ROUČKA Jaromír Brno University of Technology

Spoluautoři HRBÁČEK Karel, ŇUKSA Petr

In nickel-based turbocharger castings, defined macrostructure and microstructure are required in addition to internal homogeneity and mechanical and creep properties. The structure is given in particular by the orientation and maximum dimensions of dendritic and equiaxed grains and by the extent of admissible microporosity and carbide phases. Experiments were conducted aimed at establishing the possibility of influencing crystallisation by way of exploiting the effect of centrifugal and inertia forces acting on the metal in the course of solidification. It turned out that the effect of force action on the structure of castings was significant and enabled achieving a fundamental change in structure morphology. With these purposes in mind, a facility was developed and tested that enables shell mould casting in vacuum furnaces with the moulds rotating or oscillating. Oscillation, which consisted in periodically changing the sense of rotation of the casting bench during metal solidification, proved to be the most effective way of affecting the structure. Oscillation helps to achieve a considerably refined structure in the region of equiaxed grains and to curb the appearance of carbide network on grain boundaries. During the experiments, the effect of the mode of this action on the structure, mechanical properties and microporosity of the alloy was investigated.