Surendra Kumar Makineni

Indian Institute of Science | IISC · Department of Materials Engineering

We propose here a deformation-induced diffusive phase transformation mechanism occurring during shearing of γ′ ordered phase in a γ/γ′ single crystalline CoNi-based superalloy. Shearing involved the creation and motion of a high density of planar imperfections. Through correlative electron microscopy and atom probe tomography, we captured a superla...

The effect of Zr addition to Al rich binary α-Al - Al3Ni eutectic cast alloy (Al-3.1 at.% Ni) in enhancing the microstructural stability and strength at high temperature is demonstrated. On subsequent heat treatment after casting, nanometric coherent L12 ordered Al3Zr precipitates form inside the α-Al that strengthen the alloy. Additionally, a rema...

Single crystal Ni-based superalloys have long been an essential material for gas turbines in aero engines and power plants due to their outstanding high temperature creep, fatigue and oxidation resistance. A turning point was the addition of only 3 wt.% Re in the second generation of single crystal Ni-based superalloys which almost doubled the cree...

Co base superalloys strengthened by coherent L1 2 ordered γ′ precipitate in a disordered face-centered cubic γ matrix represent a new opportunity for high-temperature alloy development. The emergence of alloys with low density and high specific yield strength at elevated temperatures has further energized the research and development efforts in the...

Discontinuous precipitation (DP) reactions are among the most important solid-state phenomena that occur during the migration of grain boundaries (GBs) in many engineering alloys. Migration involves solute redistribution across the moving GB and the solute diffusion assumed to occur only along it. In this work, we show the atomic scale compositiona...

Kinetic and structural changes associated with grain boundary phase transition induced by Bi alloying in dilute Ni–Bi alloys (0-0.3 at.% of Bi) are investigated in a concerted manner. Grain boundary diffusion of Ni in the Ni-Bi alloys is measured in Harrison's B- and C-type kinetic regimes applying the radiotracer technique and utilizing the 63Ni r...

The paper explores the role of multimodal γ' distribution in a CoNi-based superalloy on their thermophysical and mechanical properties. Three categories of γ' size distribution as primary, secondary type-1, and secondary type-2 were obtained by varying Ti composition (2, 4, and 6 at.%) in a Co-30Ni-7Al-2Nb (at.%) alloy. The study reveals an anomaly...

In recent times, applying correlative experimental techniques using electron microscopy (EM) and atom probe tomography (APT) to interpret several materials science problems have shown promising results. Especially, getting structural and three-dimensional compositional information from the same region of interest on a material led to understanding...

While boron is added to many structural alloys primarily as a grain-boundary strengthener, it has myriad other implications on the microstructure and thermophysical properties of these alloys. In the present study, we report these effects by varying boron addition in the range of 0.02at.% to 0.8at.% on the microstructure, thermo-physical properties...

Achieving high yield strength (250-270 MPa) at elevated temperatures (250 °C and above) for precipitation strengthened aluminium-copper (Al-Cu) alloys still remains a challenge for the alloy designers. This paper presents a systematic progression of the microstructure evolution in a binary Al-0.3Hf, ternary Al-0.3Hf-0.3Si and quaternary Al-2Cu-0.3H...

The present study illustrates the effect of varying Cr content in Co51-xNi30Al10Mo5Nb2Ti2Crx (x = 2, 5, and 8 at.-%) compositionally complex alloys (CCAs). STEM-EDS analysis suggests a change in Mo partitioning from equal in both the phases (γ and γ′) in CCA-2Cr to the γ phase in CCA-5Cr and CCA-8Cr alloys. This peculiar compositional partitioning...

The paper reports the design and development of wrought Al-Cu alloys that retain high strength until 250 °C. It is achieved by minor alloying of Zr (<0.15 at%) and Nb (<0.1 at%) and inducing precipitation of stable nanometric dispersion of L12 ordered precipitates during controlled thermomechanical treatment (rolling) of cast alloys before conventi...

In this work, by equipping the high-entropy concept we designed a γ/γ′-type high-entropy alloy with high Fe content (25 at.%), and further alloyed Nb to evaluate its microstructural stability and mechanical responses. We found that after 850 °C annealing, 1.5 at.% Nb addition can completely suppress the discontinuous precipitation (DP) reaction. Th...

