In this work, the effect of pulsed laser used during the powder bed fusion (L-PBF) additive manufacturing (AM) process on Inconel 718 (IN718) material properties has been investigated. Argon gas ...atomised (AGA) IN718 powder is characterised in terms of flow, density, particle size distribution and morphology. Powder shows mostly spherical morphology with Hausner ratio of 1.17 indicating good flow characteristics. Density optimisation trials are carried out by varying laser power and exposure time. Fabricated samples are characterised in terms of porosity by area fraction analysis using light microscopy and volume fraction analysis using X-ray microcomputed tomography (micro-CT). Minimum porosity of 0.16% is achieved for laser power of 200 W and exposure time of 110 μs Microstructural analysis using the Electron Backscatter Diffraction (EBSD) technique shows limited columnar grain structure in the Z direction and more equiaxed type grains in the XY direction (normal to the Z direction). Tensile test results show 754 MPa yield strength, 1070 MPa ultimate tensile strength and ~24% elongation. Finally, hole drilling residual stress measurements show increase from ~0 MPa to over 450 MPa in tensile stress up to a depth of 1 mm from the top surface of the as-build L-PBF IN718 sample. It has been found that laser pulsing produces higher homogeneity in grain structure and better mechanical properties than that by the continuous laser method.
The powder's characteristics and its purity can greatly influence the properties of nickel (Ni)-base superalloys parts produced by near net-shape powder metallurgy hot isostatic pressing (NNS PM HIP) ...manufacturing process. In this study, Inconel 625 (IN625) powders produced using four different atomisation routes, argon, nitrogen, plasma and water atomisation (AGA, NGA, PA, WA, respectively) were investigated. The first section of this study is focused on the determination of powder characteristics which includes chemical composition, particle size distribution (PSD), tap density and powder's cross-section analysis, whereas the second section is about hot isostatic pressing (HIPping) of the four powder types and to assess the impact of the powder characteristics on the microstructure-property development after HIPping. To gain an understanding of the surface chemistry of the powders, X-ray photoelectron spectroscopy (XPS) analysis were carried out on the surface of the four powders. The latter analysis highlighted fundamental differences on the powder's surface, especially the differences in the surface and near-surface distribution of the alloying elements i.e. C, O, Cr, Mo and Nb present in the alloy chemistry. The micrographs of the four IN625 hot isostatically pressed (HIPped) powders revealed a fully dense microstructure with the presence of prior particle boundaries (PPBs). The atomisation route greatly impacted the nature and amount of PPBs, as well as on the fractions and sizes of oxides, carbides, oxycarbides and oxycarbonitrides precipitates. WA showed the most severe presence of PPBs, followed by NGA, AGA and lastly PA. The powder quality has a greater impact on the mechanical properties of as-HIPped materials, especially on ductility. Overall, PA HIPped IN625 possessed the optimum balance between tensile strength, ductility and Charpy impact properties once compared to the others and match the properties to wrought IN625 material.
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The aim of this work is to determine the impact of post-thermal treatments on the mechanical properties and microstructure of alloy 718 superalloy manufactured through modulated laser powder bed ...fusion. Three post-thermal treatments at 980 °C and 1200 °C with and without hot isostatic pressing are utilised, followed by standard ageing procedure. The tensile mechanical properties, microstructure, crystallography, morphology, fracture impact and hardness after each heat treatment are determined. It has been found that the heat treatment procedure at 980 °C significantly affects the tensile properties while leading to no change in grain size or orientation, and formation of twined grains. A temperature of 1200 °C with and without pressure causes considerable grain growth in comparison with the as-built and 980 conditions and significant formation of twinned grains. Hot isostatic pressing was found to produce the tensile mechanical properties close to those of wrought alloy 718.
