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This work investigated laser aided additive manufacturing (LAAM) high-strength steel by leveraging the intrinsic tempering effect to facilitate the formation of high-fraction of metal carbides (e.g. M23C6 and M7C3) in the as-built samples. The intrinsic tempering effect contributes to a superior mechanical property than traditional manufacturing methods in as-built condition, promoting subsequent heat treatments (HTs) for excellent mechanical properties. The influence of HTs on the microstructures and mechanical properties were characterised in multi-scales. A large number of carbides are intrinsically formed due to the tempering effect during deposition. The high-density dislocations in the as-built sample facilitate the formation of massive nano-twins and carbides during HT. The HTed sample achieves a true tensile stress of about 1.81 GPa together with a true strain of about 21%, achieving an excellent strength-ductility combination compared to wide-range high-strength steels processed by additive manufacturing and conventional methods. The grain and twin boundaries strengthening, precipitation strengthening and dislocation strengthening contribute to the high strength, while the good ductility originates from twinning induced plasticity (TWIP) and transformation-induced plasticity (TRIP) effects, and high work-hardening rate, during deformation. The findings imply a potential way to develop AM-customised materials by fully understanding and utilising the IHT effect. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) enables the processing of heterogeneous materials with customised architectures to improve strength-ductility synergy. Herein, layerwise-heterostructured high-strength steels were processed by AM of two steel powders following the designed architectures. The fabricated high-strength steels with hierarchical heterogeneous characteristics at the layer, melt-pool and grain scales, exhibit good strength-ductility combination, reaching a strength of 1.32 GPa together with an elongation of 7.5%. The increased strength attributes to hetero-deformation induced strengthening. In-situ deformation monitoring reveals many unique deformation bands in heterostructure materials, which delays necking and improves ductility. The findings demonstrate a novel potential approach to circumvent material property trade-offs. Additively manufactured heterogeneous materials with controllable architectures achieved a good strength-ductility combination; the underlying strengthening mechanism and unique deformation behaviour are revealed. [ABSTRACT FROM AUTHOR]

In this study, functionally graded material (FGM) was deposited on cast iron substrate by laser-aided additive manufacturing (LAAM). Inconel 625 nickel-base superalloy was firstly deposited on the substrate as a buffer layer, on which the stainless steel 420 (SS420) layers were subsequently prepared. The cracking issue was successfully eliminated in the deposited materials. With the optimized process parameters, the FGM with thickness up to 4.0 mm was achieved without cracks and other obvious defects. The SS420 layers showed fine dendritic microstructure derived from the rapid cooling rate of the LAAM process. Wear test results indicated that the FGM shows excellent wear resistance, especially under lubricated condition. [ABSTRACT FROM AUTHOR]

