Dy Addition Research Articles

Existence patterns of Dy in β-NiAl from first-principles calculations

Intermetallic compound β-NiAl is a promising material in high temperature applications due to its high melting temperature, high strength, low density, and good oxidation resistance. However, its application remains limited because of its relatively poor cyclic oxidation resistance. Addition of reactive element (RE) Dy can improve the cyclic oxidation of NiAl alloys significantly. However, the mechanism of Dy addition is not clear. Even the existence pattern of Dy in NiAl is unspecified. Therefore, in the present study, the impurity formation energies of Dy in stoichiometric NiAl, Ni-rich, and Al-rich NiAl for the substitution cases were studied by first-principles density functional theory. The results show that Dy could hardly substitute for either Ni or Al atoms in NiAl. However, calculations for dissolution energies show that Dy could be easily dissolved in Al vacancies in all three types of NiAl, which provides a new existence pattern of Dy in NiAl beyond experimental detection.

Enhancement of glass-forming ability and plasticity of Cu-rich Cu–Zr–Al bulk metallic glasses by minor addition of Dy

Abstract

Effect of Nd and Dy Addition on AZ91D Ignition Temperature and Microhardness

Magnesium alloys are very active and readily ignite during heating and melting. In this study, the ignition-proof property of AZ91D with Nd and Dy addition was discussed, and the effects of these ignition-proof elements on the microstructure and microhardness of AZ91D investigated. The results show that the ignition-proof performance of magnesium alloy is improved obviously. The ignition resistance is attributed to the compact oxide films, which consist of MgO, Al2O3, Nd2O3, Dy2O3. When Dy content increased beyond 0.5%, the change tendency of ignition point of the alloy follows the shape of “v” curve, and the ignition point increased with Nd addition. The optimum composition of the newly developed magnesium alloy is AZ91D-3Nd-0.5Dy with the ignition point about 60K higher than AZ91D. And also AZ91D-3Nd-0.5Dy has fine microstructure and higher microhardness.

Thermal stability, magnetic and mechanical properties of Fe–Dy–B–Nb bulk metallic glasses with high glass-forming ability

The effects of Dy addition on the thermal stability, glass-forming ability (GFA), magnetic and mechanical properties of quaternary (Fe0.76−xDyxB0.24)96Nb4 (x = 0–0.07) bulk metallic glasses (BMGs) were investigated. Increasing Dy content from x = 0 to 0.05 extended the supercooled liquid region up to 112 K, allowing the fabrication by copper mold casting of BMGs rods with 5.5 mm in diameter. The high GFA was found to be related to the structure of primary crystalline phase. For the x = 0.05 alloy, the competitive formation process of the complex Fe23B6 and Dy2Fe14B phases enabled to obtain the largest GFA value. Moreover, the Fe–Dy–B–Nb BMGs exhibited good soft-magnetic properties, i.e., high saturation magnetization of 1.18–0.56 T and low coercive force of 1.9–21.6 A/m. In addition, the glassy alloy rods also showed high compressive fracture strengths of 4400–4150 MPa and high Vickers hardness of 1110–1090 kg/mm2.

Electrochemical Impedance Spectroscopy Studies of Corrosion of Two-phase Ni-Dy Alloys in Molten (0.62Li,0.38K)2CO3 at 650 °C

AbstractThe dissolution of the NiO cathodes and the corrosion of bipolar plates are great obstacles to the commercialization of molten carbonate fuel cells (MCFC). Rare earth element dysprosium is effective in inhibiting the corrosion of Ni in molten carbonates. In this presentation, electrochemical impedance spectroscopy was employed to study the corrosion behavior of two-phase Ni-Dy alloys containing 1 and 3 wt.% Dy, respectively, in molten (0.62Li,0.38K)2CO3 at 650 °C in air. The experimental results indicate that the Nyquist plots for the corrosion of both Ni-1Dy and Ni-3Dy are all composed of a small capacitive loop at high frequencies and a line at low frequencies, but with larger impedance values for Ni-3Dy. The emergence of Warburg impedance at low frequencies suggests that the corrosion of alloys is controlled by the diffusion of oxidants in molten carbonates, as observed for pure nickel. The addition of dysprosium to nickel can decrease its corrosion rate, with a better effectiveness for the 3% Dy addition. Based on the diffusion impedance, the oxidants involved in corrosion are also discussed.