In this work, pure Nb processed by Powder Metallurgy Hot Isostatic Pressing (PM HIP) was investigated as a potential alternative to C-103 Nb-based alloy for the manufacture of near-net-shape thruster ...combustion chambers. Three Nb powders with varied particle size range (fine, mid-range and coarse) and C-103 powder were investigated to understand the differences in particle size distribution (PSD), morphology and oxygen (O) content present in the alloy chemistry. The as-HIPed microstructures of pure Nb and C-103 are characterised by a near to fully dense microstructure and the absence of PPBs. Microstructural analyses performed on pure Nb highlighted the influence of particle size on the average as-HIPed grain size. Additionally, it was observed that O content plays a crucial role in the microhardness of pure Nb. Tensile tests performed on Nb mid-range and on Nb mid-range sieved showed that a simple sieve operation was effective in increasing the strength of the material while maintaining good levels of elongation. Alternatively, it was also demonstrated that pure Nb powder heat treatment can be regarded as an effective way to increase the O levels in pure Nb powders as witnessed by the high hardness levels. On the other hand, as-HIPed C-103 powder showed superior tensile properties if compared to the minimum specifications for wrought C-103. Finally, to summarise, the work performed on pure Nb, a simple structure-property relation model was developed to predict the YS of pure Nb based on the O levels and grain size of the as-HIPed microstructure.
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•PM HIP was successfully used to consolidate pure Nb and C-103 with absence of PPBs.•Powder characteristics play a crucial role in the as-HIP properties of pure Nb.•Oxygen levels strongly affect the mechanical properties of as-HIPed Nb.•HIPed C-103 showed superior tensile properties if compared to wrought C-103.
The cyclic dynamic loading behaviour of a multilayer TiAlSiN coating on M2 steel was systematically investigated using repetitive nano-impact over a wide range of impact load. Its behaviour was ...compared with a monolayer TiN on the same substrate. When the load was increased to 10mN and 30mN for the TiN and TiAlSiN coatings, respectively, cracks started to appear during the tests demonstrated as depth steps in the impact depth curves. The improved crack resistance of TiAlSiN coating is consistent with its higher H/Er and H3/Er2 measured by nanoindentation. The impact footprints were studied from both top-view and cross-sectional view using a focused ion beam microscope and SEM. Spallation was observed in both coatings at higher impact loads. TiAlSiN coating shows much less spallation due to its multilayer structure. The cross-sectional study discovered that the cracks were initiated within the coating. A simple model has been used to study the power law relationship between the impact volume loss and the impact velocity.
► A systematic study of the effect of nano-impact force. ► FIB/SEM was used to study the cross-sectional and top views of the impact footprints. ► At low loads, TiAlSiN showed improved crack resistance consistent with its higher H/Er and H3/Er2. ► At high loads, TiAlSiN showed much less spallation due to its multilayer structure. ► A simple model to study the power law relationship between the volume loss and the velocity.
•Additive manufacturing enables the design of the new generation of heat exchangers.•Topological optimisation and CFD modelling improve the performance of heat exchangers.•Additively manufactured ...heat exchangers exhibit superior thermal properties.•Material selection can enhance the performance of heat exchangers.
The current review is mainly focused on exploring Additive Manufacturing (AM) methods suitable for the fabrication of complex-shaped compact Heat Exchangers (HXs) used in the aerospace industry. The introduction of Additive Manufacturing technologies, thanks to the freedom of design and the ability to produce topologically optimised complex parts, aims at the production of high-efficiency Heat Exchangers. These new Heat Exchangers are characterised by very thin features and a substantial reduction in the weight of the parts compared to the products conventionally manufactured, maintaining a leak-proof structure and excellent mechanical properties. The current L-PBF systems along with software packages are not yet fully ready for the creation of thin leak-proof features needed for highly efficient complex-shaped compact Heat Exchangers and most of the studies in the literature are in the initial development stages. This literature review is covering the current advanced manufacturing technologies which can be employed to manufacture the new generation of compact Heat Exchangers, with particular reference to the Laser-Powder Bed Fusion. The advantages and the current challenges of the Additive Manufacturing processes are described. Furthermore, the state-of-art of topological optimisation and CFD analysis as design tools to support the production of additively manufactured were critically analysed. Finally, new criteria of how to down-select compact Heat Exchanger materials for Additive Manufacturing in the aerospace industrial sector are presented, with particular attention to Aluminium alloys.
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•PM HIP was successfully employed to consolidate IN625-based metal matrix composites.•Increasing ceramic reinforcement contributed to an improvement in wear properties.•IN625-10v%SiC ...showed lower %EL, YS and absorbed energy if compared to IN625.•Mechanical seals were successfully manufactured using NNS PM HIP technique.
