A CoZr composite material with ultra-wide temperature range zero thermal expansion and corrosion resistance x base composite material

Abstract

The application discloses a CoZr x composite material with super-wide temperature range zero thermal expansion and corrosion resistance, a CoZr3 α phase structure is constructed by precisely controlling the Zr content, and the synergistic optimization of thermal expansion and mechanical properties and corrosion resistance is realized. The chemical formula of the material is CoZr x , wherein x =3~4.2, preferably x =3.8. The alloy shows super-wide temperature range zero thermal expansion characteristics in the temperature range of 120~680 K, and has significantly improved mechanical properties and excellent corrosion resistance, and is suitable for precision instruments, marine engineering, aerospace and other fields.

Description

Technical Field

[0001] This invention belongs to the field of zero thermal expansion composite material technology, specifically relating to a CoZr composite material with zero thermal expansion over an ultra-wide temperature range, high strength, and excellent corrosion resistance. x Based on biphase composite materials. Background Technology

[0002] Zero-thermal-expansion materials are those whose dimensions remain almost unchanged as external temperature changes. They have irreplaceable value in fields such as precision optical instruments, space remote sensing satellite structures, high-precision measurement benchmarks, and liquefied natural gas storage and transportation equipment. However, the zero-thermal-expansion temperature range of these alloys is usually narrow, making it difficult to meet the extreme requirements for dimensional stability in ultra-wide temperature range scenarios such as deep space exploration and cryogenic engineering. In recent years, researchers have discovered a class of negative-thermal-expansion intermetallic compounds driven by anomalous vibrations of lattice phonons, such as CoZr3. These materials exhibit near-linear negative thermal expansion behavior over a wide temperature range, providing an ideal matrix for designing wide-temperature-range zero-thermal-expansion materials. However, these materials are usually brittle intermetallic compounds, and their extremely low plasticity and fracture toughness make them difficult to process and form, resulting in poor reliability and seriously hindering their practical application.

[0003] To improve brittleness, a common approach is to mechanically combine materials with negative thermal expansion properties with materials with positive thermal expansion properties and good plasticity, hoping to achieve zero thermal expansion and improve toughness through "positive and negative cancellation". However, composite materials prepared by this method often have problems such as weak interfacial bonding and mismatched coefficients of thermal expansion. During thermal cycling, stress concentration is easily generated at the interface, leading to microcracks or even interfacial delamination, resulting in easy material failure.

[0004] Furthermore, the corrosion resistance of both single-phase brittle intermetallic compounds and mechanically composite materials in harsh service environments is often overlooked or poorly demonstrated, while corrosion resistance is one of the key indicators determining the service life and reliability of materials in engineering applications. Traditional Invar alloys also have relatively limited corrosion resistance in chlorine-containing environments.

[0005] Therefore, developing an integrated metallic material that can simultaneously achieve zero thermal expansion over an ultra-wide temperature range, good mechanical properties, and excellent corrosion resistance has become a pressing technical challenge in this field. Summary of the Invention

[0006] This invention addresses the problems of narrow temperature range, high brittleness, and insufficient corrosion resistance in existing zero-thermal-expansion materials, proposing a CoZr material with ultra-wide temperature range zero thermal expansion, high strength, and excellent corrosion resistance. x Based on biphase composite materials.

[0007] The technical solution for implementing the present invention is as follows:

[0008] In a first aspect, the present invention provides a CoZr with zero thermal expansion over an ultra-wide temperature range, high strength, and excellent corrosion resistance. x A two-phase composite material, comprising an orthogonal CoZr3 phase and a hexagonal α-Zr phase, with the chemical formula CoZr3+. x , where x = 3.4~4.2.

[0009] Furthermore, in atomic percentage, x = 3.8.

[0010] Furthermore, the composite material exhibits zero thermal expansion characteristics in the temperature range of 120~680 K.

[0011] Furthermore, the composite material has a compressive strength ≥ 575 MPa and a certain plastic deformation capacity.

[0012] Furthermore, the composite material exhibits a self-corrosion potential ≥ -0.26 V and a self-corrosion current density ≤ 1.74 × 10⁻⁶ V in a 3.5 wt% NaCl solution. -7 A·cm -2 .

[0013] In a second aspect, the present invention provides a method for preparing the composite material described in the first aspect, which is prepared by arc melting and includes the following steps:

[0014] (1) Weigh out Co and Zr raw materials according to stoichiometry;

[0015] (2) Arc melting is carried out under argon protection, and the melting is repeated more than 4 times to ensure uniform composition;

[0016] (3) The obtained ingot was annealed at 850 °C for 5 days to obtain a composite material with a uniform two-phase structure.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1) Ultra-wide temperature range with zero thermal expansion: Through in-situ composite two-phase design, continuous and precise control is achieved from negative thermal expansion to zero thermal expansion and then to positive thermal expansion. Optimal component: CoZr 3.8 It exhibits excellent zero thermal expansion characteristics in an ultra-wide temperature range of 120~680 K up to 560 K, with a temperature range width significantly exceeding that of traditional Invar alloys.

