A high-surface-quality ceramic matrix composite self-repairing processing method

Abstract

The application relates to the technical field of ceramic matrix composite self-repairing machining, and discloses a high-surface-quality ceramic matrix composite self-repairing machining method. In view of the difficulties that micro cracks, micro defects, continuous fiber breakage or damage are easily generated during machining of ceramic matrix parts, a special tool with a BCC metal gradient layer on the surface is adopted, high-speed dry milling is used to make the cutting point temperature exceed 800 DEG C, Si elements are diffused with the BCC metal gradient layer as a carrier, and the surface of the part is repaired. The method can reduce the local hardness of the material, inhibit crack propagation, improve the interface bonding between the fiber and the matrix, realize low-damage cutting, and is reliable in process, thereby providing support for batch manufacturing of hot end parts of an aero-engine.

Description

Technical Field

[0001] This invention relates to the field of ceramic matrix composite material processing technology, and specifically to a self-healing processing method for high surface quality ceramic matrix composites. Background Technology

[0002] With the rapid development of aerospace technology, the thrust-to-weight ratio of aero engines continues to rise, placing increasingly stringent demands on the high-temperature resistance, high-pressure resistance, and lightweight performance of hot-end components. While traditional high-temperature alloys have been widely used in aero engines in the past, their high-temperature strength, oxidation resistance, and weight advantages are gradually approaching their limits under ultra-high temperature conditions, making them unsuitable for the design requirements of future advanced engines. Against this backdrop, fiber-reinforced ceramic matrix composites have emerged as a unique and comprehensive solution. Not only do they have a density only 1 / 3 to 1 / 2 that of high-temperature alloys, but they also possess excellent high-temperature resistance, wear resistance, and corrosion resistance, along with ultra-high specific modulus and specific strength. This effectively reduces component weight and improves engine thrust and efficiency, thus attracting significant attention from governments, militaries, and research institutions worldwide, and is widely recognized as one of the ideal substrates for replacing high-temperature alloys and creating next-generation aero-engine hot-end components.

[0003] However, the unique structure and properties of ceramic matrix composites make them typical difficult-to-machine materials. As the substrate for hot-end components in aero-engines, fiber-reinforced composites require extremely high machining precision while ensuring a defect-free finish. These materials exhibit extremely high hardness, significant brittleness, and marked anisotropy and heterogeneity, with a complex interfacial bonding between the fibers and the matrix. Traditional machining methods such as turning and milling easily lead to a series of machining defects: cutting forces result in excessive surface roughness, scratches, and other quality problems; fibers are prone to breakage and shedding, compromising the overall structural integrity of the material; and microcracks are easily generated at the fiber-matrix interface. These defects not only fail to meet the requirements for high-precision, defect-free machining but also severely weaken the mechanical properties and reliability of components, leading to a sharp reduction in fatigue life and even premature failure in the complex and harsh service environment of aero-engines. This significantly restricts the large-scale application of ceramic matrix composites in practical aerospace components. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art and provide a self-healing processing method for high surface quality ceramic matrix composites.

[0005] The present invention provides a self-healing processing method for high surface quality ceramic matrix composites, characterized in that the high temperature of cutting during the processing induces Si elements to accumulate in the surface layer, thereby reducing the local hardness of the material and inhibiting crack propagation, and improving the surface quality of the processed area.

[0006] The self-healing processing method for high surface quality ceramic matrix composites provided by the present invention includes the following steps: A. Processing parameter control; B. Construct a BCC metal gradient layer on the tool surface; C. Fabrication of BCC metal gradient layers; D. Setting high-speed milling machining parameters; E. Control of contact depth in milling processes; F. Tool movement direction control; In step A of the above method, the processing parameters are controlled to ensure that the cutting point temperature is greater than 800°C, thereby inducing Si elements to accumulate on the surface of the part using the BCC metal gradient layer as a diffusion carrier.

[0007] In step B of the above method, the BCC metal gradient layer has a thickness of 100 μm-1 mm and is made of stable or metastable BCC metal. The stable BCC metal is one or more of Ti, V, Cr, α-Fe, Nb, and Ta, with the addition of Mo or W. The metastable BCC metal is formed by low-temperature deposition or thin film size effect induction of FCC-based metal, with the addition of Mo or W. The W or Mo content in the direct contact layer between the gradient layer and the tool is higher than 80 wt.%.

