Aerospace is a key market driver for the advancement of additive manufacturing (AM) due to the huge demands in high-mix low-volume production of high-value parts, integrated complex part geometries ...and simplified fabrication workflow. Rapid and significant progress has been made in the laser additive manufacturing (LAM) of aeroengine materials, including the advanced high-strength steels, nickel-based superalloys and titanium-based alloys. Despite the extensive investigation of these three families of materials by the research community, there is a lack of comprehensive review on LAM of high strength steels, and existing gaps in published reviews on Ti-based alloys and Ni-based superalloys. Furthermore, although emerging materials such as high/medium entropy alloys and heterostructured materials exhibit promising mechanical performance, rigorous characterization, testing, qualification, and certification are still required before actual application in engine parts. Thus, it is still important and relevant to have a deep understanding on the relationship between process parameters – microstructures – mechanical properties in these widely used aeroengine materials, to drive the development of superior high-value alloys. This review aims to provide a critical and in-depth evaluation of laser powder bed fusion (LPBF) and laser directed energy deposition (LDED) technologies of the mentioned aeroengine materials. The review will summarize the material properties, performance envelops and outlines the research gaps of these aeroengine materials. Furthermore, perspectives on research opportunities, materials development, and new R&D approaches of LAM for the aeroengine materials are also highlighted.
This work comprehensively reviews the recent development status of the laser additive manufacturing (LAM) process and key aeroengine materials in terms of process window, microstructure characteristics, mechanical properties, and their relationship (inner circle). On this basis, the perspectives on research opportunities, materials development and new R&D approaches for the aerospace components are also highlighted (outer circle). Display omitted
•Summarized correlations among process, microstructure and mechanical properties.•Outlined strength and weakness of laser additive manufacturing key aeroengine materials.•Elucidated Advancement of new laser additive manufacturing technologies.•Highlighted future directions of laser additive manufacturing aeroengine materials.
High-performance grade 300 maraging steels were fabricated by selective laser melting (SLM) and different heat treatments were applied for improving their mechanical properties. The microstructural ...evolutions, nanoprecipitation behaviors and mechanical properties of the as-fabricated and heat-treated SLM parts were carefully characterized and analysed. The evolutions of the massive submicron sized cellular and elongated acicular microstructures are illustrated and theoretically explained. Nanoprecipitates triggered by intrinsic heat treatment and amorphous phases in as-fabricated specimens are observed by TEM. High-resolution TEM (HRTEM) images of the age hardened specimens clearly exhibit massive nanosized needle-shaped nanoprecipitates Ni3X (X=Ti, Al, Mo) and 50–60nm sized spherical core-shell structural nanoparticles embedded in amorphous matrix. XRD analyses reveal austenite reversion and probable phase transformations during heat treatments. The hardness and tensile strength of the as-fabricated and age-treated SLM specimens absolutely meet the standard wrought requirements. Furthermore, the lost ductility after aging can be compensated by preposed solution treatments. Relationships between massive nanoprecipitates and dramatically improved mechanical performances of age hardened specimens are elaborately analysed and perfectly explained by Orowan mechanism. This study demonstrates that high-performance grade 300 maraging steels, which is comparable to the standard wrought levels, can be produced by SLM additive manufacturing.
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•Evolutions of the typical SLMed microstructures are illustrated and theoretically explained.•Precipitation behavior and phase transformation of SLMed maraging steel are characterized by TEM and XRD.•Significant improvement of strength after solution and aging treatment was evaluated and explained.•Relationships between massive nanoprecipitates and improved mechanical performances are elucidated.
A nearly fully dense grade 300 maraging steel was fabricated by selective laser melting (SLM) additive manufacturing with optimum laser parameters. Different heat treatments were elaborately applied ...based on the detected phase transformation temperatures. Microstructures, precipitation characteristics, residual stress and properties of the as-fabricated and heat-treated SLM parts were systematically characterized and analyzed. The observed submicron grain size (0.31 μm on average) suggests an extremely high cooling rate up to 10
7
K/s. Massive needle-shaped nanoprecipitates Ni
3
X (X = Ti, Al, Mo) are clearly present in the martensitic matrix, which accounts for the age hardening. The interfacial relations between the precipitate and matrix are revealed by electron microscopy and illustrated in detail. Strengthening mechanism is explained by Orowan bowing mechanism and coherency strain hardening. Building orientation-based mechanical anisotropy, caused by 'layer-wise effect', is also investigated in as-fabricated and heat-treated specimens. The findings reveal that heat treatments not only induce strengthening, but also significantly relieve the residual stress and slightly eliminate the mechanical anisotropy. In addition, comprehensive performance in terms of Charpy impact test, tribological performance, as well as corrosion resistance of the as-fabricated and heat-treated parts are characterized and systematically investigated in comparison with traditionally produced maraging steels as guidance for industry applications.