[0019] 2) Significantly improved mechanical properties: The introduction of the plastic α-Zr phase fundamentally changes the brittle fracture mode of the CoZr3 matrix, enabling the composite material to have plastic deformation capabilities and increasing the compressive strength by more than 7 times compared with single-phase CoZr3.

[0020] 3) Excellent corrosion resistance: Thanks to the self-passivation ability of the Zr-rich component, the material exhibits extremely high stability in simulated marine environments. Its self-corrosion potential is higher, and its self-corrosion current density is reduced by an order of magnitude compared to Invar alloy, resulting in a significant extension of its service life. Attached Figure Description

[0021] Figure 1 The different Zr contents (x=3, 3.4, 3.8, 4.2) of CoZr in the embodiments of the present invention are shown. x XRD pattern of the alloy.

[0022] Figure 2 CoZr in the embodiments of the present invention x SEM image of the alloy in backscattered mode.

[0023] Figure 3 CoZr in the embodiments of the present invention x Thermal expansion curve of the alloy.

[0024] Figure 4 CoZr in the embodiments of the present invention x The room temperature compressive stress-strain curve of the alloy.

[0025] Figure 5 CoZr in the embodiments of the present invention 3.8 Comparative photographs of the macroscopic surface morphology of alloy and Invar alloy after immersion in 3.5 wt% NaCl solution for different numbers of days.

[0026] Figure 6 CoZr in the embodiments of the present invention 3.8 Electrochemical test results of alloy and Invar alloy in 3.5 wt% NaCl solution, where (a) is the open circuit potential-time curve and (b) is the potentiodynamic polarization curve. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0028] It should be noted that this invention is not limited to the arc melting preparation method described below, but also includes CoZr with the same dual-phase structure prepared by other techniques such as powder metallurgy and rapid solidification. x Materials are also within the scope of protection of this invention.

[0029] This invention achieves precise control of the chemical formula CoZr xThe Zr content (x = 3~4.2) in the alloy allows for the in-situ formation of a two-phase microstructure consisting of a CoZr3 intermetallic compound phase and an α-Zr solid solution phase during solidification via a eutectic reaction. The brittle but negatively thermally expanded CoZr3 phase acts as the functional phase, contributing negative thermal expansion over a wide temperature range; the highly ductile α-Zr phase, dispersed throughout the matrix, acts as the toughening phase, strengthening and coordinating deformation. By optimizing the ratio of the two phases (especially when x = 3.8), the positive and negative thermal expansion effects can be perfectly compensated macroscopically, achieving zero thermal expansion characteristics over an ultra-wide temperature range of 120~680 K. Simultaneously, the introduction of the α-Zr phase transforms the material from a completely brittle fracture mode to one with a certain degree of plasticity, significantly improving strength. Furthermore, the abundant Zr in the material rapidly forms a dense and stable ZrO2 passivation film in corrosive media, endowing it with corrosion resistance far exceeding that of traditional Invar alloys.

[0030] Example 1

[0031] According to the chemical formula CoZr 3.8 High-purity Co and Zr metal raw materials were weighed according to their atomic ratio and placed in a water-cooled copper crucible in an electric arc melting furnace. After evacuation, high-purity argon gas was introduced as a protective atmosphere. During melting, a small current was used for arc initiation and preheating. After the raw materials had initially melted, the current was increased to 120 A to fully melt the alloy, and magnetic stirring was activated to ensure uniform composition. This process was repeated at least four times to finally obtain an alloy ingot with uniform composition and dense structure. Under vacuum, the ingot was annealed at 850 °C for 5 days to relieve stress.

[0032] Example 2

[0033] The other processes are the same as in Example 1, respectively according to the chemical formulas CoZr3 and CoZr. 3.4 and CoZr 4.2 The raw materials and preparation process are the same as in Example 1.

[0034] XRD analysis was performed on the four ingots obtained from Examples 1 and 2 after annealing, and the results are as follows. Figure 1 As shown, by comparing the diffraction peaks with those of the standard PDF card, it can be found that: CoZr 3.8 、CoZr 3.4 and CoZr 4.2 All three ingot alloys consisted of orthorhombic CoZr3 and hexagonal α-Zr phases, without any other impurities. Furthermore, the intensity of the α-Zr phase diffraction peaks gradually increased with increasing Zr content (x), indicating that the volume fraction of the α-Zr phase in the alloy increased with increasing Zr content. The prepared CoZr3 ingot exhibited a single-phase structure without any other phases.

[0035] The microstructure of the four ingots obtained in Examples 1 and 2 after annealing was observed in backscattered electron mode, and the results are as follows: Figure 2 As shown. For the x=3 alloy sample, a relatively uniform gray contrast was observed, corresponding to a single CoZr3 phase, with no second phase characteristics observed. With increasing Zr content, a distinct two-phase distribution began to appear in the microstructure. The light gray second phase α-Zr was uniformly dispersed in the dark gray CoZr3 phase matrix in the form of isolated islands or short rods. The content of the α-Zr phase gradually increased, and its morphology became more continuous. In some areas, a network structure began to form, and the area of ​​the clump-like α-Zr phase also became larger.

