Self-propagating high-temperature synthesis of high-entropy carbides and borides: features of combustion

Recently, works have appeared devoted to the production and study of high-entropy ceramics (HEC), in particular, high-entropy carbides and high-entropy borides. It is assumed that the properties of HEC, due to the distortion of the crystal structure, will exceed the properties of one or two-component borides and carbides. Previously, HEC containing high-entropy carbide and high-entropy boride were obtained by mechanical alloying in a ball mill and electric spark plasma sintering. The strength of this two-phase HEC exceeded the average strength of the high-entropy carbide and high-entropy boride included in its composition. The effect of the ratio of components and compression of samples on the combustion velocity, elongation of samples, morphology and phase composition of synthesis products in the system х(Ti+Hf+Zr+Nb+Ta+5С) + (1 – х)(Ti+Hf+Zr+Nb+Ta+10В) is investigated. With an increase in the content of boron in the composition of mixtures, the combustion velocity of the samples increased. A significant influence of impurity gas release on the combustion process of samples was discovered. Combustion velocity of compressed samples has increased significantly. The elongation of the samples increased with an increase in the carbon content of the mixture. Due to the significant elongation, the synthesis products had high porosity, and powders were easily obtained from them. By the XRD method, reflexes of the high entropy diboride [Ti, Hf, Zr, Nb, Ta]B2 were recorded in the composition of the combustion products of the mixture Ti+Hf+Zr+Nb+Ta+10B. Three multi-element carbides have been identified in the composition of the synthesis products of the Ti+Hf+Zr+Nb+Ta+5C mixture: medium-entropy [Ti, Hf, Ta]C and two high-entropy [Ti, Hf, Zr, Ta]C and [Ti, Hf, Zr, Nb,Ta]C. The combustion products of a mixture of 50%(Ti+Hf+ +Zr+Nb+Ta+5C)+50%(Ti+Hf+Zr+Nb+Ta+10B) contain five multi-element high-entropy phases: two diborides and three carbides based on metal solid solutions. In this work, high-entropy ceramics containing high-entropy carbides and borides were obtained for the first time using the SHS method. The SHS method allows synthesis to be carried out in one stage, varying the composition of the products. The results of the work can be used to obtain high-entropy ceramics in the system х(Ti+Hf+Zr+Nb+Ta+5С)+(1-х)(Ti+Hf+Zr+Nb+Ta +10В).