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New thermochemical treatment of Titanium parts improving their wear resistant characteristics and their life time

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Titanium has been known as a common element for nearly 200 years and is the fourth most commonly occurring mineral. Although titanium is such a common element, the pure metal is still expensive. Nevertheless, titanium is being more and more used in a wide range of applications, from the aerospace industry to leisure uses. In fact, the main drawback of titanium, despite its cost, is that it usually needs additional treatments to enhance its wear resistance capabilities. These treatments are usually expensive which limit their use to high added value parts. The aim of the TINITRON project is consequently to develop a treatment giving excellent wear resistance to titanium parts at the lowest cost possible for a wide range of applications. This thermo chemical treatment is based on nitrogen diffusion in titanium. The diffusion of nitrogen will create a compound layer of TiN + Ti2N and a diffusion layer Ti(N) underneath. As the treatment is based on diffusion there are no adhesion problems. These layers harden the surface of the material and the compound layer increases its wear resistance. Furthermore, this treatment is performed under low pressure, which minimises the gas consumption and the environmental impact. TINITRON permits a homogeneous treatment of complex shaped parts (grooves, hole, etc.) in bulk. This treatment can be used in the medical field, as it is 100 % biocompatible because of the superficial TiN layer. Finally, TINITRON is 5 to 10 times less expensive than usual ionic implantation surface treatment of titanium: the necessary equipment is really simple and very easy to use. The treatment performed on the industrial applications met in this project shows in all cases an increasing of the titanium parts behaviour.For example, it increases the life time of the treated sonotrodes for welding and cutting at a minimum of 2 to 3 times, even if the conditions are very rough like in the case of fibre glass polymer welding. On mechanical automotive applications, the treatment improves the wear and the galling resistance particularly with highly loaded parts. As a conclusion, the treatment will be proposed to the racing car industry customers, who will adopt it soon. The treatment is a solution proposed to the biomedical rachis prosthesis applications too. Indeed, it considerably reduces the fretting corrosion degradations and increases the prosthesis lifetime. Finally, the treated titanium index guides used in transfer machines do not show any wear after the work period during which the first solution failed (Aluminium alloy index guide with tool steel inserts). The main prospect of the TINITRON process would be its acceptance in the aeronautical field. Indeed, we discovered during this project a means to put out the hydrogen atoms diffused in the material in the same time as the nitrogen ones. Before that, the use of this treatment was forbidden in the aeronautical field because of the fatigue properties loss risks. We developed several treatments, which allow refining the standard concentration of hydrogen in titanium parts (< 150 ppm). Moreover, the fatigue resistance is only decreased by 10 % compared to a non-treated Ti6Al4V alloy. These results show that the nitriding treatment developed during the EURO-TIN project seems to promise a good development in industrial fields.

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