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Cold Spraying of Armstrong Process Titanium Powder for Additive Manufacturing D. MacDonald1 • R. Ferna´ndez1 • F. Delloro1 • B. Jodoin1

Submitted: 6 July 2016 / in revised form: 22 August 2016 Ó ASM International 2016

Abstract 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. Keywords additive manufacturing  Armstrong process  cold spray  powder morphology  titanium

& D. MacDonald [email protected] 1

University of Ottawa Cold Spray Laboratory, Ottawa, ON, Canada

Introduction Titanium is the ninth most abundant element on earth, has one of the highest specific strengths for a pure metal, maintains good properties at elevated temperatures, and has excellent corrosion resistance. However, the high cost to produce titanium components limits its use to high-end applications where cost is not a primary factor, usually in the aerospace, defense, and medical sectors (Ref 1, 2). This high cost is the result of two factors: The production of titanium mill product from primary materials requires many costly steps, and its reactivity and poor workability make it difficult to cast, forge, and machine (Ref 1). Typically, titanium is converted from raw primary materials (such as rutile) to titanium sponge through the Kroll process (Ref 1). It must then be purified through acid leaching and undergo vacuum arc remelting to form an ingot. The latter must then undergo primary fabrication into mill products, casting to a near-net shape (Ref 1), or atomized into powder form. Forging is difficult and expensive, requiring many steps and various heat treatments; only rarely is titanium directly forged into finished components. Casting is also possible but challenging due to the materials’ high reactivity to the atmosphere and to the other r