Beneficial Effect Of Yttrium Research Articles

Effect of Yttrium as Alloying Element on a Model Alumina-Forming Alloy Oxidation at 1100 °C

In order to study the effect of yttrium as alloying element on the high-temperature oxidation of an alumina-forming alloy, 0.093 wt% yttrium was incorporated into a model FeCrAl alloy. Yttrium has a beneficial effect on the isothermal oxidation behavior in air at 1100 °C. Glancing angle X-ray diffraction made on a sample oxidized for 1000 h under thermal cycling conditions indicated that yttrium is located at the internal interface as Y3Al5O12. Secondary neutral mass spectrometry results showed that the diffusion mechanism is modified by the presence of yttrium as an alloying element. Moreover, the beneficial effect of yttrium on the alloy oxidation is also related to a reduced metallic grain size. The growth of metal grains during oxidation was especially observed on the yttrium-free FeCrAl alloy. It is also well established that the diffusion mechanism in the oxide scale is modified by yttrium. The aim of the present work was to show that yttrium also plays a role on the aluminum diffusion in the metallic substrate and has a strong influence on the kinetic transient stage during the FeCrAl–0.1Y oxidation.

Effect of Rare Earth Yttrium on the Hot Ductility of Eco-friendly Bi-S Based Free Cutting Steel

AbstractThe hot ductility of eco-friendly Bi-S based free cutting steels micro-alloyed with and without yttrium was studied using a Gleeble-1500 thermal–mechanical simulator over the temperature range 850–1200 °C. The results showed that the addition of rare earth yttrium had a substantial improvement in the hot ductility of Bi-S based free-cutting steel, especially at 1000 °C. The beneficial effect of yttrium on the hot ductility of Bi-S based free-cutting steel at the temperature no less than 1000 °C was mainly associated to the refinement of austenite grain size, which could effectively reduce the segregation density of bismuth at the grain boundary, and the lowering of the DRX onset temperature by yttrium addition. At 850–950 °C, the improvement of the hot ductility in these steels by yttrium addition might be attributed to the reduction of the low melting point sulphides at grain boundary and the refinement of the austenite grain size. However, the hot ductility of these steels micro-alloyed with yttrium was still poor at 850–950 °C, which was mainly owning to the presence of pro-eutectoid ferrite films and the absence of dynamic recrystallization as well as the segregation of liquid bismuth films at austenite grain boundaries.

Beneficial effects of yttrium on the performance of Mg–3%Al alloy during wear, corrosion and corrosive wear

Magnesium has attracted considerable attention from industry especially from the transportation sector due to its high strength-to-weight ratio. However, poor wear resistance and especially low corrosion resistance of Mg are barriers to extensive use of Mg alloys. Yttrium is one of the rare-earth elements, which has been demonstrated effective in improving the corrosion resistance and tribological properties of some metallic alloys. In this work, effects of yttrium on wear, corrosion and corrosive wear of as-cast Mg–3%Al alloy were investigated. It was shown that the added Y increased the wear resistance of the alloy through the formation of a harder second phase, Al2Y. In the case of corrosion, a small amount of added Y improved the corrosion resistance but such benefit decreased when the yttrium contents was higher than 2wt%Y. When worn in tap water involving corrosion, yttrium also improved the performance of Mg–3%Al alloy. Possible mechanisms responsible for these changes are discussed.

Effect of oxygen content in NiCoCrAlY bondcoat on the lifetimes of EB-PVD and APS thermal barrier coatings

The effect of oxygen content in NiCoCrAlY bondcoat on the cyclic oxidation lifetimes of EB-PVD and APS thermal barrier coatings (TBC) has been studied. The EB-PVD TBC system with an oxygen content of 0.05 wt. % in NiCoCrAlY bondcoat shows five times longer lifetimes compared to a TBC system with 0.2wt% oxygen in the bondcoat. In the bondcoat with the high oxygen content the minor (0.3wt.%) yttrium addition was found to be tied up by oxygen into fine precipitates of yttrium aluminates. Thereby the beneficial effect of yttrium onto the adherence of the alumina scale was significantly reduced. The critical scale thickness at failure was by about a factor of two lower for the high oxygen bondcoat than for the low oxygen bondcoat. In contrast to EB-PVD TBC systems, no detrimental effect of increasing oxygen content on the lifetime of APS-TBC systems was observed. This can be explained by a different failure mechanism of APS-TBC systems, whereby the lifetime is mainly determined by the rate of crack propagation through the ceramic topcoat.

