Microstructure and mechanical properties of pure titanium models fabricated by selective laser melting

The pore structure, the hardness and the mechanical properties of three-dimensional titanium models formed by the selective laser melting method with a neodymium-doped yttrium aluminium garnet (Nd:YAG) pulsed laser are investigated. The optical and scanning electron micrographs show that pore structure depends on the peak power, the scan speed and the hatching pitch. The Vickers hardness of the laser formed specimens is around 240 HV (0.2 kgf), higher than that of the wrought material (125-160HV). Depth profiling by X-ray photoelectron spectroscopy (XPS) indicates that oxygen pick-up occurs during laser forming of the titanium model processed in a closed chamber filled with argon. The fatigue strength of the titanium models formed by changing the hatching pitch and the laser power were measured. It is possible to improve the fatigue strength of the as-formed models by decreasing the hatching pitch or by hot isostatic pressing (HIP). The specimens after HIP have a fatigue strength comparable to the wrought material.