Research On The Synthesis And Properties Of Ta2AlC

Recently, a family of layered ternary ceramics, referred to as Mn+1AXn, where M is a transition metal, A is a IIIA or IVA element and X is either carbon and/or nitrogen, n=1,2,3, has attracted the attention of physicists as well as material scientists due to its unique properties. As a relatively new member of this family, Ti2AlC ceramic, the typical representation of H-phase, 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 drill 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. So it is a new promising structure & function integrated ceramic material that will be widely used in the future. So in this work, we conducted the research on the fabrication ofTa2AlC 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.Dense bulk Ta2AlC ceramics was fabricated by hot pressing with the mixture power Ta,TaC and Al. XRD in different temperatures was used to investigate the possible reaction path and scanning electron microscope (SEM) was observed to investigatthe the microstructure of samples synthesized respectively. It is shown that TaC and Ta-Al intermetallic are intermediate phases for the synthesis of Ta2AlC by hot pressing. It was found that Ta2AlC formed through the reactions between Ta2C and Al,or between TaC and Ta-Al intermetallics. When the temperature reach to 1550℃, Ta4AlC3 was in large existed.Physical properties of Ta2AlC have been also carefully investigated. Ta2AlC possesses Vickers hardness of 4.7 GPa, high compressive strength of 748 MPa, flexural strength of 402MPa and fracture toughness of 6.9 MPa·m1/2. The high toughness and low hardness make in machinable. Ta2AlC2 is a good electrical and thermal conductor. The heat capacity and thermal conductivity at room temperature are 84.5J/(mol·K),31.3 W/m·K, the average thermal expansion coefficient from 25℃to 1100℃is 8.1×10-6 K-1, indicating that Ta2AlC is a metallic conductor.The corrosion behavior of Ta2AlC in various acid solutions and NaOH have been studied with the method of immersion testing and electrochemical testing. Ta2AlC displayed good corrosion resistance after immered in 150 days with little weight loss. Electrochemical curve shows Ta2AlC possess wide dimension blunt interval.The reason of passivation is that Ta ions deviate from the crystal surface equilibrium position, there are oxygen with unpaired electrons to form strong chemical bonds, leading to oxygen adsorption and adsorbed layer. After adsorption of oxygen unsaturated bonds of Ta atoms saturated, and so Ta surface atoms lost their original activity, Ta atoms are no longer removed from the lattice, passivation generated.