Study On Fabrication And Performance Of Ti-Al-C/TiB₂ Composites

New layered ternary Ti₂AlC and Ti₃AlC₂ attract increasing interest owing to their unique properties. Ti₂AlC and Ti₃AlC₂ combine unusual properties of both metals and ceramics. Like metals, it is a good thermal and electrical conductor, relatively soft. Like ceramics, it is elastically stiff; exhibit excellent high temperature mechanical properties. 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, Ti₂AlC and 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 (3-5GPa) 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 Ti-Al-C/TiB₂ composites to increase the hardness and strength of Ti₂AlC and Ti₃AlC₂. Both spark plasma sintering and hot pressing were utilized for the synthesis of Ti₂AlC-TiB₂ and Ti₃AlC₂-TiB₂composites. Also, the microstructures, the physical properties as well as reaction mechanism of the obtained materials were investigated, respectively.In chapter 2, the synthesis of Ti₂AlC-TiB₂ and Ti₃AlC₂-TiB₂ composites were conducted by HP method. For the synthesis of Ti₂AlC-TiB₂ composite, two kinds of powder mixtures Ti/TiC/Al and TiC/Ti/B4C/Al were used. Additionally, different TiB₂ content was incorporated to explore the synthesis rule of Ti₂AlC-TiB₂ composite. Also, for the synthesis of Ti₃AlC₂-TiB₂ composite, when silicon was chosen as the synthesis additive, the effect of different TiB₂ content on the synthesis rule were specially studied Characterized by XRD, SEM and EDS, the results indicated that direct addition of TiB₂ in the starting mixtures Ti/TiC/Al lead to the fabrication Ti₂AlC-TiB₂ composite with impurity. Dense Ti₂AlC-TiB₂ composite (5-25%TiB₂) can be obtained by sintering TiC/Ti/B4C/Al mixture at 1400 ℃ with a pressure of 30 MPa in argon atmosphere, Al may easily vapor, it needs exceeds 0.05mol during the whole reaction. However, too much Al and higher temperature may not be in favor of forming Ti₂AlC. Dense Ti₃AlC₂ has been sintered by hot pressing with the start molar ratio2TiC/Ti/Al/0.2Si/TiB₂ at 1350 ℃ with a pressure of 30MPa in argon atmosphere. The additive Si accelerates the reaction synthesis and favors the crystal growth of Ti₃AlC₂.Incoporation of too much TiB₂ content can influence the reaction of Ti₃AlC₂.Through in-situ synthesis, addition of TiB₂ can not exceed 10vol%.In chapter 3, SPS was used to synthesize Ti₂AlC-TiB₂ and Ti₃AlC₂-TiB₂ composites X-ray diffraction (XRD) and scanning electron microscope (SEM)...