EFFECT OF SCRAP USING IN CHARGE ON THE STRUCTURE AND PROPERTIES OF ZhS6U NICKEL-BASED SUPERALLOY. PART 1. MICROSTRUCTURE ANALYSIS AND PHASE COMPOSITION OF ZhS6U ALLOY PREPARED WITH SCRAP

Expensive nickel superalloys are used for manufacture of cast blades of gas turbine engine (GTE). However, for the blades only a small amount of alloy was used and the remainder is used for gating system. Therefore, the most proportion of alloy after casting is a scrap, the use of which as raw material for blades production significantly reduces their cost. However, the use of scrap is associated with some risks: the possibility of alloy contamination by nonmetallic inclusions and loss of alloying elements. So, the investigation of a scrap usage effect on the blades properties is very important. In the first part of article the influence of the scrap amount on the microstructure and phase composition of the ZhS6U-VI nickel-base superalloy were examined. The GTE blades samples, fully produced from the scrap of ZhS6U-VI superalloy by investment casting were investigated. The scrap before using was cleaned from contaminations and ceramic mold remains. Samples were cut from blade dowetail and gating system near dowetail. In addition, cylindrical samples that were casted into the copper mold from the virgin alloy ZhS6U-VI without the scrap and from alloys with 50 % and 100 % of scrap were researched. The alloys microstructures were investigated using scanning electron microscopy and optical microscopy. The phase’s identification was carried out using the energy-dispersive X-ray spectroscopy (EDS) and the calculations of phase composition were made by Thermo-Calc software and literature data about phases in nickel-based superalloys. Content of alloying elements (except carbon) was measured by EDS analysis. The studies were carried out on the samples as-casted and annealed for 4 hours at 1210 °C. It is shown that the use of scrap does not fundamentally change the alloy phase composition at both during vacuum induction melting and vacuum arc melting.

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