Inert Gas Atoms Research Articles

Defect production in silicon carbide irradiated with Ne and Xe ions with energy of 2.3 MeV/amu

In the present work specimens of mono-crystalline silicon carbide (4H polytype) were irradiated to three successively increasing ion fluences ranging from 7.2×1014 to 6.0×1016ions/cm2 (corresponding to the peak displacement damage of 1, 4 and 13dpa) with Ne and Xe ions respectively with the energy of 2.3MeV/amu. The irradiated specimens were subsequently annealed at temperatures of 1173 and 1273K. Defect structure was investigated with transmission electron microscopy (TEM) using a cross-sectional specimen preparation technique.The typical microstructures of the annealed specimens irradiated with Ne or Xe ions to high fluences are characterized by small gas bubbles in high concentration in the peak damage region and black dots and dislocation loops (located in the basal plane) in a shallower and broader depth region. Larger dislocation loops were observed in the Xe-ion irradiated specimen than in the Ne-ion irradiated specimen at the same peak damage level. The enhanced formation of dislocation loops in the case of Xe-ion irradiation is understandable by assuming stronger inclination of heavier inert-gas atoms to occupy substitute site in the peak damage region.

The Effect of In-Flight Bulk Metallic Glass Particle Temperature on Impact Behavior and Crystallization

NiTiZrSiSn bulk metallic glass powder was produced using inert gas atomization and then was sprayed onto a SS 41 mild steel substrate using the kinetic spraying process. Considering the principle of kinetic spraying and the temperature dependent deformation behavior of the bulk metallic glass, an attempt to change the in-flight particle temperature was tried by modifying the kinetic spraying apparatus. Through this study, the effects of thermal energy of in-flight particle and crystallization degree by powder preheating temperature were evaluated. The deformation behavior of bulk metallic glass is very interesting and it is largely dependent on the temperature and the strain rate. The crystalline phase formation at impact interface was dependent on the in-flight particle temperature. In addition, variations in the impact behavior need to be considered at high strain rate and in-flight particle temperature.

Crystal Nucleation Behavior Caused by Annealing of SiC Irradiated with Ne at Liquid Nitrogen Temperature or at 573 K

Silicon carbide(SiC) TEM specimens were annealed, in-situ, at 1273 K for 30 minutes after amorphization with 30 keV Ne þ irradiation to the fluence of 1.9 or 2:3 � 10 20 Ne þ /m 2 at 573 K or liquid nitrogen temperature. The crystal nucleation and bubble coalescence accompanied by recrystallization were observed for both specimens subjected to the annealing after the irradiation to the fluence of 2:3 � 10 20 Ne þ /m 2 in both irradiation temperature cases. The Debye-Sherrer rings of the nucleated crystals well fitted the net pattern of the matrix, even though no ring corresponding to (200) of � -SiC appeared. No effect of the irradiation temperature occurred within the present experimental range. It appears that the concentration of implanted inert gas atoms played more important roll than the amorphous structure itself in the crystal nucleation behavior under the condition that the inert gas bubbles were formed in amorphous SiC. [doi:10.2320/matertrans.MRA2007608]

Long-range interaction and the dynamics of nonadiabatic transitions in collisions of the I2(E) molecule with inert gas atoms

A special form of perturbation theory based on intermolecular interaction was used to analyze the contributions to the interaction energy between a homonuclear diatomic molecule with dipole-coupled electronic states n and n′ and a neutral particle A. At large distances, the energy of the system in both states n and n′ is determined by the induction contribution similar to the induction interaction of particle A and a polar molecule. The presence of a constant electric moment of particle A gives an electrostatic contribution to the matrix element of the nonadiabatic coupling of the states n and n′. The equations obtained were specialized to describe the interaction of the iodine molecule excited to ion-pair states with an inert gas atom and used as corrections to the potential energy surfaces of this system constructed within the diatomics-in-molecule approximation. The dynamics of transitions between the ion-pair states of the I2 molecule induced by collisions with the Ar and He atoms was calculated. The results demonstrate the importance of correctly including long-range interaction.

