Yttrium Ion Implantation Research Articles

The influence of yttrium ion implantation on the oxidation behaviour of powder metallurgically produced chromium

The beneficial effect of adding yttrium by ion implantation on the oxidation behaviour of powder metallurgically (PM) produced chromium at 900 °C has been investigated. Comparative studies were made in which yttrium was added as an oxide dispersoid. For further insight into the oxidation process, a two stage oxidation, using oxygen isotope tracers, was performed. The oxide scales formed were analysed by a wide range of analytical techniques, but mostly secondary neutral mass spectroscopy (SNMS). The addition of yttrium changes the oxide scale growth processes. Its presence in the oxide scale, possibly as a segregated phase on the oxide grain boundaries, reduces cation diffusion, causing the oxide growth to be dominated by anion transport. This segregation can cause many, if not all, of the reported beneficial reactive element effects. Ion implantation is shown to be a powerful tool in oxidation studies, and thus for advanced material development.

High cycle fatigue life improvement of polycrystalline alpha-iron modified by silver, chromium, aluminium, and yttrium ion implantation

HCF tests on polycrystalline alpha-iron with and without silver, chromium, yttrium, and aluminum ion implantation have been conducted. The stress-life curves obtained were best fit by using the power function. It was shown that the fatigue property had been improved to different extent after ion implantation. Enhanced strengthening of the implanted layer due to radiation induced defects, super solid solution, and formation of intermetallic compounds in implantation was the prominent mechanism for property improvement.

Powder synthesis, sintering, and characterization of Ba 1+xZr 6−2xSi 2xO 24 -A low thermal expansion system

HCF tests on polycrystalline alpha-iron with and without silver, chromium, yttrium, and aluminum ion implantation have been conducted. The stress-life curves obtained were best fit by using the power function. It was shown that the fatigue property had been improved to different extent after ion implantation. Enhanced strengthening of the implanted layer due to radiation induced defects, super solid solution, and formation of intermetallic compounds in implantation was the prominent mechanism for property improvement.

Residual stress in metal ion implanted titanium nitride films studied by glancing incidence x-ray diffraction

The effect of yttrium and molybdenum ion implantation on the lattice parameters, residual stress, and strain distribution (integral peak breadth) in TiN coatings made by chemical vapor deposition was studied by glancing incidence x-ray diffraction in Seemann–Bohlin focusing geometry. It was found that there were no changes in the former two, but that the peak breadth was increased, and particularly between the {220} and {222} families of planes. It is considered that this may be due to grain size comminution or the development of a dislocation network down to depths of the order of 0.5 μm, which is well below the depth where the implant resides. The data also indicate that the limit of usefulness of the Seemann–Bohlin geometry is at the lower end of the angles of incidence set here, namely, 2°–3°.

Tribological effects of yttrium and nitrogen ion implantation on a precipitation hardening stainless steel

Yttrium, nitrogen and combined yttrium and nitrogen implantations have been carried out on an ASTM A286 precipitation hardening iron base alloy to evaluate the benefits in their tribological behaviour. Microindentation tests have shown a significant 20%–60% increment in hardness on the nitrogen implanted material, with a limited improvement in elastic recovery of the indentation. An abrasive test on the same material has also produced a 50% reduction in scratch depth. Y + and Y + + N + implantations also hardened the material but to a lesser extent. Reciprocating ball on disk friction and wear testing at 400 °C resulted in very severe damage in all cases. X-ray photoelectron spectroscopy analyses combined with Ar sputtering have disclosed that nitrogen is mainly in a nitrided form, yttrium remains oxidized at the surface, below which there is an apparent increase in the metallic bond.

A study of the effects of yttrium additions on the initial stages of oxidation of Ni-20Cr using glancing angle x-ray techniques

Glancing angle X-ray techniques have been used to characterise yttrium-containing Ni-20Cr alloys during the initial stages of oxidation at 700°C. A direct comparison is made between the oxide dispersoid strengthened alloy MA 754 (Ni-20Cr containing 0.6 Y 2O 3) and a Ni-20Cr alloy subjected to yttrium ion implantation at a dose of 1 × 10 17 ions cm −2. Depth profiling of samples corroded from 1 to 8 min using glancing angle X-ray diffraction was used to identify the initial phases developed as a function of depth. EXAFS (extended X-ray absorption fine structure) studies at the Cr K-edge complemented the diffraction data and also gave an indication of the degree of disorder in the fee lattice after implantation with yttrium, and its rearrangement on initial heat treatment.

