A Ferrochromium-Based Composite Material and Its Preparation Method

Abstract

This invention provides an iron-chromium-based composite material and its preparation method. The material consists of a matrix material, a reinforcing phase, and unavoidable impurities. The matrix material is composed of Fe, Cr, and Ti elements, and the reinforcing phase is TiB2. By adding excess Ti, the occurrence of the (Fe,Cr)2B phase in the TiB2 / Fe-Cr composite material is effectively suppressed, resulting in a significant improvement in the material's mechanical properties. Specifically, the hardness is significantly increased to 861 HV0.5, and the fracture toughness is improved from 2.91 MPa·m. 1 / 2 (K c1 Increased to 5.47 MPa·m 1 / 2 The aforementioned materials and preparation methods fill a technological gap and lay the foundation for the potential application of TiB2 particle-reinforced metal matrix composites under ultra-high temperature and complex load conditions.

Description

Technical Field

[0001] This invention relates to the field of metallic materials, and in particular, to an iron-chromium-based composite material and its preparation method. Background Technology

[0002] In recent years, metal matrix composites (MMCs) have attracted widespread attention due to their excellent designability and comprehensive performance. MMCs combine the high ductility and toughness of the metal matrix with the high strength and high elastic modulus of the reinforcing phase, exhibiting excellent properties such as high specific strength, high specific stiffness, wear resistance, and high temperature resistance. They have broad application prospects in aerospace, military, automotive, and optical industries. Meanwhile, combining high-strength, high-melting-point ceramic particles with traditional high-temperature alloys has become an important approach to improving high-temperature mechanical properties. Cho investigated the high-temperature mechanical properties of titanium carbide (TiC) reinforced stainless steel composites. The results showed that the TiC-SUS431 composite exhibited higher ductility and stronger compressive strength at high temperatures, and TiC successfully suppressed the softening of the SUS431 matrix.

[0003] Literature indicates that TiB2 possesses a high microhardness and melting point of 3400 HV and 3225 °C, respectively, exhibiting excellent wear resistance and thermodynamic stability, as well as good wetting properties with molten metal. Therefore, TiB2 particle-reinforced composites have gradually become a research hotspot. Tjong's research found that the addition of TiB2 can improve the strength and wear resistance of 304 stainless steel. Furthermore, Zhang prepared Fe-Ti-Cr-BC composite coatings using laser cladding, finding that adding Cr effectively improved the coating's hardness, wear resistance, and high-temperature oxidation resistance. However, due to the strong bonding between Cr and B, a brittle Cr2B intermediate phase is easily formed, leading to a deterioration in mechanical properties. Summary of the Invention

[0004] The purpose of this invention is to provide an iron-chromium based composite material to solve the technical problem of deteriorated mechanical properties of existing TiB2 / Fe-Cr composite materials due to the large amount of brittle Cr2B intermediate phase.

[0005] To achieve the above objectives, the present invention proposes the following technical solution:

[0006] The first aspect of this application is to provide an iron-chromium-based composite material, which consists of a matrix material, a reinforcing phase, and unavoidable impurities, wherein the matrix material is composed of Fe, Cr, and Ti elements, and the reinforcing phase is TiB2.

[0007] Furthermore, the mass fractions of the above elements are as follows: Cr: 25.04%–25.15%; Ti: 9.35%–15.54%; B: 2.97%–3.08%; the remainder is Fe and unavoidable impurities.

[0008] Furthermore, the nominal content of Ti in the matrix material is 5wt% to 7wt%.

[0009] Furthermore, the nominal content of Ti in the matrix material is 6 wt%.

[0010] Furthermore, the reduced volume fraction of the reinforcing phase is 13% to 18%.

[0011] Furthermore, the reinforcing phase includes primary TiB2 and dendritic eutectic TiB2.

[0012] Furthermore, the morphology of the nascent TiB2 is a regular polygon.

[0013] Furthermore, the surface oxide layer formed after the material is oxidized at high temperature includes a three-layer structure, namely an outer TiO2 layer, a transition layer Cr2O3 layer, and an inner TiO2 layer.

[0014] Furthermore, the TiB2 is generated through an in-situ elemental reaction.

