Al matrix composites fabricated by solid-state cold spray deposition:A critical review

Cold spraying(CS),or cold gas dynamic spray(CGDS),is an emerging solid-state powder deposition process,allowing fast and mass production and restoration of metallic components.CS of metal matrix composites(MMCs)has attracted increasing attention from academia and industry over the last decades,especially in the area of Al matrix composites(AMCs),which have demonstrated a high potential for applications in aerospace,automotive,and electronics industries.This article aims to summarize the recent development of CS-processed AMCs in terms of composite powder preparation,deposition pro-cessing,microstructure evolution,mechanical and corrosion properties.Furthermore,this review also reports the relevant research progress with the focus on post-treatments of the AMCs for CS additive manufacturing applications including heat treatment,hot rolling,and friction stir processing.Finally,the challenges and perspectives on the fabrication of advanced AMCs by CS are addressed.     

Progress in additive manufacturing on new materials: A review

Recent efforts and advances in additive manufacturing (AM) on different types of new materials are presented and reviewed. Special attention is paid to the material design of cladding layers, the choice of feedstock materials, the metallurgical behavior and synthesis principle during the AM process, and the resulted microstructures and properties, as well as the relationship between these factors. Thereafter, the trend of development in the future is forecasted, including: Effects of the particles size and size distribution of powders; Approaches for producing fine microstructures; Opportunities for creating new materials by AM; Wide applications in reconditioning of damaged components; Challenges for deep understanding and applications of the AMed new materials. The idea of “Develop Materials” or “Create Materials” by AM is highlighted, but a series of scientific, technological and engineering problems remain to be solved in future.     

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.     

Enhanced strengthening and hardening via self-stabilized dislocation network in additively manufactured metals

The advent of additive manufacturing (AM) offers the possibility of creating high-performance metallic materials with unique microstructure. Ultrafine dislocation cell structure in AM metals is believed to play a critical role in strengthening and hardening. However, its behavior is typically considered to be associated with alloying elements. Here we report that dislocations in AM metallic materials are self-stabilized even without the alloying effect. The heating–cooling cycles that are inherent to laser power-bed-fusion processes can stabilize dislocation network in situ by forming Lomer locks and a complex dislocation network. This unique dislocation assembly blocks and accumulates dislocations for strengthening and steady strain hardening, thereby rendering better material strength but several folds improvements in uniform tensile elongation compared to those made by traditional methods. The principles of dislocation manipulation and self-assembly are applicable to metals/alloys obtained by conventional routes in turn, through a simple post-cyclic deformation processing that mimics the micromechanics of AM. This work demonstrates the capability of AM to locally tune dislocation structures and achieve high-performance metallic materials.     

Cold spray additive manufacturing of Invar 36 alloy: microstructure,thermal expansion and mechanical properties

In this work,the Invar 36 alloys were manufactured using cold spray (CS) additive manufacturing technique.The systematic investigations were made on the microstructural evolution,thermal expansion and mechanical properties under as-sprayed (AS) and heat-treated (HT) conditions.XRD (X-ray diffraction)and ICP-AES (inductively coupled plasma atomic emission spectroscopy) analyses show that no phase transformation,oxidation,nor element content change have occurred.The X-ray computed tomography (XCT) exhibited a near fully dense structure with a porosity of 0.025％ in the helium-produced sample under as-sprayed condition,whereas the nitrogen-produced samples produced at 5 MPa and 800 ℃ show more irregular pore defects.He-AS sample shows a more prominent grain refinement than that of nitrogen samples due to the more extensive plastic deformation.The post heat-treatment exhibited a promoted grain growth,inter-particle diffusion,as well as the formation of annealing twins.Between 25 ℃ and 200 ℃,the nitrogen samples possessed lower CTE (coefficient of thermal expansion) values (1.53 × 10-6/℃) compared with those produced by casting and laser additive manufacturing.The He-AS samples exhibited a noticeable negative CTE value between 25 ℃ and 200 ℃,which may due to the significant compressive residual stress (-272 MPa) compensating its displacement with temperature increase during CTE test.The N2-HT and He-HT Invar 36 samples present a notable balance between strength and ductility.In conclusion,the CS technique can be considered as a potential method to produce the Invar 36 component with high thermal and mechanical performance.     