The effects of yttrium ion implantation on the oxidation of nickel-chromium alloys. I. The microstructures of yttrium implanted nickel-chromium alloys

Yttrium ions of 150 keV energy were implanted into the alloys Ni-20Cr, Ni-4Cr, and into nickel. The microstructures were then characterized using transmission electron microscopy, selected area channeling patterns and back-scattered electron images. Low yttrium fluences between 1×1014 and 5× 1015 Y+/cm2 did not alter the microstructures of Ni-20Cr. However, fluences of 1×1016, 5×1016, and 7.5×1016 caused the crystalline structures of the alloy to be replaced by an amorphous phase. Fluences of 7.5×1016 Y+/cm2 also rendered Ni-4Cr and nickel amorphous. Self-ion implantation experiments on Ni-20Cr did not cause the amorphous phase to form. The depth distribution of elements in Ni-20Cr following yttrium ion implantation (7.5× 1016 Y+/cm2) was determined by Auger electron spectroscopy. This showed in addition to the added yttrium a surface depletion in nickel concentration and a simultaneous enrichment in chromium concentration. At approximately 500 A, the chromium concentration is approximately 32 at.%. This depletion/enrichment zone extends throughout the implanted layer. Annealing the Ni-20Cr implanted with 7.5×1016 Y+/cm2 in vacuum for one hour at 600°C resulted in the recrystallization of Ni-Cr solid solution and the formation of very fine grains of Y2O3. Annealing at 800°C for 5 minutes showed recrystallized Ni-Cr, Y2O3, and an additional phase or phases.

Surface modification of iron and steel by zirconium or yttrium ion implantation and their electrochemical properties

A study has been made of the corrosion behaviors of zirconium or yttrium ion implanted iron and Fe-5%Cr substrates, and of their surface characterization. Implantations of Zr + or Y + ions were carried out with fluences of around (0.1−1)×10 17 ions cm -2 at an energy of 100 keV at room temperature. The anodic dissolution behavior of ion-implanted iron or steel electrodes was measured by cyclic voltammetry in a pH 5 acetate buffer solution. Microscopic characterization of the implanted layers was performed by X-ray photoelectron spectroscopy (XPS) measurements combined with argon sputtering. Suppression of the anodic dissolution of iron is observed for both zirconium and yttrium implantations, and the former is more effective than the latter. It was also found that zirconium implantation into Fe-5%Cr alloys has a remarkable effect on the suppression of anodic dissolution. The suppression effects become clearer as the zirconium fluence increases. XPS results show that implanted zirconium atoms form a gaussian-like distribution, and in the case of high-fluence zirconium ion implantation, either carbon or oxygen atoms invaded near-surface layers to form a diffusion-like distribution. The binding energy spectra corresponding to C 1s and Zr 3d suggest that the invading carbon combines with iron to form iron carbides, and the invading oxygen combines with zirconium to form zirconium oxides. In conclusion, implanted zirconium atoms play an important role in the improvement in corrosion resistance of steels.

Distribution of ion-implanted yttrium in Cr 2O 3 scales and in the underlying Ni-25wt.%Cr alloy

Implantation of yttrium and other reactive metals has been known to have significant effects on the oxidation behavior of Cr 2O 3 - forming alloys. The oxide growth rate decreases by nearly a factor of ten, and the adhesion of oxide scales to alloys is greatly improved. To understand better the mechanisms by which these elements affect oxidation, it is important to know whether or not they are present in the metal ahead of the oxide layer. In this study, the diffusivity of implanted yttrium in an Ni-25wt.%Cr alloy and its distribution in the oxide scale after different oxidation times were evaluated using secondary ion mass spectroscopy. It was found that only 17 ppm yttrium was left in the alloy after just 20 min of oxidation at 1000 °C. The implanted yttrium remained concentrated at the oxide-gas interface as the oxide thickened with time. Within the oxide layer, the yttrium concentration progressively dropped to zero at the scale-alloy interface. These results are discussed in relation to several important mechanisms proposed for the beneficial effects of reactive element additions on scale adhesion.

The effect of ion-implanted yttrium on the oxidation of austenitic stainless steel

The effect of ion-implanted yttrium on the oxidation of austenitic stainless steel is studied by combining ion backscattering (RBS) and SIMS characterizations of implanted and unimplanted specimens. Elemental depth distributions are measured after oxidation in 〈114〉 single crystals (17Cr13Ni) and type-304 polycrystalline samples (18Cr10Ni). Implantation of 5 × 10 15 and 2 × 10 16Y/cm 2 (200 keV) reduces the extent of oxidation (10 min at 800°C) by ~ 20%. In addition, the 2 × 10 15Y/cm 2 implantation changes the oxidation mechanism from being iron out-diffusion to be predominantly oxygen in-diffusion. This effect is believed to be beneficial for preventing spallation. While the single crystal oxidizes more than a micron for 10 min at 800°C, type 304 oxidizes less than 100 nm. At 1000°C the oxidation of 304 steel amounts to less than 200 nm. Yttrium implantation reduces the oxidation rate, but both in the implanted and unimplanted case, the oxidation mechanism appears to be chromium out-diffusion.

