Sintering of titanium in argon and vacuum: Pore evolution and mechanical properties

Abstract

Reducing porosity can help to improve the mechanical properties of an as-sintered material. An alternative is, however, to tailor the size, distribution and morphology of the residual pores without having to further reduce porosity. This study investigates the sintering of commercially pure titanium (CP Ti) in a flowing argon (Ar) atmosphere and compares the results with sintering in a vacuum of 10−2 Pa. The CP Ti sintered in Ar at 1300 °C for 2–3 h exhibited a marginally lower density but clearly better tensile ductility than Ti sintered in vacuum. The sensitivity of tensile ductility to residual pores was analyzed. Samples sintered in Ar exhibited much lower sensitivity than those sintered in vacuum. The superior ductility arises from the beneficial effect of sintering in Ar, which resulted in a greater number of but smaller residual pores with lower pore aspect ratios and finer matrix grains due to the grain-growth inhibiting role of the residual pores. The reason is attributed to the entrapped Ar in the closed pores during sintering, which is insoluble in Ti at the sintering temperature. The ever-increasing internal pore pressure prevents further pore shrinkage after reaching a critical size. The final pore size range is predicted and compared with experimental observations. Sintering of titanium in Ar is advantageous over sintering in vacuum in terms of both pore size distribution and pore morphology within a reasonable isothermal sintering period (e.g., 3 h at 1300 °C). Therefore, it can be more attractive for non-fatigue critical applications than sintering in vacuum.