Complex metallic alloys as new materials for additive manufacturing

Additive manufacturing processes allow freeform fabrication of the physical representation of a three-dimensional computer-aided design (CAD) data model. This area has been expanding rapidly over the last 20 years. It includes several techniques such as selective laser sintering and stereolithography. The range of materials used today is quite restricted while there is a real demand for manufacturing lighter functional parts or parts with improved functional properties. In this article, we summarize recent work performed in this field, introducing new composite materials containing complex metallic alloys. These are mainly Al-based quasicrystalline alloys whose properties differ from those of conventional alloys. The use of these materials allows us to produce light-weight parts consisting of either metal–matrix composites or of polymer–matrix composites with improved properties. Functional parts using these alloys are now commercialized.     

Microstructure and performance optimisation of stainless steel formed by laser additive manufacturing

In the present study, laser engineered net shaping technology was successfully utilised to fabricate 316L stainless steel bulk specimens using unidirectional scanning path and weaving scanning path. Influence of scanning path and post-heat treatment on microstructural and mechanical properties of the as-deposited builds has been investigated. The results show that scanning paths have a significant impact on the grain morphology evolution. Consequently, the as-made samples by different scanning strategies show a great difference in the mechanical properties. Furthermore, the experimental results also demonstrate that post-heat treatment is an essential step in further optimising microstructure and improving mechanical properties.     

Solid-state additive manufacturing and repairing by cold spraying: A review

High-performance metal additive manufacturing (AM) has been extensively investigated in recent years because of its unique advantages over traditional manufacturing processes. AM has been applied to form complex components of Ti, Fe or Ni alloys. However, for other nonferrous alloys such as Al alloys, Mg alloys and Cu alloys, AM may not be appropriate because of its melting nature during processing by laser, electron beam, and/or arc. Cold spraying (CS) has been widely accepted as a promising solid-state coating technique in last decade for its mass production of high-quality metals and alloys, and/or metal matrix composites coatings. It is now recognized as a useful and powerful tool for AM, but the related research work has just started. This review summarized the literature on the state-of-the-art and problems for CS as an AM and repairing technique.     

Additive manufacturing of high entropy alloys:A practical review

The novel idea of alloying,which is based on the utilization of multiple principal elements in high concen-trations,has created a novel class of promising materials called high entropy alloys(HEAs).So far,several HEAs with outstanding properties beyond those of conventional alloys have been discovered,and new superior high-entropy alloys are still expected to be developed in the future.However,the fabrication process of HEAs through conventional manufacturing techniques suffers from significant limitations due to the intrinsic requirements of HEAs.Additive manufacturing(AM),on the other hand,has provided new opportunities for fabricating geometrically complex HEAs with the possibility of in situ tailoring of their microstructure features.Considering the growing interest in AM of HEAs during most recent years,this review article aims at providing the state of the art in AM of HEAs.It describes the feedstock requirements for laser based AM techniques.Thereafter,a comprehensive picture of the current state of nearly all HEAs processed by laser metal deposition(LMD),selective laser melting(SLM)and selec-tive electron beam melting(SEBM)is presented.Special attention is paid to the features of AM derived microstructures along with their outstanding properties and underlying mechanisms for various mate-rial processing combinations.The AM of interstitial solute hardening HEAs,HEA matrix composites as well as non-beam based AM of HEAs will also be addressed.The post-AM treatments and the strategies to fabricate defect-free HEAs are summarized.Finally,a conclusion of current state and future prospects of additive manufacturing of HEAs will be presented.     

金属增材制造技术发展趋势综述

近年来金属增材制造技术的快速发展,使其在航空航天、医疗行业、汽车制造等领域得到了大量应用.本文简要介绍了金属增材制造的典型工艺、金属粉末和金属丝材的制备方法以及基于文献统计的方法分析金属增材制造目前的研究热点和发展趋势.结果 表明,金属增材制造技术在仿真设计、制造工艺、过程监控、质量评估、后续处理等领域还没有形成完善的...     

