In the realm of materials science and engineering, the pursuit of advanced materials with tailored properties has been a driving goal behind technological progress. Scientific interest in laser powder bed fusion (L-PBF) fabricated NiTi alloy has in recent times seen an upsurge of activity. In this study, we investigate the impact of varying volume energy density (VED) during L-PBF on the microstructure and corrosion behaviour of NiTi alloys in both scan (XY) and built (XZ) planes. The microstructural evolution in both planes was characterized by electron backscatter diffraction and phase change temperatures were characterized using differential scanning calorimeter measurements. Electrochemical experiments were carried out to compare the specimens produced at high laser energy density and low laser energy density. The results indicate that employing high laser energy density in the production of NiTi alloy induces discontinuous dynamic recrystallization, contributing to grain refinement. This in turn enhances the corrosion resistance of the specimen. X-ray photoelectron spectroscopy was employed to examine the type of oxide layer that developed on the samples. The increased resistance to corrosion in a high laser energy density sample can be associated with the formation of a stable and homogeneous passive layer with enriched TiO2 as opposed to Ti2O3. This exploration has unravelled the intricate relationship between VED, the microstructure, and the corrosion properties of L-PBF fabricated NiTi alloys, offering valuable insights into their performance for diverse applications.

In this research, we explore the possibility and effectiveness of using laser-induced surface oxidation methods to enhance the durability and effectiveness of PEF (Pulsed Electric Field) systems. Despite advantages over thermal pasteurisation, PEF faces challenges like electrode corrosion and biofouling, hindering its adoption. This research introduces laser-induced oxidation to mitigate metal ion release during PEF, directly targeting electrode alteration. Our examination adopts a comprehensive method, integrating Design of Experiments (DoE) parameter sets for PEF trials, morphological analysis, evaluation of metal ion release via Inductively Coupled Plasma Quadrupole Mass Spectrometry (ICP-QMS), waveform capture utilizing a Data Acquisition (DAQ) system, electrochemical assessment via impedance spectroscopy, and examination of oxide layer composition employing X-ray photoelectron spectroscopy. Pulse waveform characteristics shows the intricate relationship between PEF processing parameters with metal ion release, alongside XPS analysis providing insights into surface chemistry. Optimized results show a three-fold reduction in metal ion release post-PEF, with laser-treated samples outperforming untreated stainless steel due to selective surface chemistry alteration, notably an increased Cr/Fe ratio, reducing harmful elements. This study highlights laser-induced oxidation as a practical solution for enhancing PEF electrode performance and reducing metal ion release, addressing key challenges in PEF technology. It advances sustainable food processing, promising extended PEF system lifespan while maintaining efficiency and product quality.

AbstractThis paper presents the development of a model for Nd:YAG laser surface oxidation of 316L stainless steel. A full factorial design of experiments (DOE) are implemented to produce a model for the prediction of elemental composition and color. The elemental composition of the films produced where measured using an X‐ray photoelectron spectroscopic (XPS) and the color is measured using optical reflectance spectroscopy. Oxide layers produced have a Cr/Fe ratio in the range of 0.13–2.09, and highly controllable color variation via single‐pass laser process. The effect of the process parameters used such as power, frequency, and scan speed on laser‐induced oxides is examined with an aim to produce a model suitable for predictive control of the elemental composition and color of the oxide film. Surface morphology control via alteration of the laser power is an important factor for defining the resulting coloration. A new finding from this work is the discovery that within the range of laser surface processing parameters investigated, the molybdenum concentration is inversely proportional to the chromium concentration. This paper provides data required for control of 316L‐SS surface chemistry, and for the expansion of the current thermokinetic model to incorporate the mechanistic effect of molybdenum.

