Papers by Author: Dermot Brabazon

Abstract: This study provides a comprehensive investigation into the effects of different scanning parameter combinations—specifically scanning speed and hatch distance—on the material properties of IN939 fabricated using the powder bed fusion-laser beam (PBF-LB) process under a constant volumetric energy density (VED). Despite the fixed VED, the fabricated samples experienced different thermal cycles, resulting in distinct microstructural features and corresponding variations in material performance. In-situ infrared monitoring indicated that the sample with the narrowest hatch distance and highest scanning speed (Sample 1) reached the highest normalized temperatures with intense heat accumulation, whereas wider hatch distances (Sample 3) promoted lower and more stable temperature distributions. The results revealed that the intermediate parameter set (Sample 2) achieved the highest relative density (99.29%) and the lowest surface roughness. In contrast, both the narrowest and widest hatch spacing combinations promoted increased porosity, primarily consisting of lack-of-fusion (LoF) and gas pores. Electron backscatter diffraction (EBSD) analysis showed that the area-weighted average grain size increased from 29.5 µm to 36.7 µm as the hatch distance increased. Texture analysis indicated generally weak crystallographic texture development, with only slight intensification of <001>//BD and <111>//BD components, attributed to the 67^o rotation strategy. Furthermore, the microhardness values demonstrated negligible variation across the samples, ranging from 356.7 ± 14.3 HV1 to 360.1 ± 10.5 HV1. This limited variation indicates that the strengthening behavior was predominantly governed by the combined influence of defect density and matrix–defect interactions, rather than being directly correlated with grain size.

Abstract: Laser Powder Bed Fusion (L-PBF) is turning out to be very promising for biomedical components production and stents are among the devices that would be suitable for tailor-made production. One of the most common stent types are the self-expandable, manufactured with Nitinol (NiTi). The use of NiTi alloy with L-PBF needs to be well controlled, as Ni evaporation during the process leads to significant variations in the final component properties. In the present work, prototype NiTi stents were produced via L-PBF and heat treated to examine the possibility of employing this technology for their application, also considering the Ni evaporation resulting from the layer-by-layer deposition. Samples were characterized through differential scanning calorimetry (DSC), microstructural observations, and compression tests in plate-to-plate configuration according to the standard. In parallel, a commercially available stent manufactured with traditional technology was tested for comparison.

Abstract: Aluminium alloy 6061 has a versatile application within industrial heat exchangers, heat sinks, chemical equipment, and frames of aircraft and ships. Its physical and mechanical properties such as lightweight, high strength, corrosion resistance, and thermal and electrical conductivity make it a suitable material choice for these applications. Within thermal and micro-electromechanical applications, such as heat exchanges, radiators, and heat sinks used in microelectronics, the dissipation of heat plays an important role. For optimum heat dissipation, a higher surface area is required. This can be achieved by modifying the surface by fabricating microchannels. A number of processing techniques are used for fabricating microchannels on different materials. A laser is a flexible non-contact machining tool that may be used to create any profile or contour on practically any material. In recent times due to the advancement in laser technology, the use of ultrafast laser material processing is one potential route toward further extending the fabrication of high-quality microchannels without defects caused due to heat-affected zones and in a sustainable manner. In this paper, we present an experimental work of fabrication of microchannels on an aluminium alloy 6061 surfaces by using a low power (<4 W) 400 fs laser system. The dimensional accuracy of the fabricated microchannels is assessed using scanning electron microscopy and 3D profilometry. Furthermore, as processing speed and scale is of importance in industrial laser processes, the use of scanning optics is examined as a means of developing a rapid and scalable ultrafast laser process.

Abstract: As additive techniques such as laser powder bed fusion find increasing adoption industry, the ability to adapt these processes to industrially relevant materials is paramount. This adaptation can represent a significant challenge when working with wrought alloy feedstocks, which often result in brittle or porous parts lacking the mechanical properties of their conventionally wrought counterparts. One such alloy, aluminium 6061, is a highly used alloy in the aerospace, automotive, and semiconductor manufacturing industries. The conventionally manufactured components can have complex morphologies and may be assemblies of multiple individual components. As such, the ability to use an additive approach, and produce these as single parts can lead to significant benefits.In this work, we examine laser powder bed fusion of aluminium alloy 6061. The effects of process parameters such as laser power, beam scan speed, hatching distance, spot size was examined with a view towards developing an optimised process for this traditionally wrought alloy. Parts were examined for porosity and microstructure, with an aim to develop greater than 95% relative densities. To aid in process optimisation, in-situ pyrometry was deployed to understand the effects of the process parameters and develop a robust and repeatable process for producing 6061 components.

Abstract: Recent decades seen the success of Additive Manufacturing (AM) in many industrial applications including aerospace, biomedical, automotive, and tooling. In the manufacturing of metallic parts, AM technology has the ability to produce parts with complex geometries which are difficult or impossible to produce using the conventional fabrication methods, such as machining and casting. Another benefit of AM is the employment of metal and metal alloys which are difficult to machine. Alloys such as titanium, nickel-titanium, and stainless steel have a wide range of applications particularly in the aerospace and biomedical industry. Selective Laser Melting (SLM), also known as Laser Powder Bed Fusion (L-PBF) is a type of AM technology used for the 3D printing of metal and alloy parts. The major drawback in L-PBF technology is the anisotropic properties of the produced parts. From L-PBF, these anisotropies exist due to instant melting and re-solidification of the metal powder, the ultra-high cooling rates and the variant temperature levels across the build layers and within the single layer itself. This article explores the essential role of the melt-pool temperature and temperature gradients that occur during the L-PBF process and their effects on the additively manufactured part’s properties.