A review of additive manufacturing of metamaterials and developing trends

The concept of metamaterials originates from the proposal of left-hand materials with negative refractive index, followed by which, varieties of metamaterials with kinds of fantastic properties that cannot be found in natural materials, such as zero/negative Poisson’s ratio, electromagnetic/acoustic/thermal cloaking effect, etc., were come up with. According to their application fields, the metamaterials are roughly classified into four categories, electromagnetic metamaterials, acoustic metamaterials, thermal metamaterials, and mechanical metamaterials. By designing structures and arranging the distribution of materials with different physical parameters, the function of metamaterials can be realized in theory. Additive manufacturing (AM) technology provides a more direct and efficient way to achieve a sample of metamaterial and experiment verification due to the great advantages in fabricating complex structures. In this review, we introduce the typical metamaterials in different application situations and their design methods. In particular, we are focused on the fabrication of metamaterials and the application status of AM technology in them. Furthermore, we discuss the limits of present metamaterials in the aspect of design method and the disadvantages of existing AM technology, as well as the development tendency of metamaterials.     

Laser additive manufacturing of Zn porous scaffolds: Shielding gas flow,surface quality and densification

Zn based metals have exhibited promising prospects as a structural material for biodegradable applications. Pure Zn porous scaffolds were produced by laser powder bed fusion(LPBF) based on data files of designing and CT scanning. Massive Zn evaporation during laser melting largely influenced the formation quality during LPBF of Zn metal. The metal vapor in processing chamber was blown off and suctioned out efficiently by an optimized gas circulation system. Numerical analysis was used to design and testify the performance of gas flow. The surface of scaffolds was covered with numerous particles in different sizes. Processing pores occurred near the outline contour of struts. The average grain size in width was8.5m, and the hardness was 43.8 HV. Chemical plus electrochemical polishing obtained uniform and smooth surface without processing pores, but the diameter of struts reduced to 250 αm from the design value 300 m. The poor surface quality and processing pores were resulted by the splashing particles included spatters and powders due to the recoil force of evaporation, and the horizontal movement of liquid metal due to overheating and wetting. The insufficient melting at the outline contour combined with good wetting of Zn liquid metal further increased the surface roughness and processing pores.     

Adopting feature resolution and material distribution constraints into topology optimisation of additive manufacturing components

Additive manufacturing (AM), known for its ability to manufacture complex shapes, is becoming an essential companion of topology optimisation (TO) to optimise the structure. However, the topology-optimised structure may result in suboptimal performance or even have features, which are difficult to manufacture in a given AM process. This study attempts to refine the outcome from TO with AM-specific considerations, such as minimum feature resolution and material continuity-related constraints by introducing a neighbourhood density function, subsequent to the solid isotropic material with penalisation approach. The four different cases have been studied to demonstrate the effectiveness of the presented approach yielding better results when compared with the conventional TO under the three-point bending test. The current study provides optimised geometry with the decreased number of voids and ensuring the minimum feature size without substantial loss in the structural behaviour and becomes the basic framework to integrate manufacturability into structural TO for the AM process.     

Hollow-walled lattice materials by additive manufacturing: Design,manufacture, properties,applications and challenges

The rapid growth of additive manufacturing (AM) technologies has enabled the emergence of geometrically sophisticated materials or structures with tailored and/or enhanced mechanical responses. In addition to dense-walled lattice structures, innovation within the past decade has identified that hollow-walled lattice topologies exhibit the multifaceted potential of competitive strength and rigidity, whilst displaying unique deformation behaviours, indicating that they may be an important subsequent step in lattice evolution. Hollow-walled sections facilitate density and geometrical parameters well below what is achievable by dense-walled sections, providing additional hierarchies of architecture at micrometre to even nanoscale proportion. Their wall thickness can range from 20 nm to 800 µm while the relative density can span three orders of magnitude between 0.01% and 30%. Despite nearly a decade of research into hollow-walled lattice topologies, no meta-analysis exists to provide an informative overview of these structures. This research addresses this deficiency and provides a data-driven review of hollow-walled lattice materials. It elucidates how these hollow-walled lattices deviate from the current limitations of dense-walled lattices and the underlying mechanisms that dictate their performance, with data accumulated from an exhaustive collection of literature sources. A range of new insights into their design and manufacture is discussed for their future research and applications in different engineering fields.     

