Design / preparation method for corrosion-resistant cemented carbide with multi-principal-element binder phase, and use of same

Abstract

Disclosed in the present invention are a design / preparation method for a corrosion-resistant cemented carbide with a multi-principal-element binder phase, and the use of same. The design method comprises: acquiring a target corrosive service environment, and formulating a target cemented carbide system; establishing a phase diagram thermodynamic database; performing Pourbaix diagram calculation so as to acquire a predicted corrosion product, an immunity region and a passivation region, and selecting a multi-principal-element alloy as a binder phase; performing phase diagram calculation, so as to acquire phase composition and phase parameters; and using the multi-principal-element alloy, the phase composition and the phase parameters as a design output. By means of the design method provided in the present invention, the elemental composition and phase structure in a binder phase can be clarified, and under the guidance of a Pourbaix diagram and a phase diagram, a rational preparation process for a corrosion-resistant cemented carbide is designed, thereby improving the preparation efficiency of the cemented carbide and establishing an intrinsic relationship among the constituent ingredients, structure and properties of the corrosion-resistant cemented carbide.

Description

Design / Preparation Methods and Applications of Corrosion-Resistant Multi-Principal-Element Binder Phase Hard Alloys

[0001] This application is based on and claims priority to Chinese patent applications filed on October 31, 2024, with application number 2024115467208 entitled "A Design Method for a Corrosion-Resistant Multi-Principal-Element Binder Phase Hard Alloy" and filed on January 8, 2025, with application number 2025100337140 entitled "Design / Preparation Method and Application of Corrosion-Resistant Multi-Principal-Element Binder Phase Hard Alloy". Technical Field

[0002] This invention relates to the field of cemented carbide technology, and in particular to a design / preparation method and application of a corrosion-resistant multi-principal-element binder cemented carbide. Background Technology

[0003] The increasing demand for energy has spurred deep drilling activities in continental and marine crust, posing new challenges to the durability of drilling tools. Hard alloys, due to their high hardness, wear resistance, heat resistance, and corrosion resistance, are widely used in marine drilling equipment. For typical WC-Co hard alloys, excessive corrosion can damage the overall structural integrity due to binder phase damage, leading to reduced strength and premature fracture of the carbide skeleton. Therefore, optimizing the corrosion resistance of hard alloys is crucial to ensuring the service life of drilling components. The corrosion behavior of hard alloys is influenced by the phase structure and chemical composition of the metallic binder phase. In recent years, multi-principal element alloys have attracted attention for their excellent corrosion resistance due to the combination of controllable phase structures (such as FCC) and the benefits of surface passivation from chemical compositions (such as Cr). CoCrNi multi-principal element alloys exhibit good corrosion resistance and toughness, but their application as a binder phase in hard alloys has not yet been studied. Co, as a traditional binder phase, provides good wettability and bonding. Ni exhibits greater ductility and corrosion resistance, while Cr offers superior oxidation and corrosion resistance. Furthermore, the CoCrNi alloy binder phase and the hard phase WC demonstrate excellent wettability. Therefore, introducing a CoCrNi multi-element alloy as a binder phase into the cemented carbide system is considered to enhance its corrosion resistance.

[0004] The corrosion behavior of cemented carbides is also related to the corrosive medium; different corrosive environments lead to differences in corrosion mechanisms and corrosion products. It is well known that for the corrosion of typical WC-Co cemented carbides, Co is readily soluble in acidic and neutral solutions, while WC is relatively stable and does not readily corrode. In alkaline solutions, there is no consensus on the dissolution process of Co and WC. Furthermore, the formation of a passivation film in the corrosive medium also affects the corrosion resistance of cemented carbides. In the preparation of corrosion-resistant cemented carbides, simply adding elements is unlikely to yield satisfactory results; therefore, it is crucial to rationally design cemented carbides by introducing novel multi-component binder phases combined with theoretical calculations. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a design / preparation method and application of corrosion-resistant multi-principal-element binder phase cemented carbide.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] In a first aspect, the present invention provides a design method for corrosion-resistant multi-principal-element binder phase cemented carbide, comprising:

[0008] Obtain the target corrosive service environment, and formulate a target cemented carbide system based on the target corrosive service environment. The target cemented carbide system includes hard corresponding elements and binder corresponding elements.

[0009] Establish a phase diagram thermodynamic database for the target cemented carbide system;

[0010] Based on the phase diagram thermodynamic database, Pourbaix diagram calculations are performed on the target cemented carbide system to obtain the predicted corrosion products of the target cemented carbide system under the target corrosive service environment, as well as the immune region and passivation region corresponding to the predicted corrosion products. Multi-principal alloys are selected as the binder phase from the binder phase elements.

[0011] Based on the phase diagram thermodynamic database, phase diagram calculations are performed on the target cemented carbide system to obtain phase composition and phase parameters. The phase composition includes the proportion of the binder phase element and the proportion of the cemented phase to the binder phase. The phase parameters include the heat treatment temperature.

[0012] The multi-principal alloy, phase composition, and phase parameters are used as the design output for the corrosion-resistant multi-principal binder phase cemented carbide.

[0013] Secondly, the present invention also provides a method for preparing a corrosion-resistant multi-principal-element binder phase cemented carbide, comprising:

[0014] The above design method is used to obtain the design output under the target corrosive service environment;

[0015] Based on the design output, a corrosion-resistant multi-principal-element binder phase cemented carbide was prepared.

[0016] Thirdly, the present invention also provides the application of the corrosion-resistant multi-principal-element cemented carbide prepared by the above preparation method in the manufacture of marine drilling equipment.

