High Temperature Oxidation Behaviour of Titanium After Shot-Peening

Author:  A. Kanjer, V. Optasanu, L. Lavisse, M.C. Marco de Lucas, P. Berger, M. François, T. Montesin
Source:  ICSP-13
Doc ID:  2017040
Year of Publication:  2017
Abstract:  
Introduction: A wider use of Ti alloys at high operating temperature in gas-turbine engines and other industrial components could be reached by a better protection against high temperature oxidation. The excellent combination of light-weight and good mechanical properties makes the Ti alloys attractive for compressor section components in gas turbine engines1. Compared to Ni-super alloys and steels, Titanium offers potential weight savings in the order of 50%. High-performance coatings or surface treatments are necessary for protection against high-temperature oxidation. At low temperatures, Ti alloys show very good corrosion resistance thanks to the TiO2 passive surface layer. Above 600 °C, a deterioration of the passivation layer and then an acceleration of the oxidation rate is possible. The result is an inward diffusion of oxygen and an internal formation of a rich oxygencontent area, called the α-case2. In the case of the oxidation in air, the formation of a nitride layer between the oxide layer and the α-case area was observed3. This nitride layer slows down the oxygen diffusion and then brings a protection in terms of oxidation. A problem for the oxidation resistance can be the possible spallation of the oxide film. The development of efficient oxidation-resistant coatings for titanium alloys is necessary. Two main problems are usually encountered in the high-temperature oxidation of surface treated Ti alloys: (1)interdiffusion between the coating and the bulk and (2) the cracking of the coating or oxide layer. The most usual treatments are ion implantation4, pack cementation coatings5 and PVD ceramic coatings6. Mechanical treatments are less used for oxidation protection purposes but are widely used to obtain an enhancement of the mechanical surface properties like tribological or fatigue behaviours7-9. A recent work10 shows a positive role of the mechanical treatments in the oxidation resistance of materials after the generation of large compressive stresses on sub-surface.