Beam shaping is considered a technology capable of dramatically improving quality and robustness of Laser Metal Fusion (LMF) processes. However, systematic investigations of its effects on melt-pool dynamics, temperature field and microstructure are still required. In this work, we propose an integrated approach combining a Computational Fluid Dynamics (CFD) model, in-situ temperature measurements and metallographic analysis to explore programmable ring beam profiles, ranging from Gaussian-dominant to ring-dominant configurations. This method, initially proposed on Ti-6Al-4V bead-on-plate tracks, validates melt-pool temperatures measured in-process by a dual-wavelength pyrometer against CFD predictions, which are in turn validated with metallographic cross-sections. Ring modes lowered peak temperature by up to 35 %, transforming deep-narrow pools (aspect ratio approximate to 0.9) into shallow-wide ones (approximate to 0.4). This suppressed humping at line energies >= 0.28 J mm-1, whereas lower energies produced only superficial melting. Simulations matched pyrometer data within 5 % whenever pool width equalled the pyrometers’ sensing spot; all tracks solidified into ultrafine alpha with retained beta, independent of beam mode. Therefore, the combination of in-situ, ex-situ and CFD tools offers a practical workflow for assisting data-driven process optimization and can be easily extended to other LMF processes, with its potential implementation in industrial Laser Powder Bed Fusion.

21-6-9 stainless steel manufactured by powder bed fusion (PBF-LB/M) is expected to be used for aerospace parts due to its high strength and elevated temperature durability, coupled with the possibility to manufacture complex shapes. Defects, such as pores and lack of fusion (LoF), can be formed in PBF-LB/M manufactured material, which can be detrimental to important dynamic mechanical properties like fatigue strength. However, hot isostatic pressing (HIP) has shown great potential in closing and healing such defects. In this study, an investigation of the effects of HIP treatment on the low-cycle fatigue (LCF) properties and microstructure of PBF-LB/M manufactured 21-6-9 material was performed. It was found that the effects of HIP treatment are similar to that of solution heat treatment regarding grain coarsening and grain sensitization. In addition, HIP successfully closed the pores, reducing the defect density. The stress relief heat-treated (SR) specimens exhibited lower LCF strength than wrought material, but after HIP treatment, LCF strength was equal to wrought material. The HIP treatment consequently improved the strain-controlled LCF strength but decreased the tensile strength and hardness around 30%. 

To manufacture almost fully dense components, electron beam powder bed fusion of Ti-6Al-4V is typically combined with post-heat treatment, such as hot isostatic pressing (HIP). The standard HIP treatment performed at 920°C and 100 MPa for 2 h results in coarsening of the microstructure and impacting the yield strength. A low-temperature HIP treatment performed at 800°C and 200 MPa for 2 h resulted in limited coarsening and comparable yield strength to as-built material. A coarser microstructure is detrimental to tensile properties. Tensile testing at different temperatures revealed that thermal activation of different slip systems could possibly affect the elongation behavior, demanding additional investigation. Performing in situ neutron time of flight diffraction during tensile testing provides data to analyze strain evolution and load partitioning in the crystal lattice, which includes the slip planes. A two-phase elastic–plastic self-consistent model has been used to analyze and compare the experimental results. The lattice strain evolution results indicated that the basal slip 0 0 0 2 was activated at 20°C while the pyramidal slip 1 0 1¯ 1 was first activated during loading at 350°C. Load partitioning results showed that the β phase endures higher stresses than the α phase in the plastic regime. 

Powder bed fusion laser beam (PBF-LB) is one of the most widespread and highly researched additive manufacturing (AM) methods, spanning multiple industries. Its feedstock material is metallic powder, where a conventional particle size range is 15–50 μm. The present study focuses on Ti-6Al-4V powder with a wider particle size distribution (15–90 μm). Two process themes are evaluated: one minimising porosity and one maximising build rate through a fast laser scanning speed. The effect of two hot isostatic pressing (HIP) heat treatments on mechanical properties, one below and one above the β-transus, are compared to those of as-built and stress relieved material. Room temperature impact toughness and tensile testing are used to compare the materials by determining UTS and Yield strength, elongation and reduction of area for the different process conditions and post build heat treatments. The minimal porosity theme reaches properties comparable to conventional manufacturing processes at all heat treatment temperatures (i.e., UTS >860 MPa, 0.2 % Yield >795 MPa). The high productivity theme treated below β-transus provides further improvement in overall reduction of area (>45 %) and elongation (>20 %) with respect to the minimal porosity theme, by showing a bi-modal microstructure that is the result of a recrystallisation process. This phenomenon is triggered by the closure of lack of fusion (LoF) defects via hot isostatic pressing, due to a higher dislocation density at the tip of these particular defects. Impact energy for this condition increases whilst hardness and texture become less pronounced. It is demonstrated that in those cases where a fast scanning speed creates LoF defects, those can assist in modifying microstructure during the consolidation process which has a positive effect on ductility.