[0015] A second aspect of this application is to provide a method for preparing the above-mentioned material, comprising the following steps:

[0016] The raw materials, iron, chromium, iron boron, and titanium, are mixed and melted in a vacuum electric arc melting furnace, with the voltage set at 350V, the current at 220mA, and the vacuum degree at 1×10⁻⁶. -4 MPa, 0.05MPa argon protective gas;

[0017] When the metal melts into a liquid state, the power is turned off, and the liquid metal cools and solidifies into an alloy ingot;

[0018] Flip the alloy ingot and remelt it;

[0019] Repeat the above melting and solidification process 4-5 times in total;

[0020] The smelting process is complete, yielding alloy ingots.

[0021] Beneficial effects:

[0022] As can be seen from the above technical solutions, the technical solution of the present invention provides a novel alloy composition. By adding an excessive amount of Ti, the occurrence of the (Fe,Cr)2B phase in the TiB2 / Fe-Cr composite material is effectively suppressed, resulting in a significant improvement in the mechanical properties of the material, with the hardness significantly increased to 861 HV. 0.5The fracture toughness increased from 2.91 MPa·m 1 / 2 (K c1 Increased to 5.47 MPa·m 1 / 2 The aforementioned materials fill a gap in the application of TiB2 particle-reinforced metal matrix composites under ultra-high temperatures and complex loads. For example, they can be used as heat-resistant and wear-resistant materials in metallurgy, power, and mining, such as in rolling mill rolls, hot ore screens, burner nozzles, and preheating chamber burners. They can also be developed into components for ultra-supercritical turbine units and aero-engines, showing broad application prospects in metallurgy, thermal power generation, and aerospace.

[0023] It should be understood that all combinations of the foregoing concepts and the additional concepts described in more detail below can be considered part of the inventive subject matter of this disclosure, provided that such concepts do not contradict each other.

[0024] The foregoing and other aspects, embodiments, and features of the teachings of the present invention will be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the invention, such as features and / or beneficial effects of exemplary embodiments, will become apparent from the following description or may be learned through practice of specific embodiments according to the teachings of the present invention. Attached Figure Description

[0025] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the invention will now be described by way of example and with reference to the accompanying drawings, wherein:

[0026] Figure 1 SEM images of two types of as-cast steel samples: (a,c,e) on the left is the SEM image of S1, and (b,d,f) on the right is the SEM image of S2.

[0027] Figure 2 Oxidation kinetic curves for two types of as-cast steel samples;

[0028] Figure 3 The microhardness and fracture toughness of two experimental steel as-cast samples are shown.

[0029] Figure 4 The cross-sectional morphology of two experimental steel as-cast samples after oxidation at 900℃ for 100h is shown: (a) is the cross-sectional view of S1; (b) is the cross-sectional view of S2.

[0030] Figure 5 This is a schematic diagram of the high-temperature oxidation mechanism of sample S1;

[0031] Figure 6 This is a schematic diagram of the high-temperature oxidation mechanism of sample S2. Detailed Implementation

[0032] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0033] Various aspects of the invention are described in this disclosure with reference to the accompanying drawings, in which numerous illustrative embodiments are shown. The embodiments of this disclosure are not necessarily defined to include all aspects of the invention. It should be understood that the various concepts and embodiments described above, as well as those described in more detail below, can be implemented in any of many ways, because the concepts and embodiments disclosed herein are not limited to any particular implementation. Furthermore, some aspects of the invention disclosed may be used alone or in any suitable combination with other aspects of the invention disclosed.

[0034] An embodiment of the present invention provides an iron-chromium-based composite material, which is composed of a matrix material, a reinforcing phase, and unavoidable impurities, wherein the matrix material is composed of Fe, Cr, and Ti elements, and the reinforcing phase is TiB2.

[0035] The above embodiment represents a novel alloy composition. By adding Ti, the microstructure of the TiB2 / Fe-Cr composite material is controlled, suppressing the formation of the mesophase Cr2B. The material obtained through this method effectively eliminates the (Fe,Cr)2B mesophase while increasing the Cr content in the matrix, resulting in a significant improvement in the mechanical properties of the final material.

[0036] In this embodiment of the invention, the mass fractions of the above-mentioned elements are as follows: Cr: 25.04%–25.15%; Ti: 9.35%–15.54%; B: 2.97%–3.08%; the remainder is Fe and unavoidable impurities. In the above composition, the Ti content is significantly higher than that of traditional iron-chromium alloys, resulting in a relative reduction in the Cr content. This facilitates the precipitation and growth of TiB2 during elemental bonding, effectively inhibiting the formation of (Fe,Cr)2B and simultaneously increasing the Cr content in the matrix.

