Publications

2024

1. JALCOM

   Designing a Refractory Binary Alloy with Low Oxygen Solubility

   Vinod Sarky, Sufyan M Shaikh, P.S.V.R.A. Kishor, and Satyesh K Yadav

   Journal of Alloys and Compounds, Nov 2024

   Abs DOI

   Refractory metals such as Ti, Zr, Hf, V, Nb, and Ta can dissolve oxygen up to 33 %, 29 %, 20 %, 17 %, 9 %, and 5.7 %, respectively, at high temperatures. The high solubility of oxygen causes brittleness in these metals. When designing a refractory high entropy alloy, efforts should be focused on reducing oxygen solubility. We find that the high solubility of oxygen is related to the thermodynamic stability of oxygen interstitials in pure refractory metals. To understand the impact of alloy composition on oxygen solubility in refractory alloys, we examine the thermodynamic stability of oxygen interstitials across various refractory binary alloys. Using first-principles Density Functional Theory (DFT), we calculate the Oxygen Interstitial Formation Energy (OIFE) of nine re- fractory metals and their 24 equiatomic binary alloys. The OIFE is determined by the bond strength between oxygen and the nearest neighbor (NN) metal atoms. It is a strong function of the nature of NN atoms that sur- round the interstitial site rather than the overall composition of the alloy. For a given alloy, the OIFE can vary based on the NN atoms around the oxygen interstitial. These observations indicate that an alloy with even a small amount of metal of high oxygen affinity (or highly negative OIFE), like Ti, can result in the high stability of oxygen in specific interstitial sites where the nearest neighbors are predominantly Ti atoms. It also explains Re as a choice of alloying elements to ductilize W instead of Ti. Although both Ti and Re alloying in W similarly improve its ductility, Ti’s tendency to stabilize oxygen interstitials makes the W-Ti alloy brittle, while Re does not stabilize oxygen interstitials.

2023

1. JAP

   On the influence of enthalpy of formation on lattice distortion and intrinsic ductility of concentrated refractory alloys

   Sufyan M. Shaikh, B. S. Murty, and Satyesh Kumar Yadav

   Journal of Applied Physics, Jul 2023

   Abs DOI

   Valence electron concentration (VEC), atomic size difference (δ), and Pugh’s ratio (B/G) are a few of the empirical parameters widely used to design ductile refractory alloys. Here, we used the intrinsic ductility parameter (D), which is the ratio of surface energy (\gammas) and unstable stacking fault energy (\gammausfe), to design ductile refractory alloy. We found that the D correctly captures the experimentally observed ductility in concentrated refractory alloys. Here, we studied the enthalpy of formation (\DeltaEf), lattice distortion, and D of 9 refractory metals and 36 equiatomic refractory alloys using density functional theory simulations. We found that the \DeltaEf strongly influences the D of concentrated refractory alloys. The positive \DeltaEf and δlead to large lattice distortion in concentrated refractory alloys. However, we did not find a strong correlation between lattice distortion and D in the presently studied alloys. We found that the success of VEC and Pugh’s ratio in designing ductile refractory alloys has a strong dependence on the underlying \DeltaEf of the alloy. We have developed a bottom-up method, which drastically reduces the number of alloys to be studied, to design ductile concentrated refractory alloys that can be thermodynamically stable.

