A method for evaluating the ablation retreat of C / MeC / SiC composites

Abstract

The present invention relates to the technical field of thermal protection for hypersonic aircraft, and specifically to a method for evaluating the ablation recession of a C / MeC / SiC composite material. The method provided by the present invention determines the ablation recession of the composite material under two conditions: with or without airflow scouring. For airflow scouring, the ablation recession rate is first obtained based on the first and second physical property parameters and the oxygen molar flow rate, thereby obtaining the ablation recession. For no airflow scouring, the thickness of the oxide layer formed by ablation of the composite material under no airflow scouring conditions is first obtained based on the first physical property parameter and the oxygen molar flow rate, and then the ablation recession is obtained based on the second physical property parameter and the oxide layer thickness. Experiments have shown that the method described in the present invention can accurately analyze the ablation recession of a composite material, is universal, and can cover the same type of substances with different components. The method has the advantages of high analysis accuracy, low cost, short cycle, and simple operation.

Description

Technical Field

[0001] The present invention relates to the technical field of hypersonic aircraft thermal protection, and in particular to a method for evaluating the ablation setback of a C / MeC / SiC composite material. Background Art

[0002] High-temperature ceramics, such as C / MeC / SiC composites, offer high-temperature resistance, oxidation resistance, and minimal or zero ablation. In recent years, they have become popular with aerospace designers and are widely used for thermal protection in critical components of next-generation hypersonic vehicles. These materials are often used in hot-end components operating at temperatures exceeding 2000°C. The ablation of these ceramics depends on the oxygen partial pressure, surface temperature, and the material's microstructure and composition. This formation of a MeO2-SiO2 antioxidant film prevents direct oxygen reaction with the surface material, forcing oxygen to diffuse through the film to reach the original material surface and undergo oxidation, thus achieving minimal or zero ablation.

[0003] Testing the ablation resistance of C / MeC / SiC ceramics typically involves two methods: experimental assessment and theoretical analysis. Experimental testing is the foundation of this analysis, but it can be complex and time-consuming, depending on the composition, temperature, and oxygen partial pressure. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a method for evaluating the ablation recession of C / MeC / SiC composite materials. The method provided by the present invention can analyze the ablation recession of C / MeC / SiC three-component composite materials with different component ratios under two conditions: with and without airflow scouring, thereby greatly shortening the design cycle.

[0005] The present invention provides a method for evaluating the ablation retreat of a C / MeC / SiC composite material, comprising the following steps:

[0006] S1) ablating or simulating ablating the C / MeC / SiC composite material under airflow flushing conditions, wherein the surface of the composite material is formed with Me x O y and an oxide layer of SiO2; said Me is a metal; said x is an integer of 1 to 2, and said y is an integer of 2 to 5;

[0007] S2) obtaining the molar flow rate of oxygen entering the oxide layer, the porosity of the oxide layer, and the ablation rate of the carbon fiber during ablation or simulated ablation of the composite material in step S1);

[0008] S3) According to the porosity of step S2), combined with the mass fraction and molar mass of components C, MeC and SiC in the composite material, the component Me in the oxide layer x Oy and the molar mass and density of SiO2, the first physical property parameter is obtained by formula 1;

[0009]

[0010] Wherein, γ1 is the first physical property parameter; φ is the porosity; f Cs is the mass fraction of component C in the composite material; f MeC is the mass fraction of the component MeC in the composite material; f SiC is the mass fraction of SiC component in the composite material; M MeC is the molar mass of the component MeC in the composite material; M C is the molar mass of component C in the composite material; M SiC is the molar mass of the component SiC in the composite material; is the component Me in the oxide layer x O y molar mass; is the molar mass of the component SiO2 in the oxide layer; is the component Me in the oxide layer x O y density; is the density of the component SiO2 in the oxide layer;

[0011] The second physical property parameter is obtained by formula 2;

[0012]

[0013] Among them, γ3 is the second physical property parameter;

[0014] Obtaining an oxide layer thickening rate based on the first physical property parameter and the oxygen molar flow rate described in step S2); obtaining a MeC-SiC matrix ablation recession rate based on the oxide layer thickening rate and the second physical property parameter; obtaining an ablation recession rate of the composite material based on the MeC-SiC matrix ablation recession rate and the mass fractions of components C, MeC, and SiC in the composite material, and the ablation rate of the carbon fiber described in step S2);

[0015] S4) Obtaining an ablation retreat amount of the composite material based on the ablation retreat rate of the composite material obtained in step S3) in combination with the original dimensions of the composite material and the ablation time of the composite material.

[0016] The present invention first ablates or simulates ablation of a C / MeC / SiC composite material under airflow conditions. The C / MeC / SiC composite material of the present invention is also called a C / MeC / SiC three-component ceramic material, wherein the Me is a metal; specifically, the Me is Zr, Hf or Ta. The C / MeC / SiC composite material of the present invention will oxidize during the ablation process, forming a layer of Me on the surface of the composite material. x O y and an oxide layer of SiO2, wherein the oxide layer is a porous solid oxide and the pores are filled with glassy oxide; the value of x is an integer of 1 to 2, and the value of y is an integer of 2 to 5; during the ablation or simulated ablation process, oxygen must diffuse through the oxide layer to reach the C / MeC / SiC composite material, that is, to reach the original material layer, and react with it.