[0037] The aforementioned Ti is present in both the matrix material and the reinforcing phase, wherein the nominal content of Ti in the matrix material is 5 wt% to 7 wt%, preferably 6 wt%.

[0038] Compared to the conventional microstructure without the addition of excessive Ti, the aforementioned reinforcing phase exhibits significant changes in content and morphology. In terms of content, the reduced volume fraction of the reinforcing phase is 13%–18%, and in terms of morphology, the reinforcing phase comprises regular polygonal primary TiB2 and dendritic eutectic TiB2.

[0039] The high-temperature resistance of iron-chromium based composite materials is crucial. In this embodiment, the oxide layer formed on the surface of the material after high-temperature oxidation has a three-layer structure: an outer TiO2 layer, a transition layer Cr2O3 layer, and an inner TiO2 layer. The presence of the inner TiO2 layer indicates that the oxidation resistance of this embodiment is slightly poor. Therefore, it is necessary to strictly control the Ti content so that the addition of Ti can both inhibit the formation of (Fe,Cr)2B and ensure high-temperature oxidation performance.

[0040] Embodiments of the present invention also provide a method for preparing the above-mentioned material, comprising the following steps:

[0041] The raw materials, iron, chromium, iron boron, and titanium, are mixed and melted in a vacuum electric arc melting furnace, with the voltage set at 350V, the current at 220mA, and the vacuum degree at 1×10⁻⁶. -4 MPa, 0.05MPa argon protective gas;

[0042] When the metal melts into a liquid state, the power is turned off, and the liquid metal cools and solidifies into an alloy ingot;

[0043] Flip the alloy ingot and remelt it;

[0044] Repeat the above melting and solidification process 4-5 times in total;

[0045] The smelting process is complete, yielding alloy ingots.

[0046] The alloy obtained by the above smelting method has a uniform composition and the particles are evenly distributed in the matrix. The above process involves in-situ synthesis reactions of atomic elements, that is, the reinforcing phase of the TiB2-reinforced iron-chromium-based composite material is synthesized in situ, which avoids pollution problems, and the preparation process is simple and the production cost is relatively low.

[0047] The following section compares the alloy ingots prepared using the smelting methods described in the above embodiments, with the traditional iron-chromium-based alloy composition S1 and the composition S2 of the present invention listed in Table 1.

[0048] Table 1

[0049]

[0050] Figure 1 SEM images of two types of as-cast steel samples. Figure 1 As shown in (a), the microstructure of the S1 as-cast sample mainly consists of radial petal-shaped particles, fine hexagonal particles, gray stripes, and a light gray matrix. The petal-shaped particles and fine hexagonal particles in the S1 sample are TiB2, and the gray stripes are (Fe,Cr)2B. Figure 1 As shown in (b), the S2 as-cast sample mainly contains dark gray hexagonal particles, irregular gray dendrites, and a light gray matrix; from Figure 1(e,f) clearly shows fine hexagonal particles (S1) and irregular gray dendrites (S2), which are TiB2 phase. No gray strip (Fe,Cr)2B phase was observed.

[0051] Both Cr and Ti can form borides with B, and their enthalpy of mixing (ΔH) mix The concentrations were -279.49 kJ / mol (TiB2) and -31 kJ / mol (Cr2B), respectively. During the solidification of the TiB2(p) / Fe-Cr based composite, the two phases competed for nucleation and growth. When the relative Cr content was high (e.g., in sample S1), elongated (Fe,Cr)2B phases formed first, followed by the precipitation of a small amount of radially petal-shaped primary TiB2 phase. Increasing the Ti content (e.g., in sample S2) further promoted the sequential precipitation and growth of hexagonal primary TiB2 particles and dendritic eutectic TiB2, effectively inhibiting the formation of (Fe,Cr)2B while simultaneously increasing the Cr content in the matrix.

[0052] Figure 2 The microhardness and fracture toughness of the two samples are shown. The microhardness of sample S2 is 860 HV. 0.5 Compared to S1 (401HV) 0.5 This represents a significant improvement. Compared to the S1 sample's 2.91 MPa·m... 1 / 2 (K c1 ) and 1.73 MPa·m 1 / 2 (K c2 The fracture toughness of sample S2 was also significantly improved, K c1 and K c2 5.47 MPa·m 1 / 2 and 3.30 MPa·m 1 / 2 As mentioned earlier, the addition of excess Ti suppressed the non-uniformly distributed, coarse, elongated (Fe,Cr)₂B brittle phase, promoting the formation and random distribution of higher-toughness primary TiB₂. Considering that Cr element strengthens the matrix through solid solution, and that TiB₂ has a high bonding energy with the matrix, when a crack encounters and penetrates the eutectic TiB₂, energy is released, delaying crack growth. Subsequently, interfacial debonding also consumes energy, slowing down the crack propagation rate and changing the crack propagation direction, thereby achieving a dual improvement in microhardness and fracture toughness.

