Study Of Interfacial Modification Coating In GSI SiCf/SiC Composites

SiCf/SiC composites have been one of the promising candidate materials for structural applications in areas of aerospace and nuclear power reactor owing to a series of advantages such as high specific strength, high specific modulus, excellent high temperature oxidation resistance and irradiation resistance. One of the key factors for the wide application of SiCf/SiC composites is to realize the preparation of SiCf/SiC composites at low cost. PIP process combined RI process is one of the effect ways to fabricate SiCf/SiC composites at low cost. This work has studied the interfacial coating modification for the fabrication of 2.5D SiCf/SiC composites via RI process and optimized the carbon content in the SiCf/C performs, and it has also discussed the effects and mechanisms of single BN, single PyC, single SiC, double BN/SiC and PyC/SiC interfacial coating on the mechanical properties of SiCf/SiC composites.It has studied the effect of carbon content in the SiCf/C performs on the constitution and mechanical properties of the as-fabricated SiCf/SiC composites. For composites without interfacial coating, the composites fabricated from the SiCf/C performs which undergo 5 PIP C cycles have a better mechanical properties, and its flexural strength, modulus and fracture toughness are 106±18.4MPa, 55.7±4.6GPa and 1.89MPa·m^1/2, respectively. As for performs with interfacial coating, the perform undergo 4 PIP C cycles have relatively appropriate carbon content and open porosity, and the composites fabricated from this perform have the best mechanical properties, then the flexural strength, modulus and fracture toughness of the composites are 122.5±12.7MPa, 86.5±3.1GPa and 2.02MPa·m^1/2, respectively.It has studied the effect of BN interphase thickness on the mechanical properties of the SiCf/SiC composites. As the thickness of BN interfacial coating increases, the flexural strength, modulus and fracture toughness of the composites both exhibit a trend of firstly increasing and then decreasing. The SiCf/SiC composites with the 0.6?m thick BN interfacial coating have relatively good mechanical properties, and its flexural strength, modulus and fracture toughness are 134.6±15.4MPa, 166.7±7.9GPa, 3.10MPa·m^1/2, respectively. The BN interfacial coating acts as a “sacrificial layer”, and it has barriered the erosion of Si to SiC fiber to some degree. However, it has failed to optimize the interfacial bonding and adjust the stress distribution, and as a result, the fracture toughness of the composites has no significant improvement.It has studied the effect of PyC interphase thickness on the mechanical properties of the SiCf/SiC composites. The SiCf/SiC composites with the 1050 nm thick PyC interfacial coating have relatively good mechanical properties. The interfacial bonding of the SiCf/SiC composites with the 730 nm thick PyC interfacial coating is weak and the fracture toughness of the composites is the largest, and at the same time its function of load transfer is poor, which can be contributed to the lowest flexural strength.It has studied the effect of SiC interphase thickness on the mechanical properties of the SiCf/SiC composites. The SiCf/SiC composites with the 720 nm thick SiC interfacial coating have relatively good mechanical properties and its flexural strength, modulus and fracture toughness are 98.9±4.3MPa, 76.2±4.1GPa, 2.43MPa·m^1/2, respectively. The role that SiC interfacial coating played in improving the composites' fracture toughness is less obviously, but the SiC interfacial coating can improve the modulus of the composites.It has studied the effect of double BN/SiC and PyC/SiC interfacial coating on the mechanical properties of the SiCf/SiC composites. The BN/SiC coating can transfer the load and protect the fiber from the damage of Si effectively, and the PyC/SiC coating can effectively weaken the fiber-matrix interfacial bonding and transfer the load.It has discussed the mechanisms for the effect of interfacial coating on the mechanical properties of SiCf/SiC composites. The mechanism of BN coating' interfacial modification is acting as “sacrificial layer” to barrier the erosion of the Si to fiber and transfering the load. The mechanism of PyC coating' interfacial modification is acting as “barrier layer” to hinder the erosion of the Si to fiber and acting as “debonding layer” to weak the fiber-matrix interfacial bonding. The mechanism of SiC coating' interfacial modification is acting as “protective layer” to protect the fiber from Si's erosion and transfering the load.