I. I. Chernov

Microstructure development and helium behavior in nickel and vanadium base alloys

Abstract Transmission electron microscopy and thermal helium desorption spectrometry (TDS) have been used to investigate the influence of alloying elements on helium behavior and bubble microstructure evolution in FCC (Ni+1…7.5 wt%Al) and BCC (V+10…40 wt%Ti) metals. The samples were irradiated by 40-keV He+ ions at room temperature up to a fluence of 5×1020 m−2. Post-irradiation annealings were performed at 1023 K (Ni–Al) and 1075 K (V–Ti) for 1 h. It was shown that alloying elements reduced the bubble size ( d b ) and increased their density (ρb) in both types of alloys. In the Ni–Al alloys the TDS peaks are displaced to higher temperatures with increasing Al concentration in contrast to V–Ti alloys where the TDS peaks are displaced to lower temperatures with increasing Ti content. However in both systems of alloys the effective activation energy for helium desorption grows with alloying element concentration. The results are discussed in terms of alloying element influence on the mechanisms of bubble growth and migration.

Influence of alloying elements in Ni and Fe on ion-implanted helium behavior

Abstract Behavior of ion-implanted helium and bubble microstructure evolution in Ni-base (Ni C, Ni Al) and Fe-base (Fe C) model alloys, as well as in homogeneous austenitic 16–15 type steel with various carbon contents and in age hardening 15–35 type steel as a function of alloying element concentration, have been investigated by means of thermal desorption spectrometry (TDS) and transmission electron microscopy (TEM). The results show the different nature of influence of carbon and aluminium on bubble parameters formed during postirradiation annealings. Calculated by means of the ‘tempering’ method, helium release effective activation energy proved to be higher for alloys than for pure metals. The effect of these observations is discussed from the standpoint of diffusion parameter change in metals by alloying.

Investigation of oxygen-titanium interaction in vanadium by internal friction method

The temperature dependences of the internal friction, Q−1, of vanadium and of V-(0.3–10%) Ti alloys are measured in the range from room temperature to 900°C. Three peaks at 227, 295, and 375°C attributed to the O-V, O-Ti, and Ti-V complexes are detected for the alloys with a low content (<5%) of titanium. In the alloys containing 5–10% titanium, these peaks disappear, but a new peak attributed to the V-O-Ti complex arises at 475°C. The binary complexes are found to make the main contribution to retardation of dislocations in the V-Ti alloys with a low content of titanium and, consequently, to strengthening and embrittlement of these alloys.

Formation of Gas Pores in Nickel Alloys and Structural Steel under Irradiation by Helium Ions

Transmission electron microscopy is used to study the development of helium porosity in binary alloys of nickel with elements possessing a different dimensional atomic mismatch with nickel – from negative (beryllium and silicon) to positive (molybdenum, tungsten, aluminum, titanium, tantalum, tin, and zirconium), in structural steels ChS-68, ÉP-150, and the nickel alloy KhNM. The gas pores were produced by irradiation with 40 keV He+ up to fluence 5·1020 m–2 at 650 and 20°C followed by annealing at 650°C for 1 h. It is shown that under high-temperature annealing beryllium and silicon, relative to nickel, give rise to the formation of larger bubbles, while elements with a larger positive size mismatch with nickel atoms substantially decrease the size and increase the density of the bubbles. On the whole, as atomic radius and the concentration of the alloying element increases in alloys, the gas swelling of the irradiated layer decreases. Under post-irradiation annealing, bubbles with the largest diameter and the lowest density develop in nickel. Any alloying used decreases the size and increases the density of bubbles. The data obtained are discussed from the standpoint of the formation of various vacancy complexes of helium and their thermal stability.

Microstructure investigation of 13Cr-2Mo ODS steel components obtained by high voltage electric discharge compaction technique

Refractory oxide dispersion strengthened 13Cr-2Mo steel powder was successfully consolidated to near theoretical density using high voltage electric discharge compaction. Cylindrical samples with relative density from 90% to 97% and dimensions of 10 mm in diameter and 10–15 mm in height were obtained. Consolidation conditions such as pressure and voltage were varied in some ranges to determine the optimal compaction regime. Three different concentrations of yttria were used to identify its effect on the properties of the samples. It is shown that the utilized ultra-rapid consolidation process in combination with high transmitted energy allows obtaining high density compacts, retaining the initial structure with minimal grain growth. The experimental results indicate some heterogeneity of the structure which may occur in the external layers of the tested samples due to various thermal and electromagnetic in-processing effects. The choice of the optimal parameters of the consolidation enables obtaining samples of acceptable quality.

