## 1 Introduction  
Additive manufacturing (AM) has become very interesting due to its advantages compared to conventional technologies. It has found its place in various fields of industry. Biomedicine is a field whose development is supported by technology. The increasing need for patient-specific biomedical implants has driven rapid advancements in both conventional and additive manufacturing of titanium alloys, with Ti-6 Al-7 Nb being recognized for its biocompatibility [1], corrosion resistance, and mechanical strength, making it a preferred material for orthopedic and dental applications [2; 3; 4; 5]. It is an alloy consisting of an \(\alpha\) and \(\beta\) phase, where the \(\alpha\) phase is a hexagonal close packed structure providing strength and corrosion resistance, and the \(\beta\) phase is a body-centered cubic structure which contributes to improved ductility. When produced as an \(\alpha+\beta\) alloy by conventional production processes, it has good overall mechanical properties [6] with a Young's elasticity modulus E = 110,000 MPa, and a tensile strength Rm = 1050 MPa. In addition to their mechanical strength and biocompatibility, Ti-6 Al-7 Nb alloys exhibit favorable tribological properties, making them suitable for load-bearing biomedical implants such as hip prostheses [7]. The Ti-6 Al-7 Nb alloy emerged as a commercially available alternative to Ti-6 Al-4V due to concerns about the potential carcinogenicity of vanadium [8]. Recent developments in additive manufacturing have enabled sophisticated lattice structures that address fundamental limitations of conventional solid titanium implants [9], which provide solutions to osseointegration challenges and mechanical property mismatch between the implant and bone tissue. There is a significant stiffness mismatch between conventional titanium alloys and human bone, as the Ti-alloys exhibit a Young's modulus of approximately 110 GPa, at least three times higher than cortical bone (10-29 GPa) and substantially greater than trabecular bone (0.8-5 GPa) [9]. This mechanical disparity leads to stress shielding phenomena, where implants carry disproportionate loads, resulting in inadequate stress levels in surrounding bone. Research demonstrates that lattice structures can reduce the elastic modulus from over 100 GPa to 6-28 GPa [1]. Recent research in additive manufacturing emphasizes the development of new materials to address the growing need for advanced alloy design and process optimization. This is particularly important for SLM, where controlling fracture behavior remains a significant challenge. Efforts are increasingly focused on designing alloys and refining processing methods to improve the mechanical reliability and fracture resistance of SLM-produced parts [10]. Conventional processing techniques such as drawing remain the standard for mechanical reliability and ductility but are limited in design by geometry and produce significant material waste, which is particularly problematic for complex implant geometries and high-cost materials [11]. Additive manufacturing, especially SLM, a production process which uses a laser beam to melt the metal powder [12], has emerged as an alternative, enabling the freedom of design and production of customized implants with minimal waste [5; 13]. However, concerns still exist regarding the fatigue and fracture performance of SLM-produced Ti-6 Al-7 Nb due to its well-known porosity [1; 14], heterogenous microstructure, and residual stresses, which can significantly affect the durability of the produced components [3; 4; 15]. The main research hypothesis of this study is that the fracture mechanics parameters, specifically threshold stress intensity factor, fracture toughness, and crack growth behavior of the Ti-6 Al-7 Nb alloy, differ significantly between specimens produced by conventional production process and those produced by SLM.