A method for researching failure mechanism of thermal barrier coating cyclic oxidation based on numerical simulation

Abstract

The present application relates to a kind of based on numerical simulation thermal barrier coating cyclic oxidation failure mechanism research method, steps are as follows: (1) in combination with the control equation of oxygen diffusion to generate aluminum oxide under the cyclic oxidation of thermal barrier coating, establish the growth finite element model of thermal barrier coating under cyclic oxidation;(2) the growth finite element model established in step (1) is combined with constitutive relation, and the growth law of oxidation layer and stress evolution result of thermal barrier coating under cyclic oxidation are simulated by multi-physics field coupling;(3) the stress distribution result of oxidation layer and ceramic layer simulated in step (2) is introduced into the parameter reflecting interface stress state, and the interface crack initiation is evaluated, and coating failure mechanism is analyzed in combination with experimental results.

Description

Technical Field

[0001] This invention is a numerical simulation-based method for studying the cyclic oxidation failure mechanism of thermal barrier coatings. It is used to study the mechanism of spalling failure of thermal barrier coatings under heating-heating-cooling working environment, and belongs to the field of aerospace engine technology. Background Technology

[0002] Thermal barrier coating (TBC) is a high-temperature metal protection technology developed to meet the operational requirements of hot-end components in aero-engines. It involves coating the surface of turbine blades with advanced ceramic materials possessing properties such as corrosion resistance, low thermal conductivity, and high-temperature resistance, thereby providing thermal protection to the high-temperature alloy substrate and extending the service life of the turbine blades. A typical thermal barrier coating is a multi-layered structure, usually composed of four layers of materials with specific properties and functions: a ceramic layer (TC), a binder layer (BC), an oxide layer (TGO), and an alloy substrate (Sub).

[0003] During service, thermal barrier coatings (TBCs) continuously undergo heating-holding-cooling cycles. Due to the mismatch in physical parameters between the ceramic layer, oxide layer, and adhesive layer, a certain level of thermal stress exists within the TBC during the heating and cooling stages. During the holding stage, the thermal growth stress generated by the oxide layer further exacerbates the internal stress level of the TBC, leading to internal cracking and interfacial delamination. Once interfacial delamination occurs, the coating will delaminate and fail, exposing the blade substrate directly to a high-temperature exhaust gas environment exceeding the material's temperature resistance, resulting in blade ablation and breakage. Therefore, it is essential to establish a growth model of TBCs under cyclic oxidation to predict the stress evolution of TBCs, which is crucial for studying the failure mechanism of TBCs under cyclic oxidation.

[0004] Current numerical simulation studies of thermal barrier coatings assume uniform oxide layer thickness, neglecting stress concentration caused by localized non-uniform oxide layer growth, and failing to discuss the relationship between the coupling effect of interfacial normal and tangential stresses and crack initiation. This invention uses multiphysics coupling simulation to obtain the growth law and stress evolution results of the oxide layer under cyclic oxidation in thermal barrier coatings. By introducing parameters reflecting the interfacial stress state, it can more accurately analyze the failure mechanism of the coating. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a research method for the failure mechanism of thermal barrier coatings under cyclic oxidation, which can reflect the stress distribution and evolution results inside and at the interface of the thermal barrier coating under cyclic oxidation, and is used to analyze the failure mechanism of the coating.

[0006] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a method for studying the cyclic oxidation failure mechanism of thermal barrier coatings based on numerical simulation, used to study the mechanism of spalling failure of thermal barrier coatings under heating-heating-cooling working environment. By establishing representative components of the thermal barrier coating with cosine interface morphology under cyclic oxidation, the growth law of the oxide layer and the stress distribution of the thermal barrier coating are simulated. Parameters reflecting the interface stress state are introduced to evaluate interface cracks. The failure mechanism is analyzed in conjunction with the experimental results of cyclic oxidation of the thermal barrier coating. The steps are as follows:

[0007] Step 1: Simplify the oxide layer growth model by making the following assumptions: (1) Assume that oxide layer growth only occurs during the heat preservation period; (2) Assume that the oxide layer is made of pure alumina; (3) Only consider the growth of the oxide layer towards the bonding layer; (4) Assume that oxygen diffusion within the ceramic layer is unrestricted, i.e., the oxygen diffusion rate is infinite; (5) Do not consider the effect of stress on oxygen diffusion. A finite element model of oxide layer growth is established in a multiphysics coupling simulation software by combining the governing equations of the chemical diffusion field and chemical reaction field under the cyclic oxidation of the thermal barrier coating.

