Department of Metallurgical and Materials Engineering

The occurrence of multiple generations of annealing twins (MGAT) in low stacking fault energy (SFE) materials leads to significant texture weakening with the evolution of some new prominent texture components. However, the exact correlation between MGAT and texture evolution is a long-standing enigma. In the current research, the presence of MGAT was confirmed by transmission Kikuchi diffraction (TKD) and high resolution electron backscattered diffraction (EBSD) in partially (700 °C/5 min) and fully (700 °C/1 h) recrystallized specimens of equiatomic CoCrFeMnNi high entropy alloy, respectively. Further, the twin clusters in the vicinity of the potential nucleation sites (Brass, Goss and S orientations) were investigated to gain insights on the contribution of MGAT on texture development. The newly developed (φ1 = 90°, Φ=30°, φ2 = 45°) orientation showed its roots originating from 2nd generation twin of the Brass orientation while Cube orientation was evolved from the 1st and 5th generation twins of the S orientation.

Antimony is one of the promising anode materials for lithium-ion batteries due to its high volumetric and gravimetric capacity (theoretical specific capacity 660 mAh g−1) and stable voltage window (0.87–0.91 V vs Li/Li+). However, a high-volume expansion ( ∼130%) of Sb on lithiation degrades the electrochemical performance and restricts its application. In this work, a novel strategy is explored to use antimony halide (SbBr3) instead of Sb as the starting anode material. In the first step, Li will react with SbBr3 to form LiBr and pure Sb, leading to a 78% contraction in volume, and then this pure Sb further lithiates to form Li3Sb expanding the volume (of the lithiated Sb by 130%). LiBr, which is a byproduct of the first reaction, dissolves into the solvent, leaving a porous Sb. In a nutshell, the two-step lithiation process results in a net volume-contacted porous antimony, ideal as an electrode to counter volumetric stress in subsequent charge-discharge cycles. The electrochemical performance of this electrode is much superior when compared with the pure antimony electrode, taking advantage of initial volume reduction and porous scaffold. It achieves a high specific discharge capacity of 345 mAh g−1 at a rate of 100 mA g−1 even after the end of the 100th cycle and losing only 20% of its capacity. This shows that this volume contractible technique can be successfully employed for metals and metallic alloys having drastically higher Li-storing capacities than graphite.

Mg–Sn–Gd alloys can be considered prospective contenders for creep applications owing to the formation of thermally stable phases. In the present investigation, the solidification behaviour of Mg–Sn–Gd alloys was analysed from cooling curves obtained from thermal analysis within the temperature range of 700–300 °C. The phase evolution as a function of Sn and Gd content was studied by varying the ratio of Sn to Gd (Sn/Gd) at three levels (0.5, 1, and 2) up to a maximum concentration of 3 wt% Sn and Gd, respectively. The phases in the as-cast microstructure were compared with the phases predicted by a commercially available thermodynamic database, and a deviation was observed. The results indicated that the addition of Sn and Gd promoted the formation of a ternary MgSnGd phase. Moreover, the presence of the MgSnGd phase in the microstructure led to significant grain refinement, and its role as a potential grain refiner has been recognized.

The current study focuses on the effect of a post-heat treatment such as solutionizing at 520 °C for 0.5–2.5 h followed by artificial ageing at 165 °C for 2–14 h (T6-like heat treatment) on the microstructure and mechanical properties of selective laser melted (SLM) AlSi10Mg alloy. XRD & DSC analysis shows the Al, Si, and Mg2Si phases present in as-built and heat-treated conditions, which are well correlated with the Thermo-Calc simulation results. The density of as-built AlSi10Mg was 2.66 g/cm3, and it decreased to 2.63 g/cm3 after solutionization, and after artificial ageing, it further decreased to 2.61 g/cm3 due to the lattice strains. As-built sample microstructure consists of fine α-Al cells containing ultra-fine Si particles surrounded by a eutectic Si network due to the high heating and cooling rates involved in SLM processes. After solutionizing, the eutectic Si network structure disappeared by the thermally activated diffusion process forming Si particles in the aluminium matrix. Vickers hardness for as-built condition was 126.6 HV, and after solutionization for 30 min, it decreased to 95.6 HV. However, after subsequent artificial ageing (for 12 h), the hardness value again increased to 119.7 HV. As-built condition showed absorbed impact energy of 8 J and it increased to 17.33 J during solutionization for 0.5 h and again decreased to 9.33 J after subsequent artificial ageing.

