High entropy alloy (HEA) involves the addition of five or more elements into the materials system. This provides a multidimensional configuration space that is limitless in terms of its properties and functions. Some high-entropy alloys have already been shown to have superior properties over conventional alloys, especially the CoCr-based HEA materials. Better high-entropy alloy applications may be discovered, especially in micro- and nano-level structures, hence the development of thin film/coating -based HEA materials. Therefore, in this review paper, we are aiming to provide recent studies on the thin film/coating-based high-entropy alloy on fundamental issues related to methods of preparation, phase formation and mechanical properties. We found that sputtering has been extensively used to grow thin-film-based HEAs as it allowed parameters to be controlled with homogeneous growth. The evolution from bulk to thin samples can also be observed with the mechanical properties has exceeded the bulk-based HEA expectations, which are high hardness, better interfacial bonding and tribological behaviour and higher corrosion resistant.

The electron transfer layer (ETL) plays a vital role in achieving high-performance perovskite solar cells (PSCs). Titanium dioxide (TiO₂) is primarily utilised as the ETL since it is low-cost, chemically stable, and has the simplest thin-film preparation methods. However, TiO₂ is not an ideal ETL because it leads to low conductivity, conduction band mismatch, and unfavourable electron mobility. In addition, the exposure of TiO₂ to ultraviolet light induces the formation of oxygen vacancies at the surface. To overcome these issues, doping TiO₂ with various metal ions is favourable to improve the surface structure properties and electronic properties. This review focuses on the bulk modification of TiO₂ via doping with various metal ions concentrations to improve electrical and optical properties, charge carrier density, and interfacial electron–hole recombination, thus contributing to enhancing the power conversion efficiency (PCE) of the PSCs.

The present work investigates the influence of Indium (In) additions at 4, 8, and 12 wt.% on the microstructure, phase stability, anisotropic lattice behavior and mechanical performance of Sn-58Bi solder alloy. Alloys were fabricated via casting and characterized using differential scanning calorimetry (DSC), tensile testing, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX), and synchrotron-based techniques including in situ X-ray diffraction (XRD) and micro-X-ray fluorescence (XRF). Indium addition progressively reduced the melting temperature from 142.52 °C (Sn-58Bi) to 116.33 °C (Sn-58Bi-12In), while broadening the pasty range. Microstructure analysis revealed the formation of BiIn intermetallic compounds and coarsened Bi-rich regions with increased In content. Synchrotron micro-XRF mapping confirmed the elemental segregation of Bi and In. In situ synchrotron XRD demonstrated that the BiIn phase is stable at room temperature but dissolves above 80 °C. Lattice parameter refinement of the rhombohedral Bi phase indicated anisotropic stabilization, with suppression of contraction along the a-axis upon In addition. Solderability assessment showed that Sn-58Bi-12In achieved the shortest wetting time of 1.356 s, and a thinner Cu₆Sn₅ intermetallic layer was observed at the solder/Cu interface. Mechanical testing revealed a tradeoff between strength and ductility where tensile strength decreased from 69 to 53 MPa, while elongation improved to 15.5% at 12 wt.% In. Fracture surface analysis indicated a transition from brittle to ductile failure with increasing In content. These results demonstrate that Indium addition effectively tailors the microstructural, thermal, and mechanical behavior of Sn-58Bi solder, making Sn-58Bi-xIn a promising candidate for low-temperature electronic packaging applications.

Solder interconnection in three-dimensional (3D) electronic packaging is required to undergo multiple reflow cycles of the soldering process. This paper elucidates the effects of multiple reflow cycles on the solder joints of Sn-3.0Ag-0.5Cu (SAC305) lead (Pb)-free solder with the addition of 1.0 wt.% kaolin geopolymer ceramics (KGC). The samples were fabricated using powder metallurgy with the hybrid microwave sintering method. Apart from using conventional cross-sectioned microstructure imaging, advanced synchrotron real-time in situ imaging was used to observe primary IMC formation in SAC305-KGC solder joints subjected to multiple reflow soldering. The addition of KGC particles in SAC305 suppressed the Cu₆Sn₅ IMC’s growth as primary and interfacial layers, improving the shear strength after multiple reflow soldering. The growth rate constant for the interfacial Cu₆Sn₅ IMC was also calculated in this study. The average growth rate of the primary Cu₆Sn₅ IMCs decreased from 49 µm/s in SAC305 to 38 µm/s with the addition of KGC particles. As a result, the average solidified length in the SAC305-KGC is shorter than SAC305 for multiple reflow soldering. It was also observed that with KGC additions, the growth direction of the primary Cu₆Sn₅ IMC in SAC305 changed from one growth to two growth directions. The observed results can be attributed to the presence of KGC particles both at grains of interfacial Cu₆Sn₅ IMCs and at the surface of primary Cu₆Sn₅ IMC.

This research was conducted to examine the corrosion behaviour of mild steel bar embedded in geopolymer paste based fly ash Class F during curing and non-curing process. The geopolymer paste was fabricated by blending in the fly ash with alkaline activators (NaOH solution with molarity of 12 M, 2.5 ratio of solution Na2SiO3/NaOH). The paste was produced in 50 mm × 50 mm × 50 mm mould where the mild steel bar of 100 mm (length) × 12 mm (diameter) was embedded at the center of geopolymer paste. This is to comprehend the corrosion behaviour of mild steel embedded in geopolymer paste with and without curing process. Process of curing is carried out for 24 hours at a temperature of 60°C in oven. While on the contrary, the non-curing process will only be leave at room temperature. Both samples were tested after 28 days of curing to determine the corrosion behaviour, phase analysis and morphology analysis. In accordance with the morphology analysis, it shows that the fly ash was totally reacted with alkaline solutions in curing geopolymer paste sample while the non-curing geopolymer paste has shown the unreacted fly ash with high number of pores. The phase analysis of mild steel embedded in this geopolymer paste during curing and without curing process has proven that the presence of new crystallographic peak which also known as passive layer occurred. The potential values result by OCP testing shows the curing sample has highest potential values as compared to the non-curing sample ones.