Gradient functional material and design method thereof

Abstract

This invention discloses a design method for graded functional materials, comprising the following steps: determining the alloy composition of the matrix material and the cemented carbide; combining the matrix material and the cemented carbide in different proportions to obtain different alloy systems; inputting the alloy composition of the combined alloy system into material performance simulation software to simulate the simulation parameters corresponding to different alloy systems; comparing the simulation parameters with set parameters to obtain the alloy system whose simulation parameters fall within the set parameter range, which is the graded functional material. This method for designing graded functional materials can design and screen graded transition materials from the matrix material to the cemented carbide layer in terms of composition, microstructure, and properties through computational methods, overcoming the need for extensive component proportioning and long-cycle melting-rolling-machining processes in traditional material design to complete material screening and evaluation; it also greatly expands the design and application scope of graded materials.

Description

Technical Field

[0001] This invention belongs to the field of graded functional materials technology, specifically relating to a design method for graded functional materials for valve sealing surfaces and a graded functional material for valve sealing surfaces obtained according to the design method, which can be applied to the manufacturing, repair and remanufacturing of valve sealing surfaces. Background Technology

[0002] Functionally graded materials (FGMs) are novel heterogeneous composite materials that combine two or more raw materials with different properties. Through advanced composite technology, the composition and structure of the constituent materials are controlled to exhibit a continuous gradient along a specific direction, resulting in a gradient in both properties and functions. With the advancement of technology, FGM research has become relatively mature, and its applications have expanded to materials science fields such as electronic components, optical devices, automobiles, and biomedicine. Furthermore, the types of material combinations have broadened from the initial metal / ceramic approach to include combinations of metals, alloys, and non-metals.

[0003] In surfacing welding, when there are significant differences in the physicochemical and mechanical properties between the weld overlay and the base material, a transition material surfacing method is employed. This involves first welding a gradient material transition layer onto the base material, followed by welding a hardening material onto the transition layer. The transition layer material differs from both the base metal and the hardening metal, and is generally a metal with good weldability and plasticity of its weld metal. While transition layer surfacing can reduce abrupt changes in hardness and lower residual stress to some extent, it cannot eliminate the hardness "step"; it merely divides the primary step into secondary or multiple steps, and the stress reduction is limited. Gradient material surfacing, on the other hand, achieves a gradient transition in hardness and properties, essentially eliminating the hardness "step" and effectively reducing residual stress. Applying this method to valve sealing surface surfacing could potentially be an effective way to address welding defects on valve sealing surfaces.

[0004] Traditional design and experimental methods for graded functional materials are time-consuming, labor-intensive, costly, and have poor results. Summary of the Invention

[0005] In view of this, in order to overcome the shortcomings of the prior art, the object of the present invention is to provide a design method for gradient functional materials suitable for valve sealing surfaces.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A design method for gradient functional materials suitable for valve sealing surfaces includes the following steps:

[0008] Determine the alloy composition in the base material and cemented carbide;

[0009] Different alloy systems are obtained by combining the matrix material and cemented carbide in different proportions.

[0010] The alloy composition of the combined alloy system is input into the material property simulation software to simulate the simulation parameters corresponding to different alloy systems.

[0011] By comparing the simulated parameters with the set parameters, alloy systems whose simulated parameters fall within the range of the set parameters are identified as graded functional materials.

[0012] If no suitable alloy system is found, the combination ratio of the matrix material and the hard alloy is readjusted, and the above calculations are performed iteratively until an alloy system with simulation parameters falling within the set parameter range is obtained. Specifically, in the valve sealing surface, this means a graded functional material with a microstructure (brittle phase) and coefficient of linear expansion and hardness that meet the requirements.

[0013] According to some preferred embodiments of the present invention, the simulation parameters and setting parameters include one or more of the phase composition, density, coefficient of linear expansion, thermal conductivity, Young's modulus, specific heat capacity, and hardness of the deposited metal corresponding to the alloy system.

[0014] According to some preferred embodiments of the present invention, the phase composition setting parameter is such that the mass percentage of brittle phase in the phase composition after the deposited metal crystallizes is less than 10%. When the proportion of brittle phase in the deposited metal is greater than 10%, the content of alloys affecting brittle phase in the mixture is increased or decreased, and material property simulation calculations are performed iteratively until the proportion of brittle phase is less than 10%.

[0015] According to some preferred embodiments of the invention, the brittle phase includes various carbides such as M2(C,N), M6C, M7C3 and M23C6.

[0016] According to some preferred embodiments of the present invention, the parameter for setting the coefficient of linear expansion is such that the coefficient of linear expansion of the deposited metal is between the coefficients of linear expansion of the base material and the corresponding coefficients of linear expansion of the cemented carbide.

