Structure Regulation And Anti-corrosion Performance Of Tac-based Solid Solution Ceramics

The purity of metals and alloys is an important indicator to ensure the performance of materials,therefore,the selection of crucibles has become a key factor affecting the purity of metals and alloys.Traditional crucible materials such as graphite crucibles are widely used in the field of uranium and uranium alloys due to their advantages of resistance in high temperature,thermal shock resistance,easy processing,and low price.However,due to the high reactivity of uranium and uranium alloys,it is easy to react with graphite and CO at high temperatures and thus causing carbon pollution.Ultra-high temperature ceramics such as titanium carbide,zirconium carbide,hafnium carbide,vanadium carbide,niobium carbide,tantalum carbide and other metal elements are in the IVB,VB And VIB group carbide ceramics,with melting point exceeds 3000°C.The strong covalent bonds between transition metals and carbon atoms give them high hardness,stiffness and melting point.Strong covalent bonds and a certain degree of metal bonds make these ceramics capable of serving under extreme conditions.However,this also makes these ceramics difficult to sinter,shape and process.In this paper,carbide composite powder with low oxygen content and small particle size is prepared by the mix of transition metal oxide powder and carbon source,and then use hot press sintering to prepare solid solution ceramics.The solid solution between the transition metal carbides is used to promote densification.Ta Cbased solid solution ceramics with a density of more than 98% were prepared,and the effect of the type of second component on its microstructure and mechanical properties was discussed.Among the prepared four kinds of ceramics(Ta5Ti)C6,(Ta5Zr)C6,(Ta5Nb)C6 and(Ta5Cr)C6,(Ta5Cr)C6 has the highest density of 99.5%.The grain sizes of(Ta5Ti)C6,(Ta5Nb)C6 and(Ta5Cr)C6 are all larger than that of Ta C ceramics,which is about 21μm.The grain size of(Ta5Zr)C6 is the smallest 6.2 μm.The Vickers hardness of the four solid solution ceramics is greater than that of Ta C ceramics.(Ta5Cr)C6 has the highest hardness of 22.5GPa;(Ta5Ti)C6 has the lowest hardness of 18.5GPa.It can be seen that the hardness between solid solution ceramics and the hardness of the second component carbide is inconsistent.(Ta5Nb)C6 has the highest fracture toughness of 3.2MPa*m1/2,and(Ta5Cr)C6 has the lowest value of 2.6MPa*m1/2.According to the calculation of thermodynamic equilibrium,it is preliminarily judged that(Ta5Zr)C6 has the best corrosion resistance and(Ta5Cr)C6 has the worst corrosion resistance under the same conditions.It is difficult to judge the corrosion resistance of the material from the surface morphology,but the eroded parts and erosion products can be preliminarily judged based on it.Regarding the source of surface grains,there are three possibilities.First,the grains were eroded,leaving a low-index,low-energy crystal plane;second,during the contact between the material and molten cerium,a mass transfer occurred and more stable grains were formed;third,after the grains were dissolved,it is precipitated from the melt in the process of cooling,attached and grown on the surface of the material.Further research is needed to give a definite answer.