JIANG Wei ¹, YU Rong ², PAN Haijun ², DENG Peilin ², DUAN Shichang ², YANG Bo ²

(1. AECC Shenyang Engine Research Institute, Shenyang 110179, Liaoning, China;

2. Shaanxi Huaqin Technology Industry Co., Ltd., Xi'an 710100, Shaanxi, China)

Extended abstract:[Background and purposes] With the rapid progress of modern society, the widespread application of 5G communication technology has quietly changed every corner of our lives. However, the accompanying issue of electromagnetic pollution has become a severe challenge that we must face. The problems such as electromagnetic interference and electromagnetic radiation are becoming increasingly serious, posing potential threats to human physiological and psychological health and even affecting the normal operation of electronic devices. Therefore, the prevention and control of electromagnetic radiation interference from electronic equipment and weapons has become the top priority of scientific research. Silicon carbide fiber-reinforced silicon carbide (SiC_f/SiC) ceramic matrix composites have been widely used in aerospace and electromagnetic shielding fields, due to their high specific strength and specific stiffness, excellent corrosion resistance, oxidation resistance and high temperature stability, as well as adjustable parameters. Platinum (Pt) has good electrical and thermal conductivity, which can effectively absorb and conduct electromagnetic waves, thereby reducing the impact of electromagnetic radiation on the surrounding environment and improving the electromagnetic shielding effect. Moreover, Pt has extremely high chemical stability, strong corrosion resistance and oxidation resistance, and can maintain stable performance even under high temperature and harsh environments. Therefore, it is widely used in the manufacture of rocket engines such as combustion chambers. In this study, SiC_f/SiC composites with Pt interface layer were prepared by using magnetron sputtering method combined with the precursor impregnation pyrolysis (PIP) process, where the thickness of the Pt interface layer was controlled by adjusting the magnetron sputtering process parameters and the mechanical and electromagnetic shielding properties of the composites with different thicknesses of Pt interface layer were explored.[Methods] 2D SiC fiber cloth (50 mm×50 mm) was arranged in a vacuum tube furnace [TCL1200-1200(Ⅱ.), Tianjin Mafuer Technology Co., Ltd.], vacuumed to below 10 Pa, and heated to 800 ℃ for 1 h at a heating rate of 5 ℃·min^−1. Then, ultrasonic cleaning in absolute ethanol for 15 min to remove impurities was carried out, followed by drying at 70 ℃. The SiC fiber cloth was placed as the sputtering substrate into the vacuum chamber of the automatic magnetron sputtering coating system (TRP-450, Shenyang Scientific Instrument Co., Ltd., Chinese Academy of Sciences) for the preparation of the Pt interface layer. The sputtering was carried out on both the front and back sides of each layer of SiC fiber cloth. The precursor solution was configured with solid polycarbosilanes (PCS) and xylene in a mass ratio of 1:1. The precursor slurry was evenly dispersed through ultrasonic oscillation. The samples No. 1# and No. 2# with Pt coating and sample No. 3# without Pt coating were layered, with 10 layers, while the molding thickness was 3 mm. The SiC matrix was prepared on the surface by the PIP method. To densify the composite, the impregnation and pyrolysis process were repeated for more than 10 cycles until the weight gain was ≤1%. The three-point flexural strength was measured using an HD-609B universal testing machine, where the sample size was 50 mm×4 mm×3 mm and the span was 30 mm. During the measurement, loading was performed at a speed of 0.5 mm·min⁻¹ and all measurements were averaged over three samples. The Archimedes' principle was used to calculate density and porosity of the composites. A scanning electron microscopy (SEM-S4800) was used to characterize the surface and cross-sectional topography of the samples and characterize the elemental distribution in combination with energy dispersive spectroscopy (EDS). Resistance of the samples was tested by using a direct current source, while dielectric properties and S parameters were measured by using the rectangular waveguide method. The size of the sample was 22.86 mm×10.16 mm× 3 mm and the test band was X-band (8.2–12.4 GHz).[Results] It can be seen from the SEM and EDS results that the Pt interface layer of sample No. 1# shows a flat and smooth distribution and there is no obvious defect coating, while the thickness of the Pt interface layer deposited on the surface of silicon carbide fiber is relatively uniform and the thickness of the Pt interface layer is 150 nm. The surface of sample No. 2# is uneven, because the excessively high sputtering power made particles fail to relax to the lower energy before encountering the new particles and nucleate with them, resulting in a significant reduction in the diffusion ability of the deposited particles, thereby reducing the uniformity of the surface of the film. The thickness of the Pt interface layer is 280 nm. According to the results of flexural strength, the strength of the composite without the interface layer is only 322 MPa. When the Pt interface layer is 150 nm, the mean flexural strength can reach 425 MPa, with an increase by 32%. When the interlayer thickness increases from 150 nm to 280 nm, the enhancement effect is weakened. As the thickness of the interface layer increases, the dielectric constant of SiC_f/SiC composites shows a trend of increasing first and then decreasing. The real part (ε') of the complex permittivity increases from 2.5 to 9.0 and then decreases to 5.0, while the imaginary part (ε") increases from 11.4 to 48.9 and then decreases to 39.6 at 10 GHz, with a more pronounced trend in the imaginary part. Absorption and shielding efficiency of the SiC_f/Pt/SiC (Pt=150 nm) was significantly increased from 16.65 dB to 32.01 dB, showing excellent electromagnetic shielding performance. It can be seen from the absorption efficiency that the SiC_f/Pt/SiC (Pt=280 nm) composites for incident electromagnetic waves are more than 99.0% and the SiC_f/Pt/SiC (Pt=150 nm) composites can reach more than 99.5%. Therefore, when the thickness of the interfacial layer is 150 nm, the electromagnetic shielding effect is the highest.[Conclusions] When the Pt interface thickness is 150 nm, the mechanical properties of SiC_f/SiC composites are the highest, with typical ductile fracture characteristics, while the mean flexural strength at room temperature is 425 MPa, which is 32% higher than that of the non-interface layer composites. The introduction of the Pt interface layer increases dielectric constant of the SiC_f/SiC composites, in which the fluctuation degree of the imaginary part is also correspondingly enhanced and the electromagnetic energy is converted into heat energy due to polarization loss, which enhances the sample's absorption of electromagnetic waves. When the thickness of the Pt interface layer is 150 nm, conductivity loss and interface polarization loss of the SiC_f/SiC composites are enhanced and the electromagnetic shielding efficiency can reach about 32 dB, which is mainly attributed to the improvement of absorption shielding efficiency.

Key words: Pt interface layer; SiC_f/SiC composite; electromagnetic shielding performance; magnetron sputtering method