Laser-arc hybrid welding (LAHW) is more often used in shipbuilding and oil and gas industries in recent years. Its popularity arises due to many advantages compared to conventional arc welding processes. The laser beam source is used to achieve much higher penetration depths. By adding filler wire to the process area, by means of an arc source, the mechanical properties can be improved, e.g. higher toughness at low temperatures. Therefore, LAHW is a perspective process for low-temperature service. Applicability of LAHW is under concern due to process stability and mechanical properties related to heterogeneous filler wire distribution through the whole weld metal in deep and narrow joints. This can cause reduced mechanical properties in the weld root as well as problems with solidification cracking. The fast cooling rate in the root provides hard and brittle microconstituents lowering toughness at low temperatures. Numerical simulations and experimental observations showed that an increase in heat input from the laser beam is an effective way to reduce the cooling rate, which is also possible by applying preheating.

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Accelerated bone grow (osseointegration) can be achieved by modifying the surface of medical implants. For this purpose, pulsed lasers can be used to successfully texture such beneficial surfaces on titanium, e.g. a BioHelix™ structure. This surface typically includes ridges and droplets with a size range between 1 and 20 μm. This paper presents the results of an experimental program where a range of laser parameters was used to create different surface textures on titanium substrates, using pulsed laser spattering. The resultant surfaces are analysed by scanning electron microscope and X-ray Micro Computer Tomography. It is shown that optimisation of the laser parameters results in a robust process which produces a surface that has proven to be beneficial for osseointegration. The results are also deeper analysed, explaining how different types of surface are created by the laser-material interaction under different conditions. Further, droplet flight distances and the formation of the spongeous nano-scale surface that characterizes the surface structure depends on very fast cooling and is also evaluated.

Pulsed lasers can be used to modify the surface of medical implants in order to accelerate bone growth (osseointegration). A surface covered in attached droplets with diameters between 1 and 20 μm is a beneficial surface for rapid osseointegration. This paper presents the results of an experimental program in which a broad range of laser parameters and different atmospheres were used to create different surface textures on titanium substrates, including the desired "attached droplet" topology. The resulting surfaces were analyzed by scanning electron microscopy and micro-computer tomography. The paper explains how different types of surfaces are created by the laser-material interaction under different conditions and focus characteristics. It is shown that optimization of the laser parameters results in a robust process, which produces a surface that is fundamentally different from those created by nonlaser methods.

Additive Manufacturing provides many opportunities to design and manufacture parts that are difficult or not possible to produce with conventional methods. In Selective Laser Melting (SLM) in powder bed fusion (PBF), melt pool dynamics and stability is dependent on a large number of factors, e.g. laser power output, power density, travel speed, reflectivity of powder bed, rapid heating and vaporization. Since travel speeds are often very fast and the laser interaction zone is small, the physical events become difficult to predict but also to observe. This work aims to describe the formation and geometrical characteristics of the vaporization zone during processing. Using a combination of theoretical descriptions, resulting material structures and a comprehensive analysis of high-speed images of the processing zone for different heat inputs and travel speeds, explanations for the dynamic melt pool behaviour are derived. The melting and pressures from processing involved moves powder particles next to it, changing the conditions for neighbouring tracks due to lack of material. These findings can provide a basis for creating more efficient and stable SLM processing, with fewer imperfections.

During welding, wire consumables can essentially contribute to the resulting microstructures and mechanical properties. In order to maintain high toughness even for high strength steel, certain microstructures are desirable, particularly acicular ferrite. An efficient, controllable test method was developed during which the wire is molten and experiences a thermal cycle by a shaped laser pulse, or a sequence of pulses, which shall resemble continuous laser-arc hybrid welding or narrow gap multi-layer laser welding. Different thermal cycles and wire chemistries have led to manifold microstructures. The morphology of the microstructures can become complex. Therefore, more detailed characterization of essential morphology aspects was carried out, to distinguish different results. The thermal cycles from quenching have led to shorter, thicker laths with more random orientation. The latter can be favourable for high toughness. Short reheating cycles by about 200 K/s caused finer, longer and more parallel laths, as for bainite, in varying size of blocks. Other aspects considered were grain boundary ferrite and non-metallic inclusions. Systematic variation of the thermal cycle by the testing method along with systematic description of microstructure morphology in more detail is a promising method to identify and optimize favoured routes for wire chemistry and welding techniques.

Porosity and solidification cracking in joining of thick sections are very common issues in deep penetration keyhole laser-arc hybrid welding (LAHW). In the present work, 45 mm thick high strength steel was joined by a double-sided technique. With combined use of fast welding speeds and larger air gap between plates, higher amount of porosity was found because of the dynamic behavior of the keyhole walls. Solidification cracking formed at the centerline in the bottom of the weld due to high-depth-to-width geometrical ratio. Numerical simulations have been performed and showed very high cooling rate and stresses occurred in the root of the deep welds, which corresponds with higher cracking tendency.

A robust method is introduced to simulate and study the filler wire metallurgy for controlled cooling conditions after melting, enabling efficient mapping with prompt analysis of trends. Proposed is a reduced, though representative, process with more controllable conditions. Short lengths of filler wires are preplaced in a cavity, drilled into a base metal sheet. Irradiation by a pulsed laser beam melts the wire to generate a sample nugget. Pulse shaping influences the cooling rate, granting the ability to tailor weldament microstructures. The method is demonstrated for S1100QL steel and undermatched filler wire, to obtain high toughness for processes like laser-arc hybrid welding, where a representative thermal cycle is needed. For high toughness, a controlled amount of acicular ferrite and, in turn, nonmetallic inclusions is desirable. This “snapshot” method has revealed a characteristic histogram of inclusion sizes, for different pulse shapes. Additional information on the thermal cycle can be acquired by employing thermocouples, a pyrometer, or advanced methods like high speed imaging or modeling. The method offers a wide spectrum of variants and applications.

The concept using an off-axis filler wire during laser welding is introduced here in order to provide added process robustness considering gap width variations. Its stability is investigated with respect to gap width, welding speeds and powers. Geometry of the welds is analysed by tracing of weld cap edges and joint cross sections, connecting trends to weld parameters. High speed imaging and streak images are used to further study and describe sequences of events, including undercut formation. Formation of imperfections are found to be mainly correlated to wire feed position variations at the surface due to irregular melting of the wire tip.

Many heavy industrial applications, e.g. shipbuilding and offshore, rely on thick-section, high-quality welds. Unfortunately, traditional arc-based techniques are often found wanting due to a limited penetration depth and excessive heat-affected zone. The former is typically solved by having a wide groove filled by multiple weld passes, which is both costly and time consuming. Other processes such as autonomous laser or electron beams can join thick materials, but have disadvantages such as increased hardness and solidification cracks inside the welds. A promising in-between technique to join thick sheets is narrow gap multi layer laser welding (NGMLW), using less filler material while also offering more control of weld properties. This technique is often used with laser scanning optics and cold wire, or a defocused laser and electrically heated wire. This paper investigates the limitations of the latter during NGMLW, mainly using high-speed imaging to directly observe and explain process behavior. Increased deposition rates are wanted, but heating also consequently needs to be increased for proper bead fusion. Arc occurrences are found to be the cause of instabilities. They are observed occasionally even at low voltages, but more frequently at higher outputs, and then are also more disruptive to the process.