[0017] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include at least the following:

[0018] The technical solution provided by this invention establishes a thermodynamic database and uses methods for Pourbaix diagram and phase diagram calculations based on the electrochemical Nernst equation. It predicts potential corrosion products and the corrosion-immune and passivation zones, and verifies these predictions through micro-area electrochemical experiments. The invention selects the optimal multi-principal element binder phase for different binder phases in cemented carbide, thereby obtaining a WC-based cemented carbide with excellent corrosion resistance. The provided design method clearly defines the elemental composition and phase structure of the binder phase. Using Pourbaix and phase diagrams, it guides the design of a reasonable corrosion-resistant cemented carbide preparation process, improving the preparation efficiency of cemented carbide and establishing the intrinsic relationship between composition, structure, and performance of corrosion-resistant cemented carbide. Micro-area electrochemical testing verifies the efficient design of cemented carbide with improved corrosion resistance, and guides the design and preparation of high-performance corrosion-resistant multi-principal element cemented carbide from the perspective of corrosion product prediction.

[0019] The above description is merely an overview of the technical solution of the present invention. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below in conjunction with detailed drawings. Attached Figure Description

[0020] Figure 1 is a schematic diagram of the design and verification process of corrosion-resistant multi-principal-element binder phase cemented carbide provided in a typical embodiment of the present invention.

[0021] Figure 2a is a Pourbaix diagram of the W-Co system under different electrode potentials and pH values ​​provided in a typical embodiment of the present invention;

[0022] Figure 2b is a Pourbaix diagram of the W-Co-Cr-Ni system under different electrode potentials and pH values ​​provided in a typical embodiment of the present invention.

[0023] Figure 3 is a vertical cross-sectional view of the composition of the W-Co-Cr-Ni-C system at different temperatures as the carbon content of the system varies with a typical embodiment of the present invention.

[0024] Figures 4a-g are the composition and structure diagrams of the prepared WC-CoCrNi system cemented carbide TEM corresponding to a typical embodiment of the present invention;

[0025] Figure 5a is an SVET test diagram of the WC-CoCrNi system in 3.5% NaCl at pH=10, provided in a typical embodiment of the present invention;

[0026] Figure 5b is an SVET test diagram of a control classic WC-Co system cemented carbide sample in 3.5% NaCl at pH=10, provided in a typical embodiment of the present invention.

[0027] Figure 5c is a LEIS test diagram of the WC-CoCrNi system in 3.5% NaCl at pH=10, provided in a typical embodiment of the present invention;

[0028] Figure 5d is a LEIS test diagram of a control classic WC-Co system cemented carbide sample in 3.5% NaCl at pH=10, provided in a typical embodiment of the present invention. Detailed Implementation

[0029] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0030] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0031] In the field of cemented carbide preparation, some existing technologies use traditional enumeration methods to prepare high-performance corrosion-resistant cemented carbides. For example, Chinese invention patent CN101974715A discloses a WC-Co cemented carbide and its preparation method. This method mainly targets WC cemented carbides, using the traditional binder phase Co with a small amount of Y. It provides a reference for cemented carbide preparation processes, but it cannot systematically adjust or redesign the corresponding alloys for different corrosion environments. Chinese invention patent CN102031436A discloses a method to improve the corrosion resistance of WC-Co cemented carbides by introducing rare earth components to enhance corrosion resistance, but it does not elaborate on the material design, and the corrosion detection methods are relatively traditional. It does not reveal the corrosion mechanism or the essential reason for the improved corrosion resistance.

[0032] Therefore, based on existing research in this field, this invention combines theoretical calculations with micro-region characterization methods to achieve integrated design and preparation of WC cemented carbide material systems, aiming to achieve low-cost, efficient, and rapid material design.

[0033] The purpose of this invention is to provide a design and verification method for corrosion-resistant multi-principal-element binder phase cemented carbides.

[0034] Hard alloys are mainly composed of a hard phase and a binder phase. When hard alloy composites are in corrosive service environments, the potential difference between the binder and hard phases makes them prone to galvanic corrosion. This leads to the corrosion and dissolution of the binder phase, weakening the supporting role of the hard phase as a framework. Ultimately, this affects the performance matching between the hard and binder phases, resulting in failure. Corrosion-resistant multi-principal element alloys are introduced as binder phases to improve the overall corrosion resistance of hard alloys and address the short service life of traditional hard alloys in corrosive environments. Pourbaix plots are a reliable tool for studying the corrosion characteristics of alloys. Using Pourbaix calculations to guide experiments helps accelerate material design and compensates for the shortcomings of intelligent design for corrosion-resistant hard alloy materials.

[0035] In addition, using the CALPHAD method to calculate phase diagrams can further accelerate the design of cemented carbide materials. The phase structure of the binder phase also affects corrosion resistance, and the phase diagram guides the selection of appropriate phase ranges and sintering temperatures during sample preparation.

[0036] Based on the above technical concept, as shown in Figure 1, this embodiment of the invention provides a design method for corrosion-resistant multi-principal-element binder phase cemented carbide, which includes the following steps:

[0037] Obtain the target corrosive service environment, and formulate a target cemented carbide system based on the target corrosive service environment. The target cemented carbide system includes hard corresponding elements and binder corresponding elements.

[0038] Establish a phase diagram thermodynamic database for the target cemented carbide system;

[0039] Based on the phase diagram thermodynamic database, Pourbaix diagram calculations are performed on the target cemented carbide system to obtain the predicted corrosion products of the target cemented carbide system under the target corrosive service environment, as well as the immune region and passivation region corresponding to the predicted corrosion products. Multi-principal alloys are selected as the binder phase from the binder phase elements.

