Vliv krystalizačních procesů na strukturu a vlastnosti intermetalické sloučeniny Ni3Al

Abstract

Technologies of gravity and centrifugal casting together with application of directional solidification process, which were used for preparation of experimental alloys, are compared in this dissertation thesis named “The effect of solidification processes on structure and properties of the Ni3Al intermetallic compound”. Gain knowledge has contributed to the understanding of microstructure formation of the Ni-Al material containing from 22 to 25 at.% of aluminum and to the change of its morphology during controlled solidification at the rates from 10 to 70 mm/h and constant thermal gradient of 75 °C/cm. Special attention is given to the Ni-22Al alloy including the effect of boron alloying with concentrations of 0.24 and 1 at.% and to the effect of these concentrations on microstructure and mechanical properties, determined by tensile and creep tests. The conclusion were presented at scientific conferences and published in specialized journals. Synopsis of dissertation thesis is divided into several chapters. The chapters devoted to the theoretical part deals with the issue of Ni3Al phase formation, its structure and properties, brittle fracture of polycrystalline Ni3Al at room temperature and the positive effect of boron to reduce brittleness, then the creep of alloys based on Ni3Al and finally the methods of their preparation. The practical part of the thesis deals with the experimental alloy microstructure, chemical composition analysis, microstructure selection map, quantitative image analysis, porosity, microhardness, surface tension and mechanical tests, namely tensile and creep tests.