Extraordinary temperature dependence of isochoric thermal conductivity of crystalline CO2 doped with inert gases

The isochoric thermal conductivities of the solid solutions (CO2)0.905Kr0.095 and (CO2)1−xXex (x=0.052 and 0.097) of different densities are investigated in the temperature interval from 150K to the onset of melting. An unusual effect of point defects on the thermal conductivity has been detected. In pure CO2 at T>150K the isochoric thermal conductivity decreases smoothly with increasing temperature. In contrast, the thermal conductivity of CO2∕Kr and CO2∕Xe solid solutions first decreases, passing through a minimum at 200–210K, and then starts to increase with temperature up to the onset of melting. This behavior of the isochoric thermal conductivity is attributed to the rotation of the CO2 molecules, which gain more freedom as the spherically symmetrical inert gas atoms are dissolved in the CO2.

Evaluation of the effects of the crystallinity of kinetically sprayed Ni–Ti–Zr–Si–Sn bulk metallic glass on the scratch response

A bulk amorphous Ni–Ti–Zr–Si–Sn powder produced using an inert gas atomization was sprayed by a kinetic spraying process that is basically a solid-state deposition process onto a mild steel substrate and they were successfully overlaid onto the mild steel substrate. In order to evaluate the tribological behavior of the sprayed Ni–Ti–Zr–Si–Sn bulk metallic glass coatings, a partially crystallized coating and a fully crystallized coating were prepared by isothermal heat treatments. Tribological properties were investigated—friction coefficient, hardness and amorphous phase fraction of coating layer. Surface morphologies and depth in the wear tracks were observed and measured by scanning electron microscopy and α-step. From the examination of the scratch wear track microstructure, transition from ductile-like deformation micro-cutting to brittle-deformation micro-fracturing in the scratch groove was observed with the increase of the crystallinity.

Enhancement of inner tube formation from peapods in de-pressurized inert gas environment

C60 molecules encased in single-wall carbon nanotubes, so-called peapods, can be transformed into small-diameter tubes inside the host tubes after high-temperature heat treatment in vacuum at ∼1200 °C. Here, we report an experiment on high-temperature heat treatment of peapods in inert gas environment, and show the evidence of enhancing the formation rate of inner tubes, the rate being more than ∼6 times higher in Ar environment and ∼9 times higher in He than that in vacuum. This means that the inert gas atoms markedly accelerate the polymerization of C60. In contrast to Ar and He, it is found that H2 gas does not enhance the C60 polymerization.

The diffusion of hydrogen and inert gas in sputtered a-SiC:H alloys: Microstructure study

Abstract The microstructure of DC sputtered amorphous silicon carbon (a-SiC:H) is studied by effusion measurements of hydrogen and of implanted inert gases helium, neon, argon and secondary ion mass spectrometry. The results suggest that the motion of inert gas atoms is controlled by the diffusion, greatly depending on a broadening of network openings. Already at carbon concentrations of 25 at%, isolated voids disappeared presumably because interconnected voids are formed. A void formation is mainly attributed to an increase in hydrogen incorporation in the samples.

Effect of oxygen content of powder on microstructure and mechanical properties of hot isostatically pressed superalloy Inconel 718

