## 1 Introduction
Due to the expense of post-process defect-detecting tools like CT, in-situ AM techniques are gaining favor. * [PERSON] et al. [37] discussed the unmachined surface would cause earlier fatigue failure compared to machined samples. Final machining and polishing are critical for assessing Very High Cycle Fatigue (VHCF) strength. In addition to titanium and aluminum alloy, several other commercially available materials must be AM-produced. Study fracture initiation in AM-manufactured components to establish reliable design procedures and discover whether traditional design approaches may be used for AM materials. * [PERSON] et al. [38] discussed that horizontal builds offer better mechanical properties than vertical builds for SLM steel's fatigue life. Improved temperature gradients, finer microstructure, and precise alignment of linear and planar defects in horizontal specimens increase mechanical properties. Uniaxial fatigue tests are common. Multiaxial loading affects SLM steel's fatigue behavior. This gap may lead to a lack of knowledge of damage processes and an inability to anticipate industrial fatigue life. * [PERSON] et al. [39] investigated the fatigue and fracture properties of powdered titanium alloys. Powder-based approaches are more cost-effective than ingot-based processes for manufacturing equivalent or improved titanium alloys. Oxygen concentration affects Titanium alloy fatigue and fracture. Microhardness is sensitive to oxygen content; hence, its regulation is crucial. * [PERSON] et al. [40] study compares Ti-6 Al-4V and conventionally produced components for uniaxial fatigue. The inability to consistently connect microstructure and defects to fatigue performance is a challenge for AM. To create and validate such models, more complete characterizations of defect populations and their spatial distribution, for example, for free surfaces, are needed, together with fatigue sample data from well-characterized specimens, for example, surface treatment. To ensure reliable and secure functioning, the certification framework must be aware of the application and the parameters listed. * An [PERSON] et al. [41] review examines fatigue characteristics and problems in laser-based AM metallic components. Several AM techniques use process-structure-property-performance (PSPP) correlation to reduce fatigue hazards. All of these variables must be considered since the fabrication parameters (process) of AM components affect their morphology (structure), which affects their mechanical properties and quality (performance). * [PERSON] [PERSON] et al. [42] study examines Electron Beam Melting (EBM) -made Ti-6 Al-4V fatigue life. To establish fatigue parameters, the findings were compared to normally manufactured Ti-6 Al-4V via AM EBM. According to the research, Hot Isostatic Pressing (HIP) and machining are the best ways to increase EBM part fatigue life. * A review by [PERSON] et al. [43] focuses on AM Ti-6 Al-4V. This study focuses on fatigue difficulties such as fatigue crack propagation, fatigue life, and fatigue behavior. It also quantifies the influence of faults on fatigue characteristics. In this research, SLM is preferred for manufacturing Ti-6 Al-4V with enhanced fatigue performance. Wire Arc Additive Manufacturing (WAAM) has the greatest fatigue strength among AM methods. Existing research reveals that AM-manufactured Ti-6 Al-4V is inadequate for fatigue-critical applications without post-processing consolidation, notably HIP, well as surface machining and polishing. Our findings show that the field is still in its infancy, with the majority of findings emphasizing the fatigue life of AM components. Over the last two decades, the quantity of scientific papers in AM has expanded significantly. A significant number of published review papers focus on experimental investigations of AM and technical insights. Also, there are so many factors that affect materials that it is very hard to make sure of their structure, process, and fatigue life.