Titanium Coatings on AISI 316L Stainless Steel Formed by Thermal Decomposition of TiH 2 in Vacuum
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Mater. Res. Soc. Symp. Proc. Vol. 1243 © 2010 Materials Research Society
Titanium Coatings on AISI 316L Stainless Steel Formed by Thermal Decomposition of TiH2 in Vacuum Jorge López-Cuevas1, José L. Rodríguez-Galicia1, Juan C. Rendón-Angeles1, Martín I. PechCanul1 and Juan Méndez-Nonelll,2 1 CINVESTAV-IPN Unidad Saltillo, Ramos Arizpe, 25900 Coah., México 2 CIQA, Saltillo, 25253 Coah., México ABSTRACT Ti-coated AISI 316L stainless steel, for potential biomedical applications, is obtained by thermal decomposition of TiH2 under vacuum. The presence of hydrogen in the coating material facilitates the sintering process of Ti particles, with simultaneous formation of several interdiffusion layers at the substrate/coating interface, whose thickness and chemical composition depend mainly on the treatment temperature. Coatings prepared at 1100ºC exhibit formation of a wide zone at the substrate/coating interface, which is associated with the appearance of cracks, and which consists of a mixture of λ + χ + α-Fe phases. Formation of abundant microporosity is also observed in this region, which is attributed to the Kinkerdall effect. INTRODUCTION TiH2 dissociates into hydrogen and metallic Ti at ~525ºC under vacuum [1]. It contains ~96 wt % Ti and is inert to water, air and most acids [2]. During its thermal dissociation, hydrogen migrates into the furnace atmosphere, while metallic Ti covers the container walls with a thin film. This phenomenon has been employed since the 1950’s in order to produce Ti coatings at the surface of some ceramic materials such as alumina. After being coated with Ti, the ceramic pieces can be better wetted by molten metals during the preparation of metal-matrix composites, or can be joined more easily with other ceramic or metallic materials. Other applications of TiH2 include the formation of aluminum foams [3] and hydrogen storage [2]. In the latter case, hydrogen in Zn or Fe solid solutions can be easily liberated to feed internal combustion engines or fuel cells. Thermal dissociation of TiH2 under vacuum has not been reported previously for the production of Ti coatings on the surface of ferrous or non-ferrous metals or alloys. Thus, in the present work this method is used for the formation of Ti coatings on the surface of AISI 316L stainless steel, for potential biomedical applications. However, although the studied method constitutes an easy way to potentially increase the biocompatibility and osseointegration properties of AISI 316L Stainless Steel [4, 5], further work would have to be carried out in order to address several related important issues that may arise. First, the necessity to limit the formation and growth, at the substrate/coating interface, of any phases and microporosity that can be deleterious for the material’s mechanical strength [6]. Next, there could be some biocompatibility concerns if the resulting Ti coatings have a relatively high Ni concentration (although it is known [7] that some Ti-Ni alloys are biocompatible, especially when the formation of a film of TiO2 is
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