Projeção liquidus do sistema Ta-Ge-B

Abstract

Current technological progress has demanded materials that can maintain their physi cal and chemical properties and integrity when submitted to high mechanical stress for long periods and high temperatures. Ni-based superalloys belong to a class of materials currently used in these conditions, but they have reached their limit of development and, therefore, there is a demand for materials that can complement them. Among the materials with this potential it can be highlighted those based on multiphase microstructures of MR (Refractory Metals) in thermodynamic equilibrium with intermetallics. The most promis ing results have been obtained with alloys based on Nb-Si-B or Mo-Si-B. A good example is the MoSi2 phase, as it has a high melting point, 2020 °C, and excellent resistance to oxi dation at high temperatures, however, its toughness and mechanical strength are low, but if this phase reaches thermodynamic equilibrium with a refractory metal, this metal can impart the necessary ductility to the alloy. Due to the similarities in chemical structure existing between the pairs Nb, Si and Ta, Ge, this last pair of chemical elements can be used to stabilize a desired microstructure and, in addition, they can control diffusion and oxidation resistance. Thus, the study of the Ta-Ge-B system can be important to assist in the development of these alloys, especially if associated with thermodynamic modeling by the CALPHAD method. No information on the liquidus projection or thermodynamic modeling of the Ta-Ge-B system was found in the literature. Thus, this work presents the experimental study of the liquidus projection of the Ta-Ge-B system through the analy sis of the solification structure of 17 alloys associated with thermodynamic calculations by the CALPHAD method. As a result, a partial proposal for the liquidus projection is presented for the first time in the literature.