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Al 2 O 3 -13%TiO 2 coatings were deposited on stainless steel substrates from conventional and nanostructured powders using atmospheric plasma spraying (APS). A complete characterization of the feedstock confirmed its nanostructured nature. Coating microstructures and phase compositions were characterized using SEM, TEM, and XRD techniques. The microstructure comprised two clearly differentiated regions. One region, completely fused, consisted mainly of nanometer-sized grains of c-Al 2 O 3 with dissolved Ti +4 . The other region, partly fused, retained the microstructure of the starting powder and was principally made up of submicrometer-sized grains of a-Al 2 O 3 , as confirmed by TEM. Coating microhardness as well as tribological behavior were determined. Vickers microhardness values of conventional coatings were in average slightly lower than the values for nanostructured coating. The wear resistance of conventional coatings was shown to be lower than that of nanostructured coatings as a consequence of Ti segregation. A correlation between the final properties, the coating microstructure, and the feedstock characteristics is given.

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Multilayered structures are a promising route to tailor electronic, magnetic, optical, and/or mechanical properties and durability of functional materials. Sputter deposition at room temperature, being an out-of-equilibrium process, introduces structural defects and confers to these nanosystems an intrinsic thermodynamical instability. As-deposited materials exhibit a large amount of internal atomic displacements within each constituent block as well as severe interface roughness between different layers. To access and characterize the internal multilayer disorder and its thermal evolution, X-ray diffraction investigation and analysis are performed systematically at differently grown Ag-Ge/aluminum nitride (AlN) multilayers (co-deposited, sequentially deposited with and without radio frequency (RF) bias) samples and after high-temperature annealing treatment. We report here on model calculations based on a kinematic formalism describing the displacement disorder both within the multilayer blocks and at the interfaces to reproduce the experimental X-ray diffraction intensities. Mixing and displacements at the interface are found to be considerably reduced after thermal treatment for co- and sequentially deposited Ag-Ge/AlN samples. The application of a RF bias during the deposition causes the highest interface mixing and introduces random intercalates in the AlN layers. X-ray analysis is contrasted to transmission electron microscopy pictures to validate the approach.

Abstract:In this study, friction and dry sliding wear behavior of alumina and alumina-titania nearnanometric coatings have been studied. Coatings were obtained by Suspension Plasma Spraying (SPS) technique. Dry sliding wear tests were performed in an a tribometer with a ball on disk configuration, using a Al2O3 ball as a counterpart with a normal load of 2N, a sliding distance of 1200m and a sliding speed of 0.1 m/s. The influence of TiO2 addition in fabricated coatings was related with friction coefficient behavior, wear rates and wear damage patterns. A remarkable increment in wear resistance was founded by the TiO2 addition effect, in 2.6 times for the biggest amount. The analysis of wear surface was correlated with microstructural parameters, mechanical properties and wear rates.

The present study addresses the structural stability and mass outflow of Ag 10 nm/Ge 1 nm/AlN 10 nm nanomultilayers (NMLs) during thermal treatments in different atmospheres (Ar and air). The nanomultilayers were obtained by magnetron sputtering under different deposition conditions (with and without the RF (Radio-Frequency)-bias application). The microstructure of the as-deposited and thermally treated NMLs were analyzed by XRD and SEM techniques, deriving morphology, microstructure and internal stress. Bias application during the deposition is found to create highly disordered interfaces and to have a very strong influence on the morphology and structural evolution with temperature of the nano-multilayers. Complete multilayer degradation is observed for the bias sample when annealed in Ar at 700 ∘C, while the periodic multilayer structure is preserved for the non-bias samples. Structural and morphological changes are observed starting from 400 ∘C, accompanied with Ag surface migration. The highest Ag amount on the surface is detected in air atmosphere for bias and non-bias samples annealed at temperatures as high as 700 ∘C. The presence of Ge is found to strongly hinder the Ag surface migration. Ag outflow is measured to take place only through the network of surface cracks in the AlN barrier formed upon heating. The crack formation and Ag migration are discussed together with the stress relaxation. The present study demonstrates the feasibility to tailor the stress state of as-deposited NML structures and observe different structural evolution depending on the initial conditions. This paves the way for advanced experimental strategies to tailor directional mass outflow in nanoconfined filler systems for advanced nano-joining applications.

