Modelling the oxygen diffusion profile in TA3V and T40 during heat-treatment under air between 620 and 850 °C

Abstract

The great affinity of titanium for oxygen, in the course of thermal treatment, causes the formation of oxide layers on the surface of the parts treated. One of the techniques to avoid oxidation is using vacuum furnaces, be it primary or even secondary vacuum, and adding an oxygen getter to eliminate any risk of pollution. Another technique consists in using furnaces operating in a neutral atmosphere and eliminating the oxide layer after treatment. To eliminate the polluted layer and avoid losing too much material, oxidation should be evaluated and kept under control and we must have information about the effect of the atmosphere of the thermal treatment on the oxide layer formed. The research was conducted on a commercially pure titanium (T40) and an alloy of the TA3V type. The atmosphere used is O2–N2 with 20% rates of oxygen content. The primary results show that, in the 893–1123 K temperature range, the thickness of the external oxidized zone varies between 0.2 and 4 μm in the case of an air atmosphere. In the latter case, nitrogen plays certainly the role of an oxidation inhibitor as it works as a barrier to diffusion. In this paper, we also have determined all the coefficient (activation energy and autodiffusion coefficient) to predict the thickness of the oxidized layer and diffused layer.