[0040] Based on the phase diagram thermodynamic database, phase diagram calculations are performed on the target cemented carbide system to obtain phase composition and phase parameters. The phase composition includes the proportion of the binder phase element and the proportion of the cemented phase to the binder phase. The phase parameters include the heat treatment temperature.

[0041] The multi-principal alloy, phase composition, and phase parameters are used as the design output for the corrosion-resistant multi-principal binder phase cemented carbide.

[0042] As a typical application example, the above overall design method can be implemented through the following steps:

[0043] (1) Select the type of binder phase element of multi-principal alloy according to the corrosive service environment and determine the target hard alloy system;

[0044] (2) Establish a phase diagram thermodynamic database for the target cemented carbide system;

[0045] (3) Based on the thermodynamic database, Pourbaix diagrams were calculated to obtain the relationship between the system potential and pH, as well as the immune and passivation regions corresponding to the corrosion products;

[0046] (4) Based on the constructed thermodynamic database of cemented carbide system, phase diagram calculations were performed to obtain the composition ranges corresponding to different phase compositions.

[0047] In a more specific application example, taking the WC-Co-Cr-Ni pentagonal system as an example, this embodiment of the invention targets a corrosion-resistant WC cemented carbide system. This system comprises a WC hard phase with excellent strength and toughness and a CoCrNi binder phase with excellent corrosion resistance, thereby forming a pentagonal thermodynamic database containing five elements: W, C, Co, Cr, and Ni. Based on the established database and combined with the CALPHAD method, a corrosion-resistant WC cemented carbide system was designed.

[0048] Regarding the specific range of elements that can be selected, in some embodiments, the hard phase elements include any combination of W, Ti, C, and N.

[0049] In some embodiments, the binder phase element includes any combination of more than one of Co, Cr, Ni, Fe, Al, and Mn.

[0050] Furthermore, regarding how to guide the design based on the Pourbaix diagram and phase diagram, in some implementations, the selection rules for the multi-principal alloy specifically include:

[0051] Select the required types and proportions of hard phase and binder phase elements according to the applicable environment;

[0052] The immune and passivation regions of the system were obtained by calculating using Pourbaix plots.

[0053] The immune zone is the non-corrosion region (blue) in a thermodynamically stable state below the equilibrium line of the Pourbaix diagram. The larger the immune zone, the stronger the material's resistance to corrosion and the better its corrosion resistance.

[0054] The passivation zone is the area where corrosion products such as oxides and hydroxides are generated (orange). Due to the formation of a dense, insoluble protective film on the metal surface, the passivation zone provides a certain degree of protection to the sample surface and significantly reduces metal corrosion. A large passivation zone area (the passivation film can form over a wider range of corresponding pH and potential, which is more conducive to protecting the sample surface) is beneficial to the material's corrosion resistance.

[0055] Compare the Pourbaix plots of different systems to predict their corrosion resistance, and select one or more samples with relatively larger immune and / or passivation regions.

[0056] In some implementation schemes, the selection rules for phase composition and phase parameters specifically include:

[0057] Calculate the phase diagram based on the corresponding system composition;

[0058] Based on the phase diagram calculation results, the normal microstructure WC+γ of cemented carbide is selected to avoid the adverse effects of abnormal microstructures (carbide, graphite phase) on the performance of cemented carbide.

[0059] Since the phase diagram calculation results show that there is no region containing only WC+γ, the region with the C content closest to the carbon-depleted phase to the graphite phase transition line is selected to avoid the influence of carbides as much as possible.

[0060] The liquidus line of the corresponding system is determined based on the phase diagram calculation results, which guides the determination of the sintering temperature.

[0061] Furthermore, regarding the process of establishing the Pourbaix diagram and phase diagram, in some implementations, the process of establishing the phase diagram thermodynamic database may specifically include:

[0062] Acquire thermodynamic data of a low-element system, wherein the elements in the low-element system are some of the elements in the target cemented carbide system;

[0063] A thermodynamic model was established to calculate the Gibbs free energy of multiple phases in the low-element system.

[0064] All calculation results are integrated and expanded to form a phase diagram thermodynamic database for the target cemented carbide system.

[0065] Taking the WC-Co-Cr-Ni pentagonal system as an example again, step (2) above can specifically include:

[0066] (2-1) Collect thermodynamic data of all pure components, binary and ternary systems included in the target cemented carbide system;

[0067] (2-2) Evaluate and screen the collected thermodynamic data;

[0068] (2-3) Based on reliable experimental phase diagrams and thermodynamic information, select appropriate thermodynamic models to describe the Gibbs free energy of different phases;

[0069] (2-4) Integrate the above-evaluated thermodynamic parameters and perform reasonable extrapolation to obtain a self-consistent Co-Cr-Ni-WC pentagonal phase diagram thermodynamic database.

[0070] In the above process, firstly, thermodynamic databases of pure components, binary systems, ternary systems, etc., of the target cemented carbide system are collected; then, based on the phase diagram calculation method, the system phase diagrams are drawn from low to high, and comparison and correction are performed. After evaluation and optimization, all the above parameters are organically integrated until a reliable Co-Cr-Ni-WC pentagonal thermodynamic database of the target cemented carbide is obtained.

[0071] In some implementations, the process of calculating the Pourbaix graph specifically includes:

[0072] Import the phase diagram thermodynamic database into the calculation software, and use the point calculation module to input the target composition of the target cemented carbide system to obtain the chemical potential of each element in the target composition.

[0073] Based on the Gibbs free energy of pure elements, the energy difference of each element in the target component is obtained through electrochemical reaction equations and Nernst equations and converted into potential difference values.

