Matrix-modified Low-temperature RMI C/C-SiC High Frequent Cyclic Ablation Mechanism Study

C/C-SiC composites are expected to be used for rapid-fire weapon body tubes and high-power density diesel engine pistons.The single impact of ultra-high temperature fluids on the above components is short in duration and high in frequency,and the high-frequency pulse ablation behavior and mechanism of the composites in this environment are still unclear.In this paper,C/C-SiC composites were prepared by low-temperature reactive melt infiltration,and the effects of adding different contents of Al,Cu and Zr B₂ on the microstructure,thermophysical properties,mechanical properties and high-frequency pulse ablation properties of the composites were investigated to reveal the damage mechanism of high-frequency pulse ablation of the composites.This paper uses C/C composite materials as preforms and prepares C/C-SiC composite materials with different compositions modified by low-temperature reactive infiltration.The mechanical and thermophysical properties of the composite materials were investigated through compression testing and laser flash method.The high-frequency reciprocating ablation performance of the composite materials was tested using a self-developed plasma ablation platform.The phase,morphology,and properties of the materials before and after ablation were mainly studied using XRD,SEM,EDS,infrared thermometer,and other methods The surface temperature of the material during the ablation process was observed,characterized,and analyzed,and the high-frequency reciprocating ablation behavior and mechanism of C/C-SiC composite materials with different compositions were explored.The main research results are as follows:（1）Under high frequent cyclic ablation,due to the high thermal conductivity of composites containing 40 wt.%Al,the ablation surface temperature is relatively low,and there are a large number of micro-cracks in the material,so the thermal stress can be relieved during the reciprocal loading process,and there is less surface peeling,so its ablation resistance is better;during single long-time ablation,due to the high surface temperature and large amount of Al volatilization,the ablation of composites with 20 wt.%Al content The ablation holes left behind are small,and there are fewer channels for gas and oxygen to further erode the interior of the material,so it has better ablation resistance.（2）With the increase of Cu content,the microcracks in the composite increase,the density first increases and then decreases,the coefficient of thermal expansion first increases and then decreases,the phonon propagation collision probability increases,the mean free path of phonons decreases,and the thermal conductivity decreases;As the Cu content increases,the Al₂Cu phase gradually increases,and the increase in interface results in more deflection of cracks.The compressive strength of the composite material shows a characteristic of first increasing and then decreasing,with a strength of 20wt%And 30wt.%Cu composite materials exhibit pseudo plastic fracture characteristics.With the increase of Zr B₂ content,the density of the composite first increases and then decreases,the coefficient of thermal expansion decreases,and the thermal conductivity and specific heat capacity gradually decrease.This is because there are more ceramic phases in the matrix,and the microcracks in the matrix become wider,leading to the decrease of the average free path of phonons.However,the overall strength of the matrix increases,and the compressive strength of the composite shows an upward trend,and the material presents brittle fracture.（3）When high frequent cyclic ablation is carried out,with the increase of Cu content,the linear ablation rate and mass ablation rate of the composite material show an upward trend.The addition of Cu reduces the melting point of the composite material,increases the temperature of the ablation surface,softens the matrix during ablation,and increases the cracks generated in the ablation morphology,making the matrix more prone to fragmentation and peeling.As the content of Zr B₂ increases,the ablation rate of the composite material shows a trend of first decreasing and then increasing.The addition of Zr B₂ enhances the matrix’s ability to resist stress generated by high-frequency reciprocating,and the ablation morphology shows a decrease in cracks and a decrease in the matrix’s fragmentation state.At the same time,Zr B₂ preferentially reacts with oxygen,protecting the matrix.Excessive Zr B₂leads to the widening of microcracks in the composite material,making it easier for gas and oxygen to corrode the matrix during ablation,This causes the fibers to break,exacerbating the fragmentation state of the matrix due to stress,resulting in a content of 10wt.%The composite material of Zr B₂ has the best ablation resistance.When Cu and Zr B₂ are added at the same time,the ablation rate of the composite material is between that of the composite material with Cu and Zr B₂ added.The addition of Cu will reduce the melting point,leading to poor high-temperature performance of the material.However,Zr B₂ has excellent high-temperature performance,which comprehensively determines the ablation performance of the composite material.