[0017] When the C / MeC / SiC composite material of the present invention is a C / ZrC / SiC composite material, under airflow conditions, the C / ZrC / SiC composite material is ablated or simulated ablated, and an oxide layer comprising ZrO2 and SiO2 is formed on the surface of the composite material. The mass fraction of the ZrC component in the C / ZrC / SiC composite material of the present invention is f ZrC , the mass fraction of SiC component is f SiC , the mass fraction of carbon component is f Cs =1-f ZrC -f SiC When the C / ZrC / SiC composite material is ablated, oxidation reactions such as those shown in Reaction Equations 1 to 3 below will occur at the interface between the original material and the oxide layer:

[0018]

[0019]

[0020]

[0021] On the outer surface of the oxide layer, there is a volatilization of the liquid layer, which is mainly the evaporation reaction of SiO2. The specific reaction is shown in reaction equation 4:

[0022] SiO2(l)→SiO2(g) reaction equation 4;

[0023] Based on the simultaneous oxidation hypothesis, the ablation thermochemical reaction of the C / ZrC / SiC composite material is shown in reaction equation 5:

[0024]

[0025] In reaction equation 5, n1, n2, and n3 are the ratios of the amounts of the C component, SiC component, and ZrC component of the original material, respectively. The relationship between them and the mass fractions is shown in formulas a1 to a3:

[0026]

[0027]

[0028]

[0029] When the C / MeC / SiC composite material of the present invention is a C / HfC / SiC composite material, under airflow conditions, the C / HfC / SiC composite material is ablated or simulated ablated, and an oxide layer comprising HfO2 and SiO2 is formed on the surface of the composite material. The ablation behavior of the C / HfC / SiC composite material of the present invention is consistent with that of the C / ZrC / SiC composite material. The oxidation reaction can generate divalent solid oxides. It is only necessary to replace the molecular weight and density of ZrC with the molecular weight and density of HfC, and no further details are given.

[0030] When the C / MeC / SiC composite material of the present invention is a C / TaC / SiC composite material, an oxide layer comprising Ta2O5 and SiO2 is formed on the surface of the composite material when the C / TaC / SiC composite material is ablated or simulated under airflow conditions. The ablation behavior of the C / TaC / SiC composite material of the present invention is different. TaC also forms a solid porous oxide layer upon oxidation. The anti-ablation mechanism is similar to that of ZrC and HfC, generating a stable pentavalent solid oxide. The oxidation reaction of TaC is shown in Reaction Equation 6:

[0031]

[0032] During the ablation process of the C / MeC / SiC composite material of the present invention, each component thereof will experience mass loss. When the C / MeC / SiC composite material is a C / ZrC / SiC composite material, the total ablation mass flow rate is That is, the mass loss rate per unit area of the original material, in kg·m -2 ·s -1 Based on the assumption of simultaneous oxidation of all components of the material, according to reaction equations 1 to 5, the mass flow rates of each component are shown in formulas a4 to a12:

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040]

[0041]

[0042] The negative sign in formula a11 indicates that oxygen is a reactant rather than a product during the ablation process; in formulas a4 to a12, The subscript is the carbon component, which indicates the mass loss rate of the component; is the evaporation molar flow rate of SiO2 per unit area, in mol·m -2 ·s -1 ; is the evaporation mass flow rate of SiO2; the condition for the volatilization of SiO2 is that there must be some residual SiO2.

[0043] SiO2 can be considered as a gaseous component that evaporates rapidly in a flowing environment. The evaporation molar flow rate of SiO2 can be obtained using the Langmuir law, as shown in formula a13:

[0044]

[0045] in, is the molar mass of SiO2 in the oxide layer, in kg·mol -1 ; R is the universal gas constant, which is 8.3145 J·mol -1 ·K -1 ;T w is the absolute temperature of the wall, in K; p v is the vapor pressure of SiO2, in Pa, which can be obtained from the JANAF thermochemical table combined with formula a14;

[0046]

[0047] α reflects the adhesion coefficient of gas adsorption / desorption on the surface of the object, and its value range is 1×10 -3 ~1×10 -2 , or it can be approximated by formula a15; In formula a15, θ R is the rotation constant of SiO2 molecule, and its value is 6.812422.

[0048] The evaporation mass flow rate of the above SiO2 is shown in formula a16:

[0049]

[0050] After ablating or simulating ablation of the C / MeC / SiC composite material, the present invention obtains the molar flow rate of oxygen entering the oxide layer, the porosity of the oxide layer, and the carbon fiber ablation rate during ablation or simulated ablation of the composite material in step S1).

[0051] The porosity of the present invention is the porosity of the oxide layer formed on the surface of the C / MeC / SiC composite material during the ablation process. It can be directly obtained by instrument detection after a small sample of the composite material is ablated. It can be obtained by mercury intrusion or image analysis, or by an empirical formula, as shown in formula a17:

[0052]

[0053] The carbon fiber ablation rate described in the present invention is a value well known to those skilled in the art, and is related to the local flow field. It can be obtained by consulting literature or testing small samples. The empirical formula given in the literature summarizes the influence of temperature and pressure, for example, it can be found in the literature "Guo Yijun, Dai Guangyue, Gui Yewei, et al. Dual-platform theory and reaction control mechanism of oxidation ablation of carbon-based materials [J]. Acta Aerodynamica Sinica, 2014(06):755-760."