Inert gas atomized (IGA) superalloy Inconel 718 powders with varied oxygen levels of 275, 180 and 140 ppm were consolidated by hot isostatic pressing (HIPing) at 1200 °C/120 MPa/3 h. The microstructural characterization of as-HIPed alloys has shown that the densification phenomenon of the powder does not depend on its oxygen content. However, the formation of deleterious phases such as prior particle boundaries (PPBs) occur more predominantly in the HIPed material produced from the powder with high oxygen content. It was also observed that the recrystallization and formation of annealing twins in the HIPed alloy are greatly influenced by the oxygen content. Transmission electron microscopy (TEM) studies have revealed that the precipitation of γ″, γ′ and δ phases does not depend on oxygen level of HIPed alloy during heat treatment as per AMS 5662J standard schedule but the MC carbides enriched with Nb and Ti precipitated preferentially at the PPBs for the alloy with high oxygen content of 275 ppm. In contrast, the carbides were found to be precipitated more uniformly in the matrix of the alloy with low oxygen content of 140 ppm. Tensile properties of the as-HIPed and HIP + heat treated alloys have shown that the yield strength (YS), ultimate tensile strength (UTS) do not get influenced by the oxygen content, but the ductility was found to be deteriorated drastically at elevated temperatures with increasing the oxygen content of the alloy. Stress rupture properties of the heat treated alloys at 650 °C under a stress level of 690 MPa have maintained a direct relation with the oxygen content, as the alloy with 275 ppm of oxygen content has shown inferior rupture life of 27 h with 2.1% ductility as compared to 84.5 h of life with 4.5% ductility and 116 h of life with 6% ductility offered by the alloys with 180 and 140 ppm of oxygen content, respectively. A better combination of mechanical properties achieved by use of prealloyed powder with low oxygen content makes it possible to explore the near net shape advantage of HIP technology to its maximum potential for alloy 718 components.

Effect of ambient gas ionisation on the morphology of a pulsed laser deposited carbon film

The paper reports a study of the mechanism of ambient gas ionisation and its effects on a growing carbon film. Such an ionisation occurs during the expansion through an inert gas of an ablation plume generated by laser irradiation of a target. Charge transfer reactions between ablated ions and inert gas atoms lead to the formation of a charged layer in contact with plume front. The energy lost by fast ablated ions associated with plume slowing down is calculated. In the case of carbon ablated in helium and argon atmospheres, where ionisation plays a very different role, we discuss the microstructure changes observed in the deposited films in terms of dramatic differences of plume dynamics.

Microstructural features induced by spray processing and hot extrusion of an Al–18% Si–5% Fe–1.5% Cu alloy

An inert gas atomization technique was employed to produce spray deposits of an Al–18Si–5Fe–1.5Cu (wt.%) alloy. The spray-deposited alloy was subsequently hot extruded with a reduction ratio of 6:1 and extrusion temperature of 480°C. The microstructural features of the as-spray-deposited and extruded alloys were examined using optical, scanning electron and transmission electron microscopy techniques, and chemical analyses of phases were carried out using energy dispersive X-ray analysis and spectroscopic methods. The microstructure of the spray-deposited alloy revealed the presence of a cellular and plate-like morphology of β-Al5SiFe phase coexisting with δ-Al4Si2Fe phase in contrast to the presence of only δ-Al4Si2Fe phase in atomized powder particles. The formation of the β-Al5SiFe phase is suggested to arise as a result of phase transformation of δ-Al4Si2Fe phase during slow cooling of the spray deposit. The hot extrusion of the alloy resulted in fragmentation of both intermetallic phases and Si into nano-sized particles. The microstructure evolution during spray deposition and hot extrusion of the alloy is discussed.

Influence of modified processing on structure and properties of hot isostatically pressed superalloy Inconel 718

