Etch pits could form on an exposed surface of a crystal when the crystal is exposed to an etching environment or chemicals. Due to different dissolution rates along various crystalline directions in a crystal, the dissolution process is anisotropic; hence, etch pits usually have a regular shape. Here, the morphology and origin of the regular-shaped etch pits are discussed firstly; then, factors which could affect the morphology and density of etch pits are shown; finally, the state of the art of etch pit technology and the utilization of etch pits is presented. Traditionally, etch pits are utilized to evaluate the dislocation density and some defect-related properties. Now, in the modern fabrication industries, the relationship between etch pits and defects has been utilized more skillfully. High-quality crystals can be fabricated by controlling dislocations revealed by etch pits. Meanwhile, with the as-revealed dislocation as the diffusion path of atoms, new crystals will emerge in corresponding etch pits.

This study electroplates a 2 μm thick Al layer on mild steel, then uses wire-arc directed energy deposition (DED) to deposit Cu-4.2Sn alloy, forming a composite material which is subsequently cold-rolled. It investigates the microstructure, mechanical properties, and tribological behavior before and after rolling, along with underlying mechanisms. It indicates that Al coating completely suppresses penetration cracks on the steel side of the tin bronze/steel bimetal. After rolling, tin bronze grains are significantly refined (from 47.6 μm to 15.2 μm) with numerous twins formed, reducing matrix dislocation density. Compared to wire-arc DED alloy, rolled alloy hardness increases by 78%, yield strength by 51%, and tensile strength by 30%. Tribological tests indicate, under dry friction and simulated seawater conditions, the rolled alloy’s coefficient of friction (COF) and mass loss decrease by 30% and 24% respectively. Analysis of corrosion-friction synergy reveals interaction loss accounts for 13%, dominated by friction-promoted corrosion (11%).

This study investigated the mechanism of influence of the microstructure of nickel-aluminum bronze (NAB) alloy prepared by wire-arc additive manufacturing (WAAM) on cavitation erosion (CE) and the synergistic effect of CE and corrosion. Microstructural analysis revealed that the earlier-deposited area in the overlapping area exhibited finer grain size (6.8 µm), higher β' phase content (34.6 %), and dominant κ_Ⅲ/κ_Ⅳ precipitates, while the substrate featured coarser grain size (13.6 µm) and lower β' phase content (23.2 %) featured coarser grain size (13.6 µm) and lower β' phase content (23.2 %). CE testing indicated that in synthetic seawater, the cumulative mass loss in the overlapping area (75.2 mg) is lower than that in the substrate (82.32 mg), but the initial mass loss rate is faster. After CE, the alloy develops a 140 µm work-hardening layer, with peak hardness occurring at a depth of 20 µm. The synergistic effects of CE-corrosion accounted for 52 % of the total mass loss, with corrosion-promoted CE (34 %) exceeding CE-promoted corrosion.

Due to the development and utilization of nuclear energy, the safe disposal of nuclear waste needs to be urgently addressed. In recent years, the utilization of microorganisms’ adsorption capacity to dispose of radioactive waste has received increasing attention. When compared with conventional disposal methods, microbial adsorption exhibits the characteristics of high efficiency, low cost, and no secondary pollution. In the long term, microbial biomass shows significant promise as specific chemical-binding agents. Optimization of biosorption conditions, identification of rare earth element binding sites, and studies on the sorption capacities of immobilized cells provide compelling reasons to consider biosorption for industrial applications in heavy metal removal from solutions. However, the interaction mechanism between microorganisms and radioactive nuclides is very complex. This mini-review briefly provides an overview of the preparation methods, factors affecting the adsorption capacity, and the mechanisms of microbial adsorbents.