Surface asperities play a leading role in determining the fatigue life of as-built Ti-6Al-4 V components manufactured by electron beam powder bed fusion (PBF-EB). Several roughness parameters are available to characterize the surface asperities This study focuses on identifying the surface roughness parameter that correlates best with fatigue life. To this end, several fatigue test specimens were manufactured using the PBF-EB process and utilizing different contour melting strategies, thus producing as-built surfaces with varying roughness. The focus variation microscopy technique was employed to obtain surface roughness parameters for the as-built surfaces. Selected specimens were characterized using x-ray computed tomography (XCT). Tomography can detect surface-connected features obscured by other parts of the surface that are not visible through optical microscopy. The fatigue life of all specimens was determined using four-point bend testing. Through regression model analysis, maximum pit height (Sv) was identified as the statistically significant roughness parameter with the best fit affecting fatigue life. The fracture zone was closely inspected based on the data collected through XCT prior to fatigue tests. This led to another estimate of the worst-case value for the statistically significant roughness parameter Sv. The Sv parameter values obtained from optical microscopy and XCT were used as the initial crack size in a crack growth model to predict fatigue life. It is observed that life estimates based solely on optical measurements of Sv can be overly optimistic, a situation that must be avoided in predictive design calculations.

Laser powder bed fusion (PBF-LB) is one of the most widespread additive manufacturing (AM) methods, spanning multiple industrialsectors such as medical, automotive and more recently aerospace. Current limitations to its large-scale adoption include low build rates,machining often required and consolidation via hot isostatic pressing (HIP). Productivity enhancement of PBF-LB has been investigated extensively and among the strategies adopted, that of combining high-speed parameters with HIP to achieve full density, has proven to beviable. This study puts forward a new approach for Ti-6Al-4V material, investigating if employing a wide particle size distribution (PSD)of the powder, with a range between 15 to 90μm, with a high layer thickness achieves comparable levels of bulk density, whilst improvingthe sustainability of the overall process and decreasing build times. If packing density can be improved by ensuring a more varied spreadof particle sizes, the thermal conductivity of the powder bed increases. Combination of small and large diameter particles would result in a reduction of the number of interparticle cavities upon powder spreading, therefore enhancing the contact and the efficiency of melting between neighbouring particles, upon laser heating. An EOS M290 machine was used to establish a processing window for the extendedPSD and increased layer thickness. Laser power, scanning velocity and hatch distance were varied to identify and exclude parametervalues that render extremes such as lack of fusion or keyholing defects. Single, multiple tracks and cubes were produced as part of a studythat aims to characterise the material’s response in terms of microstructure, defect density and hardness. It was possible to establish correspondence between tracks and cubes behaviour and isolate a design region that yielded minimal porosity.

The effect of defects and microstructure on the mechanical properties of Ti-6Al-4V welds produced by tungsten inert gas welding; plasma arc welding; electron beam welding; and laser beam welding was studied in the present work. The mechanical properties of different weld types were evaluated with respect to micro hardness; yield strength; ultimate tensile strength; ductility; and fatigue at room temperature and at elevated temperatures (200 °C and 250 °C). Metallographic investigation was carried out to characterize the microstructures of different weld types, and fractographic investigation was conducted to relate the effect of defects on fatigue performance. Electron and laser beam welding produced welds with finer microstructure, higher tensile ductility, and better fatigue performance than tungsten inert gas welding and plasma arc welding. Large pores, and pores located close to the specimen surface, were found to be most detrimental to fatigue life.

From an industrial standpoint, cost is of one of the most important drivers for utilizing new technologies such as additive manufacturing (AM). Other important drivers for why AM can be an advantageous technology for component manufacturing is decreased manufacturing lead time, rapid demonstration capability, freedom of design/geometry, advancing technology development, and not least sustainability in terms of both material utilization and improved part/system performance. In this chapter, six selected “case studies” are compiled, in which AM techniques have been used to manufacture components for actual applications. In some case studies, a comparison between the additive manufacturing route and the corresponding conventional manufacturing route is also included.

This paper explores the effects of varying process parameters (i.e., laser power, laser scanning speed, hatch distance) on the characteristics of single tracks, triple tracks and cubes, in order to provide answers to Research Question 1. A full factorial DoE approach was adopted to produce the experiments. Data was extracted from different sources to find correlations between tracks and multilayer geometries. A digital microscope was used to obtain height profiles, whilst polished/etched cross sections cut parallel to the build direction were imaged using a LOM to obtain measurements of track height, width, melt pool depth, subsurface porosity and residual defect content in cubes. Track height was found to exceed the recoated value of 70μm for both single and triple tracks. The width of single tracks showed a clear upward trend when displayed against VED, showing a lateral expansion as energy input increased. It was also revealed that single tracks expand laterally as they grow above the substrate, indicating swelling. The melt pool depth showed a steady upward trend when plotted against LED, though less systematic than track width. A martensitic microstructure was detected, with hierarchical α’ needles growing at prescribed crystallographic directions within vertical prior-β grains. A large portion of spatter particles and unmelted powder granules were detected on the substrate and tracks, with many accumulating on the side of the tracks forming a denudation zone.