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%. 

Alloy 718 retains its mechanical properties at elevated temperatures. Furthermore, its weldability contributes to compatibility with additive manufacturing (AM) techniques such as powder bed fusion-laser beam (PBF-LB). In this study, various heat treatments, including stress relief, hot isostatic pressing (HIP), solution treatment, and aging, were applied to Alloy 718 manufactured by PBF-LB, and the stress-rupture life was investigated, as well as the effect of V-notch on its properties. The heat-treated materials exhibited longer stress-rupture life compared to the as-built material. However, significant anisotropy was observed due to the needle-like δ phase precipitated along the grain boundaries. Furthermore, material subjected to a different heat treatment conditions without δ phase precipitates promoted isotropic behavior. At the same time, notched specimens showed anisotropic stress-rupture life due to the interaction between crystallographic texture and stress state at the V-notch root.  

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.

The use of additive manufacturing, especially laser beam powder bed fusion (PBF-LB), is becoming increasingly popular for producing super duplex stainless steel (SDSS) parts. However, the rapid cooling rate, complex thermal cycles, and eventual nitrogen loss during processing can result in an unbalanced ferritic microstructure and the formation of intermetallics; hence, solution annealing heat treatment following the PBF-LB process is required. The present study aims to compare the as-built and heat-treated microstructures of 2507 SDSS manufactured via PBF-LB with varying solution annealing times. Computational thermodynamics were used to establish the solution annealing temperature (CALPHAD) and time (DICTRA). The as-built microstructure comprises predominantly ferrite, intragranular chromium nitrides with a small amount of grain boundary, and intragranular austenite. The experimental results showed the formation of a balanced two-phase ferrite and austenite microstructure within 2 min of solution annealing time, in good alignment with the DICTRA calculations. This microstructural balance was maintained with increased solution annealing time up to 60 min. The solution-annealed microstructure revealed the dissolution of intragranular chromium nitrides, the growth of grain boundary austenite, and the formation of intragranular and Widmanstätten austenite. This study exemplifies how computational thermodynamics can be successfully used in the design of solution annealing heat treatment for 2507 SDSS manufactured via the PBF-LB process.

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.

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