Beneficial effects of yttrium on mechanical failure and chemical stability of the passive film in 6061 aluminum alloy

Recent studies demonstrated that oxygen-active elements such as yttrium improved the resistance of some alloys to wear and corrosive wear. In this work, the breakdown of passive film and chemical resistance of the passive film in Y-free and Y-containing 6061 aluminum alloy samples were studied. It was demonstrated that critical load that caused failure of the passive film on Y-containing specimens was higher than Y-free samples. Also, penetration depth showed that indentation resistances of Y-containing samples were less than Y-free samples. Polarization behavior of Y-containing samples was improved in contrast of Y-free samples in water and acid environments. Y-containing samples had more power to stabilize the oxide film and make it more inert to electron transfer. Results showed that there was an optimum yttrium addition for improving the properties of Al 6061. Results showed that the best percent of yttrium addition was between 1.5 and 4% and more than this the properties of alloy did not improved

A Further Study of the Beneficial Effects of Yttrium on Oxide Scale Properties and High-Temperature Wear of Stellite 21

Alloying yttrium to Co-based alloys has been proven to considerably improve their oxide scales that play an important role in resisting wear at elevated temperatures. In addition to the formation of Y2O3 phase in the oxide scale, the yttrium addition may also change the oxidation mechanism, which could be responsible for many benefits of yttrium to the wear resistance of this alloy at elevated temperatures. In this study, the effect of yttrium on the oxidation behavior of Stellite 21 alloy was investigated and correlated to the changes in microstructure and improvement in properties of the oxide scale formed at 600 °C which in turn improved high-temperature wear behavior.

Beneficial effects of yttrium on mechanical properties and high-temperature wear behavior of surface aluminized 1045 steel

It has been demonstrated that oxygen-active elements (OAE) such as yttrium and cerium are beneficial to the wear resistance of aluminized layers or surfaces in corrosive environments. In this research, effects of yttrium on the wear behavior of Y-containing and Y-free aluminized surfaces of 1045 steel at elevated temperatures were investigated using a high-temperature pin-on-disc tribometer. Composition and structure of the aluminized layers were analyzed using the energy-dispersive spectroscopy (EDS) and X-ray diffraction technique (XRD), respectively. Mechanical properties of the aluminized surface layers were investigated using a micro-mechanical probe. In order to better understand the wear behavior of the aluminized surfaces at elevated temperatures, mechanical properties and scratch resistance of oxide films on the aluminized surfaces formed at 600 °C were investigated using nano-indentation and micro-scratch techniques. Structure of the oxide films was also determined using the grazing incidence XRD technique. It was demonstrated that the oxide film on the Y-containing aluminized surface contained Y 2O 3 phase that could be the main factor to render the oxide film harder, more elastic, and more resistant to scratch failure than that on the Y-free aluminized surface. All the results demonstrated that yttrium significantly improved the aluminized surface and its oxide film, resulting in enhanced resistance to wear at both elevated and room temperatures.

Influence of yttrium as alloying element on the oxidation at 1100°C of a model alumina-forming alloy

In order to study the effect of yttrium as an alloying element, 0.093 wt% yttrium was incorporated into the model Fe-20Cr-5Al alloy to give the FeCrAl-0.1Y substrate. During isothermal oxidation and thermal cycling tests, we have observed that yttrium has a beneficial effect on the oxidation behavior in air at 1100°C. In situ X-Ray diffraction allowed to demonstrate that yttrium favors a preferential crystallographic orientation of the α-Al2O3 scale. Glancing angle X-ray diffraction on a sample oxidized during 1000 hours under thermal cycling conditions indicates that yttrium is located at the internal interface as Y3A15O12. We think that the beneficial effect of yttrium on high temperature oxidation of the model alloy is due to its location at the internal interface and to the new crystallographic structure of the scale induced by the presence of Y3Al5Ol2.

Improvement in the corrosion-erosion resistance of 304 stainless steel with alloyed yttrium

It has been previously demonstrated that yttrium can improve the resistance of stainless steel to sliding wear in corrosive environment. However, the mechanism responsible for the beneficial effect of yttrium on corrosive wear is not well understood. In this work, the erosion behavior of Y-free and Y-containing 304 stainless steel in a dilute H2SO4 slurry containing silica sand was investigated, with the aim of exploring the role that yttrium plays. The failure and self-healing of passive films on Y-free and Y-containing 304 stainless steel samples under combined attack by corrosion and mechanical scratch were studied, using an electrochemical scratch technique. The failure of the passive films during dry scratch and identation was also investigated using a micro-mechanical probe with in situ monitoring changes in the electrical contact resistance. In addition, effect of yttrium on electron work function was investigated. All the results demonstrated that yttrium effectively improved properties of the passive film, including corrosion resistance, mechanical behavior and the film stability, resulting in enhanced resistance to corrosion-erosion.