[0008] Step 2: Using the growth finite element model established in Step 1, cyclic thermal loads (where heating and cooling are both convection conditions) are superimposed on it. Combined with constitutive relations, the cyclic oxidation simulation of the thermal barrier coating is carried out through multiphysics coupling simulation software, so as to obtain the stress field distribution and evolution results of the thermal barrier coating under thermo-mechanical coupling.

[0009] Step 3: Using the stress evolution simulation under cyclic oxidation in Step 2, the stress distribution and evolution results inside the oxide layer, at the oxide / ceramic layer interface, and at the oxide / binder layer interface are obtained. Combined with the oxide layer growth law, the stress distribution inside the oxide layer and at the interface is analyzed. By introducing the parameter β, which reflects the interface stress state, a crack initiation criterion for normal and tangential stresses at the coupled interface is established, i.e., when... At this time, cracks will initiate at the interface, and combined with the experimentally observed coating failure modes, the failure mechanism of the coating will be analyzed. Thus, the research on the failure mechanism of the thermal barrier coating under cyclic oxidation is completed.

[0010] The governing equations for the chemical diffusion field and chemical reaction field in the first step are as follows:

[0011]

[0012] Where c is the oxygen concentration, n is the volume fraction of the oxide layer, and D C denoted as the oxygen diffusion coefficient, G as the chemical reaction rate constant, and M as the molar concentration of oxygen in Al2O3.

[0013] Constitutive relations in the second step:

[0014]

[0015] Where ε is the strain tensor, λ and μ are Lamé constants, and σ is the stress tensor. kk The sum of principal stresses, α T Where T is the coefficient of thermal expansion, and T is the temperature. 0 Let I be the initial temperature, I be the identity matrix, and α be the initial temperature. n denoted as the coupling coefficient between chemical reaction and strain, and n as the volume fraction of the oxide layer.

[0016] In the third step, the parameters reflecting the interfacial stress state are:

[0017]

[0018] Wherein, σ N For normal stress, τ xy For tangential stress, [σ N [τ] represents the interfacial toughness in pure tensile mode. xy [] represents the interface resilience in pure shear mode.

[0019] The advantages of this invention compared to the prior art are:

[0020] (1) This invention obtains the growth law, stress field distribution and evolution law of thermal barrier coating under cyclic oxidation through multi-physics field coupling simulation, thereby taking into account the stress concentration caused by local non-uniform growth of oxide layer.

[0021] (2) This invention considers the influence of stress changes on coating failure after the thermal barrier coating has undergone a heating-holding-cooling process. Existing research methods only focus on stress changes caused by oxide layer growth under isothermal conditions.

[0022] (3) This invention introduces parameters that reflect the stress state of the interface, and associates the normal stress and tangential stress at the interface with the initiation of interface cracks. Attached Figure Description

[0023] Figure 1 This is the implementation process of a numerical simulation-based method for studying the cyclic oxidation failure mechanism of thermal barrier coatings according to the present invention.

[0024] Figure 2 This example uses a finite element model of a thermal barrier coating.

[0025] Figure 3 The simulation results are for the oxide layer growth pattern used in this example.

[0026] Figure 4 The stress σ at the oxide / ceramic layer interface under cyclic oxidation, as illustrated in this example. y Distribution and evolution simulation results;

[0027] Figure 5 The stress σ under cyclic oxidation inside the oxide layer, as illustrated in this example. y Distribution and evolution simulation results;

[0028] Figure 6 For this example, under cyclic oxidation, the peak stress σ at the oxide layer / adhesive layer interface... y The variation pattern with oxide layer thickness;

[0029] Figure 7 The stress σ under cyclic oxidation inside the ceramic layer, as exemplified in this case. y Distribution and evolution simulation results;

[0030] Figure 8 For this example, under cyclic oxidation, the stress σ at the center of the peak / trough at the boundary of the ceramic layer is... y The variation pattern with oxide layer thickness;

[0031] Figure 9 The distribution pattern of the stress state parameter β at the oxide / ceramic layer interface is shown in this example.

