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Introduction
I teach courses on topics such as Transport Phenomena, Solidification, Welding and Characterization at IIT Madras. My research interests are in the area of Solidification and Welding. Visit my personal website at IIT Madras for more information: https://mme.iitm.ac.in/gphani/
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Publications
Publications (165)
The phase-field method has become a useful tool for the simulation of classical metallurgical phase transformations as well as other phenomena related to materials science. The thermodynamic consistency that forms the basis of these formulations lends to its strong predictive capabilities and utility. However, a strong impediment to the usage of th...
The addition of Zn to AlCrFeCoNi high‐entropy alloy (HEA) poses intriguing questions as to how it would affect phase evolution. Herein, the phase evolution in AlCrFeCoNiZn is studied using a combination of experimental techniques (X‐ray diffraction, scanning electron microscopy, energy‐dispersive spectroscopy, and differential scanning calorimetry)...
This study explores the potential of cold spray technology for repairing high-strength Al7075 alloy components, particularly in the aerospace industry. The gas-atomized powder contains a dendritic cell structure with solutes segregated at the dendritic cell boundaries. Thus, direct aging of atomized powder fails to induce the formation of strengthe...
Scanning electron microscopy (SEM), combined with energy-dispersive spectroscopy (EDS), is an extensively used technique for in-depth microstructural analysis. Here, we present the EDS-Phase Segmentation (EDS-PhaSe) tool that enables phase segmentation and phase analysis using the EDS elemental map images. It converts the EDS map images into estima...
The detrimental phase formation in Inconel 718 weld microstructure depends on welding conditions. This study uses the FEM simulation of the welding process to establish the variation of temperature gradient and cooling rate in the weld pool boundary as a function of welding current and speed. The microstructure evolution in the weld pool was establ...
The study aims to investigate the hot deformation behavior of Co–Cr–Fe–Ni–V high entropy alloy (HEA) at temperatures ranging from 1073 K to 1373 K and strain rates of 0.001, 0.01, 1, and 10 s−1, and to generate processing maps using dynamic materials modeling (DMM) to identify the optimum processing domain for industrial applications. The material'...
Microstructure and texture evolution of the Fe11.5Co20.6Ni40.7Cr12.2Al7.8Ti7.2 (at. pct) high-entropy alloy during the high-temperature deformation has been investigated in the temperature range of 1173 K to 1373 K and strain rate of 0.1 to 0.001 s−1. The stress–strain curve obtained from the deformation indicates significant flow softening at low...
Rapid solidification during metal additive manufacturing (AM) leads to non-equilibrium microsegregation, which can result in the formation of detrimental phases and cracking. Most of the microsegregation models assume a Scheil-type solidification, where the solidification interface is planar and there exists a local equilibrium at the interface alo...
Identifying optimum processing conditions is necessary for new material development. The flow curves can be used to develop the processing map for an alloy. The current study trained multiple machine learning models such as Random Forest Regressor (RFR), K Nearest Neighbors (KNN), Extra Tree Regressor (ETR) and Artificial Neural Network (ANN) to pr...
High-pressure die casting (HPDC) is a widely used process with short cycle times to manufacture complex shapes of aluminium castings for the automotive industry. Most of the die casting companies use specialized commercial software to simulate molten metal filling and solidification. This approach works satisfactorily and is industrially accepted f...
Rapid solidification during metal additive manufacturing (AM) leads to non-equilibrium microsegregation, which can result in the formation of detrimental phases and cracking. Most of the microsegregation models, assume a Scheil-type solidification, where the solidification interface is planar and there exists local equilibrium at the interface alon...
The near-rapid solidification conditions during additive manufacturing can lead to selection of non-equilibrium phases. Sharp interface models via interface response functions have been used earlier to explain the microstructure selection under such solidification conditions. However, most of the sharp interface models assume linear superposition o...
Laser powder bed fusion (LPBF) of Haynes 282 is gaining attention recently due to its superior mechanical properties than its conventional counterparts. In spite of the superior mechanical properties, there are significant challenges concerning crystallographic anisotropy. One of the critical but less studied parameters that influences crystallogra...
The present study explores the high temperature deformation behavior of FeCoNiCrAlTi dual phase high entropy alloy (henceforth referred to as DP-HEA) in the temperature range of 900–1100 °C (1173–1373 K) and the strain rate varying from 0.001 to 0.1 s−1. The as-cast sample has been characterized using scanning electron microscopy, X-ray diffraction...