[0054] The oxygen molar flow rate of the present invention is the molar flow rate of oxygen entering the oxide layer formed on the surface of the composite material during the ablation process of the C / MeC / SiC composite material. During the ablation process of the C / MeC / SiC composite material of the present invention, due to the presence of the oxide film, oxygen first dissolves in the liquid SiO2 of the oxide layer, then diffuses therein, and finally reaches the interface between the original material and the oxide layer, and undergoes a thermochemical reaction with the original material below to form a condensed phase oxide; the generated condensed phase oxide thickens the oxide layer, wherein the solid phase Me x O y As a skeleton pinned to the surface of the material, liquid SiO2 fills the pores of the oxide layer, and the generated CO diffuses back and escapes; the surface SiO2 volatilizes, making the oxide layer thinner; the diffusion of oxygen in the oxide layer dominates the oxidation rate. In addition, under the action of high-speed airflow, the surface oxide is eroded, making the oxide layer thinner or even falling off, exposing the underlying original material to high-temperature and high-speed airflow; Figure 1 As shown, Figure 1 Schematic diagram of the oxidation process of C-ZrC-SiC ceramics.

[0055] It can be seen that the oxygen entering the oxide layer formed on the surface of the composite material during the ablation process undergoes the following process:

[0056] First, oxygen mainly dissolves and diffuses through the liquid SiO2 in the solid pores. The diffusion of oxygen in SiO2 is described by Hooke's diffusion law, as shown in formula a18:

[0057] In formula a18, is the molar concentration, the unit is mol·m -3 ; x is the position of O2 in the oxide layer thickness l; D eff is the effective diffusion coefficient of oxygen in SiO2, in m 2 ·s -1 , according to formula a19:

[0058] In formula a19, τ is the pore curvature factor, which is a known input quantity and reflects that the diffusion of gas in the voids relative to the movement in the unconstrained space has a longer connected path due to the presence of obstacles. It can be obtained by mercury intrusion or image analysis, and in the present invention, it is taken as 2; D is the diffusion coefficient of oxygen in SiC oxide SiO2 without curved voids; in the present invention, the diffusion coefficient of oxygen in SiC oxide SiO2 without curved voids is a known input quantity and can be obtained by other methods, such as consulting literature or conducting targeted experimental measurements.

[0059] When oxygen diffuses to the outer surface of the oxide layer, that is, the interface where the oxide layer meets the air, the oxygen concentration is obtained from the solubility of oxygen in SiO2, which can be obtained according to Henry's law of solubility, as shown in formula a20:

[0060] In formula a20, c w is the concentration of oxygen dissolved in the liquid layer; H is Henry's constant, which is 8.5×10 -7 mol·m -3 ·Pa -1 ; is the pressure of oxygen on the surface of the composite material, in Pa. In the present invention, the pressure of oxygen on the surface of the composite material is a known input quantity, which can be obtained by testing the environment in which the material is located.

[0061] When oxygen diffuses to the inner surface of the oxide layer, that is, the interface between the oxide layer and the original material, assuming that all the oxygen passing through the pores of the oxide layer SiO2 film reacts with the C / SiC / ZrC composite material, the oxygen molar flow rate obtained above can be expressed by formula a21:

[0062] In formula a21, is the rate constant of the material oxidation reaction. The rate constant of the material oxidation reaction of the present invention is a known input quantity and can be obtained through experiments or by consulting the literature; c i is the concentration of O2 at the interface between the oxide layer and the original material;

[0063] Formula a18, formula a20, and formula a21 give formula a22:

[0064]

[0065] Combining formula a21 and formula a22, it can be seen that the oxygen molar flow rate obtained above can be expressed by formula a23:

[0066] In formula a23, D eff 、 and is related to the local flow field and can be obtained by a person skilled in the art through a well-known method; l is the thickness of the oxide layer. In the present invention, D eff / k O2 The value is 1E-4.

[0067] According to formula a23, if the influence of airflow scouring is not considered, the oxygen molar flow rate is obtained by formula 9 based on the pressure of oxygen on the wall, Henry's constant, the oxidation reaction rate constant during ablation of the composite material, the effective diffusion coefficient of oxygen in SiO2, the thickness of the oxide layer on the surface of the composite material after ablation under no airflow scouring conditions, and the porosity:

[0068] In formula 9, l1 is the thickness of the oxide layer on the surface of the composite material after ablation without airflow scouring.

[0069] After obtaining the porosity of the oxide layer, the oxygen molar flow rate of the oxide layer and the carbon fiber ablation rate, the porosity of step S2) is combined with the mass fraction and molar mass of the components C, MeC and SiC in the composite material, the component Me in the oxide layer, and the carbon fiber ablation rate. x O y The first physical property parameter is obtained by formula 1, and the second physical property parameter is obtained by formula 2.

[0070] The present invention obtains the first physical property parameter through Formula 1; the first physical property parameter is a parameter of the oxide layer generated during the ablation process of the composite material.

[0071]

[0072] Wherein, γ1 is the first physical property parameter; φ is the porosity; f Cs is the mass fraction of component C in the composite material; f MeC is the mass fraction of the component MeC in the composite material; f SiC is the mass fraction of SiC component in the composite material; M MeC is the molar mass of the component MeC in the composite material; M C is the molar mass of component C in the composite material; M SiC is the molar mass of the component SiC in the composite material; is the component Me in the oxide layer x O y molar mass; is the molar mass of the component SiO2 in the oxide layer; is the component Me in the oxide layer x O y density; is the density of the component SiO2 in the oxide layer.