[0032] Figure 10 The distribution pattern of the stress state parameter β at the oxide / adhesive layer interface is shown in this example. Detailed Implementation

[0033] The following, with reference to the accompanying drawings, further explains the technical solution of the present invention: a method for studying the cyclic oxidation failure mechanism of thermal barrier coatings based on numerical simulation. For example... Figure 1 As shown, this invention relates to a method for studying the cyclic oxidation failure mechanism of thermal barrier coatings based on numerical simulation, and the implementation steps are as follows:

[0034] Step 1: Simplifying assumptions for the oxide layer growth model: (1) Assuming oxide layer growth only occurs during the heat preservation period; (2) Assuming the oxide layer contains pure alumina; (3) Only considering the growth of the oxide layer towards the bonding layer; (4) Assuming oxygen diffusion within the ceramic layer is unrestricted, i.e., the oxygen diffusion rate is infinite; (5) The influence of stress on oxygen diffusion is not considered. A finite element model of oxide layer growth is established in COMSOL Multiphysics multiphysics coupling simulation software, combining the governing equations of the chemical diffusion field and chemical reaction field under the cyclic oxidation of the thermal barrier coating, such as... Figure 2 As shown, the interface morphology is fitted with a sinusoidal function y = Acos(2πx / λ), where the amplitude A is 15 μm, the wavelength λ is 60 μm, and the average thicknesses of the four layers are 200 μm, 100 μm, 1 μm, and 1200 μm, respectively. The displacement in the y-direction at the bottom of the model is fixed, and the displacement in the x-direction at the left boundary is fixed, i.e., v(x,y)| y＝0 =0, u(x,y)| y＝0=0. The right boundary of the model is constrained by coupling constraints to allow displacement in the same x-direction. The initial conditions for the oxygen diffusion field of the thermal barrier coating model are: the oxygen concentration at the ceramic / oxide layer interface is 1.55 mol / m³. 3 The initial oxygen concentration of the adhesive layer is 0 mol / m 3 The governing equations for the chemical diffusion field and the chemical reaction field are as follows:

[0035]

[0036] Where c is the oxygen concentration, n is the volume fraction of the oxide layer, and D C denoted by , where G represents the oxygen diffusion coefficient, G represents the chemical reaction rate constant, and M represents the molar concentration of oxygen in Al2O3.

[0037] Step 2: Using the growth model established in Step 1, a cyclic thermal load is superimposed on it. Combined with constitutive relations, the cyclic oxidation simulation of the thermal barrier coating is performed using the solid mechanics, solid heat transfer, rare matter transport, and convection-diffusion modules in COMSOL Multiphysics multiphysics coupling simulation software. The material parameters of the coating are shown in Table 1, and the oxidation growth parameters are shown in Table 2. The cyclic thermal load is: heating and holding at 1000℃ for 45 minutes, followed by cooling to room temperature (20℃) for 15 minutes. Both heating and cooling are under convection conditions, thus obtaining the stress field distribution and evolution results of the thermal barrier coating under thermo-mechanical coupling. The constitutive relations are:

[0038]

[0039] Where ε is the strain tensor, λ and μ are Lamé constants, and σ is the stress tensor. kk The sum of principal stresses, α T Where T is the coefficient of thermal expansion, and T is the temperature. 0 Let I be the initial temperature, I be the identity matrix, and α be the initial temperature. n denoted as the coupling coefficient between chemical reaction and strain, and n as the volume fraction of the oxide layer.