[0074] A multivariate Pourbaix diagram is obtained based on the superimposed pure element Pourbaix diagram. The change in Gibbs free energy caused by alloying is calculated, and the immune region and passivation region of the multivariate Pourbaix diagram are delineated.

[0075] The specific exemplary process of the above steps is as follows:

[0076] The single-element Pourbaix diagrams of the target cemented carbide system are calculated using the aforementioned thermodynamic database and Pourbaix diagram calculation software.

[0077] The calculation process involves selecting the elements involved in the system, inputting the electrode potential range and temperature parameters, and outputting all possible products.

[0078] After selecting and optimizing the products, a single-element Pourbaix plot is generated.

[0079] Import the system thermodynamic database into the phase diagram calculation software, input the target composition using the point calculation module, obtain the chemical potential of a single element of the target composition, and obtain the energy difference of each element in the target composition and convert it into a potential difference value by using the Gibbs free energy of pure elements as a reference, through electrochemical reaction equations and Nernst equations.

[0080] The Nernst equation is expressed as:

[0081] For any electrochemical reaction equation aA + bB = cC + dD

[0082] Among them, E θ The standard electrode potential is represented by R; the gas constant is represented by 8.31441 J / (K·mol); the temperature is represented by T; the number of electrons transferred in the electrode reaction is represented by n; and the Faraday constant is represented by 96.487 kJ / (V·mol).

[0083] The calculated potential difference value is then substituted into the Pourbaix plot for correction.

[0084] The Pourbaix diagrams of different single elements obtained by the above method are superimposed to obtain the Pourbaix diagram of the target system.

[0085] In addition, in step (4) above, the phase diagram of the target cemented carbide system can be calculated by combining the thermodynamic database and phase diagram calculation software;

[0086] Then, the composition range of different binder phases of the target cemented carbide system under different conditions is calculated based on the phase diagram, as shown in Figure 2a and Figure 2b.

[0087] Then, based on the phase diagram calculation results, the relationship between phase structure and composition and temperature was obtained to determine the liquid phase sintering temperature and the carbon content range of the system, as shown in Figure 3.

[0088] Finally, based on the phase structure, cemented carbide samples were prepared using powder metallurgy.

[0089] The prepared cemented carbide samples were subjected to structural verification and corrosion electrochemical performance testing, and the composition and preparation conditions of a corrosion-resistant multi-component binder phase cemented carbide were finally determined.

[0090] Phase diagrams intuitively reflect the relationship between material composition, temperature, and structure. Starting from the expected structure and performance of the material, the phase relationship of the target cemented carbide system under different sintering temperatures and carbon contents is obtained based on the phase diagram calculation method. By selecting a reasonable composition range, ideal corrosion-resistant cemented carbides can be efficiently screened.

[0091] In some implementations, the design method may further include the following verification steps:

[0092] Verification samples were prepared using powder sintering based on the multi-principal element alloy, phase composition, and phase parameters.

[0093] The microstructure and corrosion patterns of the verification samples were characterized to verify the effectiveness of the design output.

[0094] In some implementations, the characterization of the microstructure includes transmission electron microscopy (TEM) observation, and the characterization of the corrosion mode includes micro-area electrochemical experiments. TEM analysis of the designed and prepared samples reveals the rationality of the sample composition and structure design, while micro-area electrochemical experiments reveal the improvement in the electrochemical corrosion performance of the prepared samples at the microscale, thereby guiding the development and design of corrosion-resistant cemented carbides. For example, the composition and structure of the cemented carbide system can be predicted based on the phase diagram calculation of the thermodynamic database, and the composition and structure of the prepared cemented carbide system can be verified by TEM. The galvanic corrosion relationship between the hard phase and the binder phase can be measured using micro-area electrochemical testing methods, experimentally verifying the galvanic corrosion tendency and revealing the improvement in the corrosion resistance of the sample.

[0095] A second aspect of this invention also provides a method for preparing a corrosion-resistant multi-principal-element binder phase cemented carbide, comprising the following steps:

[0096] The design output under the target corrosive service environment is obtained by using the design method provided in any of the above embodiments;

[0097] Based on the design output, a corrosion-resistant multi-principal-element binder phase cemented carbide was prepared.

[0098] In some implementations, the preparation method may specifically include:

[0099] The binder phase powder and the hard phase powder are prepared according to the design output;

[0100] The powder is mixed according to the ratio of hard phase and binder phase output as described in the design, and then ball-milled and pressed to obtain a cemented carbide block sintered billet.

[0101] The cemented carbide bulk sintered billet is subjected to vacuum sintering to obtain the corrosion-resistant multi-principal-element cemented carbide.

[0102] As a specific example, the design and fabrication process of a complete corrosion-resistant multi-principal-element binder cemented carbide includes the following steps:

[0103] (1) Select a suitable multi-principal alloy as the binder phase based on the Pourbaix diagram;

[0104] (2) Calculate and determine the appropriate carbon content and sintering temperature based on the phase diagram;

[0105] (3) Mix the binder phase powder and the hard phase powder to obtain a mixed powder;

[0106] (4) The above mixed powder is wet ball-milled and pressed into shape to obtain a cemented carbide block sintered billet.

[0107] (5) Hard alloy samples were obtained by vacuum sintering.

[0108] Specific forming and sintering processes include:

[0109] High-energy ball milling was performed by adding the binder phase powder and the hard phase powder, wherein the powder was selected as WC, CoCrNi, Co, and C powder;

[0110] The pre-mixed powder was subjected to wet ball milling, with alcohol as the ball milling medium during the wet milling process. The ball-to-powder mass ratio was 8:1 to 12:1, and the ball milling time was 10-20 hours.