2. JALCOM

   Designing a thermodynamically stable and intrinsically ductile refractory alloy

   Sufyan M. Shaikh, B. S. Murty, and Satyesh K. Yadav

   J. Alloys Compd., Jan 2023

   Abs DOI PDF

   The stringent environmental norms are pushing the aviation and power-generation industries to increase the operating temperatures of their jet-engines and gas-turbines which will improve the efficiencies of these energy conversion systems. Aviation and power generation industries are researching the alternatives for the currently used Ni-based superalloys, which is the most widely used material in the high-temperature region of these engines. Refractory alloys are being actively developed as an alternative to the Ni-based superalloys due to their high melting-points and superior strength retention capabilities at higher temperatures. Enhancing the intrinsic ductility of these refractory alloys has remained a challenge. Reducing the valence electron concentration (VEC) below 4.5 have been shown to improve the intrinsic ductility of few alloys, which means addition of Ti, Zr, and Hf can improve the ductility of refractory alloys. However, Re has been widely used to ductilize the W which goes contrary to the VEC criteria suggested in literature. The reason this seems to work is may be due to the reduced USFE of the alloy due to alloying with low USFE elements. Here we use density function theory (DFT) simulations to understand the factors affecting the ductility of refractory alloys. A DFT-based workflow is developed which reliably calculates the ductility parameter of refractory alloys. The developed workflow ensures that the error in estimating USFE is less than 50mJ/m}\^2}. The enthalpy, lattice distortion, and ductility parameter are calculated using DFT for Group IV, V, VI elements & their 25 equiatomic binary alloys. The deformability of refractory BCC alloys is correlated with their enthalpy.

3. Scrip. Mater.

   Entropy-stabilized binary alloys

   Rafshan Ul Atik, Sufyan M Shaikh, Hitanshu Sachania, and Satyesh K Yadav

   Scripta Materialia, Sep 2023

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   Alloying W with Re is an effective method for improving its intrinsic ductility. The solubility limit of Re in W is ∼ 27% at 851 K. However, this alloy possesses a high enthalpy of formation, which can result in phase-instability. Configurational entropy alone cannot stabilize this alloy as a single-phase solid solution. Recent research questions the importance of configurational entropy in determining the single-phase stability of “complex, concentrated solid solutions” and suggests that vibrational entropy may play a critical role. The question arises: Can vibrational entropy contribute significantly enough to ensure single-phase stability in a binary alloy? Our first-principles phonon calculations using density functional theory demonstrate that vibrational entropy is equally essential as the configurational entropy in promoting the formation of a single-phase solid solution in WRe binary alloys. This finding necessitates revisiting the role of vibrational entropy in the single-phase stability of binary alloys.

4. Designing an oxidation resistant Refractory Binary Alloys

   Vinod Sarky, Sufyan M Shaikh, PSVRA Kishore, and Satyesh Kumar Yadav

   Apr 2023

   Abs DOI

   Refractory metals and their alloys are promising, as they possess high-temperature strength and melting points at elevated temperatures. But the fundamental limitation associated with these metals is high-temperature oxidation. The literature mentions that the Ti, Zr, and Hf dissolve oxygen atoms up to 33 at.%, 29 at.%, and 20 at.% respectively, in the octahedral interstitial site of the HCP metal system. This has led to investigations on understanding the behavior of oxygen in an octahedral interstitial site just after penetrating in refractory metals and alloys. In the present work, the first principle DFT calculations were done to report the oxygen interstitial formation energy (OIFE) of 9 refractory metals, such as Ti, Zr, Hf, V, Nb, Ta, Mo, W, and Re, and 25 equiatomic BCC binary alloy systems, such as V-Ti, Nb-Ti, Ta-Ti, Mo-Ti, W-Ti, Nb-Zr, Ta-Zr, Mo-Zr, Nb-Hf, Ta-Hf, Mo-Hf, W-Hf, Nb-V, Ta-V, Mo-V, W-V, Mo-Nb, W-Nb, Re-Nb, Nb-Ta, Mo-Ta, W-Ta, W-Mo, Re-Mo, and W-Re. The OIFE for an alloy system was reported for 7 different octahedral sites, such as 0-6, 1-5, 2-4, 3-3, 4-2, 5-1, and 6-0, based on the number of atoms of A-type and B-type around oxygen interstitial as an octahedral nearest neighbor(octa-NN). The variation in OIFE with change in the atoms of A-type and B-type at the third nearest neighbors (3NN) was also checked for 0-6 and 6-0 sites, and it was observed that the contribution of atoms at 3NN was minimal. The OIFE decreases with an increase in the number of atoms of B-type around the oxygen interstitial as octa-NN, following the trend of composition averaged OIFE calculated from OIFE of individual elements. In most of the cases, the OIFE of 0-6 site was minimum when the O interstitial was surrounded by all the atoms of B-type, which have low OIE in their pure bulk form, and the OIE of 6-0 site was maximum when the O interstitial was surrounded by all the atoms of A-type, which have relatively higher OIE in their pure bulk form when compared to atoms of B-type. It is not the composition averaged OIFE that determines the stability of oxygen interstitial in alloys, but it is the presence of low OIFE elements as clusters around octahedral neighbor locally that determines it. It is because, the contributions to OIFE comes from octa-NN and the contributions from 3NN is relatively minimal. The presence of low OIFE element around oxygen interstitial at octa-NN and slightly in 3NN would make the oxygen behave as if it were in the bulk of low OIFE element, making the system prone to oxidation.