In this work, a simple rectangular milling technique was demonstrated to prepare needle shape atom probe tomography (APT) specimens from Al alloys by focused‐ion‐beam (FIB) milling using Ga ⁺ ions at room temperature. Ga has high miscibility in Al owing to which electropolishing technique is preferred over Ga ⁺ ion FIB instruments for the fabricati...

We describe in detail the deformation micromechanisms operative during the compressive creep of a directionally solidified (DS) tungsten-free γ/γ' Cobalt-base superalloy across a range of stresses and temperatures and their manifestation on macroscopic creep behavior. Creep experiments were carried out at 800°C, 850°C, and 900°C under different str...

This work demonstrates the development of a strong and ductile medium entropy alloy by employing conventional alloying and thermomechanical processing to induce partial recrystallization (PR) and precipitation strengthening in the microstructure. First, the cold working of homogenized alloy resulted in a highly deformed microstructure. On annealing...

The antagonism between strength and resistance to hydrogen embrittlement in metallic materials is an intrinsic obstacle to the design of lightweight yet reliable structural components operated in hydrogen-containing environments. Economical and scalable microstructural solutions to this challenge must be found. Here, we introduce a counterintuitive...

A dynamic strain aging (DSA) regime is established for a near-α titanium alloy with a microstructure consisting of 80% equiaxed α, 15% lamellar α and 5% β with silicon in solid solution through a series of constant strain rate tests carried out in tension from 5 × 10⁻² to 5 × 10⁻⁶ s⁻¹ in the temperature range of 623-823K. Transmission electron micr...

The present work explores the effect of ruthenium (Ru) addition to the γ/γ′ strengthened Co-30Ni-10Al-5Mo-2Nb superalloy. A 2 at.% Ru increases the γ/γ′ microstructural stability at 900°C. XRD and APT revealed a reduction of γ/γ′ lattice misfit by ∼ 26% and segregation of Ru at γ/γ′ interface, respectively that contribute to the decrease of γ/γ′ in...

This work demonstrates the development of a strong and ductile medium entropy alloy by employing conventional alloying and thermomechanical processing to induce partial recrystallization (PR) and precipitation strengthening in the microstructure. The combined usage of electron microscopy and atom probe tomography reveals the sequence of microstruct...

Titanium is an important alloying addition to γ/γ′ cobalt-based superalloys that enhances the high temperature microstructural stability and make the alloys lighter. In this work, we probe the role of Ti composition on the phase stability and oxidation behavior of Co–30Ni–10Al–8Cr–5Mo–2Nb superalloys. With Ti addition, the γ′-solvus temperature is...

We report new compositions of CoNi-based superalloys that have low mass densities (7.84 g/cc to 8.20 g/cc), negative γ/γ′ lattice misfit, and high γ′ solvus temperature up to 1094 °C with promising high-temperature mechanical properties. The γ/γ′ in the base Co-30Ni-10Al-5Cr alloy was stabilized with Nb and further developed by varying Ti and Cr. T...

Atom probe tomography (APT) provides three-dimensional compositional mapping with sub-nanometre resolution. The sensitivity of APT is in the range of parts per million for all elements, including light elements such as hydrogen, carbon or lithium, enabling unique insights into the composition of performance-enhancing or lifetime-limiting microstruc...

A systematic study of the compression creep properties of a single-crystalline Co-base superalloy (Co-9Al-7.5W-2Ta) was conducted at 950 {\deg}C, 975 {\deg}C and 1000 {\deg}C to reveal the influence of temperature and the resulting diffusion velocity of solutes like Al, W and Ta on the deformation mechanisms. Two creep rate minima are observed at a...

A systematic study of the compression creep properties of a single-crystalline Co-base superalloy (Co-9Al-7.5W-2Ta) was conducted at 950°C, 975°C and 1000°C to reveal the influence of temperature and the resulting diffusion velocity of solutes like Al, W and Ta on the deformation mechanisms. Two creep rate minima are observed at all temperatures in...

We report on comparative atom probe tomography investigations of γ/γ′-forming Co–12Ti–4Mo–Cr alloys. Moderate additions of Cr (2 and 4 at%) reduced the γ/γ′ lattice misfit and increased the γ′ volume fraction of a Co–12Ti–4Mo alloy significantly. These microstructural changes were accompanied by changes in the elemental partitioning between γ and γ...