[0073] When the C / MeC / SiC composite material is a C / ZrC / SiC composite material, under the condition of airflow scouring, the thickness of the oxide layer formed during the ablation process of the composite material of the present invention is obtained according to formula a24:

[0074]

[0075] In formula a24, l is the thickness of the oxide layer, specifically the thickness of the oxide layer formed during the ablation process of the composite material, in m; t is the oxidation time, in s; φ is the porosity of the oxide layer; is the mass rate of ZrO2 formation per unit area, maintaining the solid phase; is the mass rate of SiO2 formation per unit surface, maintaining the liquid phase; and are the densities of ZrO2 and SiO2, in kg·m -3 .

[0076] Substituting formulas a7 to a9, we can obtain formula a25:

[0077]

[0078] In formula a25, is the density of SiO2 in the oxide layer, that is, the density of SiO2 when it is a condensed phase. Eliminate using formula a11 and formula a25 The thickness of the oxide layer formed during the ablation of the composite material of the present invention under the condition of airflow scouring can be obtained as shown in formula a26:

[0079]

[0080] The first physical property parameter of the C / ZrC / SiC composite material can be obtained as formula a27:

[0081]

[0082] The present invention obtains a second physical property parameter through formula 2; the second physical property parameter of the present invention is related to the thickness of the oxide layer of the composite material and the ablation retreat amount of the composite material; specifically, the second physical property parameter of the present invention is related to the thickness of the oxide layer and the ablation retreat amount of the composite material under the condition that airflow scouring is not considered;

[0083] Among them, γ3 is the second physical property parameter.

[0084] The thickness of the oxide layer without considering the airflow scouring condition can be obtained from the thickness of the oxide layer formed during the ablation process of the composite material of the present invention. When the C / MeC / SiC composite material is a C / ZrC / SiC composite material, the thickness of the oxide layer formed during the ablation process of the composite material of the present invention can be obtained according to formula a28: Combining formula a26 and formula a27, we can obtain formula a29, which is the thickness of the oxide layer formed during the ablation process of the composite material of the present invention under the condition of airflow scouring:

[0085]

[0086] Combined with the oxygen molar flow rate obtained above, the thickness of the oxide layer formed during the ablation process of the composite material of the present invention under the condition of airflow scouring can be obtained according to formula a30:

[0087]

[0088] This is a complex oxide layer evolution process, which is affected by factors such as oxygen dissolution-diffusion-reaction, oxide layer thickness, evaporation, ambient oxygen partial pressure, temperature, composition, oxide layer porosity, etc. In an environment without strong oxide blowing, there are three methods to solve the oxide layer thickness reflected by equation a30:

[0089] 1) Differentiation method: First, assume an extremely small oxide layer thickness. The specific initial value selection has a great influence on the rationality of the solution and requires multiple attempts. Then, use the oxide layer thickness in the previous time step to solve the net thickness increment (generated thickness minus evaporated thickness) in each small time interval (such as 1s). Finally, the thickness is accumulated to obtain the change of thickness over time, as shown in Formulas a31 and a32.

[0090]

[0091]

[0092] 2) Integration method, as shown in formula a33:

[0093]

[0094] This is an implicit function of l and is not easy to solve.

[0095] 3) Separation method: The oxide layer thickness represented by the right side of the equation is divided into the first term on the right side, which represents the thickening portion of the oxide generated by the oxidation reaction, and the second term on the right side, which represents the volatilization portion of the oxide gasification reaction. The solution is divided into two processes. It is assumed that these two types of reactions do not interfere with each other and can be solved independently. The thickening portion is obtained first, and then the consumed portion is subtracted. In other words, formula a30 is divided into formula a34;

[0096] In formula a34, Item is l1 is the thickness of the oxide layer without considering the airflow scouring condition; Item is l2 is the thickness of the oxide layer volatilized by the oxide gasification reaction;

[0097] Based on the first physical property parameter and the oxygen molar flow rate in step S2), the thickness of the oxide layer on the surface of the composite material after ablation under the condition of no airflow scouring is obtained by formula 7, that is, the thickness of the oxide layer under the condition of not considering the airflow scouring;

[0098]

[0099] Arranging l1 of Formula 7 gives Formula 10;

[0100]

[0101] In formula 10, B describes the gas dissolution-diffusion kinetics, as shown in formula 11; A reflects the relationship between the diffusion coefficient and the reaction coefficient per unit distance, as shown in formula 12; and B / A describes the reaction kinetics, as shown in formula a35.

[0102]

[0103] Integrating formula 10 yields formula a36 or formula a37:

[0104]

[0105] In formula a36 or formula a37, B is a parabolic rate constant, and B / A is a linear rate constant.

[0106] The oxide layer thickness follows a linear-parabolic model, indicating that the oxidation process is controlled by reaction-diffusion. As can be seen from the above equation, in the initial short period of time, the oxide layer has not yet formed, and the left side of the equation is dominated by the linear term. As the ablation time increases, the oxide layer thickens and is eventually dominated by the parabolic term.

