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A heat transfer numerical model is developed for friction stir welding of dissimilar materials Al 6061 and AZ31 alloy. Thermo-physical properties were experimentally determined for the stir zone and compared with the base alloys. Experimentally determined thermo-physical properties of the stir zone are not strictly the average values of the base alloys but exhibit a complex relationship with the microstructural features and the intermixing of Al and Mg in the weld region. The numerical model is employed to predict the temperature distribution on the advancing and retreating side. A good agreement between computed and experimentally measured results was obtained at 24-mm, 20-mm, and 16-mm tool shoulder diameter. The proposed model can be used to predict the thermal cycle, peak temperature, and thermo-mechanically affected zone for welding of dissimilar materials on friction stir welding.

In the present study, various (Ag–Cu) nanoalloy particles are embedded in the Ni matrix and synthesized by rapid solidification, namely Ni–3.8 at.% (Ag 77 –Cu 23 ), Ni–4 at.% (Ag 60 –Cu 40 ), and Ni–4.8 at.% (Ag 24 –Cu 76 ), to understand the effect of matrix on nanoparticles. The detailed TEM study reveals that Ni–3.8 at.% (Ag 77 –Cu 23 ) and Ni–4 at.% (Ag 60 –Cu 40 ) show a single phase of (Ag), while Ni–4.8 at.% (Ag 24 –Cu 76 ) indicates the presence of bi-phasic (Cu)–(Ag) alloy nanoparticles. Furthermore, thermal cycling was carried out using DSC to study the influence of solid-solution properties. Unlike Ni–3.8 at.% (Ag 77 –Cu 23 ) and Ni–4 at.% (Ag 60 –Cu 40 ), Ni–4.8 at.% (Ag 24 –Cu 76 ) shows no changes while melting and cooling. Further, in situ TEM investigation of Ni–4.8 at.% (Ag 24 –Cu 76 ) nanoparticle reveals that the bi-phasic nanoparticles undergo fully solid-state transformation to single-phase (Ag) nanoparticles prior to melting while heating. Theoretical studies on the phase stability of Ag–Cu–Ni at the nanoscale were undertaken to validate the experimental results, offering insight into the phase change of these solid-solution nanoparticles in the Ni matrix. Graphical abstract

Recent advances in the field of additive manufacturing offers significant flexibility in shaping and processing of materials. These techniques have been extensively studied for the manufacturing of entire component, typically using powder of a single composition. In this study, we explore the use of selective laser melting technique for the processing of an existing component. The Inconel 625 powder was printed onto the cast iron coupons using selective laser melting. These processed coupons were then characterised to study the interface between the Inconel 625 layer and the cast iron substrate. The microstructure near the interface region transitioned from small equiaxed grains to columnar morphology. The chemical intermixing between the Inconel 625 and cast iron was mostly confined within the first layer of Inconel 625. No new phases were observed at or near the interface which is consistent with the predictions from the thermodynamic calculations that was carried out using the FactSage® software and typical process parameters and composition data. The microhardness measurements at and near the interface region showed the highest hardness values at the interface which can be related to the fine-grained microstructure and solid-solution strengthening of the region.

A vanadium nitride alloy can be used as an alloying source of nitrogen and vanadium elements in high-strength steel. In this study, comprehensive and systematic experiments were conducted to optimize the process conditions for producing a vanadium nitride alloy from the starting materials (V2O5 and Fe2O3). The reduction and nitridation behaviors of the starting materials were investigated using thermogravimetry-differential scanning calorimetry (TG-DSC) and horizontal tube furnace experiments under various gas conditions. The phase and chemical compositions of the final alloy products were analyzed using X-ray diffraction (XRD), scanning electron microscope-electron dispersive spectroscopy (SEM-EDS), and the inert gas fusion (IGF) technique. In addition, thermodynamic calculations were performed to help in the understanding of the Nitrovan production process.

Thermoelectric (TE) materials are of great interest to many researchers because they directly convert electric and thermal energy in a solid state. Various materials such as chalcogenides, clathrates, skutterudites, eutectic alloys, and intermetallic alloys have been explored for TE applications. The Ga-Sn-Te system exhibits promising potential as an alternative to the lead telluride (PbTe) based alloys, which are harmful to environments because of Pb toxicity. Therefore, in this study, thermodynamic optimization and critical evaluation of binary Ga-Sn, binary Sn-Te, and ternary Ga-Sn-Te systems have been carried out over the whole composition range from room temperature to above liquidus temperature using the CALPHAD method. It is observed that Sn-Te and Ga-Te liquids show the strong negative deviation from the ideal solution behavior. In contrast, the Ga-Sn liquid solution has a positive mixing enthalpy. These different thermodynamic properties of liquid solution were explicitly described using Modified Quasichemical Model (MQM) in the pair approximation. The asymmetry of ternary liquid solution in the Ga-Sn-Te system was considered by adopting the toop-like interpolation method based on the intrinsic property of each binary. The solid phase of SnTe was optimized using Compound Energy Formalism (CEF) to explain the high temperature homogeneity range, whereas solid solution, Body-Centered Tetragonal (BCT) was optimized using a regular solution model. Thermodynamic properties and phase diagram in the Ga-Sn-Te and its sub-systems were reproduced successfully by the optimized model parameters. Using the developed database, we also suggested several ternary eutectic compositions for designing TE alloy with improved properties.

