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.

Ti-6Al-4 V finds application in the fan and compressor modules of gas turbine engines due to its high specific strength. Ti-6Al-4 V components manufactured using one of the additive manufacturing (AM) techniques, the electron beam powder bed fusion (PBF-EB) process, has been an active area of research in the past decade. The fatigue life of such PBF-EB built Ti-6Al-4 V components is improved by hot isostatic pressing (HIP) treatment typically performed at about 920 ˚C. The HIP treatment at 920 ˚C results in coarsening of α laths and reduced static strength and therefore a low-temperature HIP treatment is performed at about 800 ˚C to limit the impact on static mechanical properties. In the present work, the low cycle fatigue and fatigue crack growth behavior of such a modified HIP (low-temperature HIP) treated material is assessed and compared with the respective data for the standard HIP-treated material. The modified HIP-treated material has fatigue performance comparable to the standard HIP-treated material. This work suggests that the modified HIP treatment improves the static mechanical properties without significantly impacting the fatigue performance. Also, fatigue life predictions were made from the measured defect size at the crack initiation site using a linear elastic fracture mechanics tool. The life predictions show good agreement with the experimental values for defects greater than the intrinsic crack length, where life is well predicted by large-crack growth methodology. 

The idea of adding material only where needed to manufacturesolid metallic high-performing components is intriguing andone of the main reasons for the great interest in additivemanufacturing (AM) around the world. Especially whensustainability comes into play, as in recent times more thanever, AM technology is most appropriate since it enables almostfull material utilization with minimal waste. From an economicstandpoint, this becomes particularly advantageous for moreexpensive materials such as superalloys and titanium alloys.However, the route of going from a CAD drawing of a part to anadditively manufactured final component that is qualified and inserial production involves numerous challenges. The intentionof this book is to shed light on and explain some of theassociated challenges beginning with the importance of thestarting material and how it is manufactured, i.e., wire orpowder, continuing into description of the conventional andPederson, R., Andersson, J., & Joshi, S. (2023). Additive manufacturing of high-performance metallic materials. Elsevier.Created from vast-ebooks on 2024-01-08 16:09:20. Copyright © 2023. Elsevier. All rights reserved.most commonly used AM processes, followed by postbuildtreatments and nondestructive evaluations, to eventuallyproduce the final part with mechanical performance consistentwith the application requirements. In the end, selected realindustry examples of AM parts for actual applications will bepresented

Processing of metallic materials by Laser Directed Energy Deposition (LDED), with Wire (w) as the feedstock, enables the manufacturing of high precision, near-net shape components that require minimal postmachining, without compromising the performance. L-DEDw has also shown the capability to add intricate features on large structures, which makes it an attractive fabrication technique for aerospace application. The key merits of wire as the feedstock when compared to powder include; higher deposition rates, low porosity in the deposited material, excellent surface finish, and, ∼ 100% utilization of the feedstock. However, despite the attractive merits, the difference in solidification rates during L-DEDw processing when compared to other fabrication routes could induce high residual stresses, which can be detrimental to the integrity of cracksensitive alloys. Additionally, there exists an inherent challenge during L-DEDw fabrication, where controlling the process variables to ensure stable deposition conditions becomes essential to achieve repeatable, and desired results. The recent advancements in the area of monitoring and control systems, and their integration with L-DEDw processing, have enabled to overcome the processing instability related challenges. Furthermore, different L-DEDw processing strategies for alleviating residual stresses (tensile) accumulation in the deposits are discussed, which could enable defectfree, high-performance component fabrication. Although the utilization of L-DEDw for processing diverse alloy systems has been explored in the literature, the current chapter's scope is restricted to L-DEDw processing of Nickel-based and Titanium-based alloys, which are often utilized in the aeroengine. This work aims to provide a holistic perspective and shed light on the state-of-the-art, recent developments, sustainability aspects and future directions for L-DEDw processed, highperformance Ni-based and Ti-based alloys.

Atom probe tomography (APT) was utilized to supplement scanning electron microscopy (SEM) characterizationof a precipitation strengthening nickel-based superalloy, Alloy 247LC, processed by laser powder bed fusion (LPBF). It was observed that the material in the as-built condition had a relatively high strength. Using both SEMand APT, it was concluded that the high strength was not attributed to the typical precipitation strengtheningeffect of γ’. In the absence of γ’ it could be reasonably inferred that the numerous black dots observed in thecells/grains with SEM were dislocations and as such should be contributing significantly to the strengthening.Thus, the current investigation demonstrated that relatively high strengthening can be attained in L-PBF even inthe absence of precipitated γ’. Even though γ’ was not precipitated, the APT analysis displayed a nanometer scalepartitioning of Cr that could be contributing to the strengthening. After heat-treatment, γ’ was precipitated and itdemonstrated the expected high strengthening behavior. Al, Ta and Ti partitioned to γ’. The strong partitioningof Ta in γ’ is indicative that the element, together with Al and Ti, was contributing to the strain-age crackingoccurring during heat-treatment. Cr, Mo and Co partitioned to the matrix γ phase. Hf, Ta, Ti and W were found inthe carbides corroborating previous reports that they are MC.