| Due to the special lamellar structure, ternary carbide Cr2 Al C possesses the excellent properties combined ceramic with metal materials, such as better electrical and thermal conductivity, readily machinability, excellent high temperature oxidation resistance and thermal stability. However, the high synthesis temperature and lower purity of product limit its wide applications in structural materials. To prepared higher putity of ternary carbide Cr2 Al C at a lower tempareture, the molten salt method and a combination of high-energy ball milling with vacuum sintering are introduced to syudied the synthesis of Cr2 Al C in the paper.In this paper, the Cr2 Al C materials were successfully synthesized by molten-salt method(KCl act as flux) and a combination of high-energy ball milling with vacuum sintering of Cr-Al-C and Cr3C2-Cr-Al reaction systems, respectively. The reaction mechanisms of the synthesized Cr2 Al C powders by Cr-Al-C and Cr3C2-Cr-Al reaction systems were probed by differential scanning calorimetry(DSC), X-ray diffraction analysis(XRD), and scanning electron microscope(SEM) etc. The effects of Aluminum content, molten-salt content, sintering temperature and holding time on composition, grain size and microstructure morphology of synthesized Cr2 Al C powders were also investigated and the optimum technology parameters of synthesize Cr2 Al C materials were determined. In addition, the bulk Cr2 Al C was synthesized by hot pressed the as-milled powders. The relative density, hardness, flexure strength and fracture toughness properties of the bulk Cr2 Al C were studied as well.The synthesis process of Cr2 Al C powders by molten salt method showed that the Cr2 Al C powders were successfully synthesized at 1250℃ for 60 min, with KCl acted as flux. Cr3C2 instead of C as the carbon source could improve the purity of Cr2 Al C powders effectively. The reaction path of Cr2 Al C could be summarized as follows: the Cr-Al intermetallics were formed by the reaction between Cr and Al firstly, and translated into Cr2 Al phase gradually. Then the Cr2 Al C was formed by the reaction between Cr2 Al and other raw materials.The synthesis process of Cr2 Al C powders by a combination of high-energy ball milling with vacuum sintering showed that particles become finer and more active during the high energy ball milling, which result in the sinter process of massive Cr2 Al C with a lower reaction time and temperature. The high purity Cr2 Al C powders were successfully synthesized by a combination of high-energy ball milling with molten salt method at 1050℃. Compared with directly hot pressed sintering, the hardness, flexture strength and fracture toughness of massive Cr2 Al C synthesized by a combination of high-energy ball milling with hot pressed sintering were improved by 32.65%, 15.57% and 6.11%, respectively.The two-dimensional layered materials MXenes attracted a wide spread attention owing to the possession of the class of Graphene structure. The preparation of the two-dimensional layered materials MXenes was explored by corrosion of Cr2 Al C and Ti3 Al C2 powders using HF, HNO3 and Na OH solutions with magnetic stirring and hydrothermal reaction, respectively. The results showed that the Al layer of Ti3 Al C2 particles could be dissolved by 40% HF in conditions of the room temperature for 8 h effectively, and stable Ti3C2 layer existed in particles. With rising of the temperature, the stability and thickness of Ti3C2 layer reduced, accompanying with nano-scale grains generated on the layer surface. The concentration of HF was hardly determined, by corroding with Cr2 Al C powders with different density at room temperature. As for lower density HF, the Al layer was hardly corroded, nevertheless, for the higher density, the Cr-C layer will be dissolved with Al layer. Ti3 Al C2 powders were easily translated into Ti O2 in HNO3. The corrosion of Cr2 Al C powders were harder than Ti3 Al C2 powders under the same conditions. The non uniform corrode powders and irregular morphology of byproducts were achieved under the conditions of 160 ℃for 12 h. It could conclude that the corrosion resistance of particles is poor in HNO3 solution. Moreover, Ti3 Al C2 powders possess worse stability in HNO3 compared with Cr2 Al C powders. The corrosion resistance of particles in Na OH solution is better. It may hardly to come true that the preparation of two-dimension transition metal carbide through corroded in Na OH solution by hydrothermal reaction. |
PDF Full Text Request