[0107] right Arranging the l2 of the term gives formula a38, and continuing to integrate formula a38 gives formula a39

[0108]

[0109]

[0110] Combining the above l1 and l2, the thickness of the oxide layer under airflow scouring conditions can be obtained according to formula a40; l = l1 + l2 formula a40; regardless of the integration method or the separation method, it is necessary to ensure that the temperature remains unchanged within a period of time during the solution process.

[0111] The ablation retreat amount of the composite material of the present invention, that is, the ablation retreat amount of the original material, is shown in formula a41:

[0112]

[0113] In formula a41, γ2 is as shown in formula a42:

[0114]

[0115] The ablation retreat of the composite material is related to the thickness of the oxide layer without considering the airflow scouring condition. Therefore, by comparing formula a41 with formula 7, formula a43 can be obtained; thus, the second physical property parameter of the C / MeC / SiC composite material can be obtained:

[0116]

[0117] When the C / MeC / SiC composite material is a C / ZrC / SiC composite material, the ablation retreat amount of the composite material, that is, the ablation retreat amount of the original material, is expressed as formula a44:

[0118]

[0119] In formula a44, γ2 is as shown in formula a45:

[0120]

[0121] Comparing formula a44 with formula 7, we can obtain formula a46; that is, the second physical property parameter of the C / ZrC / SiC composite material is shown in formula a47:

[0122]

[0123]

[0124] When the C / MeC / SiC composite material is a C / TaC / SiC composite material, its first physical property parameter and γ2 are respectively shown in formula a48 and formula a49, thereby obtaining its second physical property parameter;

[0125]

[0126]

[0127] Regarding the ablation of the composite material of the present invention under airflow scouring conditions, after obtaining the first physical property parameter and the second physical property parameter, the present invention needs to first obtain the ablation recession rate of the composite material, and then obtain the ablation recession amount of the composite material based on the obtained ablation recession rate of the composite material, combined with the original external dimensions of the composite material and the ablation time of the composite material.

[0128] The present invention obtains the oxide layer thickening rate based on the first physical property parameter and the oxygen molar flow rate; obtains the MeC-SiC matrix ablation recession rate based on the oxide layer thickening rate and the second physical property parameter; and obtains the composite material ablation recession rate based on the MeC-SiC matrix ablation recession rate, the mass fractions of components C, MeC, and SiC in the composite material, and the ablation rate of the carbon fiber obtained above. Specifically, in a high-speed hot air flow, the oxide is blown away and lost due to the shear force of the gas, leaving only a thin oxide film of a certain thickness on the surface. The oxide layer growth rate can be expressed by formula a50:

[0129]

[0130] In formula a50, The term is the oxide layer thickening rate term, The term is the oxide layer decomposition and thinning rate term; therefore, formula a50 can be expressed as formula a51:

[0131]

[0132] In formula a51, v oxide is the final evolution rate of the oxide layer; v oxide-incr is the oxide layer thickening rate, specifically the oxide layer thickening rate without considering airflow scouring, obtained by formula a52; is the decomposition and thinning rate of the oxide layer, obtained by formula a53.

[0133]

[0134] The above oxide layer thickening rate, that is, the oxide layer thickening rate without considering airflow scouring, is obtained by formula 3:

[0135]

[0136] Comparing formula a41 with formula 7, according to the oxide layer thickening rate and the second physical property parameter, the MeC-SiC matrix material ablation retreat rate can be obtained by formula 4;

[0137] v materal =γ3v oxide-incr Formula 4; In Formula 4, v materal is the MeC-SiC matrix ablation retreat rate.

[0138] According to the ablation recession rate of the MeC-SiC matrix material and the mass fractions of the components C, MeC, and SiC in the composite material, combined with the ablation rate of the carbon fiber, the ablation recession rate of the composite material is obtained by formula 5;

[0139] v ceramic =(f Mec +f Sic )v matera1 +f Cs v Cs Formula 5: In Formula 5, v ceramic is the ablation retreat rate of the composite material; v Cs is the ablation rate of carbon fiber.

[0140] When the C / MeC / SiC composite material is a C / ZrC / SiC composite material, its ablation retreat rate is expressed as formula a54:

[0141] v ceramic =(f ZrC +f SiC )v materal +f Cs v Cs Formula a54.

[0142] The ablation rate of C / MeC / SiC ceramic materials is obtained using Equation 6. Integrating it over the ablation time yields the ablation recession at different time intervals. By dividing the heat shield into different grid points and analyzing the ablation recession at each point, the ablation profile at different times can be determined.

[0143] R=R0-∫v ceramic dt Formula 6;

[0144] In Formula 6, R is the external dimensions of the composite material after ablation; R0 is the original external dimensions of the composite material; and t is the ablation time of the composite material.

[0145] In an environment without strong air flow, that is, without airflow scouring, after obtaining the oxide layer thickness using the above three methods, the ablation retreat of the original material can be analyzed. Specifically, based on the second physical property parameter obtained above and the oxide layer thickness under no airflow scouring conditions, the ablation retreat of the composite material under no airflow scouring conditions can be obtained using Formula 8;

[0146] x sub =γ3l1 formula 8; in formula 8, x sub is the ablation retreat of the composite material.

