## 1 Introduction  
Laser powder bed fusion (LPBF) is an additive manufacturing technique that uses a laser beam to melt and fuse metal powder on a bed in a layer-by-layer process to build three-dimensional (3D) components. The technology is currently being used in the fabrication of components for use in the automobile, aerospace, and biomedical industries [1, 2, 3]. The use of the technology in these industries is greatly motivated by its flexibility, such as the ability to manufacture parts with intricate and topology-optimized geometry, no tooling requirement, and minimal post-process machining requirements [4]. LPBF is characterized by multiple process parameters such as scanning speed, laser power, hatch-spacing, and laser diameter [5]. These parameters affect the quality and properties of produced parts, such as surface roughness, residual stress, and microstructure [6, 7]. The laser energy in LPBF could also engender patterns on the surface of materials which affect their properties such as tribology and biocompatibility [8]. Researchers around the globe have successfully endeavoured to optimize the process parameters of LPBF for fabricating different materials such as titanium-based alloys, steel alloys, and aluminium-based alloys [9, 10, 11]. In fact, Electro Optical Systems (EOS) offers a range of validated processes parameters for steel, titanium-based, and aluminium-based alloys that are optimal in order to ensure that the properties of the additively manufactured parts are consistently achieved with minimal defects [12]. The most commonly produced and investigated LPBF material is the Ti6 Al4V alloy due to its vast light-weighting applications in the aerospace and biomedical industries [13; 14]. Due to the versatile nature of AM, biomedical implants and devices can be manufactured from different materials, tailored to the needs of individual patients and medical conditions [3]. Because of this, research centres around the globe, such as the Centre for Rapid Prototyping and Manufacturing (CRPM) of Central University of Technology, Free State, have successfully been established for the additive manufacturing of biomedical implants and devices [15]. The use of AM-produced parts in the aerospace sector is more challenging due to the stringent safety requirements in the sector [2]. The production of the Ti6 Al4V(ELI) alloy via AM is attributed to the strong business case that it can be developed for complex and low production volumes of its parts with less wastage of raw material [13]. The as-fabricated LPBF Ti6 Al4V alloy is characterized by a non-equilibrium microstructure consisting of columnar prior-\(\beta\) grains filled with a hierarchical structure of acicular martensitic structure [14; 16]. The martensitic structure is considered as a hierarchical one, as primary, secondary, tertiary, and quartic \(\alpha^{\prime}\) martensite laths are formed within columnar prior \(\beta\)-grains [17]. Moreover, steep temperature gradients develop during the LPBF process due to localized heating and cooling. This causes differential expansion and contraction in different locations of the produced components [18], subsequently generating stresses and strains that remain in the parts as tensile residual stresses and strains [19]. The non-equilibrium microstructure of Ti6 Al4V (ELI) produced during LPBF exhibits high strength and low ductility [4]. Furthermore, the tensile residual stresses of its parts are detrimental since they contribute to fatigue damage and stress corrosion cracking [20]. These issues limit the usage of as-fabricated LPBF Ti6 Al4V in the aircraft industry, which has stringent safety requirements. Consequently, post-process heat treatment is employed on LPBF parts for the reduction of residual stresses and, ultimately, the transformation of the non-equilibrium microstructure to a ductile and stable \(\alpha+\beta\) microstructure.