Pre-welding surface modification method suitable for Cf / SiC ceramic prepared through LSI method

Abstract

The invention discloses a pre-welding surface modification method suitable for Cf / SiC ceramic prepared through an LSI method, and belongs to the field of brazing, HNO3 / HF mixed acid is adopted, under the condition that corrosion parameters of the internal structure of the Cf / SiC composite material are not damaged, surface corrosion is conducted on the Cf / SiC composite material, defects such as grooves and holes are formed, filling is conducted through the capillary action of brazing filler metal after welding, and the Cf / SiC ceramic prepared through the LSI method is subjected to pre-welding surface modification. And the strength of the ceramic and metal heterogeneous connection joint is enhanced by utilizing a mechanical occlusion effect. The room-temperature average shear strength of the Cf / SiC composite material and metal Mo brazed joint obtained by the method disclosed by the invention reaches 56MPa. According to the scheme, the Cf / SiC composite material is subjected to pre-welding surface modification, surface grooves, holes and other defects are prepared, the defects are filled through the capillary joint filling effect of brazing filler metal in the brazing process, a mechanical meshing structure is formed after solidification, and therefore the strength of the Cf / SiC composite material and alloy heterogeneous connection joint is greatly enhanced.

Description

Technical Field

[0001] The invention belongs to the field of brazing, and in particular relates to a C f / SiC ceramic surface modification method before welding. Background Art

[0002] Reactive melt infiltration is also known as liquid silicon infiltration (LSI). This method was first used in the early 1980s and is the famous SILCOMP process. The main process of this process is to use molten Si to infiltrate the carbon fiber preform through the corresponding process, and the molten silicon reacts chemically with the matrix carbon to generate silicon carbide, thereby producing C f / SiC composite material (Carbon Fiber Reinforced Silicon Carbide). f Due to its low density and high temperature resistance, SiC composite materials have shown great development potential in the application of hot end components of aircraft engines. f / SiC composite materials can reduce the amount of cooling air, increase the temperature before the turbine and combustion efficiency, reduce fuel consumption and harmful emissions, thereby improving the economy and environmental protection of aircraft engines. This is also an important development trend in the structure of hot end components of civil aviation engines. f / SiC composite materials can significantly reduce engine weight, increase turbine pre-temperature, and thus improve engine thrust-to-weight ratio. Decades ago, German researcher Krenkel first used liquid Si to infiltrate carbon / carbon materials and successfully developed carbon / silicon carbide composite materials. This is a simple, fast and low-cost process method. This method does not require mechanical pressure and can prepare small-sized and complex-shaped samples. It is worth noting that the C prepared by this method f / SiC, liquid Si will remain inside the composite material during the reaction, which leads to f / There will be some free Si in SiC.

[0003] Due to the brittleness of free Si, the residual Si will reduce the C f / Mechanical properties of SiC composites. Experts and scholars in the field of ceramics have been committed to reducing C by improving the impregnation process. f / The appearance of free Si in SiC composites. However, it is worth noting that some scholars have used the characteristics of free Si in some SiC composites to etch the composites with HNO3 / HF mixed acid to remove free Si, thereby preparing porous SiC. After reading the literature ("Nanoscale directional etching characteristics and mechanisms of HF / HNO3 etchant", Journal of Micromechanics and Microengineering; "Kinetics of silicon acid wet chemical etching in binary and ternary mixtures of HF, HNO3 and H2SiF6", Physical ChemistryChemical Physics), there are two main mechanisms for HNO3 / HF to corrode Si. One is that HNO3 first oxidizes Si to form SiO2, and then HF corrodes SiO2, thereby achieving isotropic corrosion of Si; the other mechanism is to regard the reaction between acid and Si as a local electrochemical process, where a cathode and an anode are formed where the reaction occurs, and a current flows between them in the reaction. The anode is a dissolution reaction of silicon, and the cathode is a consumption reaction of HNO3. Using this principle, if HNO3 / HF mixed acid is used for C f Surface modification of C / SiC composites can be achieved by adjusting the ratio of HNO3, HF and solvent to control the corrosion rate and preparing surface defects of the composites to accommodate the penetration of solder. f Mechanical enhancement of brazed joints of SiC / SiC composites. Summary of the invention

[0004] In view of the above-mentioned shortcomings, the present invention provides a C f / SiC ceramic surface modification method before welding.

[0005] Using HNO3 / HF mixed acid, without destroying C f Under the corrosion parameters of the internal structure of C / SiC composite materials, f / SiC composite materials undergo surface corrosion to form defects such as grooves and holes, which are filled by the capillary action of the brazing filler metal after brazing, and the strength of the heterogeneous joints between ceramics and metals is enhanced by mechanical bite.

[0006] Key points of the technical solution of the present invention: Corrosion process: The corrosion solution is prepared with HNO3 (60%), HF (45%) and H2O, with a ratio ranging from 14:10:10 to 14:20:10 (volume ratio), and the corrosion time is 5min-10min. After corrosion, rinse with a large amount of deionized water for standby use. The HNO3 (60%) refers to the mass percentage concentration of nitric acid in the nitric acid solution of 60%, and the HF (45%) refers to the mass percentage concentration of HF in the HF solution of 45%.