In this paper, a comparison study of CNTs and graphite addition in laser aided additive manufacturing (LAAM) Inconel 625 composites was proposed. The difference of microstructure and tensile properties between two modified Inconel 625 alloys was investigated. SEM, EDS and micro-Raman identification results showed that the CNTs structure can be found on columnar dendrite boundaries accompanied with precipitated Laves and γ′ phase in LAAM Inconel 625-CNTs composite. Based on tensile test results, 0.25 wt% of CNTs addition in LAAM Inconel 625 can significantly increase strength and ductility by 20% because of grain refinement and grain boundary pinning reinforcement. However, the graphite addition only raises strength but decreases ductility due to carbon content raise. • CNT reinforced staring powder was prepared by ball milling Ni-coated MWCNT and Inconel powder. • A comparison test between CNT and Graphite addition was carried out to avoid ball milling influence. • Clear CNT structure can be observed in both microstructure and fracture surface. • Both strength and ductility can be improved due to CNT fiber reinforcement effect. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) technologies provide more freedom to functional part design in various industries. One of the unique capabilities of AM is that multi-material parts can be produced with material compositional and geometric complexity. Multi-material parts have the advantage of achieving multiple performance requirements. In the research, we propose a framework for designing multi-material parts using AM processes. The proposed framework is composed of four interacting modules, including design requirement identification, primary material selection, AM process selection, material composition, and part geometry determination. Rules and guidelines for AM are integrated into the proposed framework with AM processes’ capabilities and constraints compiled in databases. We also introduce databases to assist in decision-making and ensure manufacturability of the designed multi-material part in various product design phases. The proposed framework is applied to a case study involving a conceptual design of a multi-material battery pack cooling plate. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is projected to have a profound impact on mass customisation. In order to benefit from this new technology, we need to incorporate AM into design processes. This paper addresses that need by introducing an AM process model for product family design. The proposed model reflects the ability of AM to produce customised and complex parts without tooling efforts. By utilising AM, we eliminate all constraints which arise in conventional product family designs from finding a compromise between commonality and performance. The proposed model starts by identifying design requirements and constraints. Subsequently, we use topology optimisation to determine an optimal design for each product. Next, finite element analysis and cost analysis are performed. We combine the analysis results in one three-dimensional plot, which displays the merits of the individual component realisations. Thus, a fair and competitive component evaluation is possible and the most suitable product family design can be selected. The final designs are fabricated using fused desposition modelling. A case study is conducted to illustrate how the proposed model facilitates the benefits of AM. The results show that the proposed model has the potential to provide affordable customisation. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, restoration of nickel-base turbine blade knife-edges with controlled Laser Aided Additive Manufacturing (LAAM) process was investigated. The alloy contains about 9 weight percent Ti/Al composition, which makes it difficult to repair due to the cracking issue. Infrared temperature signal emitted from melt pool was adopted for process control. The deposition with and without process control was compared. The deposition with process control can avoid the hot-cracking which often occurs during deposition of nickel-base super-alloys. The results showed that the process control can also guarantee a better dimensional accuracy. The microstructure of the deposited layers in the cross-section was examined under both microscope and SEM. It displayed directionally solidified fine columnar dendrites which grew following the change of the heat conduction condition. The EDX line scanning verified that chemical composition remained homogeneous distribution in the deposited thin wall. Spot EDX analysis identified that TiC is most likely the main type of carbides formed at the grain boundaries. The results demonstrated that the LAAM process is feasible for the recondition of the gas turbine blade knife-edges. [Copyright &y& Elsevier]

Abstract: Direct Laser Metallic Powder Deposition Process is one of the most popular direct additive manufacturing processes which use laser as a heat source to deposit the metallic powder layer by layer for surface modification and fabrication of three-dimensional parts. The properties of the deposited layer, such as microstructure, hardness and dimensional accuracy determine the usage properties of the processed parts. The temperature and size of the melt pool, the cooling rate and the solidification conditions dominate the microstructure, hardness and dimensional accuracy. In this work, a closed-loop process control based on the infrared (IR)-temperature signal was investigated by deposition of thin walls. Process control with constant set-values and path-dependent set-values was tried and compared. The results showed that the process control with a path-dependent set-value can notably improve the homogeneity of the microstructure and hardness as well as the dimensional accuracy of the deposited samples. [Copyright &y& Elsevier]

Abstract: This paper reports the Laser Aided Additive Manufacturing of nickel-base alloy Nimonic 80A for the purpose of direct building of die inserts for liquid forging. Low porosity level of 0.01–0.04% with reasonable deposition rate was achieved. The micro-hardness showed very good homogeneity. Directionally solidified cellular micro-structure with an average size of 5μm was observed. Very fine MC-type carbides were detected at the grain boundaries, which function as the strengthening phase of the alloy. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

IN100 Ni-based superalloy fabricated by micro-laser aided additive manufacturing (micro-LAAM) was investigated in this study. After solution treatment and aging (STA) of the micro-LAAMed IN100 alloy, hierarchical γ′ phases were recognized and characterized, which contributed significantly to the high ultimate tensile strength (~1050 MPa) and acceptable ductility (5%) at 25 °C and 600 °C. The tensile fractured surfaces of the as-built and STAed IN100 were characterized by dimples and dimples/cleavages, respectively. The high cycle vibration fatigue (HCVF) behavior was preliminarily studied through simulating the service conditions of some cantilever structures in automobile and aerospace industries. Compared with the cast IN100, the micro-LAAMed IN100 superalloys (as-built or STAed) both exhibited inferior HCVF lives. The HCVF behavior was discussed and correlated with the microstructure characteristics, such as the preferred growth direction of the grains in micro-LAAMed IN100 and the massive interfaces existing in the final obtained material. In the present study, the hierarchical γ′ phases were beneficial to the static tensile property, whereas detrimental to the HCVF behavior of the final obtained IN100 to some extent. • Hierarchical γ′ phases were clearly picked out by HR-TEM. • The tensile fractured surface was comprised of dimples or dimples & cleavage. • High cycle vibration fatigue behavior of the micro-LAAMed IN100 was reported. [ABSTRACT FROM AUTHOR]