[0111] The ball-milled powder is shaped and sintered, the ball-milled mixed slurry is dried and sieved, and then pressed into shape under a pressing pressure of 120-180 MPa;

[0112] The maximum liquid phase sintering temperature is determined by the phase diagram, and the temperature is maintained for 0.5 to 3 hours.

[0113] A complete typical preparation process is as follows:

[0114] WC, CoCrNi, and Co powders were selected to prepare cemented carbide, wherein the ratio of cemented carbide powder to binder phase powder was 8:2.

[0115] Add the mixed powder to the molding agent paraffin; place it in a carbide ball milling jar with a ball-to-powder mass ratio of 10:1, add the ball milling media alcohol, and mill for 16 hours;

[0116] The pressing pressure during the subsequent pressing process is 150 MPa;

[0117] Based on the phase diagram, the maximum sintering temperature was determined to be 1450℃, and the temperature was held for 90 minutes to obtain a cemented carbide sample.

[0118] After the samples are prepared, the composition and structure of the corresponding cemented carbide system can be predicted based on the constructed cemented carbide system thermodynamic database. Combined with the TEM characterization results of the prepared cemented carbide, the rationality of the thermodynamic database prediction of the cemented carbide system can be verified, thus promoting the efficient design of cemented carbide systems.

[0119] By combining the Pourbaix diagram, the required pH and electrochemical test potential of the electrochemical test solution are selected; electrochemical tests are performed on the cemented carbide sample to obtain the overall and corrosion kinetic information of the cemented carbide, evaluate its corrosion resistance, and verify the corrosion resistance of the cemented carbide.

[0120] In a typical embodiment of the present invention, a corrosion-resistant multi-principal-element binder phase cemented carbide was designed, and the corrosion resistance of the cemented carbide samples was further verified. The composition and phase structure of the cemented carbide were fully considered. Pourbaix diagrams were used to calculate and predict the corrosion products of the corresponding cemented carbide system. Cemented carbide systems that generate the target protective corrosion products were screened. In the predicted corrosion products of the WC-CoCrNi system, the corresponding immune zone expansion and passivation corrosion products Cr2O3 and NiO were generated, as shown in Figure 3. The phase structure of the cemented carbide system was initially screened using a combination of phase diagram calculations and first-principles calculations. The phase diagram calculation results showed that WC and FCC structures CoCrNi and corresponding metal carbides were generated at corresponding sintering temperatures and composition ranges. Based on the selected phase structure and the composition range of the phase diagram, the experimental powder ratio was further designed. Simultaneously, the powder metallurgy preparation method and electrochemical corrosion resistance were tested. TEM was used to characterize the composition and structure of the prepared cemented carbide, and micro-area electrochemical testing was used to verify the galvanic corrosion characteristics of the hard phase and the binder phase. The design, rationale, and performance improvement of the prepared cemented carbide system were revealed through Pourbaix calculations, phase diagram calculations, experimental design, powder metallurgy, TEM, and micro-area electrochemical corrosion testing. This has important significance for the design of novel corrosion-resistant multi-principal-element binder phase cemented carbides.

[0121] A third aspect of this invention provides the application of the corrosion-resistant multi-principal-element binder phase cemented carbide prepared by the above-described method in the fabrication of marine drilling equipment. For example, according to the technical solution provided by this invention, a corrosion-resistant multi-element binder phase cemented carbide can be obtained, wherein the hard phase includes WC and the binder phase includes CoCrNi. The good compatibility and low corrosion tendency between the two give it excellent corrosion resistance, making it suitable for future drilling environments. More importantly, the verification conditions for the above-described corrosion-resistant multi-element binder phase cemented carbide are also determined based on the above-described design method.

[0122] The technical solution of the present invention will be further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only for illustrating the present invention and do not limit the scope of the present invention.

[0123] Example 1

[0124] This embodiment illustrates the overall process of designing and experimentally verifying a corrosion-resistant multi-principal-element binder phase cemented carbide, as detailed below:

[0125] (1) Determine the types of alloying elements based on the target multi-principal binder phase to obtain the target hard alloy system;

[0126] (2) Establish a thermodynamic database for the target cemented carbide system;

[0127] (3) Based on the thermodynamic database, calculate the Pourbaix diagram of the W-Co-Cr-Ni system at different electrode potentials and pH to obtain the immune region and passivation region;

[0128] (4) Calculate the phase diagram of cemented carbide based on the thermodynamic database W-Co-Cr-Ni-C to obtain the composition range of different phase formations;

[0129] (5) Prepare cemented carbide samples using powder metallurgy;

[0130] (6) The prepared cemented carbide samples were characterized in structure and tested for corrosion performance;

[0131] (7) The composition and structure of the cemented carbide system were calculated based on the phase diagram of the thermodynamic database, and the prepared cemented carbide system was verified by TEM;

[0132] (8) The galvanic corrosion relationship between the hard phase and the binder phase was measured using the micro-area electrochemical testing method. The galvanic corrosion relationship was experimentally verified, and the differences in the corrosion resistance of cemented carbide were revealed.

[0133] Regarding the implementation details, in step (1), the types and composition of the alloying elements of the multi-component binder phase are determined according to the corrosion resistance of the target cemented carbide; by consulting relevant cemented carbide and related thermodynamic calculation literature, the wetting relationship between the cemented phase and the binder phase is fully considered, the electrochemical corrosion characteristics of the corresponding metal elements of the corresponding cemented carbide system are calculated, and a reasonable multi-component alloy is selected as the binder phase to prepare the cemented carbide.

