Study On Synthesis And Properties Of Ti₃AlC₂/TiB₂ Composites By SPS

The laminated ternary carbide Ti₃AlC₂, 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. Like metals, it is a good thermal and electrical conductor, relatively soft. Like ceramics, it is resistant to thermal shock and unusually damage tolerant, and exhibit excellent corrosion resistance. Above all, unlike conventional carbides, they can be machined by using conventional tools without lubricant, which is of great technological importance for their application. Additionally, Ti₃AlC₂ is an exceptional solid lubricant with an ultra-friction. These excellent properties mentioned above make them another family of technically important materials. Unfortunately, there are relatively soft and low creep strength, limit the potential application of as a high-temperature structural material.Incorporation of second phase is an effective way to overcome these weaknesses. Owing to the high hardness, high modulus, excellent chemical stability, and approximate thermal expansion coefficient, TiB₂ herein is chosen to produce Ti₃AlC₂/TiB₂ composites in order to increase the hardness and strength of Ti₃AlC₂. Also, the microstructures, the physical properties as well as reaction mechanism of the obtained materials were investigated, respectively.In this study, fully dense Ti₃AlC₂/TiB₂ composites were synthesized the in-situ SPS sintered at 1250℃with different volume content of TiB₂ from 5 to 30vol. %, and Si was chosen as the synthesis additive. Investigated by X-ray diffraction (XRD) of samples sintered at different temperature from 600 to 1300℃, the phase formation mechanism of the composites was studied. Meanwhile, the effect of different TiB₂ content on the synthesis rule was specially studied by SPS parameter. The results indicated that:(1) The bulk Ti₃AlC₂/TiB₂ with a relative density of 98% was fabricated by SPS under 30 MPa and at 1250℃for 8 min. The main phases were Ti₃AlC₂ and TiB₂, including a few of TiC.(2) The results of SEM indicated that: The grains of Ti₃AlC₂/TiB₂ composites are structured in a layered form. The obtained Ti₃AlC₂ grains are well developed and plate-shape with a size of 5μm and 15μm, in thickness and elongated dimension, respectively. But the incorporation of too much TiB₂ content can influence the reaction of Ti₃AlC₂.(3) When the sintering temperature below 900℃, the main phase was Ti-Al intermetallics, and was not other phases. Sintered at 1000℃, main peaks of Ti₃AlC₂ were detectable despite their weak intensity. Sintered at 1100℃, Ti reacted with B₄C to produce TiB₂. Meanwhile, there was no evidence that showed the reaction between Ti₃AlC₂ and TiB₂.The physical properties and room electrochemical corrosion of the Ti₃AlC₂/TiB₂ composites with the different content of TiB₂ were studied in the paper. Results revealed that the Vickers hardness, the flexural strength and fracture toughness and electric conductivity of Ti₃AlC₂/TiB₂ composites are greatly enhanced with the addition of TiB₂. The Vickers hardness and electric conductivity of Ti₃AlC₂/30vol. % TiB₂ are 10.39GPa and 3.7×10⁶S/m, respectively. When the volume fraction of TiB₂ is 10%, the flexural strength and fracture toughness reach the maximum values, which are 696MPa and 6.6MPa.m^1/2, respectively. Ti₃AlC₂/5vol. % TiB₂ composite showed trans-passive behavior with the current density suddenly increasing at potentials more positive than≈1.5V, evolution of Cl₂ gas is observed.