Study On Synthesis And Properties Of Ti₃SiC₂/TiB₂ Composites By Hot Pressing

The laminated ternary carbide Ti₃SiC₂, which is a new kind of structural ceramics material, becomes the focus of material researchers attributing to its perfect combination of both merits of metals and ceramics. However, some weaknesses, such as low hardness and low creep strength, limit the potential application of Ti₃SiC₂ as a high-temperature structural material.Owing to the high hardness, high modulus, excellent chemical stability, and approximate thermal expansion coefficient, TiB₂ herein is chosen to produce Ti₃SiC₂/TiB₂ composites in order to increase the hardness and strength of Ti₃SiC₂.In this study, fully dense Ti₃SiC₂/TiB₂ composites were synthesized by the additive mix—method hot pressing (TiC/Ti/Si/Al/TiB₂ powders ) and in-situ hot pressing (TiC/Ti/Si/B₄C/Al powders) sintered at 1400℃. In the additive mix —method, it was worth noting that there was no other phases contained in either pure Ti₃SiC₂ or its composites. Investigated by X-ray diffraction (XRD) of samples sintered at different temperatures, the phase's formation mechanism of the composites was studied. When the sintering temperature was below 900℃, the main phase was Ti₅Si₃. Sintered at 1000℃, main peaks of Ti₃SiC₂ were detectable despite their weak intensity. Meanwhile, there was no evidence that showed the reaction between Ti₃SiC₂ and TiB₂. TiB₂ only diluted the initial powders and delayed Ti₃SiC₂ formation process. In the in-situ synthesis, when the TiB₂ content was less than 10vol%, the main phases were Ti₃SiC₂ and TiB₂. When the TiB₂ content was more than 10 vol %, TiC impurity was contained in the composites. At 1100℃, Ti reacts with B₄C to produce TiB₂. The grains of Ti₃SiC₂ are plate-like and have a size of 10μm in elongated dimension. In the case of TiB₂, the microstructure has remained relatively fine- grained, with a grain size of about 5 m as opposed to the few hundred microns of the coarse-grained, this confirms the assumption that TiB₂ inhibits the grain growth of2. When the TiB2 content was more than lOvol %, TiB2 grains were agglomerated and agglomerates were at most 1-4 m large. The above results show that. Ti3SiC2/TiB2 composites can be synthesized between 1300°C to 1450°C.The physical properties and room temperature corrosion resistance of the Ti3SiC2/TiB2 samples by the additive mix-method hot pressing were also studied in the paper. Results revealed that Ti3SiC2/TiB2 possessed excellent mechanical, electrical and thermal properties. When the TiB2 content was 10vol%, the hardness, compressive strength, flexural strength and fracture toughness were remarkably improved. After heat treatment, the flexural strength of Ti3SiC2/10vol%TiB2 composite increased from 367.5MPa to 485.1MPa , which was raised by 32%,the hardness increased to 8.2GPa.Meanwhile, Ti3SiC2/TiB2 is a good thermal and electrical conductor. The electrical conductivity of Ti3SiC2 , Ti3SiC2/5vol%TiB2 , Ti3SiC2/10vol%TiB2 and Ti3SiC2/20vol%TiB2 composites at room temperature were 3.86xlO6S-m"1 , 4.4xlO6S-m'1, 3.76xlO6S-m"1 and 3.79x106S-m"1, respectively, indicating that Ti3SiC2/TiB2 composite is a metallic conductor. The corrosion resistance of Ti3SiC2/TiB2 in dilute HNO3 was more excellent than T13S1C2.