Properties of Coatings Deposited from Filtered Vacuum Arc Plasma with HEA Cathode

Ti-V-Zr-Nb-Hf metallic and nitride films were deposited by filtered vacuum arc plasma from a single equiatomic HEA cathode. The composition, microstructure, mechanical properties, thermal stability and corrosion properties were investigated. The deposited metallic film has a two-phase structure with bcc and hcp-lattice. The nitride films were found to have only an fcc structure. All coatings have nano-grained structures, with grain sizes 5 nm for metallic and 36 nm for nitride. The nitride coatings have a compressive stress of around – 12,5 GPa, high hardness ~ 40 GPa and elastic modulus ~ 450 GPa. After annealing in vacuum in range 400-1200 °C, 3 h for every temperature, hardness decreased to 25 GPa. It was found that both the metallic and nitride coatings exhibited their best corrosion resistance than steel samples in a 3,5 wt. % NaCl solution. The metallic coatings showed better corrosion resistance than the nitride coatings. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3532

Effects of Deuterium Implantation Dose on Hardness and Deuterium Desorption Temperature Range from High Entropy TiVZrNbHf and TiVZrNbHfN Coatings

High entropy TiVZrNbHf and TiVZrNbHfN coatings prepared by filtered vacuum arc plasma from a single equiatomic HEA cathode. Similarly were obtained titanium and titanium nitride coatings. The structure of coatings was investigated by X-ray analysis and the changes in nanohardness by nanoindentation method. The effusion of the implanted deuterium was studied by thermal desorption spectroscopy (TDS). It is shown that the structure of effusion spectrum is a function of deuterium dose. With increasing implantation dose deuterium desorption temperature range from coatings is expanding in the direction of lowering the temperature and the temperature of the peak maximum gas emission gradually shifts to lower temperatures. For nitride coatings deuterium desorption starts at about room temperature and the maximum rate of desorption at a temperature of ~500 K. When irradiation doses more than 5×1017 D/cm2 hardness of nitride coatings decreased by half. Hardness reduction of coatings is caused by occurrence hydride structural formations in coatings. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3536

High-temperature short-term and long hardness of sintered compact and porous titanium-siliceous carbide ti3sic2

The ternary compound of titanium-siliceous carbide Ti3SiC2, one of the representatives of Nan laminates, prepared by solid-phase sintering is investigated in compact and porous (q=0.03-0.41) states. Features of its short-term and long-term hardness (Р=10 N) behavior in the temperature range from 20 to 1200˚С at a holding time of 1-60 min were studied. It is shown that a temperature of about 700°С and holding time under load of about 10 min are critical values of the indentation procedure that correspond to an intensive decrease of hardness. The presence of porosity results in a decrease in hardness. a deformation scheme of compact and porous titanium-siliceous carbide Ti3SiC2 in the temperature range from 20 to 1200˚С is proposed.

Transition from microstructures to nanostructures and ultimate hardening

Regularities of change in the dependence of the yield stress on grain size in transition from the microstructured to the nanostructured state are discussed. It is shown that, using S-functions, a generalized equation for the yield strength dependence on the grain size with regard to changes in the hardening mechanisms of polycrystals in the vicinity of critical grain sizes dcr₁ and dcr₂ can be obtained. This equation enables to describe the softening effects in transition to nanostructures (the so-called "negative" trend of the Hall-Petch relationship) and an abrupt hardening under conditions of increased intergranular cohesive strength.Обговорюються закономірності зміни залежності напруги плинності при переході від мікро- до наноструктурованого стану. Показано, що за допомогою 8-функцій можна отримати узагальнене рівняння залежності границі плинності від розміру зерна з урахуванням зміни механізмів зміцнення полікристалів в околі критичних розмірів зерен dкр₁ і dкр₂. Це рівняння дозволяє описати як ефекти знеміцнення при переході до наноструктур (так званий "негативний" хід залежності Холла-Петча), так і, навпаки, різке зміцнення за умови підвищеної міцності межзеренного зчеплення.Обсуждаются закономерности изменения зависимости напряжения течения при переходе от микро- к наноструктурированному состоянию. Показано, что с помощью 8-функций можно получить обобщенное уравнение зависимости предела текучести от размера зерна с учетом изменения механизмов упрочнения поликристаллов в окрестности критических размеров зерен dкр₁ и dкр₂. Это уравнение позволяет описать как эффекты разупрочнения при переходе к наноструктурам (так называемый "отрицательный" ход зависимости Холла-Петча), так и, напротив, резкое упрочнение при условии повышенной прочности межзеренного сцепления