Preparation, Structure And Properties Of Nano-Layered Ternary Compound Ti3AlC2
Recently, a family of ternary layered ceramics Mn+1AXn has received wide attention from materials scientists and physicists because of its unique properties. M is a transition metal element, A is a group IIIA or IVA element, and X is a C group. And/or N, n=1, 2, 3. As a new compound discovered only recently, compared with the other two ternary compounds Ti3SiC2 and Ti2AlC, there is much less research on Ti3AlC2.
Ti3AlC2 belongs to the hexagonal crystal system, and the spatial point group is P63/mmc. Similar to other ternary layered compounds, Ti3AlC2 has both metal and ceramic properties. Like metal, Ti3AlC2 has good electrical and thermal conductivity. It is relatively soft and can be processed with high-speed steel tools without lubrication and cooling. Similar to ceramics, Ti3AlC2 has high elastic modulus and excellent high temperature mechanical properties. At the same time, it also has good thermal vibration resistance, anti-destructive ability and excellent chemical resistance.
So far, researchers have used various methods to study the synthesis of Ti3AlC2, such as high temperature self-propagating synthesis (SHS), hot isostatic pressing (HIP), hot pressing (HP) and spark plasma sintering (SPS). However, the resulting product usually contains a lot of impurities, such as TiC, Ti2AlC and so on. Therefore, in this study, the synthesis of Ti3AlC2 was exploratively studied, and a simple preparation method for preparing high-purity bulk Ti3AlC2 was obtained. At the same time, the microstructure, mechanical properties, electrical and thermal properties, and high temperature oxidation properties of the prepared materials were studied.
Under 1300～1500℃, 30 MPa pressure and Ar protective atmosphere, the molar ratio of hot pressing is n(TiC): n(Ti): n(Al): n(Si)=2:1:(1.0～1.1): (0.2～0.1) of mixed powder can obtain single-phase dense Ti3AlC2 bulk material. The doped Si is dispersed and distributed in the Ti3AlC2 matrix to form a replacement solid solution. Electron probe (EPMA) analysis shows that the sample obtained by hot pressing the mixed powder with Si content of 0.2 at 1300℃ for 2h can be expressed by the chemical formula Ti2.83Al)0.78Si0.22C2. The process of hot pressing Ti3AlC2 is a dissolution-precipitation process. Using TiC instead of elemental powder as the raw material can reduce the large amount of heat generated during the elemental powder reaction, reduce the volatilization of the product Al/Si, and thereby reduce the content of TiC in the product. The doped Si can inhibit the nucleation of Ti2AlC and promote the synthesis of Ti3AlC2. The k value method has determined the relationship between the TiC content and the relative intensity of XRD diffraction peaks.
Afterwards, the mechanical properties, electrical properties and thermal properties of Ti3(Al/Si)C2 solid solution materials were studied. The compressive strength, flexural strength, fracture toughness and Vickers hardness of Ti3(Al/Si)C2 with a grain size of 16-22 μm are 785 MPa, 350 MPa, 5.3 MPa·m1/2 and 3.54 -6 GPa, respectively. Low hardness and damage resistance ensure the machinability rarely seen in ceramics. At the same time, Ti3 (AUsi) CZ has good electrical and thermal conductivity, and the resistivities of 25"c and 800"C are 3.24xlo’7 and 1.02xlo’s respectively. ·M, the corresponding conductivity is 3.09, 1065·m-, and 9.80x10s s.m-, respectively. The resistivity becomes larger with the increase of temperature, and it has the characteristics of a typical metal conductor. The calculated temperature coefficient of resistance is 2.80xlo-3K-1. The coefficient of thermal expansion (T EC) is 8.71xlo stone K-’. Because Shisheng iq and Shi 3Alq have the same structure and similar properties, the solid solution Si has only a small effect on the properties of the material.