Abstract
	Aircraft industry often uses nickel super-alloys for blades of jet engine turbines. It is so because this material must satisfy numerous extreme requirements, such as e.g. heat-resistance at high temperatures, resistance to fatigue damage, resistance to aggressive effect of combustion products, etc. Long-term service life and reliability of material is directly related to its microstructure, i.e. to its stability at long-term exploitation. Used materials are usually alloyed in a complex manner and their structure is very complicated [1, 2]. One of materials used for these applications is cast, complex alloyed nickel super-alloy INCONEL 713LC on the basis of Cr-Al-Mo-Ti-Nb-Zr. Several strengthening mechanisms take effect in this alloy, the main mechanism is precipitation strengthening by coherent precipitates of inter-metallic phase Ni3Al, or Ni3(Al, Ti) [3]. Nickel super-alloy has in as cast state heterogenous structure with distinct dendritic segregations. In the zones of segregations there were found particles of carbides or niobium and titanium carbo-nitrides of the type (Nb, Ti) (C, N), moreover large particles of inter-metallic phase of the type Ni3Al, and finally multiphase formations with higher contents of Mo, Nb, but particularly of Zr, the reason of which we were unable to identify precisely. This paper is focused on investigation of structure of castings made of nickel super-alloy INCONEL 713LC after various variants of heat treatment. Laboratory annealing at the temperature of 1240 0C showed that fine strings of carbidic particles were present in material at the grain boundaries, probably already in initial state. Heat treatment 1240 0C/2 hours/furnace to 940 0C/air already triggered intensive precipitation of the phase ?’.