# Laser-Based Additive Manufacturing of Zirconium
## 1 Introduction  
Additive manufacturing of zirconium (Zr) metal was done using the Laser Engineered Net Shaping (LENS(tm)) technique. Zirconium is commonly used in the nuclear, space, and aerospace industries due to its exceptional corrosion and oxidation resistance [1; 2; 3; 4]. Zirconium has also found uses in the biomedical device industry for load-bearing implants due to its wear and corrosion resistance [5; 6; 7]. These applications utilize Zr metal in the form of bulk components. Besides these bulk components, zirconium is also a popular choice for coatings to enhance high temperature oxidation resistance. For coatings on titanium alloys, Zr is used to serve the dual purpose of oxidation resistance at high temperatures and maintain the structural integrity with Ti6 Al4V components when used in compositionally graded structures with other alloys. Zirconium is a highly reactive metal in molten state and in the open atmosphere in presence of oxygen and hydrogen. It is pyrophoric in powdered state. This requires a special inert atmosphere or high vacuum in furnaces and smelting plants to maintain the purity of the metal as well as prevent fire hazards. Furthermore, due to its enhanced chemical activity in molten state, it can also take a toll on the crucible materials. Thus, processing of zirconium parts can be cumbersome, which can cause wastage of the precious metal. Due to rapid work hardening and formation of a brittle oxide layer on the surface, metal forming practices such as wire drawing and rolling are also challenging for Zr metal. Multiple annealing-cold working cycles are necessary. Annealing and other heat treatment practices are difficult due to the affinity of zirconium to common gases like oxygen and hydrogen at higher temperatures [8]. Hence, these difficulties necessitate processes that can be used safely to fabricate Zr components in a single step without degrading the desired properties. Additive manufacturing techniques, especially the direct energy deposition-based techniques have several advantages over traditional metallurgical practices. These advantages include 3D forming capability along with complex geometries, rapidly cooled microstructures, and the ability to form sitespecific compositionally graded structures. Along with bulk fabrication capability, these methods can also be used for surface modification. Thus, zirconium metal can be utilized in the form of coatings and these coatings can be processed in a single step process. Compositionally graded structures of zirconium with other important metallic materials such as Ti-based alloys can also be designed and fabricated in one operation. It is also possible to carry out laser-assisted repair of existing structures using zirconium instead of fabricating completely new structures. This could lead to cost savings and efficient use of precious metals like zirconium. These direct energy-based techniques or, more specifically, laser-based additive manufacturing techniques are carried out in a controlled, inert environment with low levels of oxygen. Such environmental control prevents any detrimental oxidation as well as fire hazards. All of these combined features of the additive manufacturing techniques can thus simplify the processing of materials like zirconium as well as make the processing safer and more economical. Laser engineered net shaping (LENS(tm)) is one such direct energy deposition-based additive manufacturing technique [9]. The LENS(tm) process is capable of fabricating near net shaped components, fabricating compositionally and structurally graded components, fabricating surface coatings and repairing existing components. Additive manufacturing via the LENS(tm) technique has been demonstrated previously for various specialty materials that were otherwise difficult to process owing to their higher melting temperature, phase stability, or high cooling rate requirements.