22 - Cold-spray processing of titanium and titanium alloys
Abstract
The knowledge base for cold spray has grown significantly in recent years and advances in the technology have shown viability for the process for titanium-based materials. For titanium and its alloys, the capability to rapidly produce thick, unoxidized deposits in open air makes cold spray a particularly attractive process. Here, selected results from the available literature are discussed to highlight key practical and fundamental aspects in cold-spray processing of titanium-base powders. An overview is presented for the general process and its underlying particle deformation and bonding mechanisms. The properties of cold-sprayed titanium material are characterized and process–microstructure–property relationships reviewed. Coating and additive manufacturing applications are then briefly outlined with a discussion of practical considerations. In the concluding remarks, views are offered on the current status and possible future directions of development for the technology.
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A design and optimisation framework for cold spray additive manufacturing of lightweight aerospace structural components
2023, Additive ManufacturingCold spray additive manufacturing (CSAM) is a solid-state deposition process with the potential to produce near-net shape components with complex geometry at a high fabrication rate, making it an attractive alternative to more widely established additive manufacturing (AM) processes. However, CSAM is still in its early stages and requires numerous advancements. The current literature highlights the lack of a design framework for fabricating structural components that encompasses the advantages and constraints of CSAM. This work proposes such a framework to guide product and process engineers, with its novel aspects including (i) accounting for different spray trajectories and their effect on anisotropic mechanical properties, (ii) accounting for the primary constraint for toolpath planning (maximum overhang angle ‘MOA’), and (iii) virtual development and optimisation of a real-world structural component with complex geometry. To exemplify this framework, tensile properties under two spray trajectories were determined experimentally for a common lightweight metal (titanium) supplemented with a ceramic to form a metal matrix composite with improved strength and hardness. Optimisation of the design was conducted via finite element analysis and topology optimisation (TO). Two different TO processes were conducted, namely (i) minimising the strain energy of the structure and reducing the weight by 60% (best stiffness-to-weight ratio) and (ii) minimising the weight by targeting a maximum factor of safety (FoS) value of 1.2. The final design was fabricated via CSAM with relatively little raw material wastage and reasonably close geometric accuracy. Fabrication defects were, however, noticed after making a demonstration component and mitigation measures are discussed within the context of the design framework proposed here.
Microstructure and mechanical properties of cold spray additive manufactured Cu-Cr-Nb and Fe-Ni-Cr alloys
2023, Additive ManufacturingThe main objective of this work was to investigate the microstructure and mechanical properties of Cu-Cr-Nb (GRCop-42) and Fe-Ni-Cr (HR-1) alloy deposits produced using a high-pressure cold spray process. GRCop-42 powder blended with varying content of HR-1 powder (0, 15, 25, 50, 75, 85, and 100 wt%) was cold spray deposited, and the microstructure and mechanical properties of the deposits were evaluated. The deposits were characterized using optical microscopy, X-ray diffraction, and scanning electron microscopy. The use of He process gas resulted in relatively lower porosity and better mechanical properties compared to the deposits produced with N2 process gas. In the as-deposited condition, all the cold spray deposits exhibited brittle behavior with no appreciable ductility. Post-deposition heat treatment significantly improved ductility and tensile strength for both GRCop-42 and HR-1 deposits. However, post-deposition heat treatment resulted in coarsening of Cr2Nb precipitates in GRCop-42, the formation of η phase in HR-1, and the formation of σ phase at the interface in GRCop-42 and HR-1 composite deposits.
Characterization of cold-sprayed material consolidations
2023, Advances in Cold Spray: a Coating Deposition and Additive Manufacturing ProcessThis chapter considers the utility of various contemporary and emergent characterization methods and techniques for cold-sprayed material consolidations and their respective feedstock powders. The chapter is divided into seven sections, focusing on metal materials for cold spray and their counterpart metallurgical material consolidations. The first section considers advanced microscopy. The second considers nanoindentation and micromechanical testing within the cold spray materials literature. Building upon said content, the third section explores the utility of micropillar compression and microtensile testing. After that, the fourth section bridges the nano- and micromechanical length scales by focusing on macrohardness and instrumented indentation testing. The fifth section considers the emergence and applicability of bulk plasticity assessment of cold-sprayed metallurgical materials through profilometry-based indentation plastometry. After that, as-sprayed and modified deposit surface roughness and topography testing methods are explored in section six. The final section of the present chapter presents static and dynamic mechanical properties and damage mechanisms of cold-sprayed light metals.
Effect of diffusion annealing on duplex coated pure titanium produced by hot-dip aluminizing and micro-arc oxidation
2022, Surface and Coatings TechnologyCitation Excerpt :However, the natural oxide layer formed on the titanium surface causes titanium to be easily damaged in aggressive environments with applied loads leading to devastating results [2,3]. To cope with these catastrophic results, various surface modification methods such as physical vapor deposition (PVD) [4], laser surface modification (LSM) [5], chemical vapor deposition (CVD) [6], anodizing [7], cold spraying (CS) [8], hot-dip aluminizing (HDA) [9] and micro-arc oxidation (MAO) [10] are applied to titanium and its alloys. Among these methods, MAO stands out by generating a hard, thick, uniform, and wear- and corrosion-resistant coating on titanium surfaces using various MAO parameters (e.g., electrolyte, time, voltage, etc.) [11–13].