[0007] The solder used in the present invention is Ag28Cu3Ti.

[0008] In the present invention, C f The metal material for brazing of SiC / SiC composite materials is metal Mo.

[0009] The metal Mo and C f The surface of the SiC composite material to be welded is polished and cleaned, and then the brazing material is prepared into solder paste. f The solder paste was applied to the surface of the SiC composite material to be welded, and then assembled with metal Mo to form a sample to be welded, and then placed in a vacuum furnace for vacuum heating treatment. The heating process was: heating from room temperature to 830℃ at 10℃ / min for 10min, then cooling to 200℃ at 10℃ / min, turning off the heating and cooling the furnace to room temperature to obtain C f / SiC composite material and metal Mo brazing joint. f The room temperature average shear strength of the brazed joint between the / SiC composite material and metal Mo reaches 56MPa.

[0010] Beneficial effects brought about by the technical solution of the present invention: C f The forming of SiC composite materials cannot be separated from the support of welding technology. f / SiC composite materials are surface modified before welding to prepare surface defects such as grooves and holes. These defects are filled by the capillary filling effect of the brazing material during brazing, and a mechanical bite structure is formed after solidification, thereby greatly enhancing the C f / SiC composite and alloy heterogeneous joint strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 After corrosion, C f Microstructure of the joint obtained by brazing SiC composite material and metal Mo; Figure 2 After corrosion, C f Fracture of brazed joint between SiC / SiC composite material and metal Mo, C f / SiC composite material side; Figure 3 After corrosion, C f Fracture of brazed joint between SiC composite material and metal Mo, metal Mo side; Figure 4 Solder from C f Shear marks left by pulling out the SiC composite material along the shear direction from the surface defects. DETAILED DESCRIPTION

[0012] Comparative Example 1 A C suitable for LSI preparation f / SiC ceramic surface modification method before welding, the specific steps are as follows: (1) Metal Mo and C f The surface of the SiC composite material to be welded was polished with 1500 sandpaper and ultrasonically cleaned with acetone for 10 minutes.

[0013] (2) Ag28Cu3Ti solder and pine alcohol are mixed into solder paste, and the solder paste is printed on C f The solder paste is applied to the surface of the SiC composite material to be welded, and then assembled with metal Mo to form a welded sample. The assembly form is: Mo / Ag28Cu3Ti solder / C f / SiC, clamped with graphite fixture, and placed in a vacuum furnace.

[0014] (3) Wait until the vacuum degree reaches 5×10 -4 Pa, the heating process is: from room temperature to 830℃ at 10℃ / min, keep the temperature for 10min, then reduce the temperature to 200℃ at 10℃ / min, turn off the heating and cool the furnace to room temperature, and obtain C f / SiC composite material and metal Mo brazing joint.

[0015] (4) C obtained by this method f The room temperature shear strength of the brazed joint between the / SiC composite material and metal Mo is 32MPa.

[0016] Example 1 A C suitable for LSI preparation f / SiC ceramic surface modification method before welding, the specific steps are as follows: (1) Preparation of etching solution for C prepared by LSI method f The surface to be welded of the SiC / SiC composite material was corroded. The corrosive solution was prepared with HNO3 (60%), HF (45%) and H2O in a ratio of 14:10:10 (volume ratio). The corrosion time was 10 minutes. After corrosion, it was rinsed with a large amount of deionized water for standby use.

[0017] (2) Metal Mo and C f The surface of the SiC composite material to be welded was polished with 1500 sandpaper and ultrasonically cleaned with acetone for 10 minutes.

[0018] (3) Ag28Cu3Ti solder and pine alcohol are mixed into solder paste, and the solder paste is printed on C f The solder paste is applied to the surface of the SiC composite material to be welded, and then assembled with metal Mo to form a welded sample. The assembly form is: Mo / Ag28Cu3Ti solder / C f / SiC, clamped with graphite fixture, and placed in a vacuum furnace.

[0019] (4) Wait until the vacuum degree reaches 5×10 -4 Pa, the heating process is: from room temperature to 830℃ at 10℃ / min, keep the temperature for 10min, then reduce the temperature to 200℃ at 10℃ / min, turn off the heating and cool the furnace to room temperature, and obtain C f / SiC composite material and metal Mo brazing joint, the joint microstructure is as follows Figure 1 shown.

[0020] (5) C obtained by this method f The average room temperature shear strength of the brazed joint between the / SiC composite material and the metal Mo is 54MPa. Figure 2 , Figure 3 and Figure 4 shown.