Effect of Doping on Helium Behavior and Bubble Structure Development in Nickel and Vanadium Alloys

Transmission electron microscopy and thermal desorption spectrometry are used to study the behavior of ion-implanted helium and formation of a gas bubble structure in fcc and bcc metals as a function of the concentration of the alloying elements (aluminum in nickel and titanium in vanadium). It is shown that during post-radiation annealing of room-temperature irradiated samples alloying in both types of alloys substantially decreases the size and increases the density of the bubbles formed. In nickel–aluminum alloys, with post-radiation uniform heating, the thermal desorption peaks shift to high temperature with increasing aluminum content and, conversely, in vanadium–titanium alloys a shift to low temperature with increasing titanium concentration occurs, though the effective gas release activation energy increases in both alloys with increasing concentration of the alloying element. The data obtained are discussed from the standpoint of the influence of doping on the mechanisms of growth and migration of bubbles.

Influence of structural-phase state of ferritic-martensitic steels on the helium porosity development

Transmission electron microscopy (TEM) has been used to study the effect of the initial structural-phase state (SPhS) of ferritic-martensitic steels EK-181, EP-450 and EP-450- ODS (with 0.5 wt.% nanoparticles of Y2O3) on the of helium porosity formation and gas swelling. Different SPhS of steel EK-181 was produced by water quenching, annealing, normalizing plus tempered, intensive plastic deformation by torsion (HPDT). Irradiation was carried out by He+-40 keV ions at 923 K up to fluence of 5-1020 He+/m2. It is shown that the water quenching causes the formation of uniformly distributed small bubbles ( ~ 2 nm) of the highest density (ρ~ 1025 m-3). After normalization followed by tempering as well as after annealing bubbles distribution is highly non-uniform both by volume and in size. Very large faceted bubbles (pre-equilibrium gas-filled voids) are formed in ferrite grains resulting in high level of gas swelling of the irradiated layer with S = 4,9 ± 1,2 and 3.8 ± 0.9% respectively. Nano- and microcrystalline structure created by HPDT completely degenerate at irradiation temperature and ion irradiation formed bubbles of the same parameters as in the annealed steel. Bubbles formed in EP-450-ODS steel are smaller in size and density, which led to a decrease of helium swelling by 4 times (S = 0.8 ± 0.2%) as compared to the swelling of the matrix steel EP-450 (S = 3.1 ± 0.7%).

On Reversible Hydrogen Storage by Mg ⎯Ni ⎯Mm Alloys

Possible compositions of Mg-Ni alloys with lanthanide additives as potential hydrogen storage materials are proposed on the basis of an analysis of binary and ternary equilibrium diagrams. It is shown that an approximately 100-h air exposure of the alloys between the sorption and desorption processes increases the hydrogen capacity of the samples up to ∼6 wt %, which is 25% greater than that for the samples not exposed to the air. The complete degradation of the alloy’s properties occurs after a 4500-h air exposure.

Amorphous and crystalline alloys for reversible hydrogen storage

The optimal compositions are selected and amorphous alloys based on various metals (nickel, magnesium, rare-earth elements, iron, chromium, zirconium, titanium, etc.) are developed in the form of rapid-quenched tape having amorphous, nano-, and microcrystalline structures. The obtained intermetallic compounds with various compositions might be used for hydrogen storage. The accumulation of hydrogen by Zr-based amorphous samples is established to be 1.8 times higher than the capacity of the same but crystalline sample. The crystalline samples belonging to the Mg-Ni system are found to accumulate up to 3.2 wt % hydrogen upon hydrogenation and to release a three times larger amount of hydrogen than zirconium-based alloys upon dehydrogenation. The accumulating hydrogen capacity in this case,