A review: additive manufacturing for active electronic components

Fabrication of fully functional devices is one of the ultimate goals of additive manufacturing technology. In order to achieve this goal, a critical step is to fabricate electronic components using fully additive methods. Although there are still numerous roadblocks that need to be overcome towards this goal, research activities in the field of additive manufacturing for electronic components in general, and for active components in particular, are progressing at a considerable pace and have been achieving significant successes. The purpose of this review is, therefore, to consolidate recent developments in this exciting field. Such developments include fully additive manufacturing methods for active components such as transistors, light-emitting diodes, and batteries. We discuss and compare the advantages, as well as disadvantages, of these methods. We also discuss major challenges that need to be addressed in the roadmap for additive manufacturing of active components.     

Microstructure and mechanical behavior of laser aided additive manufactured low carbon interstitial Fe49.5Mn30Co10Cr10C0.5 multicomponent alloy

Laser aided additive manufacturing(LAAM)was used to fabricate bulk Fe49.5Mn30Co10Cr10C0.5 interstitial multicomponent alloy using pre-alloyed powder.The room temperature yield strength(σy),ultimate tensile strength(σUTS)and elongation(εUST)were 645 MPa,917 MPa and 27.0％respectively.The as-built sample consisted of equiaxed and dendritic cellular structures formed by elemental segregation.These cellular structures together with oxide particle inclusions were deemed to strengthen the material.The other contributing components include dislocation strengthening,friction stress and grain bound-ary strengthening.The high εUTS was attributed to dislocation motion and activation of both twinning and transformation-induced plasticity(TWIP and TRIP).Tensile tests performed at-40℃and-130℃demonstrated superior tensile strength of 1041 MPa and 1267 MPa respectively.However,almost no twinning was observed in the fractured sample tested at-40℃and-130℃.Instead,higher fraction of strain-induced hexagonal close-packed(HCP)ε phase transformation of 21.2％were observed for fractured sample tested at-40℃,compared with 6.3％in fractured room temperature sample.     

Toward multiscale simulations of tailored microstructure formation in metal additive manufacturing

Much of the latent promise of metal additive manufacturing (AM) rests in the potential for controlled creation of spatially tailored microstructures, designed to optimize key build-scale properties through systematic variation across a build. Component optimization possibilities and performance potential expand enormously when this becomes possible. However, the extreme conditions created by AM energy sources and the nature of alloy solidification under such conditions are not adequately understood. Modeling and simulation tools capable of quantitatively predicting AM microstructural outputs would enable a major leap forward. We demonstrate through experimental validation that a multiscale (nm/ns to mm/ms) simulation framework coupling CALPHAD thermodynamic models, microstructure scale phase field simulations, and laser track scale multiphysics simulations can quantitatively predict tailored microstructure formation in laser processed Ti-Nb. Extensive simulations and analysis of detailed microstructural predictions over a broad range of conditions reveal scaling laws for characteristic microstructural features that should generalize to a wide range of materials. Several of our findings highlight the central importance of the alloy freezing range $\mathrm{\Delta }{T}_f$, which provides the basis of a generalized strategy for optimizing spatial control of microstructure during AM. This proposed strategy integrates alloy design with process design & control to identify optimal material and process condition combinations. We have also identified conditions and phenomena that appear to require a more complete treatment of far from equilibrium solidification kinetics, highlighting a fundamental need in the field. We anticipate that further development of such methodologies will contribute centrally to realizing the potential of materials with spatially tailored microstructure.     

Standardised product development for technology integration of additive manufacturing

ABSTRACT

The implementation of additive manufacturing (AM) as an industrial production process poses extraordinary challenges to companies due to the far-reaching differences to conventional processes. In addition, there are hardly any standards and guidelines or methodical process models for the relatively new technologies that enable the reproducible and target-oriented use of AM. In order to solve this problem, five industrial companies together with the Paderborn University are researching as part of the ‘OptiAMix’ research project funded by the Federal Ministry of Education and Research (BMBF). This paper focuses on the development of an ideal process chain. Reference processes of the OptiAMix partners were analysed, norms and standards from conventional production were adapted and implemented and procedure models developed OptiAMix were integrated. The resulting AM Product Development Process was then applied and validated with the aid of a previously developed integration methodology using an example component from the automotive industry.     

