## 1 Introduction  
Titanium and its alloys have garnered considerable attention for various industrial applications, particularly in the aerospace, biomedical, and marine sectors, due to their remarkable properties, including a high strength-to-weight ratio, excellent corrosion resistance, and superior biocompatibility [1]. Ti grade 2 is one of the most interesting to work with because it is widely used in industrial applications since it is of commercial purity [2]. However, the surface quality of titanium alloys is crucial for their performance and service life, which necessitates effective surface enhancement techniques [3]. In particular, improving surface quality can enhance fatigue resistance and lengthen service life, which are critical in demanding applications. Surface treatment techniques, particularly for increasing the fatigue life and improving the surface integrity of titanium alloys, are of great importance in this context. Ball burnishing has emerged as an effective cold-working process that can significantly improve surface characteristics without removing material [4]. This process involves plastically deforming the surface layers by applying controlled force using a hardened ball. As a result, it reduces surface roughness and enhances surface hardness [5]. Ball burnishing has gained attention for its ability to produce a superior surface finish compared to conventional machining processes while inducing beneficial compressive residual stresses in the surface layer [6]. These improvements are particularly beneficial in applications with paramount surface integrity and mechanical performance. In recent years, innovative surface improvement techniques such as low plasticity burnishing (LPB) have been widely used to increase the fatigue life and improve the surface integrity of materials [7]. Recent studies have demonstrated that low plasticity burnishing can significantly enhance surface integrity parameters while minimizing cold work effects. Research has shown that using appropriate burnishing pressure (typically 15-20 MPa) and an optimal number of passes (2-3 passes) can result in surface hardness improvements of up to 34 Vickers hardness, along with the formation of a stable compressive residual stress layer [8]. Studies have reported that LPB can achieve compressive residual stress improvements of up to 45-50% at the surface level, with the effects extending to depths of approximately 300 \(\upmu\)m in titanium alloys [9]. The effectiveness of the ball burnishing process is strongly influenced by a number of parameters. The burnishing environment, particularly the lubrication condition, is one of the factors that play an important role in determining the outcome of the burnishing process [10]. Although dry burnishing offers simplicity and environmental benefits, this study highlights the potential of MQL as a sustainable alternative [11]. MQL can improve process efficiency while maintaining environmental consciousness, making it a key research focus [12]. It has also been reported that finishing operations under MQL conditions can reduce surface roughness by up to 90% and minimize environmental impacts [9]. This approach aligns with the growing emphasis on sustainable manufacturing practices across industries. Furthermore, MQL machining has been found to reduce surface defects such as scratches, burrs, and cracks, which are common in dry machining. The high-pressure oil mist used in MQL provides both lubrication and cooling, reducing plastic deformation and improving surface quality [13]. However, the effectiveness of MQL is highly dependent on the lubrication amount and nozzle positioning, as insufficient lubrication can lead to poor surface quality and increased tool wear [14]. Advanced surface characterization techniques have revealed that ball burnishing not only improves surface roughness but also significantly affects the microstructural properties of the treated surface.