2022

1. CALPHAD-2022

   Conference Presentation: Strategies to improve deformability of entropy stabilized refractory solid solutions

   Sufyan M. Shaikh, B. S. Murty, and Satyesh K. Yadav

   In CALPHAD XLIX, May 2022

2021

1. MMTA

   Structure and Texture of Oxide Dispersion Strengthened Alloy 617 for Very High Temperature Applications

   M. Sivakumar, Shyam Kanta Sinha, Arup Dasgupta, and Sufyan M. Shaikh

   Metall. Mater. Trans. A, May 2021

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   High energy mechanically milled Alloy 617 ODS powder was consolidated by Spark Plasma Sintering (SPS) technique and subsequently annealed at 650 °C and 1050 °C (923 K and 1323 K). Microstructure and microtexture evolution during SPS and annealing have been investigated. SPS consolidated sample exhibited heterogeneous microstructure with ultra-fine grains surrounded by coarse grains. Inhomogeneous distribution of plastic deformation induced during ball milling resulted in heterogeneous nucleation and further grain growth during consolidation. The bimodal microstructure is advantageous with coarse grains providing ductility and fine grains providing strength by the Hall–Petch relationship. The bimodal grains structure was also retained during annealing. As-sintered specimen showed 〈100〉 texture parallel to the compression axis due to dynamic recrystallization during the SPS process. At 650 °C, annealed sample exhibited 〈111〉 annealing texture parallel to compression axis. The texture was randomized in sample annealed at 1050 °C. Precipitation analysis by SEM, XRD and TEM showed the presence of M23C6, M6C and Al2O3 in both As-sintered and annealed samples. Dispersoids analysis showed the presence of fine and uniform Y3Al5O12, Y4Al2O9 and a complex oxide rich in Ni, Y, Al and O. Stress–strain analysis from instrumented indentation test shows higher yield strength for Alloy 617 ODS in comparison with conventional Alloy 617.

2. MRS-2021

   Conference Poster: First-Principles Calculation of Stacking Fault Energy of Multi Principal Component Alloys Using Bilayer-SQS

   Sufyan M. Shaikh, B. S. Murty, and Satyesh K. Yadav

   In Materials Research Society Spring Meeting & Exhibit, Apr 2021
3. NMD-2021

   Conference Poster: Accurate Stacking Fault Energy Calculation of High Entropy Alloys

   Sufyan M. Shaikh, B. S. Murty, and Satyesh K. Yadav

   In 58^th National Metallurgists’ Day and 74^th Annual Technical Meeting, Apr 2021

2020

1. Intermetallics

   CALPHAD and rule-of-mixtures: A comparative study for refractory high entropy alloys