[0036] The thermal expansion properties of the four ingots obtained after annealing in Examples 1 and 2 were tested, and the results are as follows: Figure 3 As shown, as the x value increases, the α-Zr phase content increases, and the thermal expansion behavior of the alloy transitions from negative thermal expansion to positive thermal expansion. When x=3.8 (Example 1), the thermal expansion curve of the alloy changes very little in the entire test temperature range of 120~680 K. The calculated average thermal expansion coefficient is close to zero, achieving zero thermal expansion in an ultra-wide temperature range.

[0037] Four ingots obtained from Examples 1 and 2 after annealing were subjected to room temperature compressive stress-strain tests, and the results are as follows: Figure 4 As shown, with increasing Zr content, the maximum compressive strength of the alloy significantly increases from 77 MPa at x=3 to approximately 1170 MPa at x=4.2. Of particular note is the sample at x=3.8 (Example 1), which exhibits the optimal ZTE behavior, with a maximum compressive strength of 575 MPa, nearly 500 MPa higher than that of a single CoZr3 intermetallic compound, representing an increase of more than 7 times. This successfully achieves a synergy between ZTE properties and high strength.

[0038] The CoZr prepared in Example 1 3.8 and commercial Fe 0.65 Ni 0.35 Invar alloys were immersed in 3.5 wt% NaCl solution for up to 26 days, and the morphological evolution during this process was observed. The results are as follows: Figure 5 As shown, the sample with x=3.8 (Example 1) maintained its intact metallic luster throughout, without any pitting, rust spots, or discoloration. In contrast, the Invar alloy began to show localized rust spots on the 5th day of immersion, and by the 26th day, the surface was completely covered with red and green corrosion products, and the solution became noticeably turbid. This comparative result clearly demonstrates that Example 1 exhibits significantly superior surface stability and corrosion resistance in a chloride-containing environment.

[0039] The CoZr prepared in Example 1 3.8and commercial Fe 0.65 Ni 0.35 Electrochemical tests were performed on Invar alloy in 3.5 wt% NaCl solution, and the results are as follows: Figure 6 As shown in Figure (a), the open-circuit potential-time curves show that Example 1 exhibits a rapid potential response, stabilizing at a relatively high potential of approximately -0.18 V at the start of the test, and exhibiting minimal potential fluctuations during the subsequent 30 minutes of testing, demonstrating excellent electrochemical stability. Furthermore, Figure (b) reveals that the self-corrosion potential of Example 1 is -0.26 V, significantly higher than the -0.59 V of the Invar alloy, with a self-corrosion current density of 1.74 × 10⁻⁶ V. -7 A·cm -2 Compared to the self-corrosion current density of Invar alloy, which is 2.0 × 10⁻⁶, -6 A·cm -2 This represents a reduction of an order of magnitude. According to Faraday's law, corrosion current density directly reflects the corrosion rate of a material, and this result also indicates that the corrosion rate of Example 1 is significantly slower in a real corrosive environment.

[0040] The above experiments demonstrate that this invention, through its innovative in-situ two-phase composite design, achieves [the desired effect] in CoZr [a specific process / structure]. x The system successfully achieved synergistic optimization of thermal expansion, mechanical properties, and corrosion resistance. In particular, CoZr... 3.8 The composition achieves a balance between zero thermal expansion over an ultra-wide temperature range, significant toughness, and excellent corrosion resistance, solving the problem of existing materials having single or mutually restrictive properties, and has significant engineering application value.

[0041] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A CoZr compound possessing both ultra-wide temperature range with zero thermal expansion and corrosion resistance. x The matrix composite material is characterized by, The material consists of an orthorhombic CoZr3 phase and a hexagonal α-Zr phase, and its chemical formula is CoZr. x , where x = 3.4~4.

2.

2. The composite material according to claim 1, characterized in that, In atomic percentage, x = 3.

8.

3. The composite material according to claim 2, characterized in that, The material exhibits zero thermal expansion in the temperature range of 120~680 K.

4. The composite material according to claim 2, characterized in that, The material has a compressive strength ≥ 575 MPa and the ability to undergo plastic deformation.

5. The composite material according to claim 2, characterized in that, The material exhibits a self-corrosion potential ≥ -0.26 V and a self-corrosion current density ≤ 1.74 × 10⁻⁶ V in a 3.5 wt% NaCl solution. -7 A·cm -2 .

6. The method for preparing the composite material according to any one of claims 1 to 5, characterized in that, The electric arc melting method includes the following steps: (1) Weigh out Co and Zr raw materials according to stoichiometry; (2) Arc melting is carried out under argon protection, and the melting is repeated more than 4 times to ensure uniform composition; (3) The obtained ingot was annealed at 850 °C for 5 days to obtain a composite material with a uniform two-phase structure.

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