The Origin of Coercivity Enhancement of Sintered NdFeB Magnets Prepared by Dy Addition

The effect of Dy addition on the microstructure and magnetic properties of the sintered NdFeB magnets was investigated. The results of the microstructure analysis showed that Dy-free and Dy-doped samples are composed of Nd₂Fe ₁₄B (P42/mnm) and a trace of Nd-rich phase. Dy addition reduces significantly the pole density factor of (004), (006) and (008) crystal faces as estimated by the Horta formula. Accordingly, the coercivity of the Dy-doped sample increases from 2038 kA·m?1 up to 2288 kA·m?1. The Hcj(T)/Ms(T) versus /Ms(T) (Kronmuller-plot) behavior shows that the nucleation is the dominating mechanism for the magnetization reversal in these two kinds of magnets, and two microstructural parameters of αk and Neff are obtained. The Kronmuller-Plot gives evidence for an increase of the αk responsible for an increase of the coercivity as the result of the increase of the magnetic field as the magnetic domain reversed.

Preparation of ultrafine jet-milled powders for Nd-Fe-B sintered magnets using hydrogenation–disproportionation–desorption–recombination and hydrogen decrepitation processes

Dy addition is used to increase the coercivity of Nd-Fe-B sintered magnets. Given that Dy is rare and expensive, a method is needed for reducing the Dy content in such magnets without decreasing their coercivity. Refining Nd2Fe14B grains is a prospective method for increasing the coercivity of Nd-Fe-B magnets. Conventional jet milling, however, cannot crush strip-casted Nd-Fe-B alloys into powders less than 1 μm in size. We report a process for preparing ultrafine jet-milled powders with an average size of 0.33 μm for Nd-Fe-B sintered magnets: a combination of hydrogenation–disproportionation–desorption–recombination, hydrogen decrepitation, and He jet milling.

Thermal stability and crystallization behavior of (Fe0.75 − xDyxB0.2Si0.05)96Nb4 (x = 0–0.07) bulk metallic glasses

Effects of Dy addition on the glass-forming ability (GFA), thermal stability, and crystallization behavior in (Fe0.75−xDyxB0.2Si0.05)96Nb4 (x=0–0.07) bulk metallic glasses (BMGs) were investigated. The thermal stability of the supercooled liquid was greatly improved by alloying with a small amount of Dy. The largest supercooled liquid region of 100K was achieved for the x=0.04 alloy, leading to the best GFA with a diameter of 4mm. The activation energy for the first crystallization peak increased with the addition of Dy. However, adding more Dy may also increase the frequency factor and change the primary precipitation phase from Fe23B6 phase into DyFe11Si and DyFe3 phases, decreasing the thermal stability of the supercooled liquid. The possible relation between GFA and thermal stability, as well as crystallization behavior is discussed.

Mechanical and functional properties of two-phase Ni53Mn22Co6Ga19 high-temperature shape memory alloy with the addition of Dy

The effects of Dy addition on microstructure, martensitic transformation, mechanical and shape memory properties of the two-phase Ni53Mn22Co6Ga19 high-temperature shape memory alloy were investigated. It is found that a small Dy addition results in the refinement of grain size, which can effectively improve the tensile ductility and strength of the two-phase Ni53Mn22Co6Ga19 alloy. However, a Dy(Ni,Mn)4Ga precipitate forms in the alloys with the Dy addition, and its amount increases with an increase in the Dy addition. This change causes the ductility of the alloys to decrease when the Dy addition is further increased to 0.3 at.%. The results further show that the changes in the martensitic transformation temperature of the studied alloys can be attributed to the combined effects of the tetragonality (c/a) and electron concentration (e/a) of martensite. Additionally, the shape memory effects of the alloys are closely related to the refinement of grain size and the alloy strength. In this study, the (Ni53Mn22Co6Ga19)99.8Dy0.2 alloy exhibits a variety of good properties, including a high martensitic transformation starting temperature of 385.7 °C, a tensile ductility of 10.3% and a shape memory effect of 2.8%.

Effect of Dy addition on mechanical and magnetic properties of Mn-rich Ni–Mn–Ga ferromagnetic shape memory alloys

The effects of partial substitution of rare earth Dy for Ga on the mechanical and magnetic properties of Mn-rich Ni50Mn29Ga21−xDyx (0≤x≤5) ferromagnetic shape memory alloys were investigated in detail. The results show that an appropriate amount of Dy addition significantly improves the mechanical properties of Ni–Mn–Ga alloy. With an increase in Dy content, the compressive strength enhances rapidly at first and then becomes stable when the Dy content is more than 1at.%. However, the compressive strain increases dramatically and reaches a maximum value with 1at.% Dy addition. Further increase in Dy content makes the compressive strain of the alloys decrease gradually. The mechanism of the improved mechanical properties is also discussed. Moreover, Dy doping changes the fracture type from intergranular fracture of Ni–Mn–Ga alloy to transgranular cleavage fracture of Ni–Mn–Ga–Dy alloys. The Curie temperature remains almost unchanged at low Dy content and subsequently decreases.