Martensite forms by a displacive mechanism of transformation; when it first forms all the carbon atoms that it inherits from parent austenite are ordered on only one of three sub-lattices of octahedral interstitial sites resulting essentially in a body-centred tetragonal crystal structure. At higher temperatures, however, the carbon atoms disorder and martensite becomes cubic. The literature on order–disorder transition has been reviewed. It has been highlighted that the c/a ratio of martensite is not independent of the concentration of substitutional solutes. Tetragonal martensite in interstitial-free ferrous alloys has also been discussed. The ordered arrangement of carbon atoms leads to conditional spinodal decomposition during the early stages of tempering. Finally, tetragonal bainitic ferrite and its higher solubility of carbon are discussed.

A one-dimensional numerical solidification model has been developed to predict the recovery and refining efficiency of fractional crystallization applied to a blend of aircraft Al scraps with variations of Fe and Si. The model incorporates the effective partition coefficient depending on the degree of melt stirring. Moreover, the kinetic factors that affect the formation of primary Al FCC during fractional crystallization such as solidification velocity, thermal gradient, cooling rate, and solute back-diffusion are taken into account. The simulation results suggest that the optimum solidification velocities that are able to yield the highest refining can be ranged between 1.0 × 10 −6 and 1.0 × 10 −5  m/s with medium to high stirring levels. The maximum recovery of refined Al has been estimated to be 31 wt pct of the initial scrap when the process is carried out at 1 × 10 −6  m/s and the initial concentrations of Fe and Si are 1 and 2 pct, respectively.

Magnetocaloric materials (MCM) have garnered significant attention within the research community, as they can minimize the use of harmful gases such as chlorofluorocarbons and hydrofluorocarbons, and provide eco-friendly refrigeration. Heusler alloys (Ni2MnGa) are known for their magnetocaloric effects, which make them useful as energy-efficient and eco-friendly refrigerating materials. Magnetocaloric properties depend significantly on the composition of these alloys. Ni-Mn-Ga is an interesting Heusler system which exhibits magnetocaloric properties. In the present study, we performed thermodynamic optimization of two sub-binaries of the Ni-Mn-Ga system, Mn-Ga and Ni-Ga, using the CALPHAD approach. Both binaries were combined with Mn-Ni to develop a self-consistent thermodynamic database for Ni-Mn-Ga. In order to resolve the existing experimental discrepancies in the Mn-Ga and Ni-Ga system, a few alloy compositions were prepared and analysed using differential thermal analysis. Finally, the developed thermodynamic database was used to calculate the T0 (K) or the martensite start temperature. The influence of varying Mn, Ni, and Ga concentrations on T0 (K) is discussed using the hybridization theory, and the current calculation results are compared with previous experiments in the literature. Lastly, a few compositions in the Mn-rich region are proposed which exhibit comparable or better magnetocaloric properties relative to the existing alloys.

Phase equilibria in Ga-Sn-Te system plays a key role in designing multiphase thermoelectric materials. SnTe is a promising alternative to the well-known PbTe (toxic) thermoelectric phase in the Ga-Sn-Te system. In the present study, various compositions have been selected using the thermodynamically developed database of the Ga-Sn-Te system to understand the phase equilibria and microstructural features. The alloys with multiphase combinations of SnTe, Ga 6 SnTe 10 , GaTe, and Te were produced using vacuum induction melting. In addition, the developed microstructures were characterized using x-ray diffraction, optical and Scanning Electron Microscopy techniques. The microstructures reveal interesting eutectic morphologies of Ga 6 SnTe 10 /Te, Ga 6 SnTe 10 /SnTe, and GaTe/SnTe. The microstructural features were explained using Scheil-Gulliver cooling calculations. Moreover, the thermal analysis of the investigated alloys was also performed to validate the thermodynamically predicted liquidus temperatures and various phase transitions in the investigated alloys.

The investigation of IN718 alloy for aerospace and oil and gas industries focuses on cost-effective component design, specifically for turbines. Manufacturers for IN718 can achieve cost-effectiveness by acquiring recycled materials in the form of scrap. This recycling approach not only addresses economic considerations but also aligns with environmental goals such as reducing greenhouse gas emissions. In the production process, utilizing scrap with higher Si content could reduce costs. However, precise microstructure control is necessary to mitigate microsegregation and secondary phases that impact final product properties. Homogenization treatment minimizes microsegregation, making the alloy suitable for further processing. In this study, as-cast IN718 alloy with 0.2 wt pct Si is homogenized at 1100 °C, 1150 °C, and 1175 °C for 12, 36, 60, and 96 hours. Solute redistribution in as-cast and heat-treated alloys was assessed using SEM-EDS-based area analysis by scanning approximately 2000 uniformly distributed points. The SEM-EDS data analysis yielded concentration profiles for each element in the investigated alloys. Homogenization was determined based on delta values (the difference between maximum and minimum solute concentration) as a function of temperature and time. Homogenization at 1175 °C for 96 hours showed the lowest delta values and is recommended as the suitable heat treatment. Additionally, a diffusion-based homogenization model predicts homogenization extent with respect to temperature and time. The model suggests a two-stage heat treatment: 1150 °C for 25 hours and holding at 1200 °C for 30 hours.