[0147] The present invention provides a method for evaluating the ablation recession of a C / MeC / SiC composite material. The present invention determines the ablation recession of the composite material under two conditions, with and without airflow scouring. For the condition with airflow scouring, the ablation recession rate of the composite material is obtained based on the molar flow rate of oxygen entering the oxide layer during the ablation of the composite material, the first physical property parameter, and the second physical property parameter, thereby obtaining its ablation recession. For the condition without airflow scouring during the ablation of the composite material, the formula for the thickness of the oxide layer under the condition without airflow scouring is obtained by a separation method based on the formula for the thickness of the oxide layer under the condition with airflow scouring, thereby obtaining the thickness of the oxide film formed by ablation of the composite material under the condition without airflow scouring based on the first physical property parameter and the oxygen molar flow rate, and then obtaining the ablation recession of the composite material based on the second physical property parameter and the thickness of the oxide layer.

[0148] The present invention is suitable for rapidly testing the ablation resistance of heat-shielding materials used in hypersonic aircraft, providing a key evaluation parameter for material formulation control and heat-shielding structural design. It boasts strong versatility, high precision, low cost, and a short production cycle. Its core concept is that, rather than directly measuring the various matrix materials used in hypersonic aircraft heat-shielding designs, which are influenced by process and component ratios, the ratios of the C, SiC, and MeC components (MeC refers to high-melting-point, ablation-resistant carbides such as ZrC, HfC, and TaC, which oxidize to form solid oxides) can be determined or measured using a standard method before material preparation. The theoretical relationship described in the present invention can then be used to determine the desired material setback and mass loss caused by ablation of the C / MeC / SiC three-component ceramic. Experiments have shown that the method described in the present invention can accurately analyze the ablation setback of composite materials, is universal, and can cover materials of the same type with different components. The method offers advantages such as high analytical accuracy, low cost, a short production cycle, and ease of operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0149] Figure 1 Schematic diagram of the oxidation process of C-SiC-ZrC ceramics;

[0150] Figure 2 Schematic diagram of the analysis process for the specific implementation of the present invention;

[0151] Figure 3 This is the prediction diagram of the ablation shape analysis of C / HfC / SiC composite material at different times;

[0152] Figure 4 Schematic diagram of the ablation analysis and prediction results of C / HfC / SiC materials in high-speed hot air flow;

[0153] Figure 5 Screenshot of the actual ablation test video of C / HfC / SiC material. DETAILED DESCRIPTION

[0154] The present invention discloses a method for evaluating the ablation retreat of C / MeC / SiC composite materials. Those skilled in the art can refer to the contents of this article and appropriately improve the process parameters to achieve the desired effect. It should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0155] First, a C / MeC / SiC three-component ceramic composite material was prepared in the laboratory, and the component ratio, porosity parameters after ablation, mass flow rate of SiO2 during ablation, and molar flow rate of oxygen during ablation were obtained. For the case where the composite material is flushed by airflow during ablation, according to the formula v ceramic =(f ZrC +f SiC )v materal +f Cs v Cs Obtain its ablation rate, and finally according to R=R0-∫v ceramic dt analyzes the ablation retreat. For the case where there is no airflow scouring during the ablation process of the composite material, according to the formula for the oxide film thickness under airflow scouring, The formula for determining the oxide film thickness without airflow scouring using the separation method is: In this way, the thickness of the oxide film without air flow scouring can be solved, and then according to the formula Determine the amount of material retreat. Figure 2 As shown, Figure 2 Schematic diagram of the analysis process for the specific implementation of the present invention.

[0156] The present invention will be further described below with reference to the embodiments:

[0157] Example 1

[0158] Under the condition of high-temperature airflow scouring, the ablation retreat of C / HfC / SiC composite materials with mass fractions of 0.383, 0.334 and 0.283 was analyzed. The test parameters are shown in Table 1:

[0159] Table 1

[0160] Ablation time (s) Inflow pressure (kPa) Inflow temperature (K) <![CDATA[Inflow density (kg / m 3 )]]> Incoming flow velocity (m / s) 0-80 1.118 730.7 0.005168 2415.8 81-180 0.33 1021.8 0.000869 3531.6 181-320 0.4548 792.9 0.001748 2780.4 321-450 2.667 1442.9 0.005448 3593.9 451-900 26647 1297.4 0.006237 3317.1 901-1500 3.526 1100.5 0.010478 2882.7 1501-2000 1.118 730.7 0.005168 2415.8

[0161] Follow the steps 1 to 4 below:

[0162] Step 1: First, in the laboratory, a C / HfC / SiC composite material was prepared by mixing C component, HfC component, and SiC component in a ratio of 0.383, 0.334, and 0.283 by mass. The composite material was subjected to simulated ablation under airflow.

[0163] Step 2: The porosity parameter of the surface oxide film of the C / ZrC / SiC composite material after oxidation obtained in step 1 is obtained by formula a17, which is 5%;

[0164]

[0165] At the same time, the oxygen molar flow rate of the C / ZrC / SiC composite material obtained in step 1 above during the ablation process is obtained according to Formula 9. This embodiment indirectly obtains the specific value of the oxygen molar flow rate, that is, the oxygen molar flow rate is expressed by Formula 9.