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.     

Solid-state additive manufacturing for metallized optical fiber integration

The formation of smart, Metal Matrix Composite (MMC) structures through the use of solid-state Ultrasonic Additive Manufacturing (UAM) is currently hindered by the fragility of uncoated optical fibers under the required processing conditions. In this work, optical fibers equipped with metallic coatings were fully integrated into solid Aluminum matrices using processing parameter levels not previously possible. The mechanical performance of the resulting manufactured composite structure, as well as the functionality of the integrated fibers, was tested. Optical microscopy, Scanning Electron Microscopy (SEM) and Focused Ion Beam (FIB) analysis were used to characterize the interlaminar and fiber/matrix interfaces whilst mechanical peel testing was used to quantify bond strength. Via the integration of metallized optical fibers it was possible to increase the bond density by 20–22%, increase the composite mechanical strength by 12–29% and create a solid state bond between the metal matrix and fiber coating; whilst maintaining full fiber functionality.     

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.     

Feedstock powder processing research needs for additive manufacturing development

Additive manufacturing (AM) promises to redesign traditional manufacturing by enabling the ultimate in agility for rapid component design changes in commercial products and for fabricating complex integrated parts. By significantly increasing quality and yield of metallic alloy powders, the pace for design, development, and deployment of the most promising AM approaches can be greatly accelerated, resulting in rapid commercialization of these advanced manufacturing methods. By successful completion of a critical suite of processing research tasks that are intended to greatly enhance gas atomized powder quality and the precision and efficiency of powder production, researchers can help promote continued rapid growth of AM. Other powder-based or spray-based advanced manufacturing methods could also benefit from these research outcomes, promoting the next wave of sustainable manufacturing technologies for conventional and advanced materials.     

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.     

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.     

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.     

Toughening of polyamide 11 with carbon nanotubes for additive manufacturing

It has been reported that the addition of nanofillers/nanoparticles into the thermoplastic polymers could enhance the toughness of the polymer matrix. In this work, the mechanical and thermal properties of a multi-walled carbon nanotubes (CNT)/polyamide 11 nanocomposite for additive manufacturing was evaluated. Well-dispersed PA11/CNT nanocomposite powders were processed successfully by laser sintering. Compared to the pristine PA11, the fracture toughness of the PA11/CNT nanocomposite was enhanced by ～54% by incorporating of only 0.2?wt% CNTs. With differential scanning calorimetry, X-ray diffraction and scanning electron microscope fractography analysis, the nanostructure and the toughening mechanism which lead to the toughness improvement was well identified and understood.     

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.     

Powder bed fusion additive layer manufacturing of titanium alloys

Powder bed fusion (PBF) techniques for additive layer manufacturing (ALM) are reviewed with a focus on titanium alloys production. Selective laser melting and electron beam melting are discussed in terms of feedstock production and processing-microstructure relationships. To control the PBF processes, an outline is presented on the computational modelling approaches for simulating process parameters and defects such as residual stresses and porosity at different length scales. It is concluded that by improving powder production techniques, designing new alloys and further developing ALM hardware, PBF techniques can reach commercial maturity.

This review was submitted as part of the 2019 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.     

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.     

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.     

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.     

Fatigue behavior of Ti-6Al-4V cellular structures fabricated by additive manufacturing technique

Porous titanium and its alloys have been considered as promising replacement for dense implants, as they possess low elastic modulus comparable to that of compact human bones and are capable of providing space for in-growth of bony tissues to achieve a better fixation. Recently, the additive manufacturing (AM) method has been successfully applied to the fabrication of Ti-6Al-4V cellular meshes and foams. Comparing to traditional fabrication methods, the AM method offers advantages of accurate control of complex cell shapes and internal pore architectures, thus attracting extensive attention. Considering the long-term safety in the human body, the metallic cellular structures should possess high fatigue strength. In this paper, the recent progress on the fatigue properties of Ti-6Al-4V cellular structures fabricated by the AM technique is reviewed. The various design factors including cell shapes, surface properties, post treatments and graded porosity distribution affecting the fatigue properties of additive manufactured Ti-6Al-4V cellular structures were introduced and future development trends were also discussed.