The addition of Zn to AlCrFeCoNi high-entropy alloy (HEA) poses intriguing questions as to how it would affect phase evolution. On one hand, Zn has high valence-electron count that should stabilize a face-centered-cubic phase, while, on the other, it exhibits ordering (strong clustering) tendency with Ni and Co (with Cr and Fe), hinting towards pha...
Arc welding involves thermal cycles that lead to phase transformations as well as residual stresses. Alloys that are designed to have specific microstructures obtained through thermo-mechanical treatment are prone to losing their properties in the heat-affected zone as well as fusion zone. One can design a second thermal cycle in such a way as to r...
The additive manufacturing (AM) of eutectic high-entropy alloys (EHEAs) with seven components was simulated. The as-cast alloy comprised of primary dendritic phase and eutectic region between the FCC and Laves phase. The additive thermal cycle generated by the analytical model was used for phase-field and physical simulations. A thermomechanical si...
Inconel 718 as-welded structures are widely used in many critical applications. Welding will cause different types of detrimental phase formation and segregation of elements in the inter-dendritic region. The segregation of elements depends on the local curvatures during morphological evolution dictated by the thermal conditions prevailing during t...
From thermodynamical consideration, rather a monotonically increasing crystal growth velocity with increasing undercooling is expected in the crystallization of liquids, mixtures, and alloys [P.K. Galenko and D. Jou, Physics Reports 818 (2019) 1]. By contrast to this general theoretical statement, Al-rich Al-Ni alloys show an anomalous solidificati...
Laser Additive Manufacturing (LAM) is a promising technology for manufacturing gas turbine components with enhanced design capability and a significant reduction in part weight. Additive manufacturing of alloy 718 using Laser Powder Bed fusion (L-PBF) process poses certain challenges pertaining to complex residual stress, micro-segregation of Nb, a...
Cold spray coating technique is an established technology where deposition of the desired coating is carried out at temperatures below the melting point. Current literature on the application of cold spray technique, particularly using Al-6061 alloy powder was reviewed. In this work, we report the precipitation behavior of the cold sprayed Al6061 c...
Haynes 282 is a creep-resistant, γ′ strengthened nickel-based superalloy with excellent weldability. Additive manufacturing, especially laser powder bed fusion (LPBF), of Haynes 282 is being researched for its potential applications in aerospace and power generation sectors. LPBF enables us to achieve desired properties via microstructure control t...
Solidification cracking during welding is a severe concern in aluminum alloys. Hot-cracking criteria have been successful in grading the crack susceptibility of an alloy. However, they do not offer a safe window of processing conditions for a crack-free weld. This work intends to determine the processing window for crack-free welding using a high-t...
Laser metal deposited processed Ni-based superalloy IN718 is characterized by elemental micro-segregation, anisotropy, and Laves phases due to the rapid solidification and therefore needs homogenization heat treatment to achieve comparable properties of wrought alloys. In this article, we report a simulation-based methodology to design heat treatme...
2XXX series aluminium alloys are widely used in propellant tanks of space launch vehicles. In this work, friction stir welding (FSW) was performed to produce dissimilar joints between 2195 and 2219 alloys. The effect of temperature (ambient, 77K and 20K) on the tensile properties of 2195–2219 joints was investigated. Results showed that a decrease...
Establishing growth kinetics of undercooled metallic alloys is essential to understand microstructure evolution during solidification processing. The complexity of the physical processes have hitherto limited growth models to simple assumptions that do not lead to satisfactory predictive capability. Experimental measurements of growth velocity as a...
In the present study, using ICME approach, the development of Co-Cr-Fe-Ni-V based single-phase FCC high entropy alloy (HEA) has been explored. The simulation guided composition was arc melted and verified using microstructure characterization. The as-cast sample was subjected to deformation at a strain rate of 0.1 s⁻¹in the temperature range of 107...
Dual-phase microstructures arising out of eutectic reactions offer several advantages: ease of casting, composite properties and tunable characteristic length scale of the phases. Eutectic high entropy alloys (EHEA) with a multi-component solution phase and a hard intermetallic phase are candidate materials to identify alternate high-temperature ma...
Identification of compositions that form solid solution phases from a large compositional space is challenging. The current study focuses on applying multiple machine learning classification algorithms for suitably predicting new medium to high entropy alloys with solid solution phases. The current data set used for training and testing consisting...
Eutectic high entropy alloy with seven components is designed based on the integrated computational materials engineering (ICME) framework. The framework includes thermodynamic prediction using calculation of phase diagrams (CALPHAD), microstructure simulation using phase-field method, and experimental validation. The designed alloy shows the eutec...