[0166]

[0167] Wherein, l1 is the thickness of the oxide layer on the surface of the composite material after ablation under the condition of airflow scouring. Under the action of airflow, the oxide layer can only maintain a very thin layer, and in the present invention, it is 1E-6;

[0168] H is Henry's constant, which is 8.5×10 -7 mol·m -3 ·Pa -1 ;

[0169] is the pressure of oxygen on the surface of the composite material, which is obtained by fluid mechanics calculation based on the parameters in Table 1 in this embodiment;

[0170] is the rate constant of the oxidation reaction of the composite material, D eff is the effective diffusion coefficient of oxygen in SiO2, and the one used in this embodiment is (D eff / k O2 ) This ratio is 1E-4;

[0171] At the same time, the carbon fiber ablation rate is obtained according to the parameters in Table 1;

[0172] Step 3: Based on the porosity obtained in step 2, combined with the ratio and molar amount of the C component, HfC component and SiC component in the composite material, the physical property parameter γ1 related to the ratio, molar mass and porosity of the oxide layer of the three components of the composite material is obtained by formula 1, and the physical property parameter γ3 related to the composite material and its oxide layer is obtained by formula 2;

[0173]

[0174]

[0175] Where φ is the porosity of the oxide layer on the surface of the composite material; ρ i is the density of component i; M i is the molar mass of component i; f i is the mass fraction of component i of the composite material before ablation, and the mass fractions of components C, SiC and HfC are known parameters during material preparation.

[0176] According to the oxygen molar flow rate obtained in step 2, combined with the above-obtained physical property parameter γ1 related to the ratio of the three components of the composite material, the molar mass and the porosity of the oxide layer, the oxide layer thickening rate of the composite material is obtained by formula 3;

[0177]

[0178] Then according to the obtained oxide layer thickening rate v oxide-incr , combined with the obtained physical property parameter γ3 related to the composite material and its oxide layer, the ablation retreat rate of the matrix material is obtained by formula 4;

[0179] v materal =γ3v oxide-incr Formula 4;

[0180] Then, according to the obtained matrix material ablation retreat rate v materal , combining the mass fractions of the C component, the MeC component, and the SiC component in the composite material, and the ablation rate of the carbon fiber, the ablation rate of the C / ZrC / SiC composite material in the high-speed hot air flow is obtained by formula 5;

[0181] v ceramic =(f MeC +f SiC )v materal +f Cs v Cs Formula 5;

[0182] Step 4: Obtaining the ablation retreat of the composite material

[0183] The composite material test piece in step 1 is a spherical column with a spherical head radius of 20 mm. According to the ablation rate of the C / ZrC / SiC composite material obtained in step 3, the corresponding ablation retreat ∫v of the composite material is obtained by formula 6. ceramic dt is 32.9mm; Figures 3 and 4 As shown, Figure 3 This is the prediction diagram of the ablation shape analysis of C / HfC / SiC composite materials at different times. Figure 4 Schematic diagram of the ablation analysis and prediction results of C / HfC / SiC materials in high-speed hot air flow.

[0184] R=R0-∫v ceramic dt Formula 6.

[0185] The same C / HfC / SiC composite material as in Example 1 was used to conduct an actual ablation test under the same conditions. Figure 5 As shown, Figure 5 This is a screenshot of the actual ablation test video of C / HfC / SiC material. Figure 5The screenshot of the ablation test video shows the appearance and Figures 3 and 4 The ablation profiles of the C / HfC / SiC materials predicted by the evaluation method of the present invention are relatively close.

[0186] The ablation retreat of the test piece of this type of material finally obtained in the test is 36.5 mm. Combined with the analysis of the retreat amount using the method of the present invention, it is 32.9 mm, and the deviation is 9.9%.

[0187] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for evaluating the ablation retreat of a C / MeC / SiC composite material, characterized in that: The following steps are involved: S1) ablating or simulating ablating the C / MeC / SiC composite material under airflow flushing conditions, wherein the surface of the composite material is formed with Me x O y and an oxide layer of SiO2; said Me is a metal; said x is an integer of 1 to 2, and said y is an integer of 2 to 5; S2) obtaining the molar flow rate of oxygen entering the oxide layer, the porosity of the oxide layer, and the ablation rate of the carbon fiber during ablation or simulated ablation of the composite material in step S1); S3) According to the porosity of step S2), the mass fraction and molar mass of components C, MeC and SiC in the composite material, the component MexO in the oxide layer, y and the molar mass and density of SiO2, the first physical property parameter is obtained by formula 1; Wherein, γ1 is the first physical property parameter; φ is the porosity; f Cs is the mass fraction of component C in the composite material; f MeC is the mass fraction of the component MeC in the composite material; f SiC is the mass fraction of SiC component in the composite material; M MeC is the molar mass of the component MeC in the composite material; M C is the molar mass of component C in the composite material; M SiC is the molar mass of the component SiC in the composite material; is the component Me in the oxide layer x O y molar mass; is the molar mass of the component SiO2 in the oxide layer; is the component Me in the oxide layer x O y density; is the density of the component SiO2 in the oxide layer; The second physical property parameter is obtained by formula 2; Among them, γ3 is the second physical property parameter; Obtaining an oxide layer thickening rate based on the first physical property parameter and the oxygen molar flow rate described in step S2); obtaining a MeC-SiC matrix ablation recession rate based on the oxide layer thickening rate and the second physical property parameter; obtaining an ablation recession rate of the composite material based on the MeC-SiC matrix ablation recession rate and the mass fractions of components C, MeC, and SiC in the composite material, and the ablation rate of the carbon fiber described in step S2); S4) Obtaining an ablation retreat amount of the composite material based on the ablation retreat rate of the composite material obtained in step S3) in combination with the original dimensions of the composite material and the ablation time of the composite material.