[0017] According to some preferred embodiments of the present invention, the hardness setting parameter is such that the hardness value of the deposited metal is between the hardness of the base material and the hardness of the cemented carbide.

[0018] According to some preferred embodiments of the present invention, when simulating and comparing simulation parameters, the process is carried out in the order of phase composition, coefficient of linear expansion, and hardness. A suitable alloy system requires all three conditions to be met; if any one condition is not met, the alloy system is unsuitable. For example, if the proportion of the phase with the higher concentration than the brittle phase is greater than 10%, the alloy system is unsuitable, and there is no need to compare the coefficient of linear expansion and hardness.

[0019] According to some preferred embodiments of the present invention, the matrix material is low-alloy steel, high-alloy steel, or stainless steel.

[0020] According to some preferred embodiments of the invention, the cemented carbide is a cobalt-based Stellite alloy or a cobalt-free alloy (including iron-based alloys and nickel-based alloys).

[0021] According to some preferred embodiments of the present invention, the material property simulation software is JMatPro software.

[0022] According to some preferred embodiments of the invention, the matrix material and the cemented carbide have a plurality of multilayer fused metal layers formed by corresponding graded functional materials. When multiple fused metal layers are present, the proportion of the matrix material in the graded materials decreases from the matrix material to the cemented carbide layer according to the combination ratio, and the last layer contains no matrix material, only cemented carbide.

[0023] According to some preferred embodiments of the invention, the combination involves gradually increasing the mass percentage of the matrix material in the alloy system from 0% to 100%, and gradually decreasing the mass percentage of the cemented carbide from 100% to 0%.

[0024] According to some preferred embodiments of the present invention, the fusion ratio of different deposition methods and the alloy burn-off ratio of different deposition methods are used as the calculation boundary conditions during the simulation calculation.

[0025] Preferably, the microstructure, hardness, and coefficient of linear expansion under different cooling rates are calculated to provide process control parameters for the deposition of gradient materials. In actual calculations, the composition is first determined based on the microstructure and properties by mixing different materials, considering the fusion ratio, and the burn-off rate. Then, the properties are calculated based on the determined composition. After the composition and properties are determined, the cooling rate is considered. The cooling rate can be adjusted by modifying the process. That is, although the cooling rate is a very important boundary condition, it is easily achievable in engineering.

[0026] The present invention also provides a gradient functional material suitable for valve sealing surfaces, designed according to the above-described design method.

[0027] Due to the adoption of the above technical solutions, the advantages of this invention compared to the prior art are as follows: The design method of the gradient functional material applicable to valve sealing surfaces of this invention can design and screen gradient transition materials from matrix materials to hard alloy layers in terms of composition, microstructure and properties through calculation methods. This overcomes the need for material screening and evaluation through a large number of component ratios and a long cycle of melting-rolling-machining processes in traditional material design, greatly saving manpower, capital and time; at the same time, it greatly expands the design and application scope of gradient materials. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The phase composition of different alloy systems in the preferred embodiments of the present invention;

[0030] Figure 2 The above are T-Linear Expansion (temperature-linear expansion coefficient) diagrams for different alloy systems in preferred embodiments of the present invention.

[0031] Figure 3 Temperature-hardness diagrams for different alloy systems in preferred embodiments of the present invention. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0033] This invention relates to a design method for a gradient functional material for valve sealing surfaces. The material obtained using this method allows for a gradient transition in microstructure and hardness from the matrix material to the cemented carbide sealing surface. First, material property simulation software is used to calculate the microstructure and hardness values ​​of the resulting weld metal by mixing matrix material and cemented carbide in different proportions, using boundary conditions such as alloy element burn-off rate under different deposition methods, fusion ratio under different deposition methods, and non-equilibrium crystallization under different cooling rates. When the proportion of brittle phase in the resulting microstructure is greater than 10%, the amount of alloying elements affecting the brittle phase in the mixed material is increased or decreased, and iterative calculations are performed to ensure that the brittle phase in the gradient functional material is less than 10%, and the hardness and coefficient of linear expansion are between those of the matrix material and the cemented carbide weld metal. This design method achieves a smooth transition from plastic to hard-brittle microstructure in the matrix material to the cemented carbide weld layer, and a smooth transition from low to high hardness, while significantly reducing thermal stress during component operation (reducing the difference in the coefficient of linear expansion reduces thermal stress). Overcome the abrupt change in microstructure and properties from traditional matrix to hard alloy cladding layer, thus extending the service life of valve sealing surfaces.