[0008] In step C of the above method, the BCC metal gradient layer is formed by plasma spraying, supersonic flame spraying or laser cladding, and the average grain size is less than 5 μm.

[0009] In step D of the above method, the machining parameters for high-speed dry milling are: cutting speed 5000-15000 r / min, cutting depth 0.01-0.03 mm, and feed rate 1000-1500 mm / min.

[0010] In step E of the above method, during the milling process, the contact depth between the tool and the ceramic-based part is 10μm-100μm.

[0011] In step F of the above method, the angle between the tool movement direction and the ceramic fiber or particle arrangement direction of the ceramic-based part is 10°-80°.

[0012] Compared with the prior art, the present invention has the following advantages: 1) This method differs from the traditional "hard-hard cutting" process for machining ceramic matrix composites, which involves brittle fracture and material removal. During the cutting process, while removing material, the Si atoms in the BCC metal have a high diffusion coefficient due to the high temperature exceeding 800℃. This allows Si atoms to diffuse during the heating and cooling process. By relying on the BCC metal thin gradient layer tool, the reconstruction and repair of Si atoms can be achieved, resulting in high-precision, low-damage ceramic matrix parts.

[0013] 2) The controllable thin gradient layer metal distribution on the tool surface allows the bonding state between the gradient layer and the tool substrate to be controllable, enabling the controllable distribution of BCC metal and Si atoms during milling, thus completing high-precision machining of the ceramic substrate surface and providing reliable technical support for the mass production of hot-end components of the next-generation aero-engine. Attached Figure Description

[0014] Appendix Figure 1 : Dense metal gradient layer on the tool surface; Appendix Figure 2 : Schematic diagram of the self-healing process; Appendix Figure 3 Surface roughness after processing. Detailed Implementation

[0015] The present invention will be further described below through specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Example 1

[0016] The material being processed is a 2.5D woven ceramic matrix composite prepared by CVI+PIP; a silicon nitride-based ceramic cutting tool is used, with a Cr-Mo stabilized BCC metal gradient layer constructed on its surface by supersonic flame spraying, the gradient layer being 500μm thick, as shown in the attached figure. Figure 1 As shown, the Mo content in the layer directly in contact with the tool is 85 wt.%, decreasing outwards to a surface layer with 60 wt.% Cr and 25 wt.% Mo, and an average grain size of 3 μm. High-speed dry milling was used, with machining parameters set as follows: cutting speed 10000 r / min, depth of cut 0.02 mm, feed rate 1200 mm / min, and cutting point temperature controlled at 850℃. The contact depth between the tool and the workpiece was adjusted to 50 μm, and the angle between the tool movement direction and the ceramic fiber weaving direction was 45°. Machining was then initiated. After machining, the stable Mo phase structure in the BCC metal gradient layer under high temperature was cut, and Si in the workpiece chips underwent a diffusion reaction, forming a dense Si-Cr-Mo surface layer. Si atoms repaired and supplemented fractured or defective surfaces, as shown in the attached figure. Figure 2 As shown, the machined surface of the part is free of fiber breakage, pores and other defects, and the surface roughness is 2.75μm. Example 2

[0017] SiC / SiC ceramic-based parts with a SiC whisker content of 15 wt.% and a whisker length of 50 μm were selected as the machining targets. Alumina-based ceramic cutting tools were used, with a Ti-W stable BCC metal gradient layer constructed on the surface by laser cladding. The gradient layer thickness was 100 μm, with a W content of 82 wt.% in direct contact with the cutting tool, decreasing outwards to a Ti content of 70 wt.% and a W content of 18 wt.% on the surface layer, with an average grain size of 2 μm. High-speed dry milling was used, with machining parameters set as follows: cutting speed 5000 r / min, cutting depth 0.01 mm, feed rate 1000 mm / min, and cutting point temperature controlled at 820℃. The contact depth between the cutting tool and the part was adjusted to 10 μm, and the angle between the cutting tool movement direction and the ceramic whisker arrangement direction was 80°. Machining was then started. After machining, the stable phase structure of W element in the BCC metal gradient layer under high temperature is cut, and Si in the part chips undergoes diffusion reaction to form a dense Si-Ti-W surface layer. The machined surface of the part is free of whisker fracture, pores and other defects, and the surface roughness is 3.16μm. Example 3

