High temperature solid-solubility limit and phase studies in the system tantalum-oxygen

Abstract

The solid solubility limit of oxygen in tantalum has been determined in the temperature range 1100 °C–2500 °C. The terminal solubility increases from 3 at.%O at 1100 °C to 5.7 at.%O at 1880 °C; the solubility line shows a slight kink at 1550 °C and 5.1 at.%O. From the determinations of the terminal solubility and from quantitative metallographic examination of arc-melted alloys containing 20–70 at.%O a partial TaTa 2O 5 phase diagram is proposed. The system shows a liquid immiscibility gap and hence a monotectic at 1880° C ± 30 ° C with the equilibrium phases α-Ta (5.7 at.%O), liquid L I(≈43 at.%O), and liquid L II(≈65 at.%O). Liquid L II decomposes by an eutectic reaction at 1550° C ± 30 ° C with the equilibrium phases α-Ta (5.1 at.%O). L II (≈71at.%O), and Ta 2O 5.