| Recently, a family of layered ternary ceramics, referred to as Mn+1AXn, where Mis a transition metal, A is a III A or IVA element and X is either carbon and/or nitrogen, n=l, 2, 3, has attracted the attention of physicists as well as material scientists due to its unique properties. Compared with the Ti3SiC2 and Ti2AlC, which have been studied in detail, Ti3AJC2 has not been extensively investigated owing to the fact that Ti3AlC2 is a relatively new member of this family and the synthesis of Ti3AlC2 is very difficult. Ti3AlC2 crystallizes as a hexagonal structure with a space group of P63/mmc. Similarly to the other layered ternaries, Ti3AlC2 combines unusual properties of both metals and ceramics. Like metals, it is a good thermal and electrical conductor, relatively soft and can be easily machined with traditional high-speed steel tools without lubrication or cooling water, . Like ceramics, it is elastically stiff; exhibits excellent high temperature mechanical properties. It is resistant to thermal shock and unusually damage tolerant, and exhibits excellent corrosion resistance. To date, many methods such as self-propagating high temperature synthesis (SHS), hot isostatic pressing (HIP), hot pressing (HP) and spark plasma sintering (SPS) have been used for synthesis Ti3AlC2. However, there are usually impurities such as TiC, Ti2AlC, et al. and the cost is expensive. So in this work, we conducted the research on the fabrication of Ti3AlC2 with a not so severe process. Also, the microstructures, the physical properties as well as oxidation behavior of the obtained materials have been investigated, respectively.The high purity bulk Ti3 A1C2 has been sintered by hot pressing with the start molar ratio n(TiC): n(Ti): n(M): n(Si)=2: 1: (1.0-1.1): (0.2-0.1) at 1300-1500 ℃ with a pressure of 30 MPa in argon atmosphere. The additive Si was uniform distributed in the matrix with the form of solid solution. The compound in which the start molar ratio of additive was 0.2 soaked at 1300 ℃ for 2 h has been determined by electronic probe microanalyses (EPMA) as the formula,Ti2.83Alo.7gSio.22C2. The formation mechanism was followed a dissolution-precipitation process. Because the main raw material TiC reduced the reaction-liberated heat, the evaporation of Al/Si, which was considered to be responsible for TiC impurity in product, was decreased. While the experimental evidence unequivocally showed the additive Si did favor to the nucleation of Ti3AlC2. The dependency of TiC content versus relative intensity of X-ray diffraction peak was also studied.Physical properties of Ti3AlC2 with the crystal dimension of 16-22 um have been also carefully investigated. The measured compressive strength, flexural strength, fracture toughness and Vickers hardness were 785 MPa, 350 MPa, 5.3 MPa m1/2 and 3.5-4.6 GPa. The high toughness and low hardness make in machinable. Ti3AlC2 is a good electrical and thermal conductor. The electrical conductivity at room temperature and 800 癈 are 3.09xl06 S m-1 and 9.80 X 105 Sm-1. The electrical resistivity increased linearly with the increasing of temperature, indicating that Ti3AlC2 is a metallic conductor. The calculated temperature coefficient of resistivity was 2.80X10-3 K-1 at the temperature range of 25-800. The thermal expansion coefficient (TEC) was 8.71 x l0-6 K-1. Because of the same structure and similar properties of Ti3AlC2 and Ti3SiC2, the additive Si had little effect on the properties of Ti3AlC2The oxidation behavior of Ti3AlC2 with the density 4.18 g/cm3 was also investigated by means of TGA, XRD, SEM and EDS in the work. The isothermal oxidation behavior at 900-1300 for 20 h in air followed a parabolic rate law as well as the cyclic oxidation behavior at 1100-1300 for 30 cycles. The defects in matrix increased the kinetics of Ti3AlC2. The calculated activation energy was 136.45 kJ/mol. It had been demonstrated that Ti3AlC2 had excellent oxidation resistance due to the dense continuous oxide scale consisted of mass a-Al203 and little TiO2 and/or Al2TiO5. Generally...
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