POHLUDKA Martin VYSOKÁ ŠKOLA BÁŇSKÁ-TECHNICKÁ UNIVERZITA OSTRAVA

Spoluautoři MALCHARCZIKOVÁ Jitka, MICHENKA Vít, KURSA Miroslav, ČEGAN Tomáš, SZURMAN Ivo

Materials based on nickel aluminides are used in high-temperature applications. Ni3Al intermetallic compound is a base of nickel alloys and it exhibits a positive dependence of deformation stress on temperature. Thereby, strength of nickel alloys increases together with temperature up to 800 °C. Unfortunately, polycrystalline Ni3Al is a brittle at room temperature. Brittleness of Ni3Al can be successfully reduced by boron alloying in small quantities. Chrome inhibits a corrosion cracking at high temperatures. Addition of molybdenum and zirconium provides ductility. Three different nickel alloys – IC221M, IC396 and IC438 – were prepared by induction melting followed by centrifugal casting. Metallographic samples were made of rod castings. The samples were used for microstructure documentation, for porosity and microhardness evaluation and for chemical composition verifying by scanning electron microscope. The rods of nickel alloys were machined to tensile specimens which were strained at normal conditions. Dendritic structure of cast nickel alloys proved to be unsuitable because it contained large shrinkage which caused premature fracture of tensile specimens. This result was opposed to tensile tests of directionally solidified samples because unidirectional solidification orientates a structure and also reduces the presence of shrinkage. Therefore, it is important to continue in searching of the processes which reduce a dendritic structure of nickel alloy castings.

Zpět