6 research outputs found
Прогнозирование стабильной композиции для высокоэнтропийных тугоплавких сплавов
No full textThe common approach for evaluation of stability of multicomponent substitutional solid solutions using thermodynamic, mechanical, and topological parameters of the constituent elements is developed. The high-temperature systems based on refractory elements (W, Ta, Mo, Nb, V, Ti, Zr, Hf, Cr) are investigated using this approach. Optimal compositions for high-entropy alloys are obtained, and influence of various factors in the formation of stable alloys is described. As shown, the most resistant alloys have non-equiatomic element-contents’ ratios. The agreement between element distribution in experimental alloys and predicted stable compositions are obtained for the W— Ta—Mo—Nb and W—Ta—Mo—Nb—V systems.Розроблено загальний підхід для оцінки стабільности багатокомпонентних твердих розчинів заміщення з використанням термодинамічних, механічних і топологічних параметрів елементів, що їх складають. Високотемпературні системи, що містять тяжкотопкі елементи (W, Ta, Mo, Nb, V, Ti, Zr, Hf, Cr), були досліджені за допомогою цього підходу. Одержано оптимальні склади для високоентропійних стопів і описано вплив різних чинників у формуванні стабільних стопів. Показано, що найбільш стійкі стопи мають нееквіатомне співвідношення складів елементів. Для систем W—Ta—Mo—Nb і W—Ta—Mo—Nb—V було одержано узгодженість між розподілами елементів в експериментальних стопах і прогнозованих стабільних композиціях.Разработан общий подход для оценки стабильности многокомпонентных твёрдых растворов замещения с использованием термодинамических, механических и топологических параметров составляющих их элементов. Высокотемпературные системы, состоящие из тугоплавких элементов (W, Ta, Mo, Nb, V, Ti, Zr, Hf, Cr), были исследованы с использованием этого подхода. Получены оптимальные составы для высокоэнтропийных сплавов и описано влияние различных факторов при формировании стабильных сплавов. Показано, что наиболее стабильные сплавы характеризуются неэквиатомным отношением составов элементов. Для систем W— Ta—Mo—Nb и W—Ta—Mo—Nb—V было получено согласие между распределениями элементов в экспериментальных сплавах и предсказанных стабильных композициях
Effect of Chemical Composition and Heat Treatment on the Shape Memory Parameters in the TiNi-Me Alloys
No full textThe TiNi-Me shape memory alloy parameters (namely, phase transformation "strength yield"
recoverable strain, reversion stress, material hardness) have been investigated as a function of the chemical
composition, heat treatment regimes and deformation condition. These parameters are found to be structurally sensitive ones both to the macroscopic and microscopic structure of the material. Their response to heat treatment regimes is usually non-homogeneous function of the aging temperature and time variation.
Effects of doping and secondary particle precipitation are of great importance. Some recommendations for the
choice of the SMA chemical composition and final heat treatment regime can be proposed
Mechanical properties of microwave sintered Si3N4-based ceramics
No full textThe mechanical properties and microstructure formation processes in Si3N4+3% AI2O3+5% Y2O3(Yb2O3) ceramic compacts sintered under microwave heating (MWH) and under traditional heating (TH) were investigated. The initial ceramic materials were powder blends of silicon nitride with oxides. The mean powder particle sizes were 0.5-1.0 mim. The content of alfa-phase in the Si3N4 powder was more than 95 %. The samples were sintered at 1800BC in nitrogen at normal pressure, the heating rate in all experiments was 60BC/min. The Vickers hardness (HV), fracture toughness (K1C) and bending strength (on) were determined. The microstructures of fracture surfaces of samples were studied by SEM. Quantitative microstructure analysis was carried out. It was shown that the values of HV and Kic of ceramic samples sintered under MWH at 1800BC rose steadily with the sintering time. This caused an increase in density, which reached maximum as fast as after 30 min of the MWH sintering; the mass loss at that time amounted to 3-4 %. The porosity of sintered samples with an addition of yttria was less than 1 %, that of ytterbia was greater, 2.4 %. For similar values of relative density, the hardness and fracture toughness of ceramic samples produced under MWH were higher as compared with those of samples sintered under TH. The microstructure of samples had the form of elongated grains in a matrix of polyhedral grains of the beta-Si3N4 phase. Measurements showed the mean size of grains in samples produced by MWH to be greater that in samples produced by TH. A larger number of elongated grains were formed. It was concluded that for sintering under MWH of Si3N4-based ceramics the growth of elongated beta-Si3N4 grains and formation of a "reinforced" microstructure were promoted and thereby improved the mechanical properties of such ceramics
