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With their exceptional strength-to-weight ratio, titanium alloys find applications in numerous key enabling technologies. However, their implementation in harsh environments comes up against their limited resistance to high-temperature oxidation. To face this problem, in this work dense, amorphous alumina, Al2O3 coatings are applied on the surface of Ti6242S alloy by metalorganic chemical vapor deposition, MOCVD, from aluminum triisopropoxide, ATI and from dimethylaluminum isopropoxide, DMAI. Isothermal oxidation tests show that the parabolic rate constants of the mass gain of the coated Ti6242S coupons are reduced up to two orders of magnitude compared with the bare material. 5000 h long oxidation of DMAI Al2O3 coated alloy at 600 °C results in 0.180 mg cm−2 weight gain to be compared with 1.143 mg cm−2 for the bare alloy. In these conditions, an interfacial layer is formed, containing the complex Ti3(Al0.5Sn0.5) (or (Ti,Sn)2N) phase. Cyclic oxidation consisting of eighty, 1 h cycles between 50 and 600 °C show null mass gain of the coated sample. Finally, the hardness profiles determined on cross sections of oxidized coupons reveal a very limited oxygen dissolution for the coated alloy. MOCVD coatings of amorphous Al2O3 have great potential for efficient, durable protection against oxidation of Ti6242S alloys. [ABSTRACT FROM AUTHOR]

The chemical vapor deposition of carbon is performed onto a commercial silicon nitride powder bed. This produces few-layered-graphene (FLG) films or islands on the Si 3 N 4 particles. The samples are characterized by several techniques including Raman spectroscopy, scanning and transmission electron microscopy. The experimental parameters of the methane (CH 4) decomposition (temperature, CH 4 concentration, dwell time) are correlated to the average number of graphene layers (N). Complete coverage of the Si 3 N 4 particles is achieved for FLG with N controlled in the range 5–12, corresponding to 4–12 wt%. of carbon. Below that, for stacks with N = 3–4, the coverage of the surface by FLG islands is not total. The value found for the activation energy of CH 4 conversion into carbon shows that island-growth is favored over layer-growth. A macroscopical method based on a carbon proportion evaluation gives an approximation of both the coverage ratio and the average number of layers in the stack. • Few-layered-graphene (FLG) deposited on the surface of Si 3 N 4 particles, without any mixing and damaging the nanocarbons. • Complete coverage of the Si 3 N 4 particles is achieved for FLG with the average number of graphene layers in the range 5-12. • Below that range, the Si 3 N 4 particles are covered by FLG islands 3-4 layers thick. • The activation energy of CH 4 conversion into carbon shows that island-growth is favored over layer-growth. • A macroscopical carbon content evaluation gives a good approximation of the coverage ratio and the average number layers. [ABSTRACT FROM AUTHOR]

• Nanoindentation of SiO x and SiO x C y films with variable composition. • Mathematical models-coupled dynamic indentation removes substrate contribution. • Intrinsic modulus and hardness are determined, unbiased by the substrate. • High temperatures favor higher film properties via dehydration and demethylation. • Simple models are more robust than models with numerous parameters. Nanoindentation is a well-known technique to assess the mechanical properties of bulk materials and films. Despite that, nanoindentation of thin films is not straightforward, given that the measured properties are composite information from a film/substrate system and depend on the indentation depth. By using dynamic indentation experiments and analytical or empirical models, we assessed the intrinsic film properties of chemical vapor deposited silicon oxide (SiO x) and silicon oxycarbide (SiO x C y) thin films with thicknesses ranging from 60 to 700 nm. In this work, the Bec rheological model and several mixing laws were reviewed. Measured Young modulus appeared to be affected by the substrate properties more than hardness: for the thinnest films, moduli were measured at ca. 90 GPa whereas intrinsic moduli were calculated at ca. 50 GPa. Using calculated intrinsic film modulus and hardness, it was possible to establish correlations between these properties, the chemical composition and the structural organization of the films. [ABSTRACT FROM AUTHOR]

Silica and silica-based materials with tunable functionalities are frequently encountered in low-k material applications, porous membranes, and microelectonic devices. In the present study, an innovative O 2 /O 3 assisted CVD process for the deposition of such films at moderate temperature is presented, based on a dual precursor chemistry from hexamethyldisilazane (HMDS) and tetraethyl orthosilicate (TEOS). Films with tunable carbon content were obtained through variation of the HMDS flow ratio. A comprehensive FT-IR study reveals the transition of the material from a SiO x C y H type film containing -CH 3 moieties, to a methyl-free SiO x film with the increase of the temperature. At the same time the water contact angle of 81.0° at 400 °C is decreased to 52.8° at 550 °C, related to the absence of methyl moieties in the latter. Ion beam analysis (IBA) confirms the lack of carbon in the films when deposition temperatures are equal to or exceed 500 °C. The resistance to liquid corrosion is investigated as a function of the deposition temperature; SiO x type films present a low Pliskin etching rate of 15 Å.s−1, with this value increasing to 60 Å.s−1 for the SiO x C y :CH 3 films produced at the lower temperatures. It is found that the addition of HMDS to a TEOS chemistry can be utilized to modulate the film composition from SiO x to SiO x C y H and by such, tune the film functional properties, in particular its etching rate, opening the way to the development of new sacrificial films. • Dual-precursor chemical vapor deposition of SiOx and SiOxCy:CH3 from TEOS and HMDS • Tunable carbon incorporation from SiOxCy:CH3 to SiOx through HMDS addition • Enhanced film-etching rate by addition of HMDS in a TEOS/O2/O3 chemistry • Adjustable wettability, constant film hardness and modulus from SiOxCy:CH3 to SiOx [ABSTRACT FROM AUTHOR]