Soft-ferromagnetic bulk glassy alloys with large magnetostriction and high glass-forming ability

The effect of Dy addition on the glass-forming ability (GFA), magnetostriction as well as soft-magnetic properties and fracture strength in FeDyBSiNb glassy alloys was investigated. In addition to the increase of supercooled liquid region from 55 to 100 K, the addition of Dy is effective in approaching alloy to an eutectic point and increasing the saturation magnetostrction (λs). Accordingly, bulk glassy alloy (BGA) rods with diameters up to 4 mm were produced, which exhibit a large λs as high as 65×10-6. Besides, the BGA system exhibits superhigh fracture strength of 4000 MPa, combined with good soft-magnetic properties.

The Effect of Dy Substitution on the Glass-Forming Ability and Crystallization Behavior of Mg65Cu10Ni10Y10Zn5 Metallic Glass

The glass-forming ability, thermal stability, and crystallization behavior of Mg65Cu10Ni10Y10-xZn5Dyx (x = 0, 2, and 4) alloys were investigated. The partial substitution of Dy for Y increases the activation energy of the first crystallization, but it decreases the glass-forming ability and thermal stability. Analyses on crystallization kinetics suggest that the substitution of Dy for Y decreases the nucleation rate. In addition, the examination of the crystallization phase after the isothermal annealing indicated that Dy addition suppresses the formations of Mg2Cu and Mg and that it promotes the formation of MgZn crystalline phase. The decreasing glass-forming ability with the Dy substitution can be attributed to the narrower supercooled liquid region, higher Gibbs free energy, and the change of crystallization products.

Influence of Dy addition on the magnetocaloric effect of La0.67Ca0.33Mn0.9V0.1O3 ceramics

The influence of partial substitution of La by Dy on the magnetocaloric response of (La1−xDyx)0.67Ca0.33Mn0.9V0.1O3, where x=0.03, 0.15 and 0.25 is studied. Rietveld refinement of X-ray diffraction pattern using GSAS method shows that the compounds adopt the orthorhombic structure with Pnma space group. The systematic change in lattice parameters and magnetic phase transition indicates the substitution effect of Dy. From the magnetization isotherms at different temperatures, magnetic entropy change close to their respective transition temperatures (TC) has been evaluated. The maximum value of entropy change near TC is found to be about 4.8J/kgK at 187.5K for LCMVDy0.03, 2.45J/kgK at 107.5K for LCMVDy0.15 and 2.15J/kgK at 92.5K for LCMVDy0.25 at 4T. Dy addition produces a reduction in TC and in magnitude of the magnetic entropy change. Even though the entropy change decreases with increasing Dy substitution the refrigerant temperature range, ΔT, is found to be 10K for LCMVDy0.03, 31K for LCMVDy0.15 and 35K for LCMVDy0.25 compounds [90%] at 4T. The field dependence of the magnetic entropy change is also analyzed showing the power law dependence, ΔSM∞Hn where n=0.75(2) for LCMVDy0.03, n=0.80(4) for LCMVDy0.15 and n=0.92(8) for LCMVDy0.25 compounds at their respective transition temperatures. The relative cooling power and its field dependance are also analyzed.

Effect of dysprosium addition on the cyclic oxidation behaviour of CoNiCrAlY alloy

The cyclic oxidation behaviour of a Co32Ni21Cr8Al0.6Y (wt.%) alloy with and without the addition of 0.2 wt.% dysprosium was investigated at 800 and 1100 °C in static laboratory air. The Dy-containing alloy showed a faster θ- to α-alumina transformation and significantly less weight gain than Dy-free alloy. Under cyclic oxidation at 1100 °C, Dy addition produced a continuous and protective Al 2O 3 scale. The Dy-free alloy exhibited poor oxidation resistance. Scale spallation led to the development of a complex oxide scale and internal precipitation: (Al,Cr) 2O 3 on the surface, followed by a Al 2O 3 layer, then (Al,N) precipitates alone beneath the external scale.

Effect of Dy additive on microstructure and magnetic propertiesof rapidly solidified Nd-Fe-B strips

Sintered Nd-Fe-B magnets made from strip cast alloys have been studied extensively owing to their strong permanent magnetic properties. Up to now the studies mainly focus on technology parameters of strip casting, including casting temperature, wheel speed and