•A new approach of processing W-Cu FGM by SLM additive manufacture is explored.•Effects of laser parameter on the performance of W-Cu FGM are investigated.•Intense Marangoni convection contributes to ...interfacial bonding.
A tungsten-copper functionally graded material was processed based on SLM additive manufacture despite encountering some difficulties from materials characters. The effect of laser parameter on the interfacial defects and bonding performance are evaluated. The SLM produced tungsten is in columnar structures with random orientation. Plenty of fine tungsten grains are present at the bonding region, owing to a high cooling rate incited by the underlying copper. A metallurgically bonded interface with a 50–80 μm inter-diffusion region is formed. The interfacial bonding mechanism, which associates with intense Marangoni convection at the interface, is revealed and discussed.
Selective laser melting (SLM) additive manufacturing of pure tungsten encounters nearly all intractable difficulties of SLM metals fields due to its intrinsic properties. The key factors, including ...powder characteristics, layer thickness, and laser parameters of SLM high density tungsten are elucidated and discussed in detail. The main parameters were designed from theoretical calculations prior to the SLM process and experimentally optimized. Pure tungsten products with a density of 19.01 g/cm
3
(98.50% theoretical density) were produced using SLM with the optimized processing parameters. A high density microstructure is formed without significant balling or macrocracks. The formation mechanisms for pores and the densification behaviors are systematically elucidated. Electron backscattered diffraction analysis confirms that the columnar grains stretch across several layers and parallel to the maximum temperature gradient, which can ensure good bonding between the layers. The mechanical properties of the SLM-produced tungsten are comparable to that produced by the conventional fabrication methods, with hardness values exceeding 460 HV
0.05
and an ultimate compressive strength of about 1 GPa. This finding offers new potential applications of refractory metals in additive manufacturing.
Additive manufacturing (AM) offers high-freedom in the design and processing of components with complex internal structures. In this work, a new injection mold with the self-supporting large cooling ...channel and tailored porous structures was designed to improve cooling efficiency and save AM build costs. The optimized internal supports suppressed the collapse and warpage of large channels, which improves the manufacturability and breaks the geometric constraints of laser powder bed fusion (LPBF). The formable diameter of self-supporting channels is significantly increased (≥20 mm). In comparison to the 8 mm normal-sized channel, the self-supporting 13 mm channel reduces the cooling time of more than 20%. Additionally, the porous diamond structure was designated in the assembly part of the mold to save the materials and build time. To tune the strength, a core-shell composite structure with solid shell surrounding inner porous structures is designed. The influence of the wall thickness on the mechanical property of the composite structure was explored, which guides the specific mold design. Finally, a mold with the above-mentioned novel design was successfully processed by LPBF, which substantiates the manufacturability of innovative design. This work also inspires other industrial applications of AM-processed components with improved performance and functionality.
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•Internal supports breaks the manufacturing constraints in LPBF large channel.•Self-supporting large cooling channels of mold increase cooling efficiency.•Tailored porous structures in the mold save build time and material costs.•A mold product with innovative design was produced by LPBF successfully.
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•Effect of Al3Sc, Al3(Sc,Zr) and Al3(Sc,Ti) on grain refinement efficiency was revealed.•Microstructure of Al-Mg-Sc, Al-Mg-Sc-Zr and Al-Mg-Sc-Ti alloys was systematically ...investigated.•Grain refinement efficiency and mechanism were elucidated.
In this study, the modification of 0.70 wt% ScH3alone did not substantially fine the grain and eliminate the hot-cracking of Al-Mg-Sc alloy, resulting in low strength of as-built material. In contrast, the 0.70 wt% ScH3 and 0.34 wt% ZrH2 modified Al-Mg alloy (hereafter denoted as Al-Mg-Sc-Zr1) was demonstrated to be an exceptionally effective inoculation for Al-Mg-Sc-Zr1 alloy, owing to the low lattice mismatch (0.4 %) between Al3(Sc,Zr) and α-Al. The considerable grain refinement was ascribed to the L12-Al3(Sc,Zr) nucleis, which efficiently promoted heterogeneous nucleants of α-Al grains, contributing to significant refined grain size. Consequently, the as-built Al-Mg-Sc-Zr1 alloy demonstrated outstanding tensile strength with sound elongation to fracture due to crack-free and fine grain strengthening. Additionally, compared with Al-Mg-Sc-Zr1 alloy, the further modification with more ScH3 and ZrH2 promoted substantial grain refinement via inoculation treatment of 1.15 wt% ScH3 + 0.55 wt% ZrH2. Moreover, the grain refinement effect of ScH3 and TiH2 modification was also studied and correlated to the resulted ultrafine equiaxed grains and performance. These results indicate that grain microstructure and mechanical properties of as-built Al alloys can be tailored by suitable inoculants which can be further employed to other engineering alloys.