Oxidation protection of 20Cr-25Ni-Nb stainless steel at 1300�C

Enhanced environmental protection of chromia-forming advanced metallic alloys at normal operating temperature, typically ≲900°C, may be provided by two well-established approaches—incorporation of reactive elements into the protective oxide scale or an amorphous ceramic coating acting as a diffusion barrier. The continued effectiveness of such approaches, namely by cerium and yttrium ion implantation and with a vapor deposited amorphous silica coating, in reducing oxidation of 20Cr-25Ni-Nb stainless steel in a carbon-dioxide-based environment has been examined during 0.5 and 1 hr transients to 1300°C. The influence of pre-oxidation of the ion-implanted, silica-coated, and uncoated steel for extended periods in the same environment at 825–900°C has also been established.

Early stages of oxidation of yttrium-implanted Ni-20% Cr

The effect of ion-implanted yttrium on oxidation at elevated temperatures (500 to 1000° C) has been studied in Ni-Cr alloys using high-voltage electron microscopy (HVEM) ofin situ oxidized specimens, electron microscopy of scales oxidizedex situ, and Rutherford back scattering. The presence of yttrium enhances nucleation and growth of Cr2O3 at the alloy surface. Although the radiation damage induced by the ion implantation accelerates oxide nucleation and the initial rate of oxidation at 500° C, the growth of a mature oxide scale is slowed down, and the main influences seem to come from the chemical characteristics of the implanted yttrium. A Cr2O3 layer forms first on the yttrium-implanted alloys. Outward diffusion of Ni2+ cations through this layer forms an outer NiO scale. The initial growth process on unimplanted alloys is opposite. Here, NiO is the predominant initial oxide. As it thickens, a porous spinel and Cr2O3-enriched layer is formed between alloy and NiO. The inner oxide layer on yttrium-implanted alloys is fully dense and contains more than 50% Cr2O3. On the unimplanted alloy, the inner spinel layer is porous and contains a lesser enrichment in Cr2O3. The porous spinel delays formation of a protective Cr2O3 layer and gives poor scale adherence. The oxide growth mechanisms are discussed in the light of TEM results.

High-temperature corrosion and mechanical properties of protective scales on Incoloy 800H: The influence of preoxidation and ion implantation

Coatings, obtained by preoxidation of Incoloy 800H at low PO2 show good sulphidation resistance due to the higher chromia content in the oxide scale. Yttrium-ion implantation of Incoloy 800H has also a beneficial effect on sulphidation, if preoxidation is applied. The reason for this is presumably the segregation of yttrium to grain boundaries of the oxide. Furthermore, the oxidation kinetics of Incoloy 800H are independent of the partial pressure of the oxygen. Mechanical testing of the preformed oxide scale/substrate combinations in air at 600°C by means of constant-extension-rate experiments shows that preoxidation at low partial pressures of oxygen leads to earlier scalecracking.

The Effect of Yttrium Ion Implantation on the High Temperature Oxidation Properties of NiAl

ABSTRACTNiAl was ion implanted with yttrium (2×1016 cm−2) in order to study its effect on the very high temperature (1000–1500°C) oxidation properties. At 1000°C, implanted Y stabilizes the faster growing θ-Al2O3 phase, thus slightly increasing the oxidation rate. At 1200°C, where predominantly α-Al2 O3 is formed with and without Y, there is a factor of 4 reduction in the oxidation rate. However at higher than 1200°C, there is little effect by Y on the oxidation rate. Cyclic testing showed that the Y implant had an imperfect and short-lived improvement on adherence relative to other Y-containing alloys. Variations in aluminum content from 23.5 to 36.0wt%(40–55at%) had little effect on the oxidation properties. Initial experiments at 1500°C with a novel Rh marker indicate that alumina grows at least partially by outward cation diffusion both with and without Y.