Herein, the symmetry of the experimentally observed soft phonons in the body-centered cubic β-phase (Im (Formula presented.) m) of titanium is analyzed. The harmonic phonon dispersion relations are calculated using the first-principles calculations. Using the group-theoretical methods, the symmetry of the calculated unstable phonons is determined. The symmetries of the unstable phonons observed at wave vectors (Formula presented.) (N) and (Formula presented.) ((Formula presented.)) are the same as the symmetries of the (Formula presented.) and (Formula presented.) irreducible representations, respectively. Transformations of the β-phase due to the atomic motion of unstable phonons and the subsequent structure relaxation are discussed. One possible way to explain the transformation of the β-phase to the hexagonal close-packed α-phase ((Formula presented.) /mmc) is through an orthorhombic structure (either Cmcm or Pnnm). The atomic motion of an unstable (Formula presented.) phonon results in the orthorhombic structure and following structure relaxation transforms the orthorhombic structure to the α-phase. Similarly, the transformation of the β-phase to another hexagonal close-packed ω-phase (P6/mmm) can be considered to be happening through a trigonal structure (either P (Formula presented.) m1 or P3m1). The atomic motion of an unstable (Formula presented.) phonon forms the trigonal structure and subsequent structure relaxation transforms the trigonal structure to the ω-phase. The space group of the intermediate phase is a common subgroup of the space groups of the initial β-phase and the final α/ω-phase. Therefore, the β–α/ω transformation can be described as an unstable phonon-induced reconstructive transformation of the second type. There is no activation energy barrier along each of the four energy-minimizing paths, and the transformation strains are accommodated.

This study examines the influence of the ERNiCr-3 (Inconel 82) butter layer on the microstructure and mechanical feature of the dissimilar weld joint (DWJ) of ferritic grade P92 and austenitic grade AISI 304 L steel, manufactured using gas tungsten arc welding (GTAW) method with IN82 filler. The butter layer aims to prevent the formation of a hard martensitic layer adjacent to the fusion line by mitigating the carbon migration from the P92 steel to the welding pool. The optical microscope, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electron probe microanalyzer (EPMA) were used to examine the microstructures of the buttered welded plate. The mechanical characteristics of the joints were assessed using the standard and sub-sized tensile and Charpy tests. The flat and round specimens underwent the tensile test to determine their relative tensile properties at room temperature and high temperature. The high-temperature tensile properties were assessed at 600 °C and 650 °C at 1 mm/min extension rates. Along the weldments, hardness profilometry was also performed. Microstructural analysis validated that the application of a buttering layer successfully eliminated the extensive martensitic layer on the P92 side. Nevertheless, in the vicinity of the interface between the buttering layer and P92, there was evidence of a narrow unmixed zone and macrosegregation. SEM/EDS and EPMA studies confirmed that the predominant phases identified in IN82 butter and weld metal are NbC and TiC. The butter layer, overall, improved elongation/ductility by 25 % without a noticeable reduction in tensile strength. During tensile testing, the specimen fractured from the IN82 butter layer, revealing the presence of dimples and voids on the fracture surface, along with the TiC/NbC phases, as confirmed by SEM analysis. Tensile specimens subjected to high-temperature testing exhibited failure at the base materials of AISI 304 L (tensile strength=404 MPa) and P92 (307 MPa), specifically at 550 °C and 650 °C, respectively, rather than at the buttering layer or weld metal. The results of the tensile tests met the minimum criteria specified for Ultra-Supercritical (USC) boilers. More importantly, the IN82 butter layer successfully serves as a protective barrier between the weld pool and the P92 HAZ. As a result, the dual hardness peaks on either side of the welding pool are eliminated. After adding the buttering layer, the peak hardness in the coarse-grained heat-affected zone (HAZ) of P92, which ranged from 450 to 500 HV in the unbuttered sample, dropped by 200 MPa. The relationships between microstructural characteristics and mechanical properties have been thoroughly examined and discussed.