The microstructure stability of welded power plant steel components is typically assessed using the precipitate growth kinetics. The long-term exposure of welded structures at high temperatures results in coarsening of precipitates which may lead to the failure of the components. The dilution of base and filler material in the weldment could give r...
Improvement in efficiency of energy conversion requires the use of high temperature materials in thermal power plants. This has led to the development of new γ' strengthened nickel based superalloy (Haynes 282). This alloy is used for advanced ultra-supercritical (AUSC) plants which are operated under the service conditions of 760 oC temperature an...
For the first time, we report here that (CoCrFeNi)90Zr10 bimodal eutectics high entropy alloy (HEA) consisting of both globular eutectics (i.e., L ⟶ FCC (α) + Ni2Zr-type Laves phases) and lamellar eutectics (i.e., L ⟶FCC (α) + Ni7Zr2) is designed and developed by an integrated approach of using thermodynamic simulation and experimental techniques....
An integrated computational materials engineering (ICME)-based workflow was adopted for the study of microstructure and property evolution at the heat-affected zone (HAZ) of gas metal arc-welded DP980 steel. The macroscale simulation of the welding process was performed with finite element method (FEM) implemented in Simufact Welding® software and...
Recent reports on γ′-L12 strengthened cobalt base superalloys showed the potential of this class of alloys to replace nickel-base superalloys for high-temperature applications. The studies on thermo-mechanical processing behavior of these new class of alloys are limited. Thus, the present study investigates the thermo-mechanical processing behavior...
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...
Multi-principle element alloy FeCoNiCu with varying Sn addition was undercooled using the meltfluxing technique to illustrate the dependence of growth kinetics on Sn addition. The alloy FeCoNiCuSn0.5 shows morphological variation in the microstructure from dendritic to equiaxed grain morphology with the increase in undercooling. The alloy FeCoNiCuS...
Undercooling studies were carried out in equiatomic CuCoNi system with an aim to understand the growth kinetics and microstructural variations as a function of undercooling. The morphological change in microstructure was observed and correlated with the undercooling obtained. Non-linear variation of growth velocity with respect to the increase in u...
Multicomponent Co25Fe25Mn5Ni25Ti20 eutectic high entropy alloy (EHEA), synthesized by vacuum arc melting followed by suction casting method resulted in two types of solid solution phases (fcc CoFeNi-rich (α) and bcc Ti-rich (β)) and Ti2(Ni, Co) type Laves phase. The hot deformation behaviours have been investigated at a temperature ranging from 107...
High entropy alloys with multiple phases are taken for undercooling studies and established the microstructure evolution with respect to undercooling. The melt fluxing technique was used for the current study to achieve undercooling. Predictions on the equilibrium phase formation of these systems was performed using CALPHAD approach and compared wi...
Equiatomic RNi (where R = Gd, Ho and Er) compounds have been prepared by undercooling. Magnetization data confirm ferromagnetic ordering of the samples at 69 K, 35 K and 10 K (TC) respectively. Magnetocaloric effect (MCE) has been estimated in terms of isothermal magnetic entropy change (ΔSm) near TC. The maximum ΔSm value (ΔSmmax) for 50 kOe field...
The non-equilibrium response of a high entropy alloy CoCuFeNiTa0.5 has been studied using undercooling as a control parameter. The solidification growth rates are rapid (30–50 m/s) at deep undercooling (>150 °C) and are comparable with conventional alloys. The elemental segregation especially that of Cu as predicted by phase field simulations in lo...
Studies on solidification of equiatomic multi-component alloys are essential in developing melt-route processing of high entropy alloys. The extent of undercooling during processing controls microstructure evolution. In this study, we present solidification studies on undercooled equiatomic FeCuNi alloy carried out using melt fluxing technique. The...
High entropy alloys with multiple phases are taken for undercooling studies and established the microstructure evolution with respect to undercooling. The melt fluxing technique was used for the current study to achieve undercooling. The equilibrium phase formation of the current systems is predicted by Thermo-Calc calculations. The metastable micr...
In recent years, several multicomponent alloys of near equiatomic composition (also known as high-entropy alloys) with excellent mechanical properties have been developed. In this study, a eutectic high entropy alloy, CoCrFeNiNb0.45, was chosen for a hot deformation study. The alloy consists of a primary face-centered cubic (FCC) phase (CoCrFeNi ri...
In recent years, several multicomponent alloys of near equiatomic composition (also known as high-entropy alloys) with excellent mechanical properties have been developed. In this study, a eutectic high entropy alloy, CoCrFeNiNb0.45, was chosen for a hot deformation study. The alloy consists of a primary face-centered cubic (FCC) phase (CoCrFeNi ri...