增材制造智能材料研究现状及展望EI北大核心CSCD

增材制造技术自问世以来成为拓展多学科发展、实现多学科研究融合以及联结材料与产品的关键性技术,该技术颠覆了传统加工设计和制造理念,同时也是实现智能制造的重要方法。智能材料是对环境具有感知、可响应、自修复和自适应的一类材料。将智能材料与增材制造技术有机结合,可实现具有感受外部刺激或环境激活的三维智能器件的一体化制造。智能材料增材制造技术被广泛应用于个性化医疗、柔性电子和软体机器人等领域。本文对增材制造中所涉及的智能材料进行综述,介绍通过增材制造方法对金属类、高分子类和陶瓷类智能材料所带来的优势及面临的问题。增材制造技术作为实现设计、材料和结构有机融合的有效手段,将成为推动智能材料发展的关键。     

A review of synthesis methods for additive manufacturing

With the design freedoms afforded by additive manufacturing (AM) processes, an increasing interest in shape synthesis methods has led to a variety of advances in topology optimisation methods and associated synthesis technologies. In this paper, we identify research issues related to the application of AM to shape synthesis methods, review recent advances in topology optimisation, and outline a vision for future synthesis capabilities.     

Electron beam melting of Inconel 718: effects of processing and post-processing

ABSTRACT

This study reports the effect of process temperature on microstructure evolution of electron beam melted Inconel 718. Samples fabricated at 915°C had fine grain boundary δ (～200?nm) along with coarse intragranular δ spanning through the length of the grains. On the other hand, samples fabricated at 990°C, only had grain boundary δ along with secondary carbides. During hot isostatic pressing, the distribution of carbides governs the grain growth vs. lack of it. The samples fabricated at 990°C having grain boundary carbides had no grain growth owing to the pinning effect of carbides. In contrast, the sample processed at 915°C had significant grain growth owing to dissolution of grain boundary δ phase and absence of grain boundary carbides.     

Research progress of ceramic matrix composite parts based on additive manufacturing technology

ABSTRACT

Ceramic matrix composites (CMCs) are materials that can be engineered for high-temperature applications in various fields including aerospace, marine, etc. It is very difficult to fabricate CMCs using traditional moulding methods due to their brittleness and high hardness. Additive manufacture (AM) technology, a digital manufacturing technology, provides multiple advantages over traditional manufacturing technologies, such as fabricating geometrically complex parts, mould-free fabrication, short development cycle, etc. In this paper, various AM technologies developed for CMCs are reviewed with emphasis on mechanisms of manufacturing, characteristics of production, and recent research progresses. With the springing up of innovative ideas and pioneering work, AM technology possesses unique forming capabilities in fabricating CMCs, demonstrating strong potentials in the application of CMCs in aerospace and other fields. However, there are still many challenges of CMCs fabricated by AM technologies, i.e. poor mechanical properties and geometric accuracies; lower reinforcement volume fraction than that of traditional manufacturing processes.     

The effect of recycling on the oxygen distribution in Ti-6Al-4V powder for additive manufacturing

Abstract

Ti-6Al-4V powder has been recycled 30 times in an electron beam melting system. A combination of electron microscopy techniques has been used to show that the recycled powder has a 35% higher oxygen content, and that the particles have a more irregular morphology, a narrower particle size distribution, and a much more variable microstructure than the virgin powder. The microstructures in the recycled powder particles vary from a martensitic α′ structure, which is identical to that in the virgin powder, to a two-phase α + β structure. This variability is related to the complex thermal history of the unmelted metal powder in the system. Despite these differences, all of the particles exhibit essentially the same surface oxide thickness; the excess oxygen in the recycled powders is instead located in the β phase. The possible consequences for the structure and properties of the resultant additively manufactured parts are discussed.     

Energy and material flow modelling of additive manufacturing processes

Additive manufacturing (AM) processes allow fabrication of three-dimensional complex parts. Due to the exact amount of material used during the manufacturing step, these new manufacturing processes offer great opportunities for sustainable manufacturing. However, existing studies on these processes focus mainly on energy consumption and information about resources consumptions and waste flows are still lacking. This study aims to quantify with accuracy inventory data of AM processes during the manufacturing step of the life cycle of products. In order to accurately assess the environmental impact of a product, a generic method for acquisitions and characterisation of inventory data for parts made by AM processes is proposed. This methodology focuses not only on the electrical energy consumption but also on material consumption. This paper also describes the development of a parametric process model, which provides to an operator, an accurate estimation of the environmental performances of the fused deposition modelling process.