   Sufyan M. Shaikh, V. S. Hariharan, Satyesh K. Yadav, and B. S. Murty

   Intermetallics, Dec 2020

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   Present work studies 126 quaternary and 126 quinary equiatomic refractory high entropy alloys (RHEAs), made from Group IV (Ti, Zr, Hf), Group V (V, Nb, Ta) and Group VI (Cr, Mo, W) elements. Rule-of-mixtures (ROM) technique is used to calculate liquidus temperature, density (ρ), Young’s modulus (E), % atomic size difference (δ), valence electron concentration (VEC) and specific heat at constant pressure and at 1273 K (Cp). CALPHAD technique is used to predict the number of phases formed at 298 K, ρand liquidus temperature. ROM calculated densities are matching perfectly with CALPHAD values. Densities and E are directly proportional to the VEC and liquidus temperature of the alloys. Ti, Zr, Hf are ductilizing the alloys and making them light; whereas Cr, Mo and W, are reducing the alloys’ ductility and making them heavy. For quinary RHEAs, Cp shows six distinct groups with δ, but a similar trend is not observed in quaternary RHEAs. A methodology is developed to screen a large number of alloys based on various properties. Correlations between those properties are also studied.

2. Materialia

   Microstructural homogenization and substantial improvement in corrosion resistance of mechanically alloyed FeCoCrNiCu high entropy alloys by incorporation of carbon nanotubes

   Sujata Singh, Sufyan M. Shaikh, Punith Kumar M. K., B. S. Murty, and Chandan Srivastava

   Materialia, Dec 2020

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   FeCoCrNiCu high entropy alloy (HEA) powder was produced by mechanical alloying. Carbon Nanotubes (CNTs) were mixed in the HEA powder (0.1, 0.2, 0.5, 1.0, 1.5, 2.0, 3.0, 5.0, 7.0 wt.% of CNT) and then the mixture was consolidated by spark plasma sintering at 800°C. Phase constitution of the pellets was sensitive to the CNT amount. With smaller quantities of CNTs (upto 2 wt.%), the pellets contained a mixture of two different face centred cubic (fcc) phases along with σphase. With increase in the CNT amount (till 2 wt.%), a gradual decrease in the volume fraction of one of the fcc phase occurred leading to microstructural homogenization. Higher CNT additions (3, 5 and 7 wt.%) led to re-evolution of inhomogeneous microstructure containing chromium carbide phase and the two different fcc phases. Corrosion behaviour measurements showed that with continued addition of CNTs, reduction in the corrosion rate happened till 2wt.% CNT. Beyond this, a significant enhancement in the corrosion rate was noticed for pellets with 3, 5 and 7 wt.% CNT additions. Between the pristine HEA pellet and the pellet with optimum CNT amount (2 wt.%), 88.6 % reduction in the corrosion rate was measured. The enhancement in the corrosion resistance was attributed to an increase in the chemical homogeneity, which reduced the possibility of galvanic coupling. The decrease in the corrosion resistance beyond the optimum CNT (2 wt.%) was attributed to the re-appearance of chemical heterogeneity and evolution of chromium carbide (Cr23C6) phase, which causes intergranular corrosion in these systems.

3. IWHEM-2020

   Conference Poster: CALPHAD and Rule-o-Mixtures: A comparative study for Refractory High Entropy Alloys

   Sufyan M. Shaikh, V. S. Hariharan, Satyesh K. Yadav, and B. S. Murty

   In 3^rd International Workshop on High Entropy Materials, Mar 2020
4. APMC-2020

   Conference Poster: Microstructural characterization of IN617 oxide dispersion strengthened alloy

   M. Sivakumar, Sufyan M. Shaikh, and Arup Dasgupta

   In Asia Pacific Microscopy Conference, Feb 2020

2014

1. NMD-2014

   Conference Poster: Effect of Surface Mechanical Attrition Treatment on 6061-T6 Aluminum alloy

   S. S. Hosmani, P. Wakadkar, P. Katti, and Sufyan M. Shaikh

   In 52nd National Metallurgists’ Day and 68th Annual Technical Meet, Nov 2014