Advances in nickel-based cast superalloys

Abstract

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.

Effect of TiN particulate reinforcement on corrosive behaviour of aluminium 6061 composites in chloride medium

“…It has been reported that in the case of TiN-reinforced Al MMCs fabricated by powder metallurgical route (Ray et al 2002) that the presence of TiN-particles at grain boundaries played a significant role in its densification and improved mechanical as well as wear resistance properties. The improved corrosion resistance in TiN-reinforced Al 6061 composites compared to matrix alloy can be attributed to good interface bonding between the ceramic TiN and Al matrix alloy (Das 2004). TiN particle reinforced composites exhibit lesser surface irregularities which is due to refined microstructure as observed during the study of electrochemical behaviour of haematite particulates reinforced Al alloys (Jagadeesh et al 2005).…”

Development and Characterization of Functionally Gradient Al–Si Alloy Using Cast-Decant-Cast Process

“…This is due to less number of nucleation sites (lower Si particles) and slow rates of conduction of heat for the alloy B liquid to cool during solidification [16]. The higher solidification rate and higher volume of Si particles at the interface results in refinement of the grain size in the FGM region [20]. Another unique observation found on the distribution of Si particles in the FGM region is that no agglomeration or porosity was noted through out the cross section of the CDC alloy.…”

“…The wear properties of Al-Si alloys mainly depend upon the microstructure, in particular, size and distribution of Si particles in the a-Al eutectic matrix [26,27]. Many previous workers [2,20,21] have reported that Al alloy with high Si content provides very good wear resistance, while Si content of about 14 to 16 wt% provides the optimum wear resistance. The presence of large Si particles in the Al-Si alloys has been recognized as the main limitation for their industrial use, because the coarse Si particles tend to rise brittleness and easy to cracking the soft Al matrix resulting in catastrophic failures during service [28,29].…”

Materials for Gas Turbines – An Overview

“…Further the cast components are intrinsically stronger than forgings at high temperatures, due to the coarse grain size of castings. Das recently reviewed the advances made in nickel-based cast superalloys (Das, 2010). Buckets (rotating airfoils) must withstand severe combination of temperature, stress and environment.…”