[0034] Implementation Cases

[0035] The following design, using ASTM A182 F304 stainless steel as a valve seat material and Norem 02 as a base alloy for welding valve sealing surfaces, aims to meet the requirements of good weld compatibility between ASTM A182 F304 stainless steel and Norem 02. The gradient alloy weld metal exhibits higher plasticity than the Norem 02 weld metal, while its hardness and coefficient of linear expansion fall between those of F304 and Norem 02. Plasticity corresponds to the brittle phase; the less brittle phase present, the better the material's plasticity.

[0036] The specific implementation steps of the design method for gradient functional materials for valve sealing surfaces using the present invention are as follows:

[0037] Step (1): Determine the alloy composition in the base material and cemented carbide

[0038] For the purpose of calculation and execution, the composition of F304 stainless steel and Norem02 alloy is preset as shown in Table 1 in this embodiment.

[0039] Table 1. Composition of F304 Stainless Steel and Norem 02 Alloy

[0040]

[0041]

[0042] Step (2): Combine the matrix material and cemented carbide in different proportions to obtain different alloy systems.

[0043] Specifically, in this embodiment, the base material and cemented carbide are combined in the following proportions: 100% Norem O2, 10% 304-90% Norem O2, 20% 304-80% Norem O2, 30% 304-70% Norem O2, 40% 304-60% Norem O2, 50% 304-50% Norem O2, 60% 304-40% Norem O2, 70% 304-30% Norem O2, 80% 304-20% Norem O2, 90% 304-10% Norem O2, and 100% 304 stainless steel.

[0044] Step (3): Simulation calculation

[0045] The alloy composition of the combined alloy system is input into the material property simulation software to simulate the simulation parameters corresponding to different alloy systems.

[0046] Using JMatPro software, the phase composition of 304-Norem02 materials with different component ratios was calculated, and the properties of the material were simulated, yielding linear expansion coefficient and hardness diagrams, as shown below. Figure 1-3 As shown. In the simulation calculation, the alloy element burn-off rate under different deposition methods, the fusion ratio under different deposition methods, and the non-equilibrium crystallization under different cooling rates were used as boundary conditions to calculate the generated microstructure and the hardness and linear expansion coefficient of the deposited metal.

[0047] Figure 1 The phase composition results show that different proportions of 304-Norem02 mixtures result in different phases, specifically in the different proportions of ferrite and austenite, and the different types and quantities of carbides.

[0048] Figure 2 The results of the temperature-linear expansion coefficient diagram show that the higher the content of the substrate in the gradient material, the closer the linear expansion coefficient is to that of the substrate; the higher the content of cemented carbide in the gradient material, the closer the linear expansion coefficient is to that of cemented carbide.

[0049] Figure 3 The results of the temperature-hardness diagram show that the higher the cemented carbide content, the higher the hardness of the gradient material.

[0050] Based on the design results, a brittle phase smaller than that of the gradient functional material powder was selected, and a laser cladding process was used to prepare the sealing surface. The results of the microstructure, hardness and residual stress of the sealing surface were examined. The results showed that the hardness of the gradient layer was between that of the matrix material and the cemented carbide cladding metal, and the residual stress was significantly reduced compared with the fully cemented carbide cladding layer.

[0051] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a design method for gradient functional materials for valve sealing surfaces. Based on material microstructure and performance simulation calculations, the method prepares the corresponding materials, avoiding the drawbacks of long time cycles and high costs associated with relying solely on experiments. It also solves the technical problem of insufficient reliability of valve sealing surfaces caused by significant performance differences between the valve sealing surface and the matrix material. The design method for gradient functional materials for valve sealing surfaces of this invention uses material performance simulation calculation software. Based on matrix materials and cemented carbide mixtures with different proportions, the content of alloying elements affecting the brittle phases of the mixture is increased or decreased to obtain a gradient functional material with microstructure and hardness from the matrix to the cemented carbide cladding layer.

[0052] This invention utilizes material performance simulation software to rapidly obtain ideal graded functional materials by accurately designing specific performance gradient materials and then verifying and correcting them through experiments. Based on this design method, the microstructure, hardness, and coefficient of linear expansion of the graded material can be calculated, as well as other characteristic performance parameters related to the graded material, enabling the design and fabrication of graded materials with arbitrary specified structures. Due to the implementation of the above technical solutions, this invention has the following advantages compared to existing technologies: Traditional material design requires extensive component proportioning and a long-cycle melting-rolling-machining process for material screening and evaluation. This invention, through calculation methods, designs and screens graded transition materials from the matrix material to the cemented carbide layer in terms of composition, microstructure, and properties, overcoming these limitations and significantly saving manpower, money, and time. It also greatly expands the design and application scope of graded materials.