The influence of implanted yttrium on the oxidation properties of a Co-25Cr1Al alloy

Yttrium ion implantation significantly improves the oxidation resistance of a Co-25Cr1Al alloy by the incorporation of this reactive element in the scale. Segregation of yttrium ions to grain boundaries in the Cr 2O 3 scale has been measured using energy dispersive X-ray analysis with scanning transmission electron microscopy. Second-phase particles rich in yttrium were also detected in the scale. The effect of the yttrium segregation to oxide grain boundaries on the rate and mechanism of oxidation as well as on the scale microstructure and its adhesion to the substrate is discussed.

The effect of ion-implanted yttrium on the oxidation of nickel

Yttrium ions with 150 keV energy were implanted to their steady state concentration into nickel and the nickel was then annealed in a vacuum of 5 × 10 −7 Torr for 1 h at selected temperatures. Yttrium diffused to the surface of nickel to form randomly oriented grains of Y 2O 3 at temperatures between 600 and 1000°C. The oxidation kinetics of nickel and yttrium-implanted nickel were measured at 990°C in air at 1 atm, and the oxidation rate was found to be less in the implanted nickel than in the unimplanted nickel. The kinetic behavior was parabolic in the latter case but non-parabolic in the former case. The surface microstructures of implanted and unimplanted specimens were studied as a function of time at 900°C in air; the yttrium-implanted specimens yielded very uniform surface microstructures which reflected a lack of an orientation relationship between the oxide and the nickel substrate. For short oxidation times (12 h and less), the oxide layer was adherent to the nickel substrate. However, after oxidation for 24 h, the oxide layer was non-adherent.

Void formation and suppression during high temperature oxidation of MCrAlY-type coatings

Oxidation studies have been conducted on cast Co-22Cr-11Al (CoCrAl) coating alloy in air at temperatures between 700 and 1000 °C. To investigate the role of oxygen-active element additions on the oxidation behavior of the MCrAlY-type coatings, some of the CoCrAl specimens were ion implanted with either yttrium, hafnium or cobalt prior to oxidation. The oxidized specimens were subsequently examined by various electron optical techniques including scanning transmission electron microscopy and electron microprobe analysis. It was observed that voids formed in the coating alloy at the metaloxide interface during oxidation. The average size and density of these interfacial voids were dependent on temperature and time. Ion-implanted yttrium or hafnium greatly reduced the rate of void growth for all experimental conditions; cobalt implantation had little effect. This behavior is explained by a vacancy kinetic model which invloves the preferential diffusion of either metal or oxygen ions through the growing oxide scale. The results of the present study have significant implications concerning the oxidation kinetics and the adherence of the oxide scale to the coating alloy.

Inhibition of scale growth on 20Cr–25Ni–Nb stabilized stainless steel by yttrium ion implantation revealed by analytical electron microscopy

AbstractYttrium ion implantation significantly improves the oxidation behaviour of the 20Cr–25Ni–Nb stabilised stainless steel in carbon dioxide at 750–900°C by the incorporation of this reactive element within the scale. The exact location and chemical state of the yttrium ion were established by transmission and scanning transmission electron microscopy. The implanted yttrium atoms are incorporated as Y2O3 grains and as ionic segregants along the oxide grain boundaries within the outer spinel layer. of the scale next to the inner Cr2O3 layer. As a consequence of the yttrium segregation, the cation diffusion along the oxide grain boundaries, which is responsible for continuing scale growth, becomes energetically less favourable. Scale growth is inhibited to an extent according to the proportion of grain boundaries so affected. The improved spallation resistance could derive from the yttria grains and yttrium segregants inhibiting scale failure, the prelude to decohesion, by increasing the energy for thro...

Reconstruction mechanisms in ion-implanted yttrium iron garnet films

Yttrium iron garnet films implanted with Ne+ ions at two different doses have been analyzed by x-ray double-crystal diffractometry and conversion electron Mössbauer spectroscopy after thermal treatment at different temperatures. The strain profile, paramagnetic fraction, hyperfine fields of both the paramagnetic and magnetic fraction, and the full width at half-maximum of the Mössbauer peaks have been measured for the different temperatures. The reconstruction mechanism of the crystalline lattice has been studied. It appears that at least two different mechanisms are involved with two activation energies. The first one, which starts at nearly 150–200 °C and is completed at nearly 500–600 °C, is on a short-range scale and is driven by oxygen diffusion, while the second one, which has a higher activation energy, is on a long-range scale. There is clear evidence that, at least for the lower dose implanted sample, the reconstruction mechanism is not an epitaxial regrowth.

Inhibition of scale growth on 20Cr–25Ni–Nb stabilized stainless steel by yttrium ion implantation revealed by analytical electron microscopy

Inhibition of scale growth on 20Cr–25Ni–Nb stabilized stainless steel by yttrium ion implantation revealed by analytical electron microscopy