Inert gas atomized (IGA) superalloy Inconel 718 powder was consolidated by hot isostatic pressing (HIPing) at 1200 °C under 120 MPa pressure for 3 h. The HIPed alloy heat treated as per the aerospace materials specification (AMS) 5662J standard schedule, viz. solution treatment (ST) at 980 °C for 1 h/water quenching (WQ) to room temperature (RT) and a two-step ageing treatment (AT) at 720 °C for 8 h/furnace cooling (FC) at 55 °C h −1 to 620 °C and holding at 620 °C for 8 h and air cooling (AC) to room temperature has exhibited the yield strength (YS) and ultimate tensile strength (UTS) comparable to that of the conventionally processed (forged and heat treated) IN 718. However, its ductility and stress rupture properties at 650 °C were found to be poor due to the presence of prior particle boundary (PPB) networks decorated with highly stable oxides (Al 2O 3 and TiO 2) and brittle MC (Nb, Ti)C carbides. To mitigate this problem, the HIPed alloy was subjected to solution treatment at 1270 °C for 1 h followed by re-HIPing at 1100 °C/130 MPa/3 h before heat-treating it as per AMS 5662J standard schedule. Optical and scanning electron microscopy (SEM) of the alloy processed under modified HIPing and heat treatment conditions have shown the dissolution of MC-carbides, breaking up of PPB networks and formation of equiaxed grains with an average diameter of about 50 μm. Transmission electron microscopy (TEM) of this alloy has revealed uniform distribution of γ″ and γ′ strengthening precipitates in the γ-matrix and the presence of δ(Ni 3Nb) phase as well as very fine oxide particles near the grain boundaries. The tensile properties of the alloy processed under modified conditions have shown quite satisfactory levels of YS and UTS combined with a significantly improved elongation (EL) values at room temperature (19.5%) and at 650 °C (8.0%). The improvement in alloy ductility was found to correlate well with the fractography of the tensile tested specimens, which showed the predominance of transgranular fracture with fine dimples at room temperature and fine dimples together with the particle boundary facets at 650 °C. The stress rupture properties of modified processed alloy at 650 °C and at a stress level of 690 MPa have shown a vastly improved rupture life of 80 h combined with 5% ductility. The improvement in tensile and stress rupture properties accomplished by the modified processing makes it possible to explore the near net shape capability of HIP technology to its full potential in the development of alloy 718 components.

A gaseous radiochemical method for registration of ionizing radiation and its possible applications in science and economy

This work presents a new possibility of registration of ionizing radiation by the flowing gaseous radiochemical method (FGRM). The specified method uses the property of some solid crystalline lattice materials for a free emission of radioactive isotopes of inert gas atoms formed as a result of nuclear reactions. Generated in an ampoule of the detector, the radioactive inert gases are transported by a gas-carrier into the proportional gas counter of the flowing type, where the decay rate of the radioactive gas species is measured. This quantity is unequivocally related to the flux of particles (neutrons, protons, light and heavy ions) at the location of the ampoule. The method was used to monitor the neutron flux of the pulsed neutron target “RADEX” driven by the linear proton accelerator of INR RAS. Further progress of the FGRM may give rise to possible applications in nuclear physics, astrophysics and medicine, in the nondestructive control of fissionable materials, diagnostics of thermonuclear plasma, monitoring of fluxes and measurement of spectra of bombarding particles.

Fluorescence spectra and polarization of jet-cooled β-dinaphthyleneoxide spiral-shaped molecules and complexes with inert-gas atoms

Fluorescence spectra and polarization of jet-cooled β-dinaphthyleneoxide spiral-shaped molecules and complexes with inert-gas atoms

Interchannel coupling effects on non-dipole photoionization parameters

Interchannel coupling effects involving non-dipole matrix elements on photoelectron angular distribution have been recently found to be of significant importance even at energies not so high above ionization thresholds. Studies have been reported on the angular distribution of photoelectrons from some inert gas atoms: Ne, Ar, Kr and Xe. In the present work, we report further studies on atomic xenon, and also results on atomic mercury, using the relativistic random phase approximation. Also, we report the angular distribution asymmetry parameters with the inclusion of non-dipole terms for a confined atom; @ Ca is considered as a model system for this study.

