Hypersonic vehicles cruising at Mach 5 or higher is considered as a candidate for advanced transportation system. Some components such as nose corn and leading edges for hypersonic vehicles are heated at 2000? or higher because of aerodynamic heating during cruising. As potential candidates for these components, carbon fiber reinforced carbon composites (C/C) with coatings (SiC, SiO₂, Ir, etc.), ultra-high temperature ceramics (UHTCs), which are well known as transition metal diborides, carbides and nitrides with the melting point of >2500?, and their composites (UHTCMCs) have been developed. However, the delamination of coatings at high temperature in oxidizing atmosphere causes drastic recession of C/C with coatings. UHTCs and UHTCMCs usually contain SiC to form SiO₂ on their surface for the barrier for oxygen diffusion. Although the addition of SiC to UHTC and UHTCMCs are effective at below 1800?, preferential oxidation of SiC with the formation of gaseous SiO and the decomposition of SiO₂ accelerates the oxidation of these materials at above 1800?. Thus, a heat resistant material without containing “Si” is required as a candidate for advanced heat resistant material exposed at above 2000?.
 In the present study, we have prepared carbon fiber reinforced Ti-Zr-Nb-V-B ceramic composites (hereafter denoted as C³MCs: Compositionally Complex Ceramic Matrix Composites) by using high-entropy alloy melt-infiltration method. Ti-Zr-Nb-V-B alloys used for melt-infiltration is designed using calculation thermodynamics. Alloys are successfully melted and infiltrated into porous C/C preform. Recession behavior of C³CMCs at below and above 2000? are evaluated by arc-wind tunnel test. After heat exposure, surface was covered by oxides with complex oxides are formed and recession is prevented compared to C/C composites. The result indicates that recession by the oxidation of materials can be suppressed by the formation of oxide scale without containing “Si”. In this presentation, the relationship between the composition of oxides, configuration entropy of material and recession behavior will be discussed.