EM studies of oxidized Y and Zr-doped β-NiAl

The highly beneficial effect of yttrium and zirconia dopants on the oxidation behaviour of β-NiAl has been known for over the past 50 years. Various theories have been proposed to explain the reactive element effect. The dopants may: improve the interfacial properties; favorably effect diffusion in the oxide scale; or getter the sulfur, which is a common impurity in nickel alloys, and prevents sulfur from diffusing to the interface where it may decrease the interfacial energy.To help determine which theory(s) explain the reactive element effect, we have examined oxidized Zr and Y doped β-NiAl by cross-section electron microscopy techniques on a VG-HB501 STEM and JEOLARM1250 in order to characterize the microstructure and the locations of the dopants.Polycrystalline 0.1% Y doped β-NiAl were oxidized at 1200°C for 24 hr and polycrystalline 0.1% Zr doped β-NiAl were oxidized at 1200°C for 200 hr. The CTEM images of the Zr (Fig. 1) and the Y (Fig. 2) doped NiAl show that α-Al2O3 scale forms after oxidation.

Influence of the chemical composition and the fabrication process on the behaviour of high temperature oxidation of Fe-Cr-Al alloys

The oxidation behaviour of four industrial Fe-Cr-Al alloys was studied. Two of them were Fe-Cr-Al alloys fabricated either by melting or by powder metallurgy. The two other ones were Fe-Cr-Al-Y alloys either produced by melting or by mechanical alloying. On these alloys, we determined oxidation kinetics and observed the morphology of the oxide layer after isothermal and cyclic exposures from 1000 o C up to 1300 o C. The beneficial effect of yttrium on the adherence of oxide layers was confirmed. The powder metallurgy fabrication route does not improve the oxidation resistance of yttrium-free alloys. On the other hand, the association of the powder metallurgy and the addition of yttrium allow the manufacturing of alloys which present an excellent behaviour to high temperature oxidation

Hot corrosion of yttrium-modified aluminide coatings

The beneficial effect of yttrium on the oxidation and hot corrosion resistance of electron beam-physical vapour deposition and low pressure plasma spraying overlay coatings has been confirmed by many studies. However, these coating processes have two disadvantages: (1) a restriction on the application of the coatings to complex geometries and (2) high equipment investment. In this study, a very simple slurry process was used to introduce yttrium into an aluminide coating. Its hot corrosion was tested in 25%NaCl + 75%Na 2SO 4 at 1123 K and the result showed that the hot corrosion resistance of the aluminide coating is greatly improved by the addition of yttrium. The internal oxidation and sulphidation of yttrium-free coating is more severe than that of the coating containing yttrium. It is observed that yttrium is enriched in the outer Al 2O 3 layer which is very adherent to the coating. However, oxide spalling occurred on the surface of the yttrium-free aluminide coating.

A study of yttrium‐modified aluminide coatings on IN 738 alloy

The beneficial effect of yttrium in high temperature protective coatings applied by EB–PVD and vacuum plasma spray against oxidation and hot corrosion has been recognized in many studies. In this study, the feasibility of adding yttrium into aluminide coatings has been successfully demonstrated by the conventional pack cementation process. It was found that yttrium oxide was the only practical inert filler material among the oxides investigated. Yttrium can be added into the aluminide coating either prior to or after the pack aluminizing process. Specimens prepared by the different pack cementation sequences were evaluated at 1000 °C for cyclic oxidation resistance up to 250 cycles. The yttriumized IN 738 and the yttriumized/aluminized IN 738 specimens showed very poor resistance compared to either the uncoated or the straight aluminized IN 738 specimens. Gross internal oxidation was found in the yttriumized/aluminized coating. On the other hand, the aluminized/yttriumized IN 738 showed marginal improvement over the straight aluminized IN 738. The aluminized/yttriumized coating had an yttrium rich outer oxide scale and an aluminum oxide inner scale, while the straight aluminized coating had a chromium rich outer oxide scale and an aluminum oxide inner scale.