Research Projects

Nickel-cobalt-chromium alloys which are a class of medium entropy alloys exhibit excellent high temperature mechanical properties as well as oxidation resistance. In recent times the GRX-810 NASA developed nickel-cobalt-chromium oxide dispersion strengthened (ODS) alloy has caught attention as it offers a combination of excellent high temperature strength, and outstanding oxidation resistance up to a temperature of 1300°C. A computational materials engineering techniques was adopted to develop (model) this alloy focusing on a new class of materials with excellent high temperature and oxidation resistant properties. At a temperature of 1093°C the GRX-810 alloy has shown to provide a two-fold improvement in strength compared to Ni based superalloys such as IN-718 and IN-625. The GRX-810 alloy has shown to exhibit a considerably longer creep rupture life as compared to 718 and 625 Ni based superalloys. This alloy further features a stable microstructure up to its melting temperature as well, avoiding the need for solution /ageing treatment as required by most Ni based superalloys. This Ni-Co-Cr based GRX-810 alloy was designed for applications such as rocket/missile engine injectors, turbines, pre-burners and various hot-section components. These components have the capacity to endure temperatures up to 1100 °C. The GRX-810 alloy was researched and developed to create an alloy that bridges the temperature gap between conventional Ni based superalloys and refractory alloys and at the same time maintaining the processing flexibility similar to that of Ni-based superalloys in terms of their ductility and formability. Ni-Co-Cr alloys face a loss of strength at temperatures above 850°C as dissolution / coarsening of strengthening phases, grain boundary sliding as well as softening of the alloy occurs. This phenomenon’s reduce the high temperature strength as well as creep strength of these alloys. On the other hand oxides such as yttria, thoria, and alumina are more stable at high temperature, and there incorporation in the Ni-Co-Cr alloy is an effective strategy to improve the high temperature mechanical properties and oxidation resistance of these alloys. ODS- NiCoCr alloys thus came into existence and are been researched for several practical applications one of which been the GRX-810 alloy. The high temperature strength of any ODS alloy is strongly dependent on attributes such as the oxide particle size, particle distribution, number density of particles and inter-particle distance. Ultrafine / nanometric and homogeneously dispersed dispersoids are required for effective blocking of the dislocations as well as to prevent grain boundary sliding at high temperatures. Yttria is generally used as a dispersoid in ODS alloys due to its stability at high temperatures The aim of this proposal is to develop oxide dispersion strengthened (ODS) GRX-810 alloys by cryo-milling and powder forging. The yttria reinforced GRX-810 powders will be produced by cryo-milling of the as procured prealloyed GRX-810 pralloyed powders with varying contents of yttria (0, 0.15, 0.3 & 0.45) by cryo-milling in a Simoloyer attritor mill. These GRX-810 powders with varying yttria contents will be further powder forged in a capsule at around 1050oC to obtain near full dense slabs. The microstructural analysis of the forged slabs will be carried out by SEM and TEM analysis. Further, the high temperature tensile strength, creep behavior as well as oxidation behavior of these GRX-810 alloys with varying yttria contents will be evaluated.