[0018] C / SiC ceramic matrix parts with 15μm fiber diameter and 3D four-way braiding using the MI process were selected as the machining object. A PCBN composite tool was used, with a Ni-Mo metastable BCC metal gradient layer constructed on its surface by plasma spraying (deposition temperature 180℃). The gradient layer thickness was 800μm, with a Mo content of 88wt.% in the layer directly in contact with the tool, decreasing outwards to a Ni content of 65wt.% and a Mo content of 23wt.% at the surface layer. The surface metastable BCC phase size was 40nm, and the average grain size was 4μm. High-speed dry milling was used, with machining parameters set as follows: cutting speed 15000r / min, depth of cut 0.03mm, feed rate 1500mm / min, and cutting point temperature controlled at 900℃. The contact depth between the tool and the part was adjusted to 100μm, and the angle between the tool movement direction and the ceramic fiber weaving direction was 10°. Machining was then initiated. After machining, the stable phase structure of Mo in the metastable BCC metal gradient layer under high temperature is cut, and Si in the part chips undergoes a diffusion reaction to form a dense Si-Ni-Mo surface layer. The machined surface of the part is free of fiber breakage, porosity, and other defects, with a surface roughness of 1.35 μm. (See attached image.) Figure 3 As shown. Example 4

[0019] ZrO2 / SiC ceramic-based parts with a SiC particle content of 20 wt.% and a particle size of 5 μm were selected as the machining target. A silicon nitride-based ceramic cutting tool was used, with its surface laser-clad at a deposition temperature of 190℃ to construct a Co-W metastable BCC metal gradient layer. The gradient layer thickness was 300 μm. The W content in the layer directly in contact with the cutting tool was 83 wt.%, decreasing outwards to a surface layer with a Co content of 62 wt.% and a W content of 21 wt.%. The surface metastable BCC phase size was 35 nm, and the average grain size was 2.5 μm. High-speed dry milling was employed, with machining parameters set as follows: cutting speed 8000 r / min, depth of cut 0.02 mm, feed rate 1300 mm / min, and cutting point temperature controlled at 880℃. The contact depth between the cutting tool and the part was adjusted to 60 μm, and the angle between the cutting tool movement direction and the ceramic particle arrangement direction was 60°. Machining was then initiated. After machining, the stable phase structure of W element in the metastable BCC metal gradient layer under high temperature is cut. Si in the part chips undergoes diffusion reaction to form a dense Si-Co-W surface layer. Moreover, Si atoms diffuse with the tool to repair and atomically replenish the broken or defective ceramic matrix parts. The machined surface of the parts is free of particle depressions, pores and other defects, with a surface roughness of 2.35μm.

Claims

1. A method for processing high surface quality ceramic matrix composites for self-repair, characterized in that, High-speed dry milling was performed using a tool with a BCC metal gradient layer on the surface. The machining parameters were controlled to keep the cutting point temperature above 800℃, which induced Si elements to accumulate on the surface of the part using the BCC metal gradient layer as a diffusion carrier.

2. The self-healing processing method for high surface quality ceramic matrix composites according to claim 1, characterized in that, The BCC metal gradient layer has a thickness of 100 μm-1 mm and is made of stable BCC metal or metastable BCC metal. The stable BCC metal is one or more of Ti, V, Cr, α-Fe, Nb, and Ta, with Mo or W added. The metastable BCC metal is formed by low-temperature deposition or thin film size effect induction of FCC-based metal, with Mo or W added. The W or Mo content in the gradient layer and the tool direct contact layer is higher than 80 wt.%.

3. The self-healing processing method for high surface quality ceramic matrix composites according to claim 2, characterized in that, The BCC metal gradient layer is formed by plasma spraying, supersonic flame spraying or laser cladding, with an average grain size of less than 5 μm.

4. The self-healing processing method for high surface quality ceramic matrix composites according to claim 1, characterized in that, The machining parameters for the high-speed dry milling are: cutting speed 5000-15000 r / min, cutting depth 0.01-0.03 mm, and feed rate 1000-1500 mm / min.

5. The self-healing processing method for high surface quality ceramic matrix composites according to claim 1, characterized in that, During the milling process, the contact depth between the cutting tool and the ceramic-based part is 10μm-100μm.

6. The self-healing processing method for high surface quality ceramic matrix composites according to claim 1, characterized in that, During the milling process, the angle between the direction of tool movement and the direction of ceramic fiber or particle arrangement of the ceramic-based part is 10°-80°.

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