A eutectic high-entropy alloy with seven components (Fe, Ni, Cr, V, Co, Mn, and Nb) was designed via the melt route guided by CALPHAD predictions. Configurational entropy estimated for the two-phase microstructure qualifies it to be referred to as a high-entropy alloy. When the Nb content exceeded 9.7 at. pct, the microstructure changed from hypoeu...
In the design of high-entropy alloys (HEAs) with desired properties, identifying the effects of elements plays an important role. HEAs with eutectic microstructure can be obtained by judiciously modifying the alloy compositions. In this study, the effect of Nb addition to FeCoNiCuNb x (x = 0.5, 5, 7.5, 11.6, 15) alloys was studied by varying the Nb...
We present experimental results, analytical calculations and phase-field simulations for undercooled Ni–Fe–Si alloy system. Undercooling experiments are performed using flux encapsulation along with in situ measurement of recalescence speed using a high-speed camera followed by microstructural characterization. Dendrite growth calculations are perf...
In the present study, the effect of Zr addition on the mechanical properties of arc melted hypoeutectic Nb−16 at. %Si alloy has been investigated. The alloys were characterized by scanning electron microscopy (SEM), electron back scattered diffraction (EBSD), hardness test, nanoindentation test, compression test and three point bend test. The desir...
In this paper, effect of friction stir welding process parameters on mechanical properties and microstructure of AA2195 welds were studied. Five levels of tool rotation speed from 400 to 1000 rpm and three levels of travel speed from 100 to 300 mm/min were considered. These parameters affected heat input generation in the welds, thereby influencing...
The case hardening process (carburizing followed by quenching to room temperature) is one of the heat treatments routinely conducted in various industrial sectors. Depending on the parameters applied during the post-carburizing stage, different microstructural constituents may develop in the interior (core) section of a case-hardened component whic...
As part of undercooling studies on high entropy alloys, we have taken up ternary, quaternary and quinary equi-atomic alloys to understand solidification microstructure evolution. In this study, undercooling experiments were carried out in Fe-Co-Cu equi-atomic alloy using glass fluxing technique. The alloy was undercooled to a maximum undercooling t...
In the present work, the role of Zr addition on the microstructure and phase formation of hypoeutectic Nb−16 at. % Si alloy has been investigated. The results showed that both binary and alloy with 2 at. % Zr resulted in two phase microstructures composed of Nbss and Nb3Si phases. In contrast, the alloys with 4 at. % Zr and 6 at. % Zr revealed two...
In this study, weld solidification cracking behaviour of AA2195 Al–Cu–Li alloy was studied and compared with conventional AA2219 and AA2014 aluminium alloys. Cracking susceptibility was evaluated using varestraint test and Gleeble® hot ductility test and the slope of liquidus temperature as function of liquid fraction was also evaluated. Solidifica...
High entropy alloys or complex concentrated alloys have recently gained wide attention due to their excellent high temperature properties. New alloys are also being explored for functional properties towards magnetic and thermoelectric applications. Unlike conventional alloy design, exploration of high entropy alloys involves the central region of...
The present study is aimed at understanding the sequence of phase evolution during solidification in Co 25 Fe 25 Ni 25 Ti 20 V 5 eutectic high entropy alloys (EHEAs), synthesized by vacuum arc melting cum suction casting technique. The detailed X-ray diffraction (XRD) and electron microscopic (SEM and TEM) coupled with energy dispersive spectroscop...
Recently, cobalt-based γ-γ′ microstructured superalloys have attracted attention. However, studies on their processing behavior [i.e., processing maps (the variation of strain rate sensitivity (m) with temperature)] are limited. Thus, the high-temperature flow behavior of a γ-γ′ Co-30Ni-10Al-5Mo-2Ta-2Ti-5Cr (at. pct) superalloy was investigated usi...
Hot deformation behaviour of AlCoCrFeNi2.1 eutectic high entropy alloy, consisting of fcc (CoCrFe-rich) and BCC (NiAl-rich) phases is studied by generating contour maps of multiple models using high temperature thermo-mechanical simulator compression test data. The workability regimes for thermomechanical processing are identified as 1073–1150 K an...
Recently there has been a surge in the synthesis and evaluation of properties of equi-atomic multi-component alloys that are referred to as “high entropy alloys” and “complex concentrated alloys”. These are multi-component alloys and have shown promise in structural and functional application, particularly due to their microstructure stability at h...
