STRUCTURE AND MECHANICAL PROPERTIES OF NICKEL ALLOYS

Three different nickel alloys - IC221M, IC396 and IC438 - were prepared by induction melting followed by centrifugal casting. Metallographic samples were made of bar castings. The samples were used for microstructure documentation, for porosity evaluation and for chemical composition verifying by scanning electron microscope. The bars of nickel alloys were machined to tensile specimens, which were strained at standard conditions. It has been confirmed that dendritic structure of cast nickel alloys is unsuitable. The castings contained large shrinks which caused premature fracture of tensile specimens. This result was opposed to tensile tests of directionally solidified samples because directional solidification orientates a structure and also reduces the presence of shrinks. Therefore, it is important to continue in searching of the processes which reduce a dendritic structure of nickel alloy castings.