In this work, we discussed the atomic-scale mass transport occurring in a Mo-doped NiCoCr medium-entropy alloy to form σ-precipitates during partial recrystallization at 700°C. We reveal the segregation of Cr/Mo to the fault planes of nano-twins/stacking faults in non-recrystallized zones. Upon annealing, the migration of recrystallized grain bound...

In sensitized (700°C for 10 h) AISI 316L stainless steel samples attacked by an HF solution, coincidence site lattice (CSL) ∑7 grain boundaries (GBs) always show corrosion while ∑5 GBs never do. This distinct corrosion behaviour can be related to the distinct precipitation behaviour of the different GBs, which itself depends on the GB characters. I...

The paper explores the influence of Ti addition to the Ta stabilized γ/γ′ two-phase Co-based superalloys having the compositions of Co-30Ni-10Al-5Mo-2Ta-xTi (x = 0, 1, 2 and 4 at. %). The microstructure of the alloys after solutionizing (1300 °C for 25 hours) and quenching show fine distribution of γ′ precipitates with spherical shape within the γ...

In this work, the nanometer-scale mass flow coupled to dislocation processes near the γ/γ′-interface during high temperature and low stress creep of a model Ni-base single crystal superalloy is investigated. In the early creep stages, the dislocation networks in the γ-phase at γ/γ′-interfaces attract γ-stabilizing elements like Cr, Co and in partic...

In the present work, we show the feasibility of microstructural control by additions of Ti and Cr to a γ/γ′ Co-30Ni–10Al–5Mo–2Nb superalloy. Solutioning at 1300 °C followed by aging at 900 °C leads to homogenous distribution of L12 ordered cuboidal γ′ precipitates in face-centered-cubic (fcc) γ matrix. Compositional measurements show Al, Mo, and Nb...

We report atomic structures and chemical compositions of defects associated to planar faults in a creepCreep deformed Co-base superalloyCo-base superalloy and discuss their formation and contribution to plastic deformation. The multinary single crystalline Co-base superalloy was creep deformed under tension along 001-direction at 850 °C and 400 MPa...

We report new compositions of γ/γ′ Co base super alloys with low mass density where the strengthening γ′ precipitates are Co3(Al0.45V0.33Nb0.21) stabilised with a systematic replacement of Mo with V in Co–10Al–5Mo–2Nb (all in at.%) superalloy. The γ/γʹ microstructure is found to be metastable in nature that decomposes into equilibrium phases after...

We investigated the flow behavior of γ/γʹ-strengthened Co-12Ti and Co-12Ti-4Mo (at.%) alloys at room and elevated temperatures (up to 900°C) by electron microscopy and density functional theory. The Mo-added alloy exhibited an enhanced compressive yield strength and strain hardening behavior as compared to the reference binary alloy. This behavior...

In this work we report new γ′ strengthened cobalt base superalloys that have low mass densities in the range of ∼ 8.3–8.5 gm/cm³, high solvus up to ∼ 1128 °C and high specific 0.2% proof strength of ∼ 90 MPa.gm⁻¹.cm³ at temperatures up to 770 °C. The basic alloy composition is Co–10Al–5Cr–2Ta that exhibits γ/γ′ microstructure on heat treatment. Ele...

The present disclosure relates to a new class of copper (Cu)-based alloys where Cu matrix is strengthened by coherent L12 precipitates of A3B type where, A represents Fe or Co and B represents Si or Al. More specifically, embodiments of the present disclosure provide high strength and high conductivity copper-aluminium-cobalt (Cu-Co-Al) alloy and c...

The influence of (Al,Zn)3Zr dispersoids on the precipitation of the main strengthening phases was investigated during isothermal aging of a model Al-Zn-Mg-Cu-Zr alloy. Upon homogenization of the alloy, dispersoids of (Al,Zn)3Zr with a L12 structure are present. Isothermal aging at 120°C for 0.5 hours leads to the homogeneous formation of spherical...

The effect of replacement of molybdenum with small amount of tungsten on the stability of cobalt base superalloys of Co-Ni-Mo-Al-Ta-Ti class has been presented. A small addition of Tungsten (W) in Co 30Ni (5-x)Mo xW 10Al 2Ti 2Ta alloys stabilizes the cuboidal morphology of precipitates and increases the γ′ volume fraction. A 2 at% addition of W cau...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

We investigated the solute diffusional behavior active during compressive creep deformation at 150 MPa / 975°C of a Co-Al-W-Ta single crystal superalloy in the [001] orientation. We report the formation of shear-bands that involves re-orientation of γ/γʹ rafts to {111} from {001} planes, referring to as γ/γ′ raft-rotation. In the shear-band regions...