[0021] Example 2 A C suitable for LSI preparation f / SiC ceramic surface modification method before welding, the specific steps are as follows: (1) Preparation of etching solution for C prepared by LSI method f The surface to be welded of the SiC / SiC composite material was corroded. The corrosive solution was prepared with HNO3 (60%), HF (45%) and H2O in a ratio of 14:15:10 (volume ratio). The corrosion time was 7 minutes. After corrosion, it was rinsed with a large amount of ionized water for later use.

[0022] (2) Metal Mo and C f The surface of the SiC composite material to be welded was polished with 1500 sandpaper and ultrasonically cleaned with acetone for 10 minutes.

[0023] (3) Ag28Cu3Ti solder and pine alcohol are mixed into solder paste, and the solder paste is printed on C f The solder paste is applied to the surface of the SiC composite material to be welded, and then assembled with metal Mo to form a welded sample. The assembly form is: Mo / Ag28Cu3Ti solder / C f / SiC, clamped with graphite fixture, and placed in a vacuum furnace.

[0024] (4) Wait until the vacuum degree reaches 5×10 -4 Pa, the heating process is: from room temperature to 830℃ at 10℃ / min, keep the temperature for 10min, then reduce the temperature to 200℃ at 10℃ / min, turn off the heating and cool the furnace to room temperature, and obtain C f / SiC composite material and metal Mo brazing joint.

[0025] (5) C obtained by this method f The average shear strength of the brazed joint between the / SiC composite material and metal Mo is 54MPa at room temperature.

[0026] Example 3 A C suitable for LSI preparation f / SiC ceramic surface modification method before welding, the specific steps are as follows: (1) Preparation of etching solution for C prepared by LSI method f The surface to be welded of the SiC / SiC composite material was corroded. The corrosive solution was prepared with HNO3 (60%), HF (45%) and H2O in a ratio of 14:20:10 (volume ratio). The corrosion time was 5 minutes. After corrosion, it was rinsed with a large amount of ionized water for standby use.

[0027] (2) Metal Mo and C f The surface of the SiC composite material to be welded was polished with 1500 sandpaper and ultrasonically cleaned with acetone for 10 minutes.

[0028] (3) Ag28Cu3Ti solder and pine alcohol are mixed into solder paste, and the solder paste is printed on C f The solder paste is applied to the surface of the SiC composite material to be welded, and then assembled with metal Mo to form a welded sample. The assembly form is: Mo / Ag28Cu3Ti solder / C f / SiC, clamped with graphite fixture, and placed in a vacuum furnace.

[0029] (4) Wait until the vacuum degree reaches 5×10 -4 Pa, the heating process is: from room temperature to 830℃ at 10℃ / min, keep the temperature for 10min, then reduce the temperature to 200℃ at 10℃ / min, turn off the heating and cool the furnace to room temperature, and obtain C f / SiC composite material and metal Mo brazing joint.

[0030] (5) C obtained by this method f The average shear strength of the brazed joint between the / SiC composite material and metal Mo is 56MPa at room temperature.

Claims

1. A C suitable for LSI preparation f / SiC ceramic surface modification method before welding, characterized in that, Using HNO3 / HF mixed acid, without destroying C f Under the corrosion parameters of the internal structure of C / SiC composite materials, f / SiC composite materials are subjected to surface corrosion to form grooves and holes, which are filled by the capillary action of the brazing filler metal after brazing, and the strength of the heterogeneous joints between ceramics and metals is enhanced by mechanical bite.

2. A C suitable for LSI preparation according to claim 1 f / SiC ceramic surface modification method before welding, characterized in that, The etching solution is prepared with 60% HNO3, 45% HF and H2O.

3. A C suitable for LSI method preparation according to claim 2 f / SiC ceramic surface modification method before welding, characterized in that, The volume ratio of 60% HNO3, 45% HF and H2O in the etching solution is 14:10:10-14:20:10, the etching time is 5min-10min, and the surface is rinsed with deionized water after etching.

4. A C suitable for LSI method preparation according to claim 1 f / SiC ceramic surface modification method before welding, characterized in that, The solder used is Ag28Cu3Ti.

5. The C suitable for LSI method preparation according to claim 1 f / SiC ceramic surface modification method before welding, characterized in that, With C f The metal material for brazing of SiC / SiC composite materials is metal Mo.

6. A C suitable for LSI preparation according to claim 5 f / SiC ceramic surface modification method before welding, characterized in that, The metal Mo and C f The surface of the SiC composite material to be welded is polished and cleaned, and then the brazing material is prepared into solder paste. f The solder paste was applied to the surface of the SiC composite material to be welded, and then assembled with metal Mo to form a sample to be welded, and then placed in a vacuum furnace for vacuum heating treatment; the heating process was: heating from room temperature to 830℃ at 10℃ / min for 10min, then cooling to 200℃ at 10℃ / min, turning off the heating and cooling the furnace to room temperature to obtain C f / SiC composite material and metal Mo brazing joint.

7. The method for surface modification of Cf / SiC ceramics before welding suitable for LSI preparation according to claim 6, characterized in that: Get C f The room temperature average shear strength of the brazed joint between the / SiC composite material and metal Mo reaches 56MPa.

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