The next-generation medical implants require locally customised biomechanical behaviour to echo the properties of hard tissues, making additive manufacturing (AM) an ideal route due to its superior ...manufacturing flexibility. AM of titanium alloys with designed porosity is the mainstream for artificial implants, which, however, hardly balance the strength-modulus combination. Here a martensitic TiNi biomaterial with low modulus and asymmetric mechanical behaviour that mimics human bones is explored. TiNi functionally graded lattice structure (FGLS) is bio-inspired by bone architecture and processed by AM. Bio-inspired FGLS shows much higher strength and ductility than the uniform lattice despite having an equivalent structural porosity. Post-process heat-treatments alter the microstructure and result in a multi-scale hierarchically strengthened behaviour in FGLS, offering one of the highest specific strengths (about 70 kN m/kg) among porous biometals, while keeping a low specific modulus and reasonable ductility. Besides, the deformation behaviour of FGLS is in-situ monitored, which, together with microscopic observations, reveal a multi-scale failure mechanism. The bio-inspired FGLS shows better biomechanical compatibility than the uniform lattice, including density, tension/compression asymmetry, modulus, and strength. The findings highlight the ability of AM in tailoring a modulus-strength-ductility trade-off through bio-inspired multi-scale hierarchical structure design.
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•Mechanically asymmetric martensitic TiNi echoes bone mechanical behaviour.•Bio-inspired functionally graded lattices can mimic natural bone properties.•Graded lattice achieves an ultrahigh specific strength among porous biometals.•A multi-scale hierarchical microstructure created unique properties.
The processing of pure tungsten encounters a substantial challenge due to its high melting point and intrinsic brittleness. Selective laser melting (SLM) technique is gaining popularity and offers an ...excellent processing approach for refractory metals. Herein, dense pure tungsten specimens are produced by optimizing SLM processing parameters. The mechanical property of the SLM‐produced tungsten with an ultimate compressive strength of about 1200 MPa, which is obviously superior to that reported in other literature, is achieved. The increased laser energy input is instrumental in raising density and surface roughness of tungsten specimens. Interestingly, additional remelting of processed layers during SLM improves the surface quality and the microstructure and achieves the highest relative density (98.4% ± 0.5%). After laser remelting, the surface roughness is reduced by 28% and a large number of fine grains are obtained. The flow of fluids caused by remelting plays a decisive role in the formation of fine grains and the defect level. Therefore, these findings offer a new insight into SLM of pure tungsten.
Selective laser melting (SLM) provides an excellent processing approach for pure tungsten. The densification of pure tungsten is promoted by optimizing SLM processing parameters. Additional remelting step improves surface quality and obtains high‐density tungsten with fine‐grain structure. Therefore, the technique offers a new insight into the manufacture of dense tungsten parts with few cracks.
The CoCrNi medium entropy alloy with different amounts of oxides was fabricated by laser aided additive manufacturing (LAAM). The cryogenic tensile properties and microstructure evolution during ...tensile deformation were investigated. For the Sample B with higher oxide content (2.03 vol%), the yield strength (YS), ultimate tensile strength (UTS) and elongation (El) were all inferior to those of the Sample A with much fewer oxides (0.47 vol%). The lower YS of Sample B was mainly attributed to the lower initial dislocation density. The oxides contributed slightly to the increase in YS, while reducing the El significantly. The El of Sample B was comparable at 298 K and 143 K, owing to the compensation effect from twin boundaries (TBs). Higher YS and UTS were obtained at 143 K for both samples. With decreasing temperature from 298 K to 143 K, the YS and UTS of Sample A increased almost linearly, whereas the El decreased. Though a large amount of TBs were formed during the tensile deformation, they were unevenly distributed among the grains near the fractured location. Under higher stress at cryogenic temperature, the interaction of grain boundaries with massive TBs caused micro-voids to initiate more readily along the grain boundaries, resulting in premature failure.
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•CoCrNi medium entropy alloys with different amount of oxides were fabricated by LAAM.•The effect of oxides on the cryogenic tensile properties of CoCrNi MEA was investigated.•Twin boundaries (TBs) were found distributed unevenly near the fracture position.•Lower elongation was attributed to the uneven-distributed TBs and internal pores.
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