High entropy alloys have shown significant promise in the recent years and the alloy design space gives freedom to control the microstructure and mechanical properties for a wide range of engineering application. Understanding of hot deformation behaviour in multicomponent high entropy alloys is necessary to establish optimum processing conditions....
Finite element simulation of heat treatment cycles in steel could be challenging when it involves phase transformation at the microscale. An ICME approach that can take into account the microstructure changes during the heat treatment and the corresponding changes in the macroscale properties could greatly help these simulations. Dual phase steel (...
Dual phase steels are versatile advanced high strength steels that are being used for sheet metal applications in automotive industry. It also has the potential for application in bulk components like gear. The inter-critical annealing in dual phase steels is one of the crucial steps that determine the mechanical properties of the material. Selecti...
The present investigation is aimed at developing and understanding the hot deformation behaviour and processing map in multi-principal elements based multicomponent alloy i.e. Fe-Co-Ni-Cr-Al eutectic high entropy alloy (EHEA), processed by vacuum arc melting cum suction casting technique under high purity Ar atmosphere. XRD and electron microscopy...
In this study, the effect of Ta, Ni, Zr additions and heat treatment on the microstructure and hardness of Nb-16Si have been investigated. It was observed that Ta addition has not changed the microstructure of the alloy, while Ni and Zr additions drastically changed the microstructure of the alloys. The alloying additions increased the hardness of...
The present investigation reports phase and microstructure evolution during solidification of novel Ni-rich Ni-Ti-based alloys, Ni60Ti40, Ni50Cu10Ti40, Ni48Cu10Co2Ti40, and Ni48Cu10Co2Ti38Ta2 during suction casting. The design philosophy of the multicomponent alloys involves judicious selection of alloying elements such as Cu, Co, and Ta in the nea...
Additive manufacturing techniques, specifically those currently employed in metal based manufacturing; involve heat transfer and fluid flow physics which are far too complex to be covered in an analytical form. This limits the control over material microstructure thus obtained in a deposited alloy component. To this need, a multi-scale numerical st...
Ni2FeGa polycrystalline alloys are synthesized by arc melting into single phase β structure and two phase mixture of γ-phase (fcc) and austenite (L21). Annealing improves atomic ordering and β transforms to L21 ordered structure. Effect of alloy composition and processing condition on different phase formation, microstructural, magnetic and electri...
The present work is aimed at understanding the phase evolution of hypereutectic Al-rich Al–Cu–Ni in situ composites consisting of ultrafine eutectic with micron scale dendrites. The hypereutectic Al90Cu10−xNix (x = 0, 5) are synthesized by vacuum arc melting technique under high purity argon atmosphere. Detailed X-ray diffraction and electron micro...
In this investigation, crystal–melt interface growth velocities of Ni–Zr alloys are investigated at different undercoolings using molecular dynamics simulation. Ni, Ni–0.1 at.% Zr and Ni–1 at.% Zr are considered and free solidification approach is adopted to measure the interface growth velocity. Further, the anisotropy in growth velocity is studie...
Compositional instability and phase formation in Ni-Fe-Ga Heusler alloys are investigated. The alloys are synthesized into two-phase microstructure. Their structures are identified as fcc and L
21, respectively. The γ-phase formation could be suppressed with higher Ga-content in the alloy as Ga stabilizes austenite phase, but Ga lowers the martensi...
Metastable b-titanium alloys are finding increasingly wider applications in structural components in aerospace, energy, and chemical industries because of their formability and heat-treatment possibilites. Components from these alloys are usually welded by processes, such as gas tungsten arc welding (GTAW), electron beam welding (EBW), and laser be...
Martensitic phase transformation of Ni2FeGa Heusler alloy was studied by differential scanning calorimetry. Atomic ordering induced in the austenite structure by quenching from high temperature plays a significant role on martensitic phase transformation. Higher magnetization and larger magneto-crystalline anisotropy of martensite phase than that o...
Phase-field method uses a non-conserved order parameter to define the phase state of a system and is a versatile method for moving boundary problems. It is a method of choice for simulating microstructure evolution in the domain of materials engineering. Solution of phase-field evolution equations avoids explicit tracking of interfaces and is often...
The microstructural evolution during varying thermal gradients of rheocast AA7075 aluminium alloy was investigated. To perform this study, semi-solid billets of non-dendritic microstructure were produced using Linear Electro Magnetic Stirrer (LEMS). Gas Tungsten arc welding (GTAW) was conducted to simulate varying thermal gradients near fusion zone...