Ti-6Al-4V has been widely used in both the biomedical and aerospace industry, due to its high strength, corrosion resistance, high fracture toughness and light weight. Additive manufacturing (AM) is an attractive method of Ti-6Al-4V parts' fabrication, as it provides a low waste alternative for complex geometries. With continued progress being made in SLM technology, the influence of build layers, grain boundaries and defects can be combined to improve further the design process and allow the fabrication of components with improved static and fatigue strength in critical loading directions. To initiate this possibility, the mechanical properties, including monotonic, low and high cycle fatigue and fracture mechanical behaviour, of machined as-built SLM Ti-6Al-4V, have been critically reviewed in order to inform the research community. The corresponding crystallographic phases, defects and layer orientations have been analysed to determine the influence of these features on the mechanical behaviour. This review paper intends to enhance our understanding of how these features can be manipulated and utilised to improve the fatigue resistance of components fabricated from Ti-6Al-4V using the SLM technology.

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An investigation into the effect of size on the quantitative estimation of defect depth in a steel specimen has been undertaken using lock-in thermography. Phase contrast measurements over circular defects of varying diameter and depth are presented for a range of excitation frequencies. It was found that the diameter of a defect had an appreciable effect on the observed phase angle which consequently has significant implications with regard to estimating defect depth. Phase contrast measurements for a range of defects in a 10 mm steel specimen indicate that an excitation frequency of 0.02 Hz is the optimal frequency for defect detection. Results obtained with an excitation frequency of 0.02 Hz are used to discuss the limitations of determining the size and depth of defects. A finite element analysis was found to have good correlation with experimental data and thus demonstrates potential in providing improved estimates of defect depth.

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