[0134] In step (2), the main steps for establishing the thermodynamic database of the target multi-component binder phase cemented carbide system are as follows:

[0135] Step 2-1: Review the literature to obtain specific thermodynamic data of binary, ternary and other low-element systems related to the target system, evaluate and screen the data in the literature, and discard unreliable data;

[0136] Step 2-2: Based on the obtained phase diagram, thermodynamic experimental information, and phase equilibrium conditions, and combined with a suitable thermodynamic model, determine the adjustable parameters, then optimize them using the least squares method to obtain suitable parameter values, and then use the obtained parameter values ​​to calculate the phase diagram and thermodynamic data.

[0137] Steps 2-3: Self-consistency verification, that is, from simple binary systems to complex multi-component systems, phase diagram calculations are performed using a thermodynamic database to obtain the composition and structure of the target system. Through multiple evaluations and optimizations of the parameters, a reliable and reasonable thermodynamic database of the target cemented carbide system is finally obtained.

[0138] Steps 2-4: Using the established multivariate thermodynamic database, phase diagrams are drawn with pressure, temperature, and composition as variables. Different regions in the phase diagram correspond to different compositions and phases. Based on the relationship between properties and structure, the composition of corrosion-resistant cemented carbide can be rationally designed according to the phase diagram, thereby preparing cemented carbide with the expected structure and properties.

[0139] In step (3), the Pourbaix diagram of the corresponding system is obtained by thermodynamic calculation and Nernst equation calculation, the corrosion resistance of the cemented carbide system is predicted, and the composition of the cemented carbide of the corresponding multi-element alloy binder phase is screened.

[0140] Step 3-1: Calculate the Gibbs free energy of the target cemented carbide system after elemental solid solution by combining thermodynamic database and phase diagram calculation software Pandat;

[0141] Step 3-2: Based on the Gibbs free energy of the corresponding element, calculate the corrosion Pourbaix diagram of the corresponding system using the Nernst equation. The Pourbaix diagram calculation process involves selecting the elements involved in the system, inputting the electrode potential range and temperature parameters, and outputting all possible products. After selecting and optimizing the products, generate a single-element Pourbaix diagram. Superimpose the different single-element Pourbaix diagrams obtained by the above method to obtain the Pourbaix diagram of the target system.

[0142] In step (4), the main steps for selecting a reasonable phase range for the system are:

[0143] Step 4-1: Calculate the phase diagram of the cemented carbide system;

[0144] Step 4-2: Calculate the composition range of different carbon contents in the cemented carbide system under different conditions based on the phase diagram;

[0145] Step 4-3: Based on the phase structure obtained from the phase diagram calculation results, determine the liquid phase sintering temperature and the corresponding sintering range.

[0146] In step (5), a cemented carbide sample is prepared using powder metallurgy. The steps are as follows:

[0147] Step 5-1: Determine the ratio of WC to the multi-principal element alloy binder phase CoCrNi and the carbon content of the system according to the calculated phase interval;

[0148] Step 5-2: The ball-to-material mass ratio during the wet milling process is 8:1 to 12:1, and the milling time is 10 to 20 hours;

[0149] Step 5-3: The pressing pressure during the pressing process is 120-180 MPa;

[0150] Step 5-4: The liquid phase sintering temperature is determined according to the phase diagram, and the liquid phase sintering time is 1 to 2 hours;

[0151] Step 5-5: Combine the liquid phase sintered sample with the phase diagram to obtain the cemented carbide of the corresponding phase range.

[0152] In step (6), the prepared cemented carbide sample is characterized by its structure and subjected to corrosion performance tests. The steps are as follows:

[0153] Step 6-1: Prepare the sample by grinding and polishing the sample surface to meet the requirements of subsequent morphology and electrochemical corrosion tests.

[0154] Step 6-2: Verify the structural composition of the designed cemented carbide using TEM; perform TEM testing on the prepared sample to characterize the internal structure and composition of the sample, and compare the corresponding intervals obtained from the phase diagram calculation to the composition and structure, thus verifying the rationality of the phase diagram calculation and prediction design.

[0155] In step (7), the prepared cemented carbide sample is subjected to micro-area electrochemical corrosion testing, the steps of which are as follows:

[0156] Step 7-1: Place the prepared electrochemical sample in a micro-area electrochemical device for region scanning to characterize the micro-area and the micro-electrochemical corrosion performance of different components, and to characterize the corrosion resistance of the corresponding multi-element alloy binder phase. This reveals the differences in corrosion resistance among different components at the micrometer scale.

[0157] Step 7-2: Perform SVET (Scanning Vibrating Electrode Test) and LEIS (Micro-area Electrochemical Impedance) tests on the sample surface respectively. The micro-area electrochemical characterization results show that the hard phase and the binder phase in the cemented carbide system exhibit different corrosion current densities and electrochemical impedances, which verifies the galvanic corrosion effect and reflects the better corrosion resistance of the WC-CoCrNi system.

[0158] Step 7-3: The current density and impedance information show a differential distribution between the hard phase and the binder phase, which verifies the galvanic corrosion effect on the surface. At the same time, the low corrosion current density and high impedance value of the binder phase characterize the excellent corrosion resistance of the corresponding system.

[0159] Of course, the specific material preparation and material characterization testing processes, methods, and items may differ from the above examples. Any variations of the main design concept are within the scope of this invention.

[0160] Example 2

[0161] This embodiment utilizes the technical solution provided in Embodiment 1 to illustrate a design method for a WC-CoCrNi corrosion-resistant multi-principal-element binder phase cemented carbide, as detailed below:

[0162] 1. The composition of alloying elements was determined based on the corrosion resistance of the target cemented carbide. By reviewing relevant literature on corrosion-resistant cemented carbides and their design, and fully considering the wetting relationship between the hard phase and the binder phase, a suitable multi-principal alloy binder phase was selected to prepare the cemented carbide. Since the prepared cemented carbide requires good corrosion resistance, a W-Co-Cr-Ni-C pentagonal system was selected as the target cemented carbide based on literature review.