Abstract: Silver nano-colloids have been generated via Laser Ablation Synthesis in Solution (LASiS) system. Nanoparticle formation with particle size below 50 nm in DI water was confirmed using UV-VIS spectroscopy, Dynamic Light Scattering (DLS) technique, and transmission electron microscopy (TEM). Supercapacitor structure, having dimension 11 mm x 10 mm, was successfully Aerosol Jet printed on an untreated polymer substrate using as produced LASiS silver nano-colloid.

Abstract: Over the recent years, Nitinol (Ni-Ti) shape memory alloys have gained popularity in the medical, aerospace and energy sectors, due to their superelasticity, shape memory effect, low stiffness, good biocompatibility and corrosion resistance. Compared to steels and other common metallic materials, it is difficult to model the mechanical behavior of Ni-Ti due to the inherent functional properties caused by the diffusion-less solid-state phase transformations. With the help of Laser Powder Bed Fusion (L-PBF) process, these transformational characteristics can be controlled. This will ultimately lead to controlling the mechanical and thermal properties for specific applications. In this work, Finite Element Analysis (FEA) was conducted to replicate the actual mechanical phenomenon occurring in Nitinol. Models were generated for simulating the superelastic and plastic behaviors, and were validated against actual experimental data. The ability to model the complex mechanical response of Nitinol will enable exploration into the sensitivity of material response to phase volumes, material composition, and strain rate. Robust models of these phenomenal also provide the potential for tailoring in-silico the microstructure required for specified desired macroscopic material properties.

Abstract: Icing, the phenomenon of the formation and accumulation of ice or frost on a surface due to the solidification of water droplets at low temperature can be undesirable in many applications. Surface icing can lead to increased energy consumption in aerospace and automotive applications due to increased aerodynamic drag. Ice formation can also present a mechanical and electrical safety hazard, and as such significant work has been done to produce surfaces with anti-icing properties through surface modification to decrease ice formation and adhesion to surfaces. One route toward the generation of anti-icing surfaces is through laser surface processing. Laser micro/nanostructuring of surfaces has advanced greatly in recent years due to advancements in laser source technology and reduction in capital costs for ultrafast femtosecond pulsed machining lasers. Laser material processing offers a rapid, scalable, and non-contact method for fabricating large area anti-icing surfaces. In this work, the production of anti-icing surfaces using femtosecond laser micro-and nanostructuring on aluminum alloy 7075 surfaces was examined. With an aim to optimize the anti-icing properties of the substrates, laser parameters such as pulse energy, repetition rate and beam scanning speed were varied to produce highly defined microstructures on the aluminum surface.Various functional properties such as hydrophobicity and surface roughness are examined.

Abstract: In this research work, brass (Cu - 37.2 wt% Zn) and Cu (99.9 wt%) wires having diameters of 200 μm were thermally oxidized in N₂ containing 5% O₂, at a flow rate of 200 sccm and in the ambient atmosphere respectively, to support the growth of nanowires. The oxidation temperature was varied from 300 to 600 °C and the as-grown nanowires were characterized by field emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray (EDX) spectroscope, and transmission electron microscope (TEM). Results show that ZnO and CuO nanowires are formed on brass and Cu wires, respectively. The ZnO nanowires are branched and CuO nanowires are straight with tapered morphology. ZnO nanowires having hexagonal wurtzite structure grow along the <1 1 0> directions whereas, CuO nanowires have monoclinic structure. A diffusion based stress induced model is proposed to explain the growth mechanism of the nanowires. Thermal oxidation process is a suitable platform for synthesizing ZnO and CuO nanowires, which can be used in in-situ device fabrication.

Abstract: Additive Manufacturing (AM) using Powder-Bed Fusion Laser-Beam (PBF-LB) has great potential; however, it has challenges due to its sensitivity to the process parameters [1]. The availability of big data generated in AM facilitates the employment of Machine Learning (ML) tools to understand the process and have a predictive control over the production. An intelligent system like this can thus reduce material wastage and energy cost while increasing a plant’s product quality and throughput. Time-series summary statistics (like mean and variance) can discard valuable discriminatory signatures embedded in raw sensor data. Therefore, special ML time-series classification (TSC) tools that can extract and utilise these signatures from the raw data are much more effective for a task like porosity prediction [1]. However, the data employed in [1] pertains to products with artificially designed pores or gaps. This study focuses on naturally occurring pores, rarer, and evaluates k-Nearest Neighbour (k-NN) with Dynamic Time Warping (DTW) over real-world manufacturing data to classify the porosity of individual raster scans. We believe that natural pores have more diverse signatures than artificial pores, as each pore varies in characteristics (like size and morphology).