[0053] (1) Suppressing Welding Defects: The composition and microstructure of the weld overlay on the valve sealing surface are directly related to welding cracks and brittle spalling. High C, high Si, and high Cr content, columnar crystal structure, and brittle-hard layer interface in the weld overlay are metallurgical factors leading to welding hot cracks, cold cracks, porosity, and brittle spalling. Since graded functional materials do not require special consideration of wear resistance, the elements that lead to welding defects and brittle phases can be appropriately reduced during composition design. Therefore, for graded transition materials, by analyzing their composition and microstructure, we can discover the distribution of graded transition deposited metal elements and the variation law of microstructure, explore the control measures of weld overlay structure, and thus discover the metallurgical suppression mechanism of weld defects and brittle spalling in the weld overlay.

[0054] (2) Reducing thermal stress: The difference in physical and chemical properties between the weld layer and the base material on the valve sealing surface results in significant residual stress in the weld overlay during welding and service. This is a mechanical factor leading to welding defects and brittle cracking in the weld overlay. The designed gradient material has a higher plasticity in the weld metal than in the hard layer, and its coefficient of linear expansion is between that of the base material and the weld metal in the hard layer. This helps to reduce the difference in the coefficient of linear expansion, thereby reducing the residual stress in the weld overlay.

[0055] (3) It does not significantly reduce the performance of the sealing surface: The dilution effect of the gradient material on the hard surface material is different from the dilution effect of the base material on the hard surface alloy during direct hard surface alloy welding. Therefore, the gradient transition material will affect both the surface hardness and cross-sectional hardness of the weld overlay, which will affect the wear resistance of the weld overlay; but it will not significantly reduce the wear resistance of the sealing surface.

[0056] The above embodiments are only for illustrating 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 gradient functional materials suitable for valve sealing surfaces, characterized in that, Includes the following steps: Determine the alloy composition in the base material and cemented carbide; Different alloy systems are obtained by combining the matrix material and cemented carbide in different proportions. The alloy composition of the combined alloy system is input into the material property simulation software to simulate the simulation parameters corresponding to different alloy systems. By comparing the simulated parameters with the set parameters, alloy systems whose simulated parameters fall within the range of the set parameters are identified as graded functional materials. The simulation parameters and set parameters include one or more of the following: phase composition, density, coefficient of linear expansion, thermal conductivity, Young's modulus, specific heat capacity, and hardness of the weld metal corresponding to the alloy system. The phase composition setting parameter is that the proportion of brittle phase in the phase composition after the deposited metal crystallizes is less than 10%; when the proportion of brittle phase in the deposited metal is greater than 10%, the content of alloys affecting brittle phase in the mixture is increased or decreased, and the material performance simulation calculation is performed iteratively until the proportion of brittle phase is less than 10%; the brittle phase includes various carbides. The parameter for setting the coefficient of linear expansion is such that the coefficient of linear expansion of the deposited metal is between the coefficients of linear expansion of the base material and the corresponding coefficients of linear expansion of the cemented carbide deposited metal. The hardness setting parameter is such that the hardness value of the weld metal is between the hardness of the base material and the hard alloy weld metal. When simulating and comparing simulation parameters, the process should be carried out in the order of phase composition, coefficient of linear expansion, and hardness. If any one of these conditions is not met, the alloy system is unsuitable. If the proportion of the phase with the highest concentration of brittle phase is greater than 10%, then the comparison of the coefficient of linear expansion and hardness is unnecessary. In the simulation calculation, the fusion ratio of different fusion methods and the alloy burn-off ratio of different fusion methods are used as the calculation boundary conditions. If no suitable alloy system is found, the combination ratio of the matrix material and the hard alloy is readjusted, and the above calculations are performed iteratively until an alloy system with simulation parameters falling within the set parameter range is obtained. In the valve sealing surface, the alloy system consists of a brittle phase and a graded functional material with the required coefficient of linear expansion and hardness.

2. The design method according to claim 1, characterized in that, The base material is low-alloy steel, high-alloy steel, or stainless steel.

3. The design method according to claim 1, characterized in that, The cemented carbide is a cobalt-based Stellite alloy or a cobalt-free alloy.

4. The design method according to claim 1, characterized in that, The matrix material and the cemented carbide have multiple multilayer fused metal layers formed by corresponding graded functional materials that meet the requirements.

5. The design method according to claim 1, characterized in that, The combination involves gradually increasing the mass percentage of the matrix material in the alloy system from 0% to 100%, while gradually decreasing the mass percentage of the cemented carbide from 100% to 0%.

6. A graded functional material, characterized in that, The graded functional material is designed using the design method according to any one of claims 1-5.

Images