[0053] Figure 3 These are the high-temperature oxidation kinetic curves for two types of as-cast steel samples. The S1 sample undergoes relatively slower high-temperature oxidation, with an oxidation increment (ΔW). S1 =2.33mg / cm 3 ) lower than S2((ΔW S2 =4.03mg / cm 3This indicates that the S1 experimental steel has superior high-temperature oxidation resistance. Referring to the national standard "Determination of Oxidation Resistance of Steel" (GB / T 13303-91), the average oxidation rates of samples S1 and S2 were 0.029 g / m³, respectively. 2 ·h and 0.044 g / m 2 Both samples exhibited complete antioxidant properties (average oxidation rate <0.1 g / m²). 2 ·h).

[0054] Figure 4 (a) and Figure 4 (b) shows the cross-sectional morphology of samples S1 and S2 after oxidation at 900℃ for 100h. As shown in the figure, the oxide layer on the surface of sample S1 is a double-layer structure of rutile TiO2 outer layer (P1) + dense Cr2O3 inner layer (P2), and its average thickness (15.6μm) is smaller than that of sample S2 (18.7μm). The oxide layer on the high-temperature surface of sample S2 has a three-layer structure: rutile TiO2 outer layer (P1) + dense Cr2O3 transition layer (P2) + TiO2 inner layer (P3), and there is a large-sized (13.23μm long) TiO2 oxide intrusion on the substrate side.

[0055] The high-temperature oxidation mechanism is explained below with reference to the accompanying diagram. For example... Figure 5 As shown in (a), during the initial stage of oxidation, the surface of sample S1 is directly exposed to high temperature and air, rapidly forming a dense Cr2O3 oxide layer. Simultaneously, the B2O3 generated by the reaction of (Fe,Cr)2B with oxygen evaporates at 1000℃, leaving pores that are filled by Cr2O3 formed from Cr+ and O- ions in (Fe,Cr)2B. Figure 5 (a) In the later stages of oxidation, the continuous Cr2O3 oxide layer blocks the diffusion of oxygen into the matrix, inhibiting the growth of the oxide layer, thus the oxidation is relatively slow; Ti in the matrix + Ions pass through the Cr2O3 layer and react with O in the air. - An ionic reaction occurs, forming a TiO2 layer on the Cr2O3 surface. O- ions from the air pass through the Cr2O3 layer and react with the Ti in the matrix. + Ions form TiO2 oxidation products in structurally weak regions such as grain boundaries, interfaces, and pores, such as... Figure 5 (b)

[0056] Compared to sample S1, sample S2 has a higher Ti content, effectively inhibiting the formation of (Fe,Cr)₂B and promoting the precipitation of coarse primary TiB₂ particles. The interface between sample S2 and the matrix is ​​O. - Ions expand inward, providing channels. Figure 6This is a schematic diagram of the high-temperature oxidation mechanism of sample S2. Similar to sample S1, rutile TiO2 and dense Cr2O3 oxide layers rapidly form on the surface during the early and middle stages of oxidation. The difference is that TiB2 and O... - The ions reacted to form B₂O₃ and TiO₂. The pores left by the volatilization of B₂O₃ were filled by TiO₂. - Ions pass through the Cr2O3 layer and interact with Ti in the matrix. + Ions formed a discontinuous TiO2 layer, such as Figure 6 (a,b); In the mid-to-late stages of oxidation, the Ti element content in the matrix is ​​higher than that in S1, and due to the presence of TiB2 particles and continuous oxidation, O - Ions diffuse more easily through the Cr2O3 layer into the matrix, eventually forming a continuous TiO2 layer, such as Figure 6 (c) In the later stages of oxidation, O - Ions continuously invade the matrix (e.g., through structurally weak regions such as the interface of primary TiB2 particles, matrix grain boundaries, and pores) Figure 6 (d) generates long strips or clumps of TiO2 intrusions.