This study delves into the corrosion resistance enhancement of stainless steel through laser processing, focusing on the interplay between surface chemistry, morphology, and electrochemical properties. Two sets of 3 × 3 full factorial design of experiment (DoE) designs were employed to explore the influence of laser process parameters, including power, scan speed, frequency, and hatching distance. The findings underscore the superiority of reduced areal energy in producing optimal corrosion resistance 10 times better then unprocessed stainless steel, demonstrating the best results under optimized conditions of a 15 µm hatching distance, 250 mm/s scan speed, 100 kHz frequency, and 80 % power. X-ray Photoelectron Spectroscopy (XPS) analysis reveals the predominant surface composition of iron and chromium oxides, with variations in the oxide combinations correlating closely with areal energy. Depth profiling revealed the transformation of oxide layers and highlights the importance of chromium-to-iron ratio in surface corrosion behaviour. Cyclic polarisation results demonstrate the formation of passive, transpassive, and pitting domains, with metastable pitting observed in some samples. The direct positive correlation recorded between corrosion current and Cr/Fe ratio underscores the significance of oxide composition in corrosion resistance. Electrochemical impedance spectroscopy (EIS) further confirmed the superior corrosion resistance of laser-processed samples to non-laser processed samples, with lower areal energy exhibiting higher resistance compared to higher areal energy. SEM morphology analysis revealed the removal of surface defects and the formation of a protective oxide layer in laser-processed samples, with lower areal energy samples exhibiting the lowest level of surface defects. The 3D optical profilometer measurements of corrosion pits corroborate these findings, with lower areal energy samples demonstrating the lowest pit depth and area, indicating superior corrosion resistance. Overall, this study provides comprehensive insights into optimizing laser processing parameters to enhance the corrosion resistance of stainless steel, offering valuable understanding and strategy for improving the metal surface corrosion resistance.

Surface fouling is a major challenge faced within various engineering applications, especially in marine, aerospace, water treatment, food and beverage, and the energy generation sectors. This can be prevented or reduced in various ways by creating artificial surface textures which have fouling resistance properties. Ultrafast laser texturing provides an efficient method for the texturing of surfaces of different materials with high accuracy, precision, and repeatability. Laser texturing methods can enhance the production of well-defined surface nano- and microscale patterns. These surfaces with nano- and micro-scale patterning can be tailored to have inherent properties such as hydrophobicity, hydrophilicity, and resistance to fouling. This review gives an overview of the various types of fouling that can occur, the properties affecting a surface's fouling resistance, as well as the latest physical and chemical strategies for the generation of antifouling surfaces. Surfaces architectures which have inherent antifouling capabilities are presented. This review focuses on the utilization of the higher precision laser-based texturing offered from femtosecond laser systems for enhance fouling resistance. The process parameters to fabricate these textures and the current state of art femtosecond laser sources are presented and discussed. The challenges and future research requirements in the field of laser-based methods to fabricate antifouling surfaces are presented.

Laser induced stainless steel colouration has evolved as an innovative technique to craft aesthetically pleasing surfaces in the automotive, product identification, home decor, and architectural fields. In addition to visual appeal, a thin coloured film on stainless steel surface can also impart corrosion resistance and functionality. By precisely employing variety of laser parameters such as power, frequency, hatching distance and scan speed it is possible to create oxide films of varying colours and compositions. However, the relationship between the laser processing parameters, colour oxide film and composition is still not fully established. In this study, we present a systematic approach to identify the colour and composition of laser-induced colouration on stainless steel using a Nd:YAG laser, focusing on the commonly used 316L stainless steel alloy. The effects of laser parameters were explored using a full factorial design of experiment (DoE) approach to gain insights into the optical and chemical characteristics of the resulting oxide films. Furthermore, spectroscopic and imaging techniques were employed to analyse the diffusion behaviour of key elements, particularly iron, chromium and molybdenum, as they play a crucial role in colouration and mitigating corrosion effects. In particular, Analysis of Variance (ANOVA) was used to correlate the laser parameters with the surface elemental composition determined by X-ray photoelectron spectroscopy (XPS) and surface optical reflectance. This investigation provides a new fundamental understanding of surface colouration and a low-cost method for the control of surface colour and enhanced functional properties.