## 1 Introduction  
Additive manufacturing (AM), also commonly known as 3D printing, is unlike subtractive methods since complex parts are produced additively layer by layer relying on a computer-aided device (CAD) file [1, 2]. During printing, the feedstock, i.e., powder or wire or a combination-off, is irradiated with an energy source either fully or partially until a desired part is complete. Distinctively, a laser beam or electrons are used as an energy source leading to AM techniques being classified as either laser AM or electron beam AM platform. In addition, a platform can be classified as either powder bed (PB) or direct energy deposition (DED); depending on how the feedstock is handled, fed, and interact with the energy source during deposition. Electron beam melting (EBM) and selective laser melting (SLM) are classified as powder bed platforms since the powder is overlaid on the depositing bed, typically a metal slab, before being irradiated and fused into the desired part. During DED powder is injected into a melt pool; that is created on the base plates, and upon solidification it fuses into a desired part. The significant difference between PB and DED system is in the complexity of structures that can be printed and the energy inputs that the built part can experience during manufacturing. DED is sustained with high energy inputs and temperature gradients that are due to the remelting of the previously deposited layer when compared to SLM systems. Hence parts which are 3D printed with DED systems are typically in-homogenous, microstructurally somewhat tempered, and highly stressed due to the thermal cycles that are experienced during manufacturing [3]. During process development most of the powder flow rates, laser spot size, laser-powder spot interaction (concentricity) are optimized to prevent powder inefficiencies, the loss in built edges, tearing, and rough surface finish. There are several DED systems, and these include direct metal deposition (DMD), direct laser metal deposition (DLMD), laser metal deposition (LMD), laser cladding (LC), and others. The Optomec 850-R LENS DED platform was used to carry out the aim and objectives of this research work. The aim was to investigate whether the 850-R LENS can be instrumental in printing ternary titanium-aluminium-niobium alloys from single-phase elemental powders as feedstock. The importance of this study was to help in elucidating and articulating the effects of niobium (Nb) on the composition (in-flight tweaking), microstructural transformation, and twinning of the gamma titanium aluminide alloys. This would be beneficial in understanding metallic alloying from the perspective of laser \"in situ\" alloying and begin to adapt the available powder metallurgy phase diagrams for laser-based 3D printed alloys from the elemental powder as opposed to pre-alloyed powders. The 850-R Optomec LENS is unique to other DED platforms since it offers freedom of operation. The 850-R LENS features include multiple hoppers that can be controlled simultaneously or independently (using software) and has an additional rotational and tilt movement that complete its five-axis movement during printing. The platform consists of three cameras, thermal sensor, and a pyrometer that are useful in melt-pool dynamics studies. Most recently, Researchers at the Council for Scientific and Industrial Research, South Africa, have demonstrated that at most four external hoppers and a substrate heating source can be integrated and feature as part of the LENS during processing. This therefore makes the 850-R LENS at the CSIR, South Africa a multiple hopper and heat-controlled platform in contrast to other 3D printers such as the Arcam EBM Spectra H, which is a powder bed system and commercially available and costly. Contrast to PB systems, the 850-R LENS can print metal structures from single-phase powder (e.g., Ti), pre-alloyed powder (e.g., Ti64), functionally graded structures (e.g., Ti: Ti64), composites (e.g., Ti-HAp), and reinforcements (e.g., WC-Ti).