Material issues in additive manufacturing: A review

Powder metallurgy (PM) of titanium is a potentially cost-effective alternative to conventional wrought titanium. This article examines both traditional and emerging technologies, including the prod...

https://www.tandfonline.com/doi/pdf/10.1080/09506608.2017.1366003

Powder metallurgy of titanium – past, present, and future

Spherical titanium alloy powder is an important raw material for near-net-shape fabrication via a powder metallurgy (PM) manufacturing route, as well as feedstock for powder injection molding, and additive manufacturing (AM). Nevertheless, the cost of Ti powder including spherical Ti alloy has been a major hurdle that prevented PM Ti from being adopted for a wide range of applications. Especially with the increasing importance of powder-bed based AM technologies, the demand for spherical Ti powder has brought renewed attention on properties and cost, as well as on powder-producing processes. The performance of Ti components manufactured from powder has a strong dependence on the quality of powder, and it is therefore crucial to understand the properties and production methods of powder. This article aims to provide a cursory review of the basic techniques of commercial and emerging methods for making spherical Ti powder. The advantages as well as limitations of different methods are discussed.

https://link.springer.com/content/pdf/10.1007/s11837-017-2513-5.pdf

Review of the Methods for Production of Spherical Ti and Ti Alloy Powder

A novel method for production of spherical Ti-6Al-4V powder for additive manufacturing

Titanium parts are ideally suited for aerospace applications due to their unique combination of high specific strength and excellent corrosion resistance. However, titanium as bulk material is expensive and challenging/costly to machine. Production of complex titanium parts through additive manufacturing looks promising, but there are still many barriers to overcome before reaching mainstream commercialization. The cold gas dynamic spraying process offers the potential for additive manufacturing of large titanium parts due to its reduced reactive environment, its simplicity to operate, and the high deposition rates it offers. A few challenges are to be addressed before the additive manufacturing potential of titanium by cold gas dynamic spraying can be reached. In particular, it is known that titanium is easy to deposit by cold gas dynamic spraying, but the deposits produced are usually porous when nitrogen is used as the carrier gas. In this work, a method to manufacture low-porosity titanium components at high deposition efficiencies is revealed. The components are produced by combining low-pressure cold spray using nitrogen as the carrier gas with low-cost titanium powder produced using the Armstrong process. The microstructure and mechanical properties of additive manufactured titanium components are investigated.

/pdf/cold-spraying-of-armstrong-process-titanium-powder-for-2tqmayv21m.pdf

Cold Spraying of Armstrong Process Titanium Powder for Additive Manufacturing

The Armstrong Process® is a novel powder production process capable of producing commercially pure titanium and Ti-6Al-4V by the reduction of titanium tetrachloride and other metal halides by sodium The process produces powder particles with a unique, low bulk density, “coral-like” morphology Postprocessing activities such as dry and wet ball milling provide a means of increasing the tap density and narrowing the particle size distribution to meet the requirements for typical powder metallurgy conversion processes The Armstrong Process powder’s unique morphology produces excellent compressibility and compaction behavior, capable of producing compacts with significantly higher green strength than other irregular powders Powders can be consolidated by traditional powder metallurgy techniques such as uniaxial compaction and cold isostatic pressing Optimal parameters for consolidation via such techniques have been established The high degree of interlocking between adjacent powder particles offers distinct advantages in roll compaction, allowing for the direct rolling of powder into titanium sheet Examinations of the sintering behavior of compacts produced from The Armstrong Process powders show that the higher surface area-to-volume ratio of the material results in the onset of sintering and shrinkage at a much lower temperature than other powders As result, less aggressive sintering conditions are required for near-full densification The Armstrong Process powders can be spheroidized by plasma induction as a means of increasing overall tap density and powder flow rate to make it ideal for applications such as metal injection molding and additive manufacturing

Production of titanium by the Armstrong Process

The processing of titanium powder has been presumed to have potential to reduce the cost of final parts. The non-melt routes to efficient powder processing require consistent flow, adequate tap density and minimal pick-up of interstitial contaminants. The powder produced by the continuous sodium reduction of titanium tetrachloride has a coral-like morphology and low tap density. In order to achieve the potential of low cost parts, the powder will need to be modified to match the optimum feed conditions of the particular processing technique. The approaches to control interstitial pick-up will be discussed in the context of manufacturing technology: contribution of raw materials (10%), passivation (60%) and densification (30%). A comparison of densification with a change of milling fluid media (argon to water will be made with the unexpected decrease in oxygen pick-up when using water). Powder spheroidization via gas atomization of Armstrong Process® powder will be discussed. The product forms where the advantages of using powder can be exploited have to be carefully selected. Sheet is one such form: the results of using titanium powder to directly make titanium sheet will be presented.

Damien Mangabhai

Papers

Production of titanium by the Armstrong Process

Processing of Titanium Powder into Consolidated Parts & Sheet