[0040] Table 1

[0041]

[0042] Table 2

[0043]

[0044] Step 3: Obtain the oxide layer thickness (h) using the cyclic oxidation simulation from step 2. TGO The roughness evolution law shows that, in this example, the interface roughness decreases as the oxide layer thickens, such as... Figure 3As shown. Further analysis revealed the variation law of oxide layer peak and trough thickness. In this example, the growth rate of oxide layer peak thickness is greater than the growth rate of trough thickness, resulting in a decrease in oxide layer roughness, as shown. Figure 4 As shown. The stress evolution simulation under cyclic oxidation in the second step yields the stress distribution and evolution results within the oxide layer, at the oxide / ceramic layer interface, and at the oxide / binder layer interface. In this example, the tensile stress σ at the oxide / binder layer interface and the center of the peak / trough at the ceramic layer boundary under cyclic oxidation is... y Both increase with the number of cycles, such as Figure 5 — Figure 8 As shown. Based on the analysis of the oxide layer evolution law, the stress distribution inside the oxide layer and at the interface is determined. By introducing parameters reflecting the interface stress state, a crack initiation criterion is established for the coupling of normal and tangential stresses at the interface, i.e., when... At that time, cracks will appear on the interface. In this example... For the oxide / ceramic layer interface, [σ N ] = 200MPa, [τ xy ] = 200MPa, for the oxide / binder interface, [σ N ] = 100MPa, [τ xy =200MPa, the interfacial stress and the corresponding β value can be calculated through stress coordinate transformation, such as Figure 9 , Figure 10 As shown, cracks tend to initiate at the troughs of the oxide / ceramic layer interface and the peaks of the oxide / binder layer interface. This concludes the research on the failure mechanism of the thermal barrier coating under cyclic oxidation.

[0045] The examples provided above are merely for illustrating the purpose of this invention and are not intended to limit the scope of the invention. The scope of this invention is defined by the appended claims. All equivalent substitutions and modifications made without departing from the spirit and principles of this invention should be covered within the scope of this invention.

Claims

1. A method for studying the cyclic oxidation failure mechanism of thermal barrier coatings based on numerical simulation, characterized in that, Includes the following steps: (1) Simplified assumptions for the oxide layer growth model: It is assumed that the oxide layer growth only occurs during the heat preservation period; it is assumed that the oxide layer is pure alumina; only the growth of the oxide layer towards the bonding layer is considered; it is assumed that the oxygen diffusion in the ceramic layer is unrestricted, that is, the oxygen diffusion rate is infinite; the influence of stress on oxygen diffusion is not considered; combined with the chemical diffusion field and chemical reaction field control equations under the cyclic oxidation of the thermal barrier coating, a finite element model of the growth of the thermal barrier coating under cyclic oxidation is established in the multiphysics coupling simulation software. (2) Using the growth finite element model established in step (1), cyclic thermal load is superimposed on it. Combined with constitutive relations, the cyclic oxidation simulation of the thermal barrier coating is carried out through multiphysics coupling simulation software, so as to obtain the stress distribution and evolution results of the thermal barrier coating under thermo-mechanical coupling. (3) The stress distribution and evolution results of the oxide layer, oxide layer / ceramic layer interface and oxide layer / adhesive layer interface are obtained by using the stress evolution simulation under cyclic oxidation in step (2). The interface cracks are evaluated by introducing parameters that reflect the interface stress state, and the failure mechanism of the coating is analyzed by combining them with the experimentally observed coating failure mode. In step (1), the governing equations for the chemical diffusion field and the chemical reaction field are: in, The concentration of oxygen. This represents the volume fraction of the oxide layer. Indicates the oxygen diffusion coefficient. Represents the rate constant of a chemical reaction. Indicates oxygen in The molar concentration in; In step (2), the constitutive relation is: in, For strain tensor, Let Lamé constant be . For stress tensor, The sum of principal stresses, The coefficient of thermal expansion is... For temperature, The initial temperature. It is the identity matrix. This is the coupling coefficient between chemical reaction and strain.

2. The method for studying the cyclic oxidation failure mechanism of thermal barrier coatings based on numerical simulation according to claim 1, characterized in that: In step (3), the parameter reflecting the interface stress state is: Among them, For normal stress, For tangential stress, For interface toughness in pure stretch mode, Interface resilience in pure shear mode.

3. The method for studying the cyclic oxidation failure mechanism of thermal barrier coatings based on numerical simulation according to claim 1, characterized in that: In step (2), the cyclic heat load is: heating and holding, and then cooling, both of which are carried out under convection conditions.

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