In the present study, an Al2O3 ceramic coating was formed on a pure titanium surface with the application of the duplex coating technology produced by combining hot-dip aluminizing (HDA) and micro-arc oxidation (MAO) processes. Due to the porous nature of MAO coating with the structural and mechanical differences between the MAO (Al2O3) and HDA layers (Al, Al3Ti), diffusion annealing treatment was applied to duplex coated (HDA + MAO) titanium samples. With the diffusion annealing treatment, a composite layer with a thickness of about 125 μm was formed beneath the modified MAO coating, which showed a denser structure by penetrating TiO2 into the MAO. MAO coatings with and without diffusion annealing exhibited compressive residual stresses with values of −1530 and −850 MPa, respectively. Microhardness and elastic modulus of the diffusion annealing-treated MAO coating reached 1230.1 HV and 241.3 GPa, respectively. The diffusion annealing-treated MAO coating provided ~29% less coefficient of friction and ~8.4 times greater relative wear resistance than that of MAO coating without diffusion annealing.
Powder bed fusion processes: main classes of alloys, current status, and technological trends
2022, Advances in Metal Additive ManufacturingMetal powder-based additive manufacturing (AM) has increasingly gained importance in the last decades. Powder-based techniques are well-known because of their versatility, allowing high degrees of geometric complexity and a wide range of chemical compositions. It enables a myriad of alloys to be printed and, e.g., the production of parts with functional gradient given the possibility of tailoring the alloy composition by changing in situ the process parameters. Moreover, the processes have been constantly developed, leading to fast, reproducible, and ready-to-use net shape parts becoming powder-based AM economically attractive. The factors mentioned above attracted the attention of aerospace, biomedical, energy and others, being the focus of intense investigations in processing and related material processing phenomena; these led to the understanding of key phenomena and consequently to the improvement of AM as a production tool.
This chapter aims to explore recent developments in the powder-based AM of elementary classes of alloys for different applications. The first section is devoted to aluminium alloys, where one discusses the general challenges of printing these alloys by laser powder bed fusion (LPBF) technique, such as crack formation, porosity and the influence of building direction on the tensile properties. Further, a general overview of essential aluminium alloys produced by laser-based techniques is given. AlSi10Mg, the most common one, is the first discussed with a focus on the heat treatment of as-produced parts and its impact on tensile behaviour. Attention is also given to AlSi12, the promising Sc, Zr-based Al alloys, the hardly processable Al-Cu, the strong AA7075, and AA6061. The following two sections clarify how LPBF and laser metal deposition (LMD) are suitable for printing tool steels. The former explores hot work tool steels, giving a complete overview of the effect of processing on microstructure, phase transformation/precipitation, and the formation of defects such as cracks; high speed and cold work tool steels are briefly explored at the end of this section. The latter section deals with printing several tool steels (hot and cold work, and high speed) by LMD, correlating, e.g., printing strategies and cooling effect on the mechanical properties (such as hardness), microstructure, phase transformation and precipitation.
Ahead, a section is dedicated to the powder-based AM of shape memory alloys (SMA). A general overview of the processes currently employed for printing SMAs is given. Moreover, some highlightable results of the effects of processing parameters on the transformation temperatures and functional properties are explored. Also, the microstructure evolution based on different process parameters of directed energy deposition samples is clarified. The fabrication of NiTi-based high-temperature SMA and in situ alloying of NiTi SMA are briefly explored. Some examples of application in the biomedical and micro-electromechanical are illustrated, followed by the last section, where the AM of alloys other than NiTi (e.g., iron and copper-based SMAs) is discussed. High entropy alloys (HEA) are in the subsequent section. An explanation about this novel class of alloys comes first, followed by a short technological overview and a concise sub-section regarding the powder development of HEAs. Successfully printed HEAs may be found in two separate tables where it is possible to find the technique and related process parameters. Lastly, in this section, one compares the mechanical properties of several printed HEAs. In sequence, it is possible to find the AM of magnetic materials. An introduction about Nd-Fe-B magnets is presented, and some techniques used to print magnets are explored within this sub-section; the same applies to the sub-section on Fe-Co alloys. Lastly, the AM of soft magnetic materials is explained using some examples of the effect of process parameters on the magnetic properties and the role of in situ alloying in overcoming the difficulties of printing magnets. Still, on the topic of in situ alloying, the last section of this block on specific classes of alloys is dedicated to exploring this method, focusing on the powder quality and mixing, the melting temperature, energy input and homogeneity, i.e., feedstock properties and process features.
The last section is preceded by one focused on the recyclability of Ti-64 powder, where it is possible to keep up the influence of the reuse on the powder itself, the built parts and respective mechanical properties. Then, this chapter finishes with an outlook of new powder-based AM processes based on sintering-debinding, binder jetting, metal AM based on extrusion of highly filled polymer filaments, lithography and cold spray-based AM. The basics of each process are enlightened, and some examples are given to illustrate the capability of each process.
Porosity effect on the tribological properties of Al-Si alloys for diamond-like carbon coating of cold sprayed
2022, Journal of King Saud University - Engineering SciencesIn this study, diamond-like carbon (DLC) coating made from spherical powder SP and Irregular powder IP manufactured for plasma of cold sprayed by gas atomization is presented. Sliding assessment is carried out at different loads on each DLC coating. All DLC coating surfaces are characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Furthermore, coatings show low porosity and extreme hardness. Irregular powder IP coatings have proved to be less hardness than SP coatings. In case of IP coatings, abrasive plowing with used particles is resulted in an increased wear, while the available porosity in SP of the used particles is formed in some points of reduced sliding of wear. Coatings of IP cause an increasing of coefficient of friction (CoF). The load limitations are associated with tribooxidation in IP coatings, while mixed particles together with tribooxidation result in lower CoF with SP coatings. The range of CoF for all test parameters is 0.24–0.32. Transmission electron microscopy (TEM) shows characteristics body-filled pores composed of a deformed material with an ultrafine microstructure and micron-sized particles. The characterization confirms that 30% of pore-filled coatings are ultra-deformed fabric with microstructure and particles, while the worn surfaces have a rough microstructure. The effects confirm that SP hardness and porosity help attract particles and reduce abrasiveness.