Investigation of the Effect of Temperature on the Microstructural and Mechanical Properties of the Ultra-High Temperature Ceramic Composite ZrB2-SiC-TiC Using the Multi-Step Spark Plasma Sintering Method

The sintering of ZrB2 presents significant challenges due to its covalent bonding and the high temperatures required for the process. Prior research has demonstrated that incorporating up to 20% by volume of SiC as an additive can enhance both the sintering process and the mechanical properties of ZrB2-based composites. The objective of this study was to fabricate and characterize an ultra-high temperature ceramic composite composed of ZrB2 containing 20 vol. % SiC, utilizing the Spark Plasma Sintering (SPS) method with a multi-step approach at various temperatures. Additionally, the study sought to investigate the influence of a TiC additive on the microstructural evolution and mechanical properties of the composite. The research focused on assessing the impact of sintering temperature, ranging from 1600°C to 1900°C under a pressure of 30 MPa, in the presence of a 10 vol. % TiC additive. The introduction of up to 10% by volume of TiC into the ZrB2-20 vol. % SiC composite, followed by sintering at 1800°C for 5 minutes, resulted in the formation of (Zr,Ti)B2 and (Ti,Zr)C solid solutions within the matrix. These solid solutions, along with reactions involving surface oxides such as ZrO2 and B2O3, contributed to a 15% increase in relative density. Furthermore, notable enhancement was observed in the mechanical properties, including a 14% increase in hardness, a 12% increase in elastic modulus, a 20% increase in fracture strength, and an 8% increase in fracture toughness. A comparative analysis with previous studies revealed that employing a multi-step SPS technique, as opposed to a single-step process, significantly reduced the temperature and time of the process to achieve a relative density exceeding 99%. However, it was also observed that increasing the maximum sintering temperature to 1900°C in the ZrB2-20 vol. % SiC-10 vol. % TiC composite resulted in excessive grain growth and a slight decrease in relative density by approximately 1%.