We demonstrate the formation of a hierarchical microstructure by optimized combination of Mo- doping and thermo-mechanical processing in a NiCoCr medium-entropy-alloy (MEA) that results in a significant improvement in yield-strength (~775 MPa) and ultimate-tensile-strength (~1200 MPa) with an elongation to fracture up to 35%. Addition of Mo slows...

The article outlines the evolution, over the last half a century, of Co-base superalloys. Recent developments have led to the emergence of these alloys as a promising alternative to high temperature commercial Ni-base superalloys that are used in fabricating components of gas turbine engines that power passenger/military aircrafts, ships and power...

A novel high-strength steel design is proposed, with a fine bainitic microstructure free from inter-lath carbides, for railway crossings applications. The design is based on the phase transformation theory and avoids microstructural constituents like martensite, cementite and large blocky retained austenite islands in the microstructure which are c...

In this article, we probe the strain partitioning between the microstructural features present in a continuously cooled carbide-free bainitic steel together with damage nucleation and propagation. These features mainly comprise of phases (bainitic ferrite, martensite, and blocky/thin film austenite), interfaces between them, grain size and grain mo...

The alloying of Ti with Cu(Sn) and Nb significantly increases the grain boundary diffusion-controlled growth kinetics of Nb3Sn accompanied with a decrease in the activation energy in the Cu(5.5 at.% Sn, Ti)/Nb and Cu(5.5 at.% Sn)/Nb(Ti) diffusion couples. In either case, the β-(Ti,Nb) precipitates form at the grain boundaries of Nb3Sn. On the other...

Although atom probe tomography (APT) reconstructions do not directly influence the local elemental analysis, any structural inferences from APT volumes demand a reliable reconstruction of the point cloud. Accurate estimation of the reconstruction parameters is crucial to obtain reliable spatial scaling. In the current work, a new automated approach...

In this study, the effect of rhenium (Re) addition on microstructural evolution of a new low-density Co-Ni-Al-Mo-Nb based superalloy is presented. Addition of Re significantly influences the γ′ precipitate morphology, the γ/γ′ lattice misfit and the γ/γ′ microstructural stability during long term aging. An addition of 2 at.% Re to a Co-30Ni-10Al-5M...

We explore the effects of the elemental site occupancy in g 0-A 3 B (L1 2) intermetallic phases and their partitioning across the g/g 0 interface in a class of multicomponent W-free Co-based superalloys. Atom probe tomography and first principles density functional theory calculations (DFT) were used to evaluate the Cr site occupancy behavior in th...

https://rdcu.be/5juE Nanoscale solute segregation to or near lattice defects is a coupled diffusionand trapping phenomenon that occurs in superalloys at high temperatures during service. Understanding the mechanisms underpinning this crucial process will open pathways to tuning the alloy composition for improving thehigh-temperature performance an...

We report on the full three-dimensional compositional partitioning among the features of a planar imperfection comprising a superlattice intrinsic stacking fault (SISF) with its leading and trailing partials, as well as the antiphase boundary (APB) in the wake of the trailing partial formed in the L12-ordered γ′ phase of a CoNi-based single crystal...

Atom probe tomography (APT) is rising in influence across many parts of materials science and engineering thanks to its unique combination of highly sensitive composition measurement and three-dimensional microstructural characterization. In this invited article, we have selected a few recent applications that showcase the unique capacity of APT to...

A dual-anneal diffusion multiple was utilized to generate a composition gradient via a first anneal at a high temperature followed by a second anneal at a lower temperature to induce phase precipitation as a function of composition/supersaturation. By adjusting the interfacial energy value in simulations using the classical nucleation and growth th...

We explore the effects of the elemental site occupancy in γ'-A3B (L12) intermetallic phases and their partitioning across the γ/γ' interface in a class of multicomponent W-free Co-based superalloys. Atom probe tomography and first principles density functional theory calculations (DFT) were used to evaluate the Cr site occupancy behavior in the γ'...

We explore the effects of the elemental site occupancy in g 0-A 3 B (L1 2) intermetallic phases and their partitioning across the g/g 0 interface in a class of multicomponent W-free Co-based superalloys. Atom probe tomography and first principles density functional theory calculations (DFT) were used to evaluate the Cr site occupancy behavior in th...