[0163] 2. Consult the literature to obtain thermodynamic data related to the target system. The known thermodynamic data for this system are as follows: Based on the collected binary, ternary, and even quaternary databases of C-Co, C-Cr, CW, Co-W, Cr-W, C-Co-Cr, Co-Cr-W, C-Co-W, C-Ni-W, and C-Co-Ni-W, the thermodynamic databases are integrated using the CALPHAD method. Thermo-Calc software is used to draw phase diagrams and verify the accuracy of the lower-element databases. The combined phase diagrams are compared with the original phase diagrams, and further literature is consulted for correction until the accuracy of the drawn phase diagrams is ensured. The above verification process is repeated until the thermodynamic database of the W-Co-Cr-Ni-C pentagonal system is obtained.

[0164] 3. Based on the aforementioned thermodynamic database, Pourbaix diagrams are calculated. For the W-Co-Cr-Ni system, thermodynamic calculations and the Nernst equation are used to obtain the corresponding Pourbaix diagram, identifying the immune and passivation regions of the system, and comparing the corrosion tendency with that of the classical W-Co system. Based on the thermodynamic database, using the Nernst equation and with the Gibbs free energy of pure elements as a benchmark, the energy differences of each element in the target composition are obtained through electrochemical reaction equations and the Nernst equation, and converted into potential difference values ​​to evaluate the galvanic corrosion tendency.

[0165] 4. Based on the aforementioned thermodynamic database, the phase diagram of the cemented carbide is calculated using the phase diagram calculation software Pandat. By fixing the ratio of the hard phase and the binder phase and changing the carbon content of the system, a vertical interface phase diagram is obtained, wherein the content of the hard phase WC is 80 wt.% and the content of the binder phase CoCrNi is 20 wt.%. The composition ranges for the formation of various different phases are calculated in the aforementioned multi-element alloy system, and a guiding range is selected based on the composition ranges and their corresponding phase structures.

[0166] 5. Prepare hard alloys using powder metallurgy.

[0167] Based on the expected structure of the binder phase, the required composition range of the binder phase is determined in conjunction with the phase diagram, and the powder is formulated according to the composition of that range.

[0168] High-energy ball milling was performed by adding the binder phase powder and the hard phase powder.

[0169] Mix 80% WC powder with 20% CoCrNi and trace amounts of carbon black powder; add carbide grinding balls with a ball-to-powder mass ratio of 10:1, and add alcohol as grinding media; and grind for 16 hours.

[0170] The ball-milled slurry was dried and sieved, and then pressed at a pressure of 150 MPa during the pressing and molding process.

[0171] The crushing sintering temperature was 1450℃, and the temperature was held for 90 min to obtain cemented carbide samples;

[0172] 6. Perform structural verification and corrosion resistance tests on the manufactured cemented carbide.

[0173] The composition and phase structure of the designed cemented carbide were verified using TEM.

[0174] By selecting a simulated drilling fluid with pH=10 as the electrolyte, hoping to apply it in the drilling environment, corrosion experiments were conducted at 25°C using electrochemical experimental three-electrode technology.

[0175] By combining the results of micro-area electrochemical tests, the differences in galvanic corrosion on the sample surface and the corrosion resistance performance are revealed, and the corrosion products on the sample surface calculated by Pourbaix and the corresponding improvement in corrosion resistance are verified.

[0176] 7. Micro-area electrochemical experiments were used to experimentally verify the tendency of galvanic corrosion.

[0177] The local corrosion current of the hard phase and the binder phase plane was tested using SVET technology. The current difference between the hard phase and the binder phase of WC-CoCrNi and WC-Co samples was compared to obtain the corrosion rate between the hard phase and the binder phase.

[0178] The local corrosion resistance of the hard phase and binder phase planes was tested using LEIS technology. The resistance values ​​between the hard phase and binder phase of WC-CoCrNi and WC-Co samples were compared to obtain the corrosion resistance between the hard phase and binder phase directly.

[0179] Based on the above embodiments, it is clear that the technical solution provided by the embodiments of the present invention, through the establishment of a thermodynamic database and the methods based on Pourbaix calculation and phase diagram calculation, combined with the unique means of micro-area electrochemical characterization of the corrosion resistance of cemented carbide, evaluates and selects the basic characteristics and corrosion resistance of the binder phase, obtains the optimal binder phase composition structure for the corresponding cemented carbide system, and matches the optimal test conditions, thereby obtaining a closed loop between the design, preparation, and verification of multi-principal element corrosion-resistant cemented carbide materials. The provided design method can clearly identify the types of corrosion-resistant binder phases, and uses Pourbaix diagram calculation and phase diagram calculation to guide the design of reasonable cemented carbide preparation processes, improving the development efficiency of corrosion-resistant cemented carbide. Furthermore, the understanding of the relationship between the phase structure and performance of cemented carbide is enhanced through TEM testing and micro-area electrochemical verification.

