Irradiation And Ablation Behaviors Of C/C-ZrC-SiC Composites And Their Zr-based Coatings

C/C-Zr C-Si C composites are widely used in aerospace and nuclear energy field.However,the exposed carbon phase on the surface is not conducive to its ability to withstand ablation and neutron irradiation damage.In order to improve the radiation and high temperature air ablation resistance of C/C-Zr C-Si C composites,Zr-based coatings of Zr-Si-Mo-C,Zr-Si-Cr-C and Zr-Si-Nb-C three systems were prepared on the surface of C/C-Zr C-Si C composites.C/C-Zr C-Si C composites and their coatings were irradiated with 6 Me V,3.6×10¹⁵ ion/cm² and 2 Me V,1.9×10¹⁶ ion/cm² Si²⁺ion.The changes in the morphology and properties of C/C-Zr C-Si C composites and their coatings after irradiation were researched,and the protective mechanism of the coatings on the matrix was analyzed.Coatings with three systems were ablated with oxyacetylene flame at 2500℃for 30 s,and the ablation behavior and mechanism were studied in detail.The main conclusions are as follows:（1）After two doses of Si²⁺ion irradiation,the I_D/I_G value of carbon fiber and interlayer spacing of graphite crystallites of carbon fiber in the surface layer of C/C-Zr C-Si C composites increase.And the Si C lattice expands,the crystallinity of Si C decreases.Many point defects and point defect clusters appeared in Zr C,while Zr C maintain a complete crystal structure without lattice expansion.After 1.9×10¹⁶ ion/cm² Si²⁺ion irradiation,both of the nanohardness and elastic modulus of Zr C,Si C and carbon fiber increase,but Zr C has the smallest change and better stability.（2）After ablation,the damage only occurs on the surface layer of the samples.And the thickness of amorphization layer at the coating interface between Zr C and Si C phase of Zr-Si-Nb-C coating section after irradiation is thinner than that of the C/C-Zr C-Si C composites.The amorphized depth of Si C in the Zr-Si-Nb-C coating is larger than the theoretical damage depth,while the damage depth of Zr C is basically the same as the theoretical value.After high dose ion irradiation,the change of the mechanical properties of the coating is much smaller than that of the matrix,indicating that coatings have better irradiation tolerance.（3）Zr-Si-Nb-C coating has the best ablation performance,with mass and linear ablation rate of 2.70 mg/s and 0.53μm/s,respectively,and there is a relatively tight bond between the coating and the matrix.A large number of t-Zr O₂ phases exist after ablation,indicating that Nb element can prevent the transformation process of t-Zr O₂ to m-Zr O₂,thereby improving the thermal stability of the coating.The outer layer in the central area of the ZSN coating is a dense Zr O₂-Nb₂O₅ composite layer,and the inner layer is a Zr O₂-Nb₂O₅-Si O₂ three-phase composite layer,which can effectively protect the matrix from ablation damage.