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New method to prepare Si-SiC coating on C/C composites by laser cladding (LC-Si-SiC) was established to improve the laser ablation resistance of the coating. Results showed that the LC-Si-SiC coating had lower roughness, better mechanical properties and superior laser-ablation resistance compared with the Si-SiC coating fabricated by the traditional coating preparation process: pack cementation (PC-Si-SiC). Due to the shorter heat treatment and less Si infiltration, the flexural strength of the LC-Si-SiC coated sample was 111.32 MPa, which was 144% higher than that of the PC-Si-SiC coated sample. Confirmed by finite element simulation, the LC-Si-SiC coating exhibited better laser-ablation resistance because of the "sweating cooling" mechanism. Under 23.89 MW∙m−2 ablation for 7 s, the surface temperature of the LC-Si-SiC coated sample was 3046 K, which was 157 K lower than that of the PC-Si-SiC, causing the mass loss rate of the LC-Si-SiC coating (0.10%) was only 45.45% of the PC-Si-SiC coating. [ABSTRACT FROM AUTHOR]

The Si-SiC-MoSi 2 and Si-SiC coatings were proposed to repair the damaged MoSi 2 -SiC/SiC coated C/C composites by laser directed energy deposition. Laser ablation was used to assess the repair effect. Results showed that both the repaired coatings with dense structure could restore the geometric size of damaged area. Compared with the Si-SiC-MoSi 2 coating, the Si-SiC repaired coating with higher laser reflectivity and more free Si could reduce the heat generation and enhance the heat dissipation during ablation, which lowered the maximum temperature by 347.49 K and 810.77 K under 300 W and 500 W ablation for 7 s separately, beneficial to avoid the secondary laser damage of the repaired area. [ABSTRACT FROM AUTHOR]

A SiO 2 -Nd 2 O 3 /Si-SiC-MoSi 2 coating was proposed to repair the damaged SiC coated C/C composites by laser cladding. Laser ablation was performed to evaluate the effect of coating repair. Results showed that the preparation of the SiO 2 -Nd 2 O 3 outer layer could improve the laser ablation resistance of the specimens by weakening heat accumulation and enhancing heat consumption, which reduced the maximum temperature by 261.99 K and 694.75 K during ablation under 300 W and 500 W for 7 s. The growth of the ablative products, including the Si nanowires and SiO x spherical particles, was based on vapor deposition and oxide-assisted growth mechanism. • The damaged SiC coated C/C composites was repaired by laser cladding technique. • A SiO 2 -Nd 2 O 3 /Si-SiC-MoSi 2 coating system was proposed for repair. • The laser ablation resistance was improved by preparing the SiO 2 -Nd 2 O 3 outer layer. • The ablation temperature was reduced significantly by the SiO 2 -Nd 2 O 3 outer layer. • Both heat accumulation and consumption were influenced by the SiO 2 -Nd 2 O 3 outer layer. [ABSTRACT FROM AUTHOR]

[Display omitted] • The damaged SiC coated C/C composites was repaired successfully. • A Mo-modified Si-SiC coating was prepared on C/C composites by laser-inducing. • The free Si of the Si-SiC coating was decreased significantly by Mo-modification. • The interface bonding of the coating modified with 10 wt% Mo was the best. • The oxidation resistance of the repaired coating was improved significantly. As the thermal structural component of aircraft, SiC coated C/C composites will fail and cause catastrophic consequences once the SiC anti-oxidation coating is damaged. Therefore, it is extremely important to develop a coating repair system with excellent oxidation protection performance. In this study, a Mo-modified Si-SiC coating was prepared by laser-inducing to repair the damaged SiC coated C/C composites. Thermal shock test between room temperature and 1773 K was conducted to study the interface bonding and 1773 K cyclic oxidation test was performed to examine the repair effect. With 10 wt% Mo-modification by laser-inducing, MoSi 2 precipitated at the interfaces while the interface bonding was not weaken. The decreased free Si, densified structure of coating and enhanced self-healing ability, which were obtained by modifying, contributed to reduce the mass loss after oxidation by ∼ 70% compared with the damaged sample without repairing. [ABSTRACT FROM AUTHOR]