasticity iron-based alloy, and a preparation method thereof, the preparation method comprising the following steps:

[0040] An electrolytic copper plate (Cu 6 at.%), a niobium-iron alloy (FeNb70, providing Nb 4 at.%), an industrial pure iron ingot (providing Fe 90 at.%), and unavoidable impurities with an atomic percentage of not more than 0.5% are smelted into an alloy liquid with uniform composition in an alumina ceramic crucible of an induction smelting furnace, and then the alloy liquid is poured into a cylindrical oxygen-free copper mold (cavity diameter Φ10 mm) with forced water cooling on the outer wall, and the cooling rate is 10 3 -10 4 K / s (calculated by measuring the secondary dendrite arm spacing), to obtain an alloy bar (high-compressive-strength high-plasticity iron-based alloy).

[0041] The obtained alloy rod was cut into a compression sample (diameter 3 mm, height 6 mm), which was tested to have a room temperature compression strength of 2613 MPa and a fracture strain of 38.0%. The typical microstructure thereof is shown in Figure 1 and Figure 2 , and the EDS line scanning results of each element are shown in Figures 3 to 5 , respectively; and the X-ray diffraction pattern thereof is shown in Figure 6 .

[0042] As can be seen from Figures 1 to 6 , the SEM result of the obtained alloy clearly shows a network structure distributed along the grain boundary; and intuitively displays the intragranular nanoscale composition modulation phenomenon (periodic concentration fluctuation of Cu and Nb elements).

[0043] Example 2:

[0044] Electrolytic copper plates (Cu 7 at.%), high-purity niobium blocks (providing Nb 3 at.%), and industrial pure iron ingots (providing Fe 90 at.%), with the atomic percentage of unavoidable impurities not more than 0.5%, were placed in a water-cooled copper crucible of a non-consumable arc furnace, and after high vacuum extraction, high-purity argon gas was filled as a protective atmosphere. The alloy liquid was repeatedly melted for 5 times, and the composition was ensured to be uniform through electromagnetic stirring. Finally, the heating was stopped, and the alloy liquid was allowed to solidify in situ in the water-cooled copper crucible, with a cooling rate greater than 10 2 K / s (calculated by measuring the secondary dendrite arm spacing), to obtain a high-compression-strength high-plasticity iron-based alloy.

[0045] The obtained alloy rod was cut into a compression sample (diameter 3 mm, height 6 mm), which was tested to have a room temperature compression strength of 2529 MPa and a fracture strain of 38.1%.

[0046] Comparative Example 1:

[0047] An alloy material, the preparation method thereof comprising the following steps:

[0048] Electrolytic copper plates (Cu 6 at.%), niobium-iron alloy (FeNb70, providing Nb 4 at.%), and industrial pure iron ingots (providing Fe 90 at.%), with the atomic percentage of unavoidable impurities not more than 0.5%, were placed in an alumina ceramic crucible of an induction melting furnace, and the alloy liquid was melted to be uniform in composition, and then poured into a cylindrical thick-walled steel mold (mold cavity diameter Φ30 mm) which was pre-heated at 600 ℃ in a furnace, so as to be slowly cooled at a cooling rate lower than 10 1 K / s, to obtain the alloy material.

[0049] The obtained alloy material has coarse structure, mainly block Laves phase, eutectic structure and ferrite grains, and no nano-scale composition modulation structure is observed Figure 7 ); the compression performance is significantly reduced, the strength is only 1752 MPa, and the fracture strain is 33.6%.

[0050] Comparative Example 2

[0051] An alloy material, a preparation method thereof comprises the following steps:

[0052] Lower-grade industrial raw materials are used, so that the total amount of impurities (such as C, O, N, B, S, P, Si, Mn, Al and the like) in the alloy after smelting is increased to about 2.0 at.%, and the same smelting and pouring method as that in Example 1 is used.

[0053] The eutectic structure in the obtained alloy is coarse and agglomerated, and the composition modulation structure in the grain does not exist Figure 8 . The mechanical property is seriously deteriorated, the compression strength is 1615 MPa, and the fracture strain is 30.4%. The results of Comparative Example 2 prove that the impurity content has constituted “substantial damage”, which highlights the necessity of controlling the impurity content.

[0054] The room temperature compression engineering stress-strain curves of the alloys obtained in Examples 1-2 and Comparative Examples 1-2 are obtained through experiments, as shown in Figure 9 .

[0055] As can be seen from Figure 9 , the high compression strength and high plasticity iron-based alloy of the present application exhibits excellent compression performance.

[0056] The above only describes the preferred embodiments of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A high compressive strength and high ductility iron-based alloy, characterized in that, It comprises the following atomic percentage components: copper 3.0-9.0%, niobium 1.0-7.0%, with the balance being iron and unavoidable impurities; The microstructure of the high compressive strength and high ductility iron-based alloy includes a Fe2Nb Laves phase network structure distributed along the grain boundaries and an intragranular nanoscale composition modulation structure. The room temperature compressive yield strength of the high compressive strength and high ductility iron-based alloy is not less than 2000 MPa, and the compressive fracture strain is not less than 30%.

2. The high compressive strength and high ductility iron-based alloy according to claim 1, characterized in that, It includes the following atomic percentage components: copper 4.0-8.0%, niobium 2.0-6.0%, with the balance being iron and unavoidable impurities.

3. The high compressive strength and high ductility iron-based alloy according to claim 1 or 2, characterized in that, The atomic percentage of the unavoidable impurities does not exceed 1.5%.

4. The high compressive strength and high ductility iron-based alloy according to claim 1 or 2, characterized in that, The atomic percentage of the unavoidable impurities does not exceed 0.5%.

5. The method for preparing the high compressive strength and high ductility iron-based alloy according to any one of claims 1-4, characterized in that, The process includes the following steps: melting iron, copper, and niobium sources under an inert or reducing protective atmosphere until the composition is homogeneous, then contacting them with a high thermal conductivity coolant, and applying a flux of not less than 10... 2 Solidification at a cooling rate of K / s yields a high compressive strength and high ductility iron-based alloy.

6. The method for preparing a high compressive strength and high ductility iron-based alloy according to claim 5, characterized in that, During solidification, the cooling rate is 10. 3 -10 4 K / s.

7. The method for preparing a high compressive strength and high ductility iron-based alloy according to claim 5, characterized in that, The iron source, copper source, and niobium source are independently selected from pure metals, metal powders, or alloys.

8. The method for preparing a high compressive strength and high ductility iron-based alloy according to claim 5, characterized in that, The high thermal conductivity cooling body is a water-cooled copper crucible, a water-cooled copper mold, a cooling roller, or a water-cooled copper substrate.

9. The application of the high compressive strength and high ductility iron-based alloy according to any one of claims 1-4 in the preparation of high pressure resistant structural components.

10. The application according to claim 9, characterized in that, The high-pressure resistant structural components include armor protection components, spacecraft load-bearing components, pressure-resistant cabins of deep-sea probes, high-performance mold cavities, or ultra-high-pressure system components.

Images