# Titanium Additive Manufacturing with Powder Bed Fusion: A Bibliometric Perspective
## 1 Introduction  
Additive manufacturing (AM), commonly known as 3D printing, has revolutionized various industrial sectors by enabling the efficient and precise creation of complex and customized geometries [1, 2]. This technology builds objects layer by layer from digital models, offering significant advantages in terms of design flexibility, material savings, and the ability to produce complex structures that are difficult or impossible to achieve with traditional manufacturing methods [3]. Printing metals is significantly more challenging and costly compared to polymers due to the higher temperatures and controlled atmospheres required for melting metals, as well as the need for more advanced equipment to handle these conditions. Additionally, achieving the desired material properties in metals demands greater precision and control, further increasing the complexity and expense of the process [4]. Among all the metals, titanium possesses exceptional properties, which make it highly valuable in various high-performance applications. Titanium exhibits an outstanding strength-to-weight ratio, making it suitable for aerospace and automotive components where reducing weight without compromising strength is crucial [5, 6, 7]. Here, spare parts management is important in these sectors [8, 9]. Its excellent corrosion resistance extends its utility in harsh environments, such as marine and chemical processing industries [10]. Moreover, titanium's biocompatibility makes it the material of choice for medical implants and devices [11, 12, 13, 14, 15]. The ability to produce complex titanium parts efficiently and with high precision through AM could lead to significant advancements in these critical industries. For this reason, significant efforts have been made to optimize the AM of titanium. AM is dominated by two primary techniques: powder bed fusion (PBF) and directed energy deposition (DED). On the one hand, PBF involves spreading a thin layer of powder material over a build platform, which is then selectively fused by a heat source, such as a laser or electron beam, to form a solid layer. This process is repeated layer by layer to create the final part [16]. On the other hand, directed energy deposition uses a focused energy source to melt materials as they are being deposited [17]. Both techniques have their unique advantages and are chosen based on the specific requirements of the application. PBF includes a variety of specialized techniques, each with unique features and uses. The main processes are selective laser melting (SLM), selective laser sintering (SLS), and electron beam melting (EBM). SLM uses a high-powered laser to fully melt and fuse metallic powders, resulting in dense and strong parts [18; 19]. On the other hand, SLS uses a laser to sinter powdered material without fully melting the particles, operating at lower power levels compared to SLM [20; 21]. Both techniques (SLM and SLS) require controlled atmospheres, such as argon or nitrogen, to enhance corrosion resistance or an oxygen-controlled environment, for example, to optimize the microstructure of titanium [22; 23]. EMB employs an electron beam as the heat source, offering high efficiency and the ability to work in a vacuum environment, which is particularly beneficial for processing reactive materials like titanium [24; 25]. Each of these techniques has its advantages, making them suitable for different applications within the field of additive manufacturing. Another major technique of additive manufacturing, DED includes advanced techniques such as laser cladding and direct deposition using wires or powders. Laser cladding utilizes a laser to melt and deposit feedstock onto a substrate, creating a strong bond and enhancing surface properties [26]. Direct deposition builds parts layer by layer, either by melting powder with a high-energy source or by using a continuous feed of metal wire [27]. Despite its versatility and benefits, DED is less commonly used in industrial and research settings compared to PBF [28; 29; 30].