K. R, Ravi

The present study investigates the microstructural evolution of the Al 7075 alloy through laser surfacing processes. The influence of varying laser parameters on microstructure formation is explored, and the impact of cooling rates on microstructural changes and defects is examined. The cooling rates during laser scanning ranged from 445 °C/s to 2350 °C/s, revealing a spectrum of microstructural changes. These microstructures encompass the development of columnar dendrites, equiaxed dendrites, dendrite fragmentation, and banded structures. Dendrite tip fragmentation is studied, revealing that cooling rates above 475 °C/s trigger fragmentation, notably within the columnar-to-equiaxed transition zone. For cooling rates below 475 °C/s, retraction was observed as the dominant mechanism for dendrite fragmentation. Moreover, the presence of porosity was identified as an impediment to the fragmentation process. Additionally, banded structures became apparent at cooling rates exceeding 1550 °C/s. Furthermore, by correlating calculated growth velocities with solidification microstructure, it was discerned that banded structures necessitated higher growth velocities compared to equiaxed dendrites. The ensuing discussion delves into these aspects, enhancing the comprehension of microstructural evolution during the laser surfacing of the Al 7075 alloy.

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.

This study primarily focused on forming pure single-phase FeSb and explored its thermoelectric, mechanical, and electrochemical properties since no reports are available. The FeSb binary alloy has been synthesized through the vacuum melting method, and the phase formation has been confirmed through powder X-ray diffraction (PXRD). The PXRD results show that the synthesized FeSb binary alloy belongs to the hexagonal crystal structure with space group P63/mmc, which coincides with ICSD no. 53971. The pure single phase has been formed by creating a deficiency of 10 % in antimony. The High-Resolution Scanning Electron Microscopy (HR-SEM) and Energy Dispersive X-ray (EDX) analysis have been used to identify the pure single-phase and various elemental components of the hot-pressed pellet of FeSb0.9. The atomic wt.% of iron (Fe) and antimony (Sb) have been identified through EDX spectral analysis. The highest Seebeck coefficient value of −5.4 μV/K is achieved at 497 K, and the lowest electrical conductivity value of 24049 S/m is achieved at 447 K. The hardness of the material is found to be 6.076 GPa, which is much more sufficient for thermoelectric material during industrial handling. The magnetic characteristics of the prepared pure phase FeSb compound have also been measured by Vibrating Scanning Magnetometer (VSM) analysis, which has a weak ferromagnetic nature. Furthermore, three electrodes were employed to study the electrochemical properties, and the alloy has attained the appreciable specific capacitance of 169.5 F/g at 2 A/g.

The present study investigates the impact of different heat transfer approaches on the precision of geometry and solidification behavior in additively manufactured thin clad walls. Employing a 2D laser scanner to assess dimensional accuracy, the study demonstrates that thin clad walls produced on a copper base plate with forced air convection exhibit notably superior accuracy compared to those on a mild steel substrate with natural convection. Microstructure analysis unveils distinct characteristics: Thin clad walls printed with natural convection on mild steel display a coarse columnar dendritic structure marked by increasing primary dendrite arm spacing (PDAS) from bottom to top (10.4 ± 0.7 to 14.5 ± 3 µm). In contrast, forced convection leads to a fine cellular and columnar dendritic microstructure with minor PDAS variation (4.6 ± 0.9 to 7.4 ± 1.7 µm) along the entire vertical span.

The study involves numerically simulating the influence of process parameters on melt pool geometry, cooling rate, and microstructure during laser surfacing of 7075 Al alloy using COMSOL Multiphysics. Both numerical simulations and experiments show that increasing scan speeds at a constant laser power reduces melt pool dimensions and increases cooling rates. At 1000 W laser power and 15 mm/s scan speed, numerically simulated melt pool width, depth, and cooling rate are 3.8 mm, 1 mm, and 1370 K/s, closely matching experimental measurements of 4.2 mm, 1.3 mm, and 1449 K/s. Calculated thermal gradient (G) and solidification rate (R) are correlated with observed solidification morphology. The G/R ratio derived from simulations has higher values at the melt pool's bottom, gradually decreasing toward the top for a given laser power and scan speed. This pattern aligns with optical micrographs showing equiaxed dendrites at the top, and columnar and cellular dendrites in the middle and bottom of the melt pool.