[0180] The composition and structure of the prepared cemented carbide, corresponding to the phase diagram calculation, were obtained by TEM testing, demonstrating the efficiency and rationality of phase diagram calculation in cemented carbide design. As shown in Figures 4a-4g, the TEM results show that the composition and structure of the corresponding cemented carbide system are consistent with the phase diagram calculation prediction results. Figures 4a and 4e respectively characterize the high-angle annular dark field (HAADF) images of two different regions inside WC-CoCrNi. As shown in the figures, W and C elements are enriched in the WC region, while the elements contained in the CoCrNi binder phase are enriched in the binder phase region. Figures 4b and 4f respectively characterize the high-resolution TEM (HR-TEM) images at the interface between WC and CoCrNi. The interplanar spacing of the WC hard phase is measured to be 0.25 nm, corresponding to the (100) crystal plane, and the d-spacing of the CoCrNi binder phase is 0.20 nm, corresponding to the (111) crystal plane. Figures 4c, 4d, and 4g show the selected area electron diffraction (SAED) patterns of the CoCrNi binder phase, WC hard phase, and Cr3C, respectively, characterizing the FCC structure of the CoCrNi binder phase and the HCP structure of the WC particles. TEM characterization results demonstrate the efficiency and rationality of phase diagram calculation for designing cemented carbides.

[0181] By combining micro-area electrochemical technology, the micro-corrosion kinetics information can be detected, which facilitates a direct comparison of the types of binder phases with excellent corrosion resistance and the cemented carbide system. The corrosion test results are shown in Figures 5a-5d.

[0182] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A design method for corrosion-resistant multi-principal-element binder phase cemented carbide, characterized in that, include: Obtain the target corrosive service environment, and formulate a target cemented carbide system based on the target corrosive service environment. The target cemented carbide system includes hard corresponding elements and binder corresponding elements. Establish a phase diagram thermodynamic database for the target cemented carbide system; Based on the phase diagram thermodynamic database, Pourbaix diagram calculations are performed on the target cemented carbide system to obtain the predicted corrosion products of the target cemented carbide system under the target corrosive service environment, as well as the immune region and passivation region corresponding to the predicted corrosion products. Multi-principal alloys are selected as the binder phase from the binder phase elements. Based on the phase diagram thermodynamic database, phase diagram calculations are performed on the target cemented carbide system to obtain phase composition and phase parameters. The phase composition includes the proportion of the binder phase element and the proportion of the cemented phase to the binder phase. The phase parameters include the heat treatment temperature. The multi-principal alloy, phase composition, and phase parameters are used as the design output for the corrosion-resistant multi-principal bonded phase cemented carbide.

2. The design method according to claim 1, characterized in that, The hard phase elements include any combination of W, Ti, C, and N; And / or, the binder phase element includes any combination of Co, Cr, Ni, Fe, Al, and Mn.

3. The design method according to claim 1, characterized in that, The selection rules for the multi-principal element alloy specifically include: The required element types and proportions of the hard phase and binder phase are selected based on the target corrosive service environment. The immune region and passivation region of the system are obtained by calculating the Pourbaix diagram. The immune region is the non-corrosion region of thermodynamic stability below the equilibrium line of the Pourbaix diagram; the passivation region is the region where corrosion products such as oxides and hydroxides are generated. The corrosion product film has a certain protective effect and reduces corrosion. In some implementation schemes, the selection rules for phase composition and phase parameters specifically include: Calculate the phase diagram based on the composition of the target cemented carbide system; Based on the phase diagram calculation results, the region of WC+γ in the normal microstructure of cemented carbide was selected; When the phase diagram calculation results show that there is no region containing only WC+γ, select the region where the C content is closest to the carbon-depleted phase to graphite phase transition line; The liquidus line of the target cemented carbide system is determined based on the phase diagram calculation results, and the determination of the sintering temperature is guided by the liquidus line.

4. The design method according to claim 1, characterized in that, The process of establishing the phase diagram thermodynamic database specifically includes: Acquire thermodynamic data of a low-element system, wherein the elements in the low-element system are some of the elements in the target cemented carbide system; A thermodynamic model was established to calculate the Gibbs free energy of multiple phases in the low-element system. All calculation results are integrated and expanded to form a phase diagram thermodynamic database for the target cemented carbide system.

5. The design method according to claim 1, characterized in that, The process of calculating the Pourbaix graph specifically includes: Import the phase diagram thermodynamic database into the calculation software, and use the point calculation module to input the target composition of the target cemented carbide system to obtain the chemical potential of each element in the target composition. Based on the Gibbs free energy of pure elements, the energy difference of each element in the target component is obtained through electrochemical reaction equations and Nernst equations and converted into potential difference values. A multivariate Pourbaix diagram is obtained based on the superimposed pure element Pourbaix diagram. The change in Gibbs free energy caused by alloying is calculated, and the immune region and passivation region of the multivariate Pourbaix diagram are delineated.

6. The design method according to claim 1, characterized in that, Also includes: Verification samples were prepared using powder sintering based on the multi-principal element alloy, phase composition, and phase parameters. The microstructure and corrosion patterns of the verification samples were characterized to verify the effectiveness of the design output.

7. The design method according to claim 6, characterized in that, The microstructure is characterized by transmission electron microscopy, and the corrosion pattern is characterized by micro-area electrochemical experiments.

8. A method for preparing a corrosion-resistant multi-principal-element binder phase cemented carbide, characterized in that, include: The design output under the target corrosive service environment is obtained by using the design method described in any one of claims 1-7; Based on the design output, a corrosion-resistant multi-principal-element binder phase cemented carbide was prepared.

9. The preparation method according to claim 8, characterized in that, Specifically, it includes: The binder phase powder and the hard phase powder are prepared according to the design output; The powder is mixed according to the ratio of hard phase and binder phase output as described in the design, and then ball-milled and pressed to obtain a cemented carbide block sintered billet. The cemented carbide bulk sintered billet is subjected to vacuum sintering to obtain the corrosion-resistant multi-principal-element cemented carbide.

10. The application of the corrosion-resistant multi-principal-element cemented carbide prepared by the preparation method according to any one of claims 8-9 in the manufacture of marine drilling equipment.

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