Sub-micrometer-sized Al2O3-TiO2 plasma-sprayed coatings exhibit superior performances compared to micrometer-sized ones. Two routes can be implemented to manufacture such finely structured coatings:i)spraying micrometer-sized agglomerates of nanometer-sized particles which results in a two-scale coating architecture and ii) spraying a suspension of sub-micrometer-sized particles (suspension plasma spraying, SPS). SPS was implemented in this study and Al 2 O 3-base coatings with 13 and 60 wt.% of titania, respectively, were manufactured by spraying a suspension made of a mixture of Al 2 O 3 and TiO 2 particles both of 300 nm, average diameter. Coating structural features and phase contents were studied. Results show that the coatings exhibit averyfine lamellar structure with a homogeneous repartition of Al and Ti. Complex phases, made of intermediate Al, Ti, and O oxides, have been also identified. Indeed, coatings formation results from rapid solid-ification rates and high transient thermal fluxes imparted by the plasma flow to the substrate due to the short spray distance encountered in SPS (in the order of 30 mm) requested by the small kinetics and thermal inertia of sub-micrometer-sized particles.

The present work deals with the problem of a possible application of current in deformation processes. A literature survey has shown an existence of publications on the electroplastic effect in single-phase materials without phase transformations and the lack of works on a study of the current impact on the deformation behavior of materials undergoing a phase transformation. Therefore, the influence of current regimes (density and impulse duration) and current mode (direct, pulse or multiple-pulse) on the deformation behavior of TRIP steel in austenite-martensite and completely martensite states is studied. Methods of mechanical tests, X-ray diffraction analysis and scanning electron microscopy observations of fracture surfaces are used. In the absence of current the steel in austenite-martensite state displays a martensitic transformation during tension that leads to an excellent combination of mechanical properties -high ultimate tensile stress and preservation of the initial ductility. It is shown that in austenite-martensite state the shape of the stress-strain tension curve and the type of flow stress jumps caused by martensitic transformation and electroplastic effect depend on the current mode. Single current pulses exert practically no influence on the mechanical properties and deformation behavior in tension. The multiple-pulse and direct current cause a considerable thermal effect, decrease in the electroplastic effect and a suppression of the TRIP effect. As a result, both the ultimate tensile stress and elongation to failure decrease. The steel in martensite state displays no TRIP effect during tension with current due to the lack of a reverse transformation, and the elongation to failure sharply decreases. According to scanning electron microscopic observations, the failure mode of samples in both states, irrespective of current, corresponds to a mechanism of ductile cleavage or shear.Keywords: pulse current; deformation; fracture; phase transformation; tension; TRIP effect. Подавление трип эффекта в метастабильных сталях электрическим токомСтоляров В.В. Работа связана с проблемой возможного применения тока при деформационных процессах. Литературный ана-лиз продемонстрировал наличие статей по электропластическому эффекту в однофазных материалах без фазовых превращений и отсутствие работ по исследованию воздействия тока на деформационное поведение в материалах, испытывающих фазовое превращение. В этой связи, исследовано влияние режимов (плотности и длительности им-пульса) и моды электрического тока (постоянного, импульсного, многоимпульсного) на деформационное поведение при растяжении ТРИП стали в аустенитно-мартенситном и полностью мартенситном состояниях. Использованы методы механических испытаний, рентгеноструктурного анализа и фрактографических наблюдений изломов ме-тодом сканирующей электронной микроскопии. В отсутствие тока сталь в аустенитно-мартенситном состоянии при растяжении испытывает мартенситное превращение, что приводит к отличной комбинации механических свойств -высокой прочности и со...