[0057] Therefore, comparing the S1 and S2 samples above, it can be seen that the TiB2 particle morphology in the sample provided in the embodiment of the present invention changes from petal-shaped to regular polygonal, and the microhardness changes from 400 HV. 0.5 Significantly increased to 860 HV 0.5 The fracture toughness increased from 2.91 MPa·m 1 / 2 (K c1 The pressure was significantly increased to 5.47 MPa·m. 1 / 2 Although the interface between the coarse nascent TiB2 particles and the matrix provides oxygen diffusion channels, and the surface oxide layer changes from a bilayer structure (rutile TiO2 outer layer + Cr2O3 transition layer) to a trilayer structure (rutile TiO2 outer layer + Cr2O3 transition layer + TiO2 inner layer), resulting in a significant decrease in oxidation resistance at 900℃ and an increase in oxidation gain rate of 307.4%, it still possesses complete oxidation resistance (average oxidation rate <0.1 g / m³). 2 ·h).

[0058] In summary, the alloys in the embodiments of the present invention have at least the following advantages:

[0059] (1) The addition of excess Ti (6wt%) effectively suppressed the (Fe,Cr)2B phase in the TiB2 / Fe-Cr composite material. The morphology of the primary TiB2 particles changed from petal-like to hexagonal block-like, and the microhardness was significantly increased to 861 HV. 0.5 The fracture toughness increased from 2.91 MPa·m 1 / 2 (K c1 Increased to 5.47 MPa·m 1 / 2;

[0060] (2) Excessive Ti addition altered the high-temperature oxidation behavior of the TiB2(p) / Fe-Cr composite material. The surface oxide layer structure changed from a bilayer (rutile TiO2 outer layer + dense Cr2O3 inner layer) to a trilayer (rutile TiO2 outer layer + dense Cr2O3 transition layer + TiO2 inner layer). The main reason is likely that the interface between the coarse primary TiB2 particles and the matrix provides a channel for O diffusion, weakening the effect of the Cr2O3 transition layer on O. - Ion blocking ability. The oxide gain rate of this alloy increased by 307.4% at 900℃, the average oxide layer thickness increased by 3.1μm, and the size of oxide intrusions in the matrix increased from 6.85μm to 13.23μm, but the TiB2 / Fe-Cr composite material still has complete oxidation resistance at 900℃;

[0061] (3) The embodiments of the present invention show the effect of Ti content on various aspects, which has positive reference value for the application and microstructure control of this type of composite material. A new type of TiB2 ceramic particle reinforced iron-chromium matrix composite material with low cost, high temperature resistance and excellent mechanical properties has been developed, which fills the gap in the application of TiB2 particle reinforced metal matrix composite material under ultra-high temperature and complex load.

[0062] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A ferrochromium-based composite material, characterized in that: The material consists of a matrix material, a reinforcing phase, and unavoidable impurities. The matrix material is composed of Fe, Cr, and Ti elements, and the reinforcing phase is TiB2. The mass fractions of the above elements are as follows: Cr: 25.04%~25.15%; Ti: 9.35%~15.54%; B: 2.97%~3.08%; the remainder is Fe and unavoidable impurities.

2. The material according to claim 1, characterized in that: The nominal content of Ti in the matrix material is 5wt%~7wt%.

3. The material according to claim 1, characterized in that: The nominal content of Ti in the matrix material is 6 wt%.

4. The material according to claim 1, characterized in that: The reduced volume fraction of the reinforcing phase is 13% to 18%.

5. The material according to claim 1, characterized in that: The reinforcing phase includes primary TiB2 and dendritic eutectic TiB2.

6. The material according to claim 5, characterized in that: The nascent TiB2 has a regular polygonal shape.

7. The material according to claim 1, characterized in that: The oxide layer formed on the surface of the material after high-temperature oxidation includes a three-layer structure: an outer TiO2 layer, a transition layer Cr2O3 layer, and an inner TiO2 layer.

8. The material according to claim 1, characterized in that: The TiB2 is generated through an in-situ reaction of elements.

9. A method for preparing the material according to any one of claims 1-8, characterized in that: Includes the following steps: The raw materials iron, chromium, iron boron, and titanium are mixed and melted in a vacuum electric arc melting furnace, with the voltage set at 350V, the current at 220mA, and the melting vacuum degree at 1×10⁻⁶. -4 MPa, 0.05MPa argon protective gas; When the metal melts into a liquid state, the power is turned off, and the liquid metal cools and solidifies into an alloy ingot; Flip the alloy ingot and remelt it; Repeat the above melting and solidification process 4-5 times in total; The smelting process is complete, yielding alloy ingots.

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