Kipkurui Ronoh

Ultrafast laser ablation provides a powerful approach for tailoring the surface properties of nickel-based alloys. In this study, picosecond laser ablation of three Alloy 602 CA variants, namely conventionally manufactured (C-602 CA), additively manufactured (SAC-UN-602 CA), and nitrided additively manufactured (SAC-ISIN-602 CA), were systematically investigated under ambient conditions. The influence of laser fluence and scanning velocity on ablation behaviour, surface morphology, surface chemistry, and wettability was examined. Picosecond laser processing produced well-defined laser-induced periodic surface structures (LIPSS) on all variants, with increasing periodicity and surface roughness at higher fluence. Ablation depth and rate increased with fluence but decreased with increasing scanning velocity, while ablation efficiency decreased at higher fluence. Nanoindentation revealed slightly lower hardness and reduced modulus for the additively manufactured alloys compared to the conventional alloy. X-ray diffraction confirmed that all variants retained a single-phase austenitic FCC Ni–Cr–Fe solid solution after processing, with no laser-induced phase transformation, indicating structural stability. SEM–EDX analysis confirmed that ultrafast laser ablation did not significantly alter the overall elemental composition of the alloys. X-ray photoelectron spectroscopy revealed laser-induced surface oxidation and hydroxylation, with Ni predominantly present as Ni(OH)2 and Cr as Cr2O3/NiCr2O4. Wettability measurements demonstrated a transition from hydrophilic polished surfaces to strongly hydrophobic laser-ablated surfaces. Despite differences in manufacturing route and microstructure, all variants exhibited comparable behaviour, indicating that surface modification is governed predominantly by the laser processing parameters. These findings demonstrate that picosecond laser processing enables controlled and reproducible surface modification of Alloy 602 CA for advanced functional applications.

This study investigates electron emission from copper broad-area emitters (CBAEs) and copper broad-area composite emitters (CBACEs) based on the principles of trapping and conductive pathways. Emission current measurements were conducted on two CBACEs, which consisted of copper coated with a 300–400 μm epoxy resin and subjected to high voltages up to 15 kV. The research specifically examines the ‘switch-on’ and collapse phenomena occurring within the epoxy layer. Field emission microscopy (FEM) was utilized in a high-vacuum environment ( 10 − 6 mbar) to observe these effects. A comprehensive model is developed to explain the formation of conductive pathways within the epoxy layer, allowing electrons transfer from traps to the surface. This model treats the composite emitter as a trap-rich capacitor. The study also clarifies the effects of trap density and epoxy layer thickness on the collapse process. To gain a deeper understanding of the model, changes in the I-V curve were examined. Simulations, scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDX) images, and Fourier transform infrared spectroscopy (FTIR) analysis were employed to understand the collapse mechanism of the epoxy collapse. Additionally, Nyquist and Cole–Cole plots were analyzed across frequencies ranging from 1 to 10 6 Hz before and after applying a high electric field on the samples, revealing changes in the capacitive component and the role of diodes in the formation of conductive channels.

Surface structuring by ultrafast lasers is a promising technique to modify surface-related properties of materials to tailor them for specific applications. In the present study, we experimentally investigated the laser structuring of commercially pure titanium (CP Ti) using ultrafast pulses to understand the role of the laser input parameters on the development of surface morphology, optical properties, surface chemistry, and wettability behaviour. The processed surfaces were characterized by a scanning electron microscope, energy-dispersive X-ray spectroscopy (EDX), Raman microscope, optical microscope, and sessile drop method. Laser-induced periodic surface structures decorated with nanodroplets were noted to be formed on the surface of the laser-structured CP Ti. The surface roughness measurements showed that the laser-structured surfaces had nanoscale roughness values. The EDX and the Raman analyses show that laser-structured surfaces of CP Ti have a thin oxide film. Different colours on different surfaces processed by different laser parameters were observed. The wettability assessment shows that CP Ti can transition from hydrophilic–hydrophobic and vice versa depending on the environmental conditions. This study shows that laser structuring can be utilized to modify CP Ti surfaces to obtain desirable surface properties that can find potential applications in different fields.

Monel^® alloy 400 has excellent corrosion resistance and finds applications in marine industries. The processing of marine components requires high processing efficiency and a quality finish. Hence, this research aims to investigate the effects of the laser processing parameters such as laser fluence, scanning velocity, hatching distance, and the scanning pass on the ablation rates and efficiency, chemistry, and nanomechanical properties of the Monel^® alloy 400 after pulsed picosecond (ps) laser ablation. From the experimental findings, the ablation depth increases as the laser fluence increases while decreasing as the scanning velocity increases. Surface roughness was noted to increase as the laser fluence increased. The findings demonstrated that the ablation rate increases as laser fluence increases while ablation efficiency decreases. Energy dispersive x-ray spectroscopy (EDX) showed that the elemental composition of laser-ablated zones is almost similar to that of the polished sample. X-ray spectroscopy (XPS) shows that the outer layer on the surface of Monel^® alloy 400 is composed of NiO and CuO. The hardness and Young’s modulus of the laser-processed alloy were found to be less than those of the bulk material. This study can be used to establish optimal processing parameters for the ultrafast ps laser processing of materials to achieve high ablation efficiency with a high-quality surface finish for industrial applications.

In this research, the effects of coolant types, cooling techniques, and grinding depth on the surface properties of the Ti-6Al-4V after surface grinding with white alumina wheel were investigated. Three coolant types namely sunflower oil, formulated sunflower oil-based emulsions and soluble cutting oil were applied to the grinding zone using two cooling techniques: wet cooling and minimum quantity lubrication. The grinding was undertaken at grinding depths of 0.005, 0.010 and 0.015 mm. An L 9 orthogonal array was used to design the experiments and undertaken the evaluation of the variable interrelationships. Surface hardness and surface morphology of the ground surfaces were determined using Vickers Macro-hardness tester and Zeiss Axio Zoom V16 optical microscope, respectively. Results from the signal-to-noise ratio analysis revealed that cooling technique has the most influence while the grinding depth has the least influence on the surface hardness of ground Ti-6Al-4V. The optimal parametric setting which gives the highest surface hardness of Ti-6Al-4V was identified from the main effect plots and were sunflower oil (SO), MQL 2 at a flow rate of 0.65 L/h and a grinding depth of 0.015 mm. Analysis of variance demonstrated that the individual contributions of coolant types, cooling techniques and grinding depths to surface hardness were 24.11%, 52.47% and 14.15%, respectively. The morphological investigations established that better surface finish was achieved through the application of sunflower oil-based emulsions in MQL cooling technique at a grinding depth of 0.005 mm.