ACERP: Vol. 6, No. 3, (Summer 2020) 15-24 Advanced Ceramics Progress Research Article Journal Homepage: www.acerp.ir The Effect of TiC Additive with Al2O3-Y2O3 on the Microstructure and Mechanical Properties of SiC Matrix Composites M. Khodaei a  , O. Yaghobizadeh b , S. A. Safavi a , N. Ehsani a , H. R. Baharvandi a , S. Esmaeeli b a Composite Materials & Technology Center, Malek Ashtar University of Technology, Tehran, Iran b Department of Materials Science and Engineering, Faculty of Technology and Engineering, Imam Khomeini International University (IKIU), Qazvin, Iran c Department of Ceramic, Shahreza Branch, Islamic Azad University, Shahreza, Iran PAPER INFO ABSTRACT Paper history: Received 23 April 2020 Accepted in revised form 20 June 2020 In this research, the SiC-matrix composite with different amounts of TiC (0, 2.5, 5, 7.5, and 10 wt%) supplemented with additives including 4.3 wt% Al2O3 and 5.7 wt% Y2O3 were utilized to initiate the required liquid phase. The sintering process was performed using pressureless sintering at 1900 °C for 1.5 hours under argon atmosphere. The composition and microstructure of the obtained composites were analyzed using X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), and Energy-Dispersive X-ray Spectroscopy (EDX). The results showed that TiC additives improved the densification of samples and impeded the growth of SiC grains. According to the phase analysis, the SiC was the main phase, while the TiC and YAG were characterized as partial phases. Additionally, due to the reaction of TiC and Al2O3, the composition of the liquid phase contained YAG and YAM. Assessments revealed that the microstructure and the final properties of composites were affected by density, produced phases and their distribution in the matrix, and grain size. According to the results, upon increasing the TiC up to 5 wt%, all the measured properties including density, hardness, elastic modulus, and fracture toughness improved and reached 97.40%, 26.73 GPa, 392 GPa, and 5.80 MPa.m 1/2 , respectively. However, with increasing the additives to more than 5 wt%, these properties deteriorated. Microscopic evaluations revealed that crack deflection and crack bridging mechanisms contributed to the fracture toughness of SiC ceramics. Keywords: Pressureless Sintering SiC-TiC Liquid-Phase Sintering Toughness Mechanisms Mechanical Properties 1. INTRODUCTION Due to high thermal conductivity, low thermal expansion coefficient, and stability of mechanical strength up to 1400-1500 °C, silicon carbide (SiC) can readily tolerate thermal cycles at elevated temperatures [1-7]. The SiC is resistant to thermal shocks [8-11]. In addition, using SiC ceramics is 10 to 50% more energy- efficient than metallic superalloys [11]. Silicon carbide is a hard material (17-25 GPa) with Young’s modulus of 400-450 GPa [8,11]. The chemical reactivity of SiC is low at room temperature, which is regarded as one of its inherent chemical properties [8]. Given the mentioned characteristics, SiC ceramics are utilized in industrial heat exchangers, steam and gas turbines, glass industry, metallurgical industries, ceramic  Corresponding Author Email: mahdi.khodaei01@gmail.com (M. Khodaei) https://doi.org/10.30501/acp.2020.109546 industry, nuclear and thermal power stations, and aeronautical constructions [12-14]. Despite these desirable characteristics, there are also other undesirable ones including low fracture toughness which not only limit the use of SiC in the industry but also encourge scientists to solve this weakness [8,11]. Some researchers argue that reinforcing the structure of SiC ceramics is the best solution to this flaw [15,16]. SiC-matrix composites are manufactured in different ways [8]. Among them, pressureless sintering is the most significant one since it provides the possibility of producing large pieces or complicated shapes [11,13]. In order to reach over 95% of the theoretical density, the methods of solid-state and liquid-state pressureless sintering were employed [17-20]. Liquid-state sintering yields superior mechanical properties to those produced