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Nickel-based superalloys have served as the most competitive high temperature structural materials under highly stressed and aggressive operating conditions in a variety of applications for more than 60 years. The most demanding among all the applications has been the gas turbine aerofoil castings of modern aero-engines. These turbine parts operate in extremely aggressive environment of high velocity hot combustion gas-air mixture carrying highly corrosive ingredients at high pressure. Gas turbine aerofoil materials should therefore possess adequate resistance to creep, fatigue and aggressive environment. Materials design for such application therefore has been extremely challenging, particularly since the engine designers always aim at higher turbine entry temperature (TET) in order to achieve greater engine thrust and better fuel efficiency. In spite of enormous efforts made in the recent past towards developing ceramics and their composites, Ni-based superalloys continue to be most reliable blade and vane materials offering always the highest TET. This has been possible through better alloy design, improved blade cooling schemes, protective coatings and directional solidification (DS) of either columnar grains or single crystals (SC) along the most favorable <001> texture. During the last six decades, TET has gone up by about 500K. This article covers recent advances in cast Ni-based superalloys, including our own efforts in this direction. Extensive research at DMRL has led to the development of new generation Ni-based superalloys, designated as DMD-4 and DMS-4 for DS and SC processing, respectively. Simultaneously, expertise has been developed to cast DS and SC components for aero-engines. Technology has also been established for pilot scale production of these components.

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Articles you may be interested inDual-resonance converse magnetoelectric and voltage step-up effects in laminated composite of long-type 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 piezoelectric single-crystal transformer and Tb0.3Dy0.7Fe1.92 magnetostrictive alloy bars Effect of B on the microstructure and magnetostriction of zoned Dy 0.7 Tb 0.3 Fe 1.95

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This paper investigates the effect of CaO‐Al2O3 flux, used in conjunction with CaSi, on the formation of inclusions in aluminium‐killed steel. 50 kg scale experiments were carried out in an air induction furnace. The amounts of CaSi (1.25–2.5 kg/t) and fluxes (CaO:Al2O3 from 40:60 to 60:40) were varied in different experimental heats. The volume fraction and size of inclusion were determined through quantitative metallography. The change in the composition of inclusions was qualitatively studied through elemental x‐ray analysis by EPMA. The size of inclusions in general was found to be larger in the case of the simultaneous addition of CaSi with flux, compared to that obtained through CaSi alone. Larger inclusions lead to easier flotation resulting in lesser volume fraction. The inclusion content was lowest with flux containing 40% CaO and 60% Al2O3. Better globularisation of alumina inclusion was observed in the case of the simultaneous addition of flux with CaSi, compared to situations where CaSi alone is added. The present investigation has therefore identified the specific amount and composition of flux necessary for restricting the inclusion content as well as improving its globularisation.

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