In this work, near-net-shape powder metallurgy hot isostatic pressing (NNS PM HIP) of Ni-base metal matrix composite (Ni-MMC) was developed to improve the hardness and wear properties of turbopumps mechanical seals. Silicon carbide (SiC) and titanium diboride (TiB2) fine powders were used as reinforcements with different ratios to improve the hardness and consequently the tribological properties of the developed Ni-MMC material. Powder characterisation was performed on the blended powders to check the homogeneity of the mixed powders. The hot isostatically pressed (HIPed) Ni-MMC microstructures were analysed using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. The HIPed material showed a fully dense microstructure with a continuous network of ceramic reinforcement particles at the prior particle boundaries (PPBs). Furthermore, microhardness tests were performed on IN625, IN625-SiC and IN625-TiB2 to understand the impact of the reinforcement on the microhardness. It was demonstrated that the volume percentage of ceramic reinforcement in the IN625 matrix plays a crucial role in achieving higher hardness by increasing the fraction of hard phases appearing in the microstructure of the developed Ni-MMC material. The final part of the work focuses on the canister design and manufacture of a near-net-shape (NNS) mechanical gas seal using IN625 based MMC to demonstrate the feasibility of manufacturing mechanical seals through the NNS PM HIP technique. Overall, IN625 based MMCs resulted in a drastic improvement in tribological properties if compared to the base material. Furthermore, the employment of the PM HIP consolidation technique resulted in a fully dense and homogeneous microstructure, highlighting the potentials of PM HIP in the generation of novel composite materials.
Making laser powder bed fusion (L-PBF) additive manufacturing process sustainable requires effective powder recycling. Recycling of Ti6Al4V powder in L-PBF can lead to powder oxidation, however, such ...impact on laser-matter interactions, process, and defect dynamics during L-PBF are not well understood. This study reveals and quantifies the effects of processing Ti6Al4V powders with low (0.12 wt%) and high (0.40 wt%) oxygen content during multilayer thin-wall L-PBF using in situ high speed synchrotron X-ray imaging. Our results reveal that high oxygen content Ti6Al4V powder can reduce melt ejections, surface roughness, and defect population in the built parts. With increasing oxygen content in the part, there is an increase in microhardness due to solid solution strengthening and no significant change in the microstructure is evident.
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•Oxidised Ti6Al4V powder (0.40 wt% oxygen) has a lower laser absorptivity than the virgin powder.•Oxides in the melt pool could reduce melt pool instabilities and droplet spatter, and improve processability.•Laser powder bed fusion of oxidised powder reduces surface roughness and porosity, enhancing printability of Ti6Al4V.
Oxide films, 7-10 µm thick, were produced on commercially pure titanium by plasma electrolytic oxidation in a sodium orthophosphate electrolyte using a pulsed unipolar current with frequency (f) and ...duty cycle (δ) varying within f = 0.1-10 kHz and δ = 0.8-0.2, respectively. The coatings comprised a mixture of an amorphous phase with nanocrystalline anatase and rutile phases, where the relative rutile content range was 17-25 wt%. Incorporation of phosphorus from the electrolyte into the coating in the form of PO
2
-
, PO
3
2-
and PO
4
3-
, as demonstrated by EDX and FT-IR analyses, contributed to the formation of the amorphous phase. Residual stresses associated with the crystalline coating phase constituents were evaluated using the X-ray diffraction sin
2
ψ method. It was found that, depending on the treatment parameters, internal direct and shear stresses in anatase ranged from-205 (±17) to-431 (±27) MPa and from-98 (±6) to-145 (±10) MPa, respectively, whereas the rutile structure is comparatively stress-free.
Laser powder bed fusion (L‐PBF) is one of the most widely used additive manufacturing techniques for fabrication of components with complex geometries for various industrial applications including ...aerospace, medical and automotive. The unconsumed powder after part manufacturing is often recovered and recycled to improve process efficiency. However, some of the particles in the recycled powder can have different physical and chemical properties from those in the virgin powder owing to their exposure to the complex environment during the manufacturing process. In addition, some contaminants can be introduced in the recycled powder due to poor process control. A number of studies have been published in the past few years revealing the effects of powder recycling on the build properties. The present work aims to highlight the key phenomena during the manufacturing process that caused degradation to the recycled powder. Further to this, some comments, gaps and areas that deserve further detailed studies are also highlighted.
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