We explore the effects of the elemental site occupancy in g 0-A 3 B (L1 2) intermetallic phases and their partitioning across the g/g 0 interface in a class of multicomponent W-free Co-based superalloys. Atom probe tomography and first principles density functional theory calculations (DFT) were used to evaluate the Cr site occupancy behavior in th...

We explore the effects of the elemental site occupancy in g 0-A 3 B (L1 2) intermetallic phases and their partitioning across the g/g 0 interface in a class of multicomponent W-free Co-based superalloys. Atom probe tomography and first principles density functional theory calculations (DFT) were used to evaluate the Cr site occupancy behavior in th...

We report evidence of Re and Mo segregation (up to 2.6 at.% and 1 at.%) along with Cr and Co to the dislocations inside of {\gamma}' precipitates in a second generation Ni-based single crystal superalloy, after creep deformation at 750{\deg}C under an applied stress of 800 MPa. The observed segregation effects can be rationalized through bridging t...

We propose here a deformation-induced diffusive phase transformation mechanism occurring during shearing of g 0 ordered phase in a g/g 0 single crystalline CoNi-based superalloy. Shearing involved the creation and motion of a high density of planar imperfections. Through correlative electron microscopy and atom probe tomography, we captured a super...

Mo-Si-B alloys are potential creep resistant materials for accessing harsh loading scenarios beyond Ni-based superalloys due to their excellent mechanical performance at ultra-high temperatures (> 1200 °C). Here, we report on the fabrication through laser additive manufacturing of a Mo rich Mo-Si-B alloy with and without dispersion of oxide (La2O3)...

We report on the sub-nanometer scale characterization of Co-12Ti-4Mo and Co-12Ti-4Cr (at.%) model alloys. Atom probe tomography reveals that Co and Cr partition to γ, whereas Ti and Mo to γ′. Additions of Mo and Cr to the reference Co-12Ti system lead to strong increases in γ′ volume fraction by about 25% and 12%, respectively. Element-specific spa...

A set of advanced single crystalline γ′ strengthened Co-base superalloys with at least nine alloying elements (Co, Ni, Al, W, Ti, Ta, Cr, Si, Hf, Re) has been developed and investigated. The objective was to generate multinary Co-base superalloys with significantly improved properties compared to the original Co-Al-W-based alloys. All alloys show t...

Elemental site occupancy in the L1 2 A 3 B ordered intermetallic phase in Co-based superalloys and its influence on the microstructure, Acta Materialia (2018), doi: https://doi. Mo atoms distribution across the γ/γ′ interface γ/γ′ Lattice mismatch = +0.48% γ/γ′ Lattice mismatch = +0.19% Spatial Distribution Maps (SDMs) [100] [100] Abstract We explo...

This paper presents a detailed investigation on the effect of small amount of Nb and Zr additions to 2219 Al alloy coupled with a novel three-stage heat treatment process. The main aim of the work is to increase the high temperature strength of 2219 alloy by introducing thermally stable L12 type ordered precipitates in the matrix as well as by redu...

Keywords: Laser additive manufacturing (LAM) Mo-Si-B based alloy Oxide dispersion Transmission electron microscopy (TEM) Atom probe tomography (APT) a b s t r a c t Mo-Si-B alloys are potential creep resistant materials for accessing harsh loading scenarios beyond Ni-based superalloys due to their excellent mechanical performance at ultra-high temp...

Keywords: Laser additive manufacturing (LAM) Mo-Si-B based alloy Oxide dispersion Transmission electron microscopy (TEM) Atom probe tomography (APT) a b s t r a c t Mo-Si-B alloys are potential creep resistant materials for accessing harsh loading scenarios beyond Ni-based superalloys due to their excellent mechanical performance at ultra-high temp...

Nanoscale solute segregation to or near lattice defects is a coupled diffusion and trapping phenomenon that occurs in superalloys at high temperatures during service. Understanding the mechanisms underpinning this crucial process will open pathways to tuning the alloy composition for improving the high-temperature performance and lifetime. Here, we...

Atom probe tomography (APT) is rising in influence across many parts of materials science and engineering thanks to its unique combination of highly sensitive composition measurement and three-dimensional microstructural characterization. In this invited article, we have selected a few recent applications that showcase the unique capacity of APT to...