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Titanium powder metallurgy materials with solid solution nitrogen elements were developed by using pure Ti powder with high nitrogen contents (Ti-(N)), which were prepared via heat treatment from 640 °C to 800 °C in a N 2 gas atmosphere. Ti 2 N compound layers were formed at the Ti-(N) powder surface as a shell, and solid solution nitrogen elements were also detected in the matrix of this powder. Ti-(N) powder was consolidated by spark plasma sintering (SPS), where Ti 2 N compounds were completely decomposed, and hot extrusion was then used to fabricate fully dense titanium with solid solution nitrogen elements. X-ray diffraction analysis showed that the lattice constant of α-Ti along the c-axis clearly increased in proportion to the nitrogen content due to the nitrogen solid solution behavior. Tensile test results revealed that the powder metallurgy titanium with 0.52 mass% nitrogen exhibited a 0.2% yield stress of 813 MPa and 31% elongation, which were remarkably superior to the strength-ductility balance of pure titanium with a 0.2% yield stress of 305 MPa and 25% elongation. In this study, the Hall-Petch equation and Labusch model were used to quantitatively evaluate the mechanism for the α-Ti grain refinement and solid solution strengthening effects of Ti-(N) powder metallurgy materials. [ABSTRACT FROM AUTHOR]

This paper investigates the cyclic elastoplastic anisotropy of Ti-6Al-4V manufactured via selective laser melting, caused by different build orientations. Tensile monotonic and cyclic stepped symmetric strain-controlled tests on coupons manufactured at 0°, 45°, and 90° build orientations were performed for both the SLM material and for a mill annealed material. The microstructure characteristics of the SLM material were examined through optical and electron microscopy revealing a unique α' martensite microstructure. The examination of the evolving tensile and compressive maximum stresses identified an interesting phenomenon, that of asymmetric cyclic softening. This phenomenon was observed only in the SLM Ti-6Al-4V, while its wrought counterpart confirmed the findings of past research reported in the literature. The residual stresses presented in the SLM coupons had a significant influence on the cyclic behaviour of the material. Mechanical anisotropy in both monotonic and cyclic tests was noticed with the diagonal (45°) coupon having the largest yield stress in both loading conditions. The findings of this research study can be very useful in engineering applications utilising as-built SLM materials. [ABSTRACT FROM AUTHOR]