Budaraju Srinivasa Murty

Developing low-density superalloys with high-temperature strength and environmental stability is essential for improving the efficiency and durability of gas-turbine and energy-conversion systems. Conventional Ni-based superalloys often rely on dense, expensive refractory additions, motivating simpler, cost-effective alternatives. Here, we investigate progressive Fe-for-Ni substitution in a Ti-rich Ni-Co-Cr-Al-Ti superalloy, selected from a previously established alloy design space, comprising a configurationally complex γ matrix reinforced by coherent L1 2-ordered γ ′ precipitates. The effects of Fe on phase stability, microstructural evolution, high-temperature strength and oxidation behaviour are systematically examined. Fe preferentially partitions to the γ matrix, reducing the γ ′ solvus temperature and volume fraction while promoting a transition from cuboidal to rounded precipitates. Moderate Fe substitution retains competitive intermediatetemperature strength, offering a favourable density-cost-strength compromise, whereas higher Fe concentrations reduce strength through diminished γ ′ stability and fraction. Isothermal oxidation at 900-1000 • C reveals a strongly composition-and temperature-dependent response: moderate Fe additions improve protection at lower temperatures but promote porous Fe-rich multi-spinel formation and breakaway oxidation at 1000 • C, while higher Fe content favours a thinner, chromiarich protective scale. Thermodynamic calculations indicate that Fe increases Cr activity and its thermodynamic availability for chromia formation and replenishment. Custom Python scripts enable pixel-resolved analysis of BSE and quantitative EPMA-WDS datasets through elementalmap reconstruction, laterally averaged depth profiling and local oxide-stoichiometry classification constrained by XRD-supported phase assemblages and thermodynamic feasibility. Together with XRD and temperature-dependent thermodynamic calculations, these analyses establish that oxidation resistance depends on the spatial organisation, continuity and chemical association of Cr 2 O 3 , Al 2 O 3 and Fe/Ni/Co-containing spinels rather than oxide thickness or Fe enrichment alone. The results reveal a concentration-dependent spinel-forming effect whereby Fe-bearing spinels either destabilise or reinforce the protective oxide architecture depending on composition and temperature. Thus, Fe substitution offers a versatile strategy for tailoring the coupled phase stability, mechanical performance, density and oxidation resistance of low-density γ ′-strengthened Ni-Cobased superalloys.

The mechanical alloying (MA) process involving cold welding, fracture, and rewelding of powder particles is a powder metallurgy powder processing technique. Currently, MA technique is one of the most widely used methods to produce oxide‐dispersion‐strengthened (ODS) alloys. ODS steels are considered as potential candidate materials for high‐temperature applications, such as blanket materials for fusion reactors, fuel cladding for Generation IV fission reactors, and blades for gas and ultra‐super critical steam turbines due to excellent properties, such as high‐temperature strength and resistance to creep, corrosion, oxidation, and neutron irradiation. It is also possible to synthesize alloys with unique constitutional effects, such as supersaturated solid solutions, metastable quasicrystalline and crystalline phases, and amorphous alloys, with this technique. This article reviews recent developments in Fe‐based ODS alloys through MA.

In this study, a new lightweight Al-Ti-Ta alloy was developed through a synergistic approach, combining CALPHAD methodology and entropy-driven design. Following compositional optimization, the Al_87.5Ti_6.25Ta_6.25 (at.%) alloy was fabricated and isothermally heat-treated at 475 °C for 24 h to attain equilibrium. X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) analyses revealed a dual-phase microstructure comprising a 50 vol.% FCC matrix enriched in Al and 50 vol.% Al₃(Ti,Ta)-type intermetallic phase (IP). Notably, the FCC phase exhibited a high-melting transition temperature of 660 °C, surpassing conventional Al-Si cast alloys. Phase-specific nanomechanical properties were evaluated using Nanoindentation. Microindentation tests demonstrated exceptional microhardness of approximately 3300 MPa. These results indicate the alloy’s superior hardness compared to conventional alloys such as Al-Si (A390), 7075 Al alloy, and CP-Ti, even exceeding Ti-64 alloy at a 15% lower density. The alloy’s stability under prolonged heat treatment at 475 °C, reflected by stable phases, microstructure, and mechanical properties, highlights its enhanced thermal stability, which can be attributed to entropy-driven phase stabilization. This study underscores the effectiveness of integrating entropy-driven design strategy with CALPHAD predictions for the accelerated development of advanced Al-based alloys.