Processing and microstructural evolution of powder metallurgy Zn-22 Pct Al eutectoid alloy containing nanoscale dispersion particles

The present article deals with the processing and microstructural evolution of powder metallurgy (PM) Zn-22Al pct eutectoid alloy. The powder material was produced through inert gas atomization and then cryomilled in liquid nitrogen. The milled powder particles were consolidated by hot isostatic pressing (“hipping”) followed by thermomechanical treatment, resulting in a two-phase microstructure. The microstructures were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The principal processing factors and microstructural characteristics associated with the major processing steps, including spray atomization, mechanical milling (MM), consolidation, and heat treatment, were evaluated and discussed. Hot isostatic pressing and extrusion followed by heat treatment to produce the superplastic structure (Al-rich phase and Zn-rich phase) are effective in elimination porosity. A TEM examination of the microstructure of the alloy after processing reveals the presence of nanodispersion particles that are not uniformly distributed. The formation of the dispersions was attributed to the interaction between the powder material (primarily Al phase) and environmental elements such as oxygen and nitrogen during milling. Moreover, the size and distribution of the dispersions present in the bulk material met the anticipated requirements for serving as inhibitors for grain growth and barriers for dislocation movement. The TEM observations on crept specimens reveal extensive dislocation/dispersion interactions.

Nucleation and growth of Ni clusters in an Ar atmosphere

Results of molecular-dynamics simulations of the condensation of Ni atoms from a supersaturated gas phase and the subsequent formation and growth of particles in an Ar atmosphere are reported. The Ni concentration and the Ar partial pressure resemble the conditions found in recent shock-tube experiments. In order to achieve a realistic description of the microscopic processes leading to particle formation, the inert gas atoms were explicitly included in the simulations. Excess energy released during the nucleation processes is thereby transferred directly to the carrier gas via collision events. The influence of temperature on the speed of Ni atom condensation as well as particle growth is investigated. Rates of formation of Ni dimers are calculated and compared with values obtained from experiment.

Elastic electron scattering from inert-gas atoms

We present a comprehensive set of theoretical values for differential, total, and momentum transfer cross sections for elastic scattering of electrons by inert-gas atoms, for energies below 1 keV. In addition, we also provide Sherman function values for the xenon atom at various energies. The present work includes a critical analysis of most available experimental and theoretical data, and systematic investigations on the effect of various choices for the atomic central, exchange, and polarization potential that we used in our calculations. The objective of the present work is to employ a relatively simple and semiempirical approach with a minimum number of adjustable parameters, which could generate a reliable set of cross sections for a wide range of energies. The present data are in very good agreement with prior accurate experimental and theoretical values.

Recrystallization behavior in SiC amorphized with He or Ne irradiation

SiC thin specimens were amorphized with 30keV Ne+ or 4.5keV He+ irradiations at room temperature and then annealed in a transmission electron microscope (TEM). The energy and flux of these ion species were determined in order to get similar dpa profiles in depth and similar dpa rates. The peak ion implantation of He was estimated to be about five times as large as that of Ne for the same peak dpa. The crystal nucleation occurred with annealing in the case of 6.3dpa (peak) He irradiation, on the other hand, it did not occur in the case of 15dpa (peak) Ne irradiation. On the basis of the obtained results, it is shown that the crystal nucleation was promoted by the implantation of the inert gas atoms.

Low energy sputtering of nickel by normally incident xenon ions

New sputter deposition processes, such as biased target ion beam deposition, are beginning to be used to grow metallic superlattices. In these processes, sputtering of a target material at ion energies close to the threshold for the onset of sputtering can be used to create a low energy flux of metal atoms and reflected neutrals. Using embedded atom method potentials for fcc metals and a universal potential to describe metal interactions with the inert gas atoms used for sputtering, we have used molecular dynamics simulations to investigate the fundamental phenomena controlling the emitted vapor atom and reflected neutral fluxes in the low energy sputtering regime. Detailed simulations of low energy, normally incident Xe + ion sputtering of low index nickel surfaces are reported. The sputtering yield, energy and angular distributions of sputtered atoms, together with the reflection probability, energy and angular distributions of reflected neutrals were deduced and compared with available experimental data. The average energy of sputtered metal atoms can be controllably reduced to 1–2 eV as the Xe + ion energy is reduced to 50–100 eV. Normally incident Xe + ion sputtering in this energy range results in reflected Xe energies that are narrowly distributed between 2 eV and 6 eV. These fluxes are ideally suited for the growth of metallic multilayers.