In this study, ultrasonic nanocrystal surface modification (UNSM) was employed to improve the performance of the top surface layer of a ferritic-pearlitic steel sheet, which is most susceptible to degradation during service. The microstructural changes induced by UNSM treatment and their underlying mechanisms were examined. Significant grain refinement within a surface layer with a maximum depth of 80 μm, and surface compressive residual stress were found for all treatment conditions. The combination of a refined microstructure and accumulated plastic deformation led to a 25–68% increase in hardness. Based on the evaluation of surface hardness, compressive residual stresses and surface roughness, the optimal processing parameters were found to be a single pass with 80 N of static load and 50 μm of vibration amplitude. The present study demonstrates the potential of UNSM as a sustainable, room-temperature surface modification technique for enhancing the durability and performance of the surface layer of pipeline steel and provides guidance for the future selection of processing parameters.

The effect of tempering and auto-tempering on the microstructure–property relationship of two ultra-high strength press hardening steels (PHS1500 and PHS2000) was studied. Both steels were austenitized, oil quenched, and subsequently tempered at four different temperatures ranging from 180 °C to 300 °C. For auto-tempering, the steels underwent austenitization and quenching using a press equipped with planar tools and were subsequently ejected at varying cooling durations. The tensile properties, hardness, microstructure, and dislocation densities after heat treatment were characterized. The results showed that the effect of tempering temperature on tensile properties and microstructure features was more pronounced than the effect of tempering time for both steels. Tensile strength and hardness decreased slightly with increasing tempering temperature up to 200 °C. Above that temperature, there was a further decrease in tensile strength and hardness, which is suggested to be due to the formation and coarsening of carbides in the highly dislocated martensitic matrix. In contrast to the tensile strength and hardness, the yield strength increased with increasing tempering temperatures, which is most probably due to internal stress relaxation. Total elongation was increased with increasing tempering temperatures, except for the samples tempered at 250 °C and 300 °C. These samples experienced a reduction in elongation at fracture, which was more pronounced after tempering at 300 °C than at 250 °C. This was most likely attributed to the so-called tempered martensite embrittlement effect. Calculation of dislocation densities before and after tempering treatments confirmed dislocation annihilation and recovery of martensitic microstructure. 

This work investigated the efficient routes for the fabrication of semi-permeable thin films for desalination using plasma polymerization technology. Acrylic acid (AAc) was selected as a precursor for plasma polymerization due to its hydrophilic properties and potential for low fouling functionalization and ability to form flexible, filtration-ready films. The plasma polymerized AAc films were deposited on the top of poly(sulfone) ultrafiltration (PSf UF) membranes to enhance the selectivity of the composite membranes. Different plasma modes such as continuous wave (CW) or pulsed plasma were applied to overcome the brittleness issue. Such narrow pore size UF membranes, with pores less than 10 nm, were further used for rejecting perfluoroalkyl substances (PFASs), a class of persistent environmental chemicals, also known as an emerging threat to public health and the environment. The selectivity and antifouling behavior of the tight UF membranes were investigated against four PFASs differentiated by molecular weight. The tight UF membranes have shown approximately 20 % higher rejection than the pristine PSf. Although the rejection rate was enhanced proportionally with the size of PFAS compounds, membrane fouling became severe as the size of PFAS became close to the molecular cut-off size of the composite membranes. The surfaces of the tight UF plasma modified membranes were more hydrophilic with a water contact angle of 15.1° and negatively charged streaming potential of −31 mV at pH 8, which contributed to the lowest total permeance decline ratio and highest flux recovery rate compared with pristine PSf during each filtration test. The outcome of this study has opened more opportunities for the application of the plasma polymerized membranes for gas separation, water treatment, fuel cells, biomedical devices, and protective coatings.

Site-specific atom probe tomography coupled with electron back scattering diffraction studies were used for the first time to elucidate the multi-element solute segregation and clustering at austenite-ferrite interface during early stages of phase transformation in Fe-Mn-Si-C steel alloyed with Ti, Mo and Nb. The results have shown the existence of negligible partitioning local equilibrium at interfaces with segregation of C, Mn, Ti and Mo to interfaces having the angle deviation in the range from 2.9 to 12° from Kurdjumov-Sacks orientation relationships (K-S ORs), but either irregular incident planes or the ones not following the matching according to K-S ORs. The segregation of Nb was less common, which was linked to the earlier occupancy of interfaces by Ti and Mo. Variation in solute segregation along the same interfaces is highlighted. Presence of clusters within and in close proximity to the interface is detected. The links between interface orientation, solute segregation, clustering and interphase precipitation are discussed.