2. The method according to claim 1, characterized in that The oxide layer thickening rate is obtained by formula 3; Among them, v oxide-incr is the oxide layer thickening rate; is the molar flow rate of oxygen.

3. The method according to claim 2, characterized in that The MeC-SiC matrix ablation retreat rate is obtained by formula 4: v materal = γ3v oxide-incr Formula 4: Among them, v materal is the ablation retreat rate of MeC-SiC matrix.

4. The method according to claim 3, characterized in that The ablation retreat rate of the composite material is obtained by formula 5; v ceramic = (f MeC + f SiC )v materal + f Cs v Cs Formula 5; Among them, v ceramic is the ablation retreat rate of the composite material; v Cs is the ablation rate of carbon fiber.

5. The method according to claim 4, characterized in that In step S4), the ablation retreat amount of the composite material is obtained by formula 6; R=R0-∫v ceramic dt Formula 6; Wherein, R is the outer dimensions of the composite material after ablation; R0 is the original outer dimensions of the composite material; and t is the ablation time of the composite material.

6. A method for evaluating the ablation retreat of a C / MeC / SiC composite material, characterized in that: The following steps are involved: S1) ablating or simulating ablating the C / MeC / SiC composite material without airflow flushing, wherein the surface of the composite material is formed with MeC x O y and an oxide layer of SiO2; said Me is a metal; said x is an integer of 1 to 2, and said y is an integer of 2 to 5; S2) obtaining the molar flow rate of oxygen entering the oxide layer and the porosity of the oxide layer during ablation or simulated ablation of the composite material in step S1); S3) According to the porosity of step S2), the mass fraction and molar mass of components C, MeC and SiC in the composite material, the component MexO in the oxide layer, y and the molar mass and density of SiO2, the first physical property parameter is obtained by formula 1; Among them, γ1 is the first physical property parameter; φ is the porosity; f Cs is the mass fraction of component C in the composite material; f MeC is the mass fraction of the component MeC in the composite material; f SiC is the mass fraction of SiC component in the composite material; M MeC is the molar mass of the component MeC in the composite material; M C is the molar mass of component C in the composite material; M SiC is the molar mass of the component SiC in the composite material; is the component Me in the oxide layer x O y molar mass; is the molar mass of the component SiO2 in the oxide layer; is the component Me in the oxide layer x O y density; is the density of the component SiO2 in the oxide layer; The second physical property parameter is obtained by formula 2; Among them, γ3 is the second physical property parameter; According to the first physical property parameter and the oxygen molar flow rate in step S2), the thickness of the oxide layer on the surface of the composite material after ablation under the condition of no airflow scouring is obtained by formula 7; Wherein, l1 is the thickness of the oxide layer on the surface of the composite material after ablation without airflow scouring; t is the ablation time of the composite material; is the oxygen molar flow rate of the oxide layer on the surface of the composite material; S4) obtaining the ablation retreat amount of the composite material according to the second physical property parameter and the thickness of the oxide layer in step S3) using Formula 8; x sub =γ3l1 formula 8; Among them, x sub is the ablation retreat of the composite material.

7. The method according to any one of claims 1 to 6, characterized in that: The oxygen molar flow rate in step S2) is obtained by formula 9 based on the pressure of oxygen on the surface of the composite material, the Henry constant, the oxidation reaction rate constant during ablation of the composite material, the effective diffusion coefficient of oxygen in SiO2, the thickness of the oxide layer on the surface of the composite material after ablation without airflow scouring, and the porosity: in, is the pressure of oxygen on the surface of the composite material, in Pa; H is Henry's constant, which is 8.5×10 -7 mol·m -3 ·Pa -1 ; is the oxidation reaction rate constant during ablation of the composite material; D eff is the effective diffusion coefficient of oxygen in SiO2, in m 2 ·s -1 ; l1 is the thickness of the oxide layer on the surface of the composite material after ablation without airflow scouring.

8. The method according to claim 7, characterized in that Based on the dissolution-diffusion kinetic parameters and the relationship between the diffusion coefficient and the reaction coefficient per unit distance, the thickness of the oxide layer on the surface of the composite material after ablation under the condition of no airflow scouring is obtained by formula 10; Where A is the relationship between the diffusion coefficient and reaction coefficient of oxygen per unit distance in the oxide layer; B is the dissolution-diffusion kinetic parameter of oxygen in the oxide layer; According to the first physical property parameter, the pressure of oxygen on the wall, the Henry constant, the effective diffusion coefficient of oxygen in SiO2 and the porosity in step S2), the dissolution-diffusion kinetic parameters of the oxygen in the oxide layer are obtained by formula 11; According to the oxidation reaction rate constant during ablation of the composite material, the effective diffusion coefficient of oxygen in SiO2, and the porosity of the oxide layer in step S2), the magnitude relationship parameter of the diffusion coefficient and reaction coefficient of oxygen per unit distance in the oxide layer is obtained by formula 12; 9. The method according to claim 7, characterized in that Based on the pore curvature factor and the diffusion coefficient of oxygen in SiC oxide SiO2 without curved voids, the effective diffusion coefficient of oxygen in SiC oxide is obtained by formula a19; Where τ is the pore curvature factor and D is the diffusion coefficient of oxygen in SiO2, an oxide of SiC without curvature pores.

10. The method according to claim 1 or 2, characterized in that The porosity of the oxide layer is obtained by formula a17;

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