Strength-ductility improvement of extruded Ti-(N) materials using pure Ti powder with high nitrogen solution

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 degrees C to 800 degrees C in a N-2 gas atmosphere. Ti2N 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 Ti2N 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 alpha-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 alpha-Ti grain refinement and solid solution strengthening effects of Ti-(N) powder metallurgy materials.