WEB Single-step oxygen diffusion hardening of titanium alloys at reduced oxygen partial pressures – a method towards improved surface propertiesWednesday (01.01.2020) 00:15 - 00:30 Part of:
Single-step oxygen diffusion hardening of titanium alloys at reduced oxygen partial pressures – a method towards improved surface properties
Daniel Dickes, Mike Mosbacher, Uwe Glatzel
Metals and Alloys, University Bayreuth, Bayreuth
Titanium alloys, e.g. deployed in orthopedic implants or in engine valves, exhibit wear due to sliding contacts with a counterpart. One method of surface treatment to improve wear characteristics of titanium alloys is thermal oxidation. Different approaches of thermal oxidation have been shown in the past. Single-step oxidation at elevated temperatures in an oxidizing environment, such as air, leads to a protective TiO2 layer with only poor adherence. Such a TiO2 layer can be removed in a subsequent thermal treatment performed in vacuum in which oxygen from the TiO2 layer diffuses into the substrate. This leads to a surface near oxygen diffusion zone with an increased hardness compared to the substrate. Aim of this work is to investigate a single-step thermal oxidation method which simultaneously produces an adherent protective TiO2 layer and a distinctive oxygen diffusion zone. For this purpose, a furnace developed in our lab, which allows oxidation at oxygen partial pressure below 10^-12 Pa, is used. The formation of TiO2 layers and oxygen diffusion zones is analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy to increase the understanding of underlying reaction- and diffusion kinetics. With regard to a better oxide layer adherence, in depth microhardness profiles of the oxidized specimens are determined and compared with oxygen concentration profiles.