The objective of this study is to develop and examine coating fluxes for SMAW electrodes intended for use in nuclear power plant steel welding. A set of 21 unique flux compositions is created using the extreme vertices design methodology. These compositions predominantly consist of SrO-CaO-Al2O3-CaF2 fluxes. At a temperature of 1373 K, an in-depth investigation is carried out to assess key properties, including the work of adhesion, spread area, contact angle and floatation coefficient. Additionally, the surface tension of these flux compositions is estimated. XRD and FTIR analysis methodologies have been employed for the purpose of examining and identifying the phases that exist within both the flux and slag. Furthermore, structural analysis of the molten material is conducted through the examination of quenched slag powder. Results reveal that the individual components CaO, CaF2 and binary interaction of Al2O3 × SrO have a significant effect on the contact angle and floatation coefficient. Individual interactions of CaO, SrO, Al2O3 and CaF2 exert a positive impact on the spread area. The individual components Al2O3 and SrO were found to have a significant effect on the work of adhesion.

Barium Titanate, a piezoelectric material having fascinating dye adsorbing properties, is forecasted as a promising material for the adsorption of cationic dyes. However, its efficiency remains a challenge that needs to be enhanced due to less surface charge. Herein, photocatalysis (PC) and piezocatalytic (PzC) induced degradation of Rhodamine B (RhB) in the wastewater using barium titanate and barium titanate hybridized with silver nanoparticles (Ag-NPs) metal particles were investigated and compared. The solid-state synthesis route was employed to synthesize Barium Titanate ceramics. Ag-NPs metal was hybridized with Barium Titanate particles (through a physical deposition technique) under ambient conditions at STP in the absence of light and heat. A broader hump was observed during UV–Vis spectrophotometry due to the surface plasmonic resonance on the Ag-NPs-hybridized Barium Titanate sample. Visible light source and vibrational energy were employed in the solution as an energy source in the PC and PzC, respectively. More than 99% of the rhodamine B (RhB) was degraded in an aqueous solution employing an Ag-NPs-hybridized Barium Titanate sample, its promising PC, and PzC activity. It was observed that the Ag-NPs-hybridized Barium Titanate powder gives more activity in RhB than pure Barium Titanate powder. It was observed that the PC and PzC performance was caused by the –OH radical species. The PC/PzC outcome was shown to be stable after five cycles, revealing the favoring property of the Ag-NPs-hybridized Barium Titanate.

The low-cost, earth abundant kesterite copper-zinc-tin-sulfide (CZTS) is the most desirable material for the upcoming sustainable energy, sensors and energy storage as well as generation. However, the research on the material was hindered due to the instability of the zinc and copper in the quaternary phase, thus, resulting in secondary complex phase with defects. This led to the structural inhomogeneity, challenges in the repeatability of the synthesis procedure and degradation (especially) in the efficiency of the solar cell. Therefore, synthesis of CZTS in right phase and purity (without any stoichiometric imbalance as well as secondary phases and defects) is a challenge to overcome. Moreover, due to the presence of copper and zinc, it is an interesting material for the scientific community as gas sensor. In this report we have synthesized CZTS through chemical synthesis and examined a spin coated CZTS thin film for probable sensing application at room temperature. We utilized the CZTS thin-film for room temperature gas sensing of the volatile organic compound (ethanol) at 68 PPM. In addition, the Phase purity of the film was confirmed by the X-ray diffraction. While, the optical characterization of the film was investigated by the UV-Spectrometer. Thickness of the film was confirmed by atomic force microscopy and the electrical characterization of the film was done by Kiethley 2420.

The model presented in our work was able to reproduce the Raman activity that is relevant to clarify the origin of the experimentally observed Raman activity in the high frequency region due to amorphization. Most of the points raised by Helmut Werheit are part of the debate in existing literature regarding the Raman spectra observed in B4C samples. In response to the comments by Helmut Werheit, here more inputs are provided to this discussion by focusing on (a) composition, (b) crystal structure, (c) Raman spectra.