O. P. Ter-Galstyan’s research while affiliated with Yerevan Physics Institute and other places

This work presents a new method for synthesizing the widely used near-α Ti–8Al–1Mo–1V alloy. To this end, we sequentially used two methods: metal hydrides were synthesized by Self-propagating High-temperature Synthesis (SHS) method, and the said alloy was synthesized by Hydride cycle (HC) method, using the SHS-produced hydrides. The main point of the SHS method is to use of heat of the exothermic reaction, locally initiated in a thin layer of metal powder. The gist of the HC method, developed by us, is to use transition metal hydrides as starting materials for alloy synthesis. The approaches, elaborated in the present work, resulted in the synthesis of Ti–8Al–1Mo–1V alloy, consisting of 94 to 95.7 wt pct α-phase and 6 to 4.3 wt pct β-phase. The formation of the alloy proceeded according to the solid-phase mechanism. The alloy without crushing interacted with hydrogen in the SHS mode, forming a reversible hydride (Ti–8Al–1Mo–1V)H1.28. Hydrogen enhanced the fragility of the hydride and made it possible to grind it to powder with particle sizes under 3 microns (even down to 100 nm and less) within 30 to 40 minutes, without contamination of the particle surfaces. Simultaneously, the presence of hydrogen in the crystal lattice of alloy hydride increased its plasticity. Compacting the hydride to the designed shape and the following by sintering dehydrogenation at temperature close to the hydride decomposition temperature, allowed us to get a product of a required form. The elaborated HC method for synthesizing of the near-α-alloy has significant advantages over the traditional methods: low temperature (1000 °C instead of 1800 °C to 2600 °C), short duration (0.5 to 1 hour instead of dozens of hours), one stage, ecologically friendly, energy-saving process, solid-phase mechanism without melting, etc. The elaborated HC methods for the synthesis of near-α Ti–8Al–1Mo–1V alloy and the synthesis of its hydride (Ti–8Al–1Mo–1V)H1.28 by the SHS method can be of commercial and industrial interest.

In the present work a new approach is proposed for Ti2AlNx MAX phase synthesis using highly efficient methods: self-propagating high-temperature synthesis (SHS) and Hydride Cycle (HC). Two ways of synthesis were developed, which differ in the use of different precursors and methods for the forming of Ti2AlNx MAX phase. The synthesis in Way 1 was carried out according to the following scheme: first stage − synthesis of a solid solution of N2 in Ti (TiN0.18) and titanium hydridonitride (TiN0.18H1.34) by SHS method. Second stage: synthesis of Ti2AlNx Max phase by HC method according to the reaction: 2TiN0.18H1.34 +Al → Ti2AlN0.25 + H2↑. The synthesis in Way 2 follows the scheme: first stage – synthesis of Ti2Al intermetallic compound by HC method according to the reaction: 2TiH2 + Al→ Ti2Al + H2↑. Second stage: synthesis of Ti2AlNx Max phase by SHS method according to reaction: Ti2Al + N2 → Ti2AlN0.63. The peculiarities of structure and materials formation processes were studied by step-by-step analysis of the intermediate products using XRF, DTA, and chemical analysis methods. The synthesized Ti2AlN0.63 and Ti2AlN0.25 compounds were identified as single-phase MAX phases with hcp crystal structure, and had the same lattice parameters a = 0.29892 nm; c = 1.36540 nm, c/a = 4.57. It has been established that in both cases the formation of Ti2AlN0.25 and Ti2AlN0.67 MAX phases proceeds according to solid-phase mechanism. Taking into account all the advantages of SHS and HC methods, the developed ways for the synthesis of Ti2AlNx MAX phases can be recommended as fundamentally new, resource-saving, economical, and “low cost” technologies.

The paper reports the results of the Self-propagating High-temperature Synthesis (SHS) in ternary Ti–Al–C and quaternary 2xTi - 2(1-x)Zr − Al – C (x = 0.5–0.9) systems, combusted in argon and hydrogen environments. The effect of the initial mixture composition on the microstructure, phase composition, and crystallographic parameters of the synthesized compounds was investigated. Rietveld analysis of X-ray diffraction patterns was used to calculate the lattice parameters and quantitative phase composition. The combustion of the Ti–Al–C system resulted in the formation of Ti2AlC and Ti3AlC2 MAX phases (85–89%), as well as TiCx phase (11–15%). The combustion of Ti–Zr–Al–C system depending on the Ti/Zr ratio and Al and C contents, along with the main Ti2AlC, Ti3AlC2, Zr2AlC MAX phases, the FCC carbides of transition metals also formed. The highest percentage (91%) of MAX phases was produced by SHS of the 0.9Ti+0.1Zr+0.5Al+0.5C mixture in the argon atmosphere.

MAX phases are new type of easily machinable cermets, demanded in modern materials science as construction materials. One of the most widely studied and promising representatives of the titanium-based MAX phases are hexagonal Ti2AlC and Ti3AlC2. Current methods of their synthesis are unsuitable for their mass production. The creation and development of new methods and technologies for their producing are urgent tasks of materials science. The modern technologies are required providing high quality and productivity, cost-effective, environmentally friendly and easily scaled methods. In 2007, in our Laboratory of High-Temperature Synthesis of the IChPh of Armenian NAS, the Hydride Cycle method (HC) for synthesis of refractory alloys and intermetallic compounds was elaborated. The gist of this method is the use of the synthesized by Self-propagating High-temperature Synthesis mode (SHS) transition metal hydrides as starting materials. In the present work, for the first time, the HC method was applied in the synthesis of Ti2AlC and Ti3AlC2 MAX phases. Preliminarily, HCP TiC0.45H1.07÷1.17, FCC TiC0.5H0.22÷0.73 and TiC0.67H0.31-0.39 titanium carbohydrides were synthesized in the SHS mode and used as starting reagents. The present work was set to study the effect on the phase composition and structure of the synthesized MAX phases of conditions of HC. The analysis methods, used to certify the synthesized MAX phases, were: chemical, differential-thermal, X-ray phase. The microstructures of the samples were snapshot on SEM Prisma E scanning electron microscope. The work resulted in the synthesis in HC of single-phase Ti2AlC and Ti3AlC2 MAX phases with unit cell parameters [а = 3.0553; c = 13.6459; c/a = 4.466; P63/mmc] and [a = 3.0552; c = 18.7396; c/a = 6.132], respectively. This work demonstrated advantages of HC over the traditional methods of MAX phases synthesis.

This work presents the results of study of combustion with carbon of transition metals of IV, V and VI groups of the periodic system in atmospheres of argon, hydrogen, nitrogen and nitrogen-hydrogen mixture. The significance of hydrogen in the formation of single-phase products in the self-propagating high-temperature synthesis (SHS) mode was underlined. The combustion of carbon containing systems in argon resulted in the synthesis of two-phase carbides with FCC lattice. In contrary, the combustion of the same systems in hydrogen atmosphere leaded to the synthesis of single-phase carbo-hydrides. The products of combustion of transition metals in nitrogen atmosphere were the multiphase nitrogen-containing compounds. Their following re-ignition in hydrogen leaded to the synthesis of single-phase nitrido-hydrides. It was demonstrated that in all the studied systems, the combustion in hydrogen atmosphere leaded to the homogenized final synthesis products. The results of these processes were the formation of single-phase carbo- and nitrido-hydrides based on the metals of IV, V and VI groups. The presence of hydrogen in the crystal lattice of synthesized refractory carbides and nitrides facilitated easy dispersion of the compound to submicron sizes. After removal of hydrogen, the single phase structure was not violated. The described results may be of commercial value in the industry of refractory materials.

The wide use of titanium alloys is limited by high costs of both their producing technology and processing. The expansion of area of their application depends on development of more efficient, resource-saving, economical methods providing reduction in the cost of titanium alloys and titanium made products. The hydride cycle (HC) method for synthesis of binary and multicomponent refractory alloys and hydrides can be suitable alternative to traditional metallurgy for production of the alloy in small quantities (small-sized products for technical/medical purposes). This work presents the results of study on the mechanism of Ti–6Al–4V alloy formation in HC. The synthesis parameters are evaluated and optimized. The physicochemical, structural and hydrogen-sorption characteristics of the alloy samples are described. Actually, a resource-saving, efficient technology for synthesis of Ti–6Al–4V alloy by HC is developed and proposed. The synthesized alloy interaction with hydrogen in Self-Propagating High-Temperature Synthesis mode was investigated.