SPECIFIC STRUCTURE OF EFFECTIVE MEMBRANE ALLOYS BASED ON NIOBIUM, VANADIUM AND ZIRCONIUM

Аморфные, нанокристаллические мембранные сплавы на основе элементов V группы с уникальными механическими и функциональными свойствами и с матричной дуплексной микроструктурой активно способствуют развитию водородной энергетики. Имеются еще не вполне разрешенные проблемы для этих новых сплавов -их низкая термическая стабильность, недосточная механическая прочность (пластичность, твердость), а также охрупчивание интерметаллидное и гидридное. Для эффективного применения разрабатываются сплавы с тройным составом - в которые помимо элементов V группы входят и легирующие металлы никель и титан. Получают не только аморфные и нанокристаллические сплавы, применимые в электронике и электроэнергетике, а также мембранные сплавы с дуплексной матричной структурой, объединяющей аморфные, так нано- и квазикристаллические дендритно упрочняющие фазы, как упрочняющие аморфную матрицу. В специализируемых мембранных тройных сплавах формируются соединения NiTi и NiTi, стабилизирующие и предохраняющие нано- и кристаллические мембраны от хрупкого разрушения. Установлено, что интенсивное образование гидридов в этих альтернативных мембранных сплавах столь же не желательно, как и для традиционных сплавов на основе палладия. Рассматриваемые сплавы действительно позволяют получить газообразный водород высокой чистоты с применением новых составов взамен дорогостоящих мембран на основе сплавов Pd - Au / Ag / Cu. With unique mechanical and functional properties, amorphous, nanocrystalline and matrix duplex microstructure membrane alloys based on group V elements actively contribute to the development of hydrogen energy. There are still not completely resolved problems for these new alloys - their low thermal stability, insufficient mechanical strength (plasticity, hardness), and intermetallic and hydride embrittlement. For effective use, alloys with a triple composition are being developed - which, in addition to the elements of group V, also include nickel and titanium as alloying metals. Not only amorphous and nanocrystalline alloys are obtained that are applicable in electronics and power engineering, as well as membrane alloys with a duplex matrix structure that combines amorphous, nano-and quasicrystalline dendritic-hardening phases strengthening the amorphous matrix. In specialized membrane ternary alloys, NiTi and NiTi compounds are formed, which stabilize and protect nano-and crystalline membranes from brittle destruction. It has been found that the intense formation of hydrides in these alternative membrane alloys is as undesirable as for palladium-based compounds. The alloys under consideration actually make it possible to obtain high-purity gaseous hydrogen using new compositions instead of expensive membranes based on Pd - Au / Ag / Cu alloys.

Microstructure and Texture Variations in High Temperature Titanium Alloy Ti65 Sheets with Different Rolling Modes and Heat Treatments

Ti65 alloy (Ti-5.8Al-4.0Sn-3.5Zr-0.5Mo-0.4Si-0.3Nb-1.0Ta-0.8W-0.05C) is the newly developed high temperature titanium alloy optimized from Ti60 alloys. The long-term service temperature of the alloy is as high as 650 °C, which is unattainable with the previous high temperature titanium alloy. It has excellent strength and excellent creep resistance, and has great application prospects in the aerospace industry. In the current study, the evolution of microstructure and texture of Ti65 alloy sheets developed by unidirectional rolling (UDR) and cross rolling (CR) followed by solution and aging treatment was investigated. The microstructure of the UDR sample consists of equiaxed α p , lamellar α s and few elongated α p , and the texture is the combination of minor B-type and major T-type texture, with the main component of basal {0001} fiber texture and { 01 1 ¯ 0 } < 2 1 ¯ 1 ¯ 0 > , respectively. Due to more active slip system resulted by transformed direction, the microstructure of the CR sample consists of more elongated α p , and the { 01 1 ¯ 0 } <0001> texture characterized as R-type texture forms in addition to B/T-type texture. With aging temperature increasing, the microstructures for both transform to duplex microstructure, and the thicknesses of lamellar α s increase. B-type texture becomes stronger, while T/R-type texture are weakened, which is caused by the combination of recrystallization, spheroidization, and variant selection. An abnormal increasing of T/R-type texture but constant B-type texture happens in the CR-600 sample, which is related to high recrystallization fraction. It is expected that the research results can provide useful references for the rolling of high temperature titanium alloy sheets and the precise control of microstructure/texture.

High-Stress Compressive Creep Behavior of Ti-6Al-4V ELI Alloys with Different Microstructures

Influence of initial microstructure of Ti-6Al-4V ELI alloys on their compressive creep behavior at ambient temperature was investigated with applying compression stresses from 695 to 1092 MPa The experimental results show that the basketweave alloys have better compressive creep resistances than those duplex ones. The constitutive equations in steady-state compressive creeps of duplex or basketweave structure are calculated to be =2.77×10-15(σ-710)2.1 and =2.36×10-14(σ-740)1.7 by fitting the linear regression creep curves after uniaxial compression tests. The noticeable compressive creep strains occur when the applied compression stresses are higher than the threshold stresses, i.e. 710 MPa for duplex Ti-6Al-4V ELI alloys and 740 MPa for basketweave alloys. Microstructural analysis indicates that the creep deformation of Ti-6Al-4V ELI alloys at ambient temperature is mainly controlled by dislocation slip. The creep behavior of Ti-6Al-4V ELI alloy with duplex microstructure is controlled by dislocation slip, like slip dislocations with a-type Burgers vector sliding on the basal or prismatic planes and a few c+a type dislocation sliding on the pyramidal planes. While creep mechanism for basketweave ones is dislocation glide controlled by c+a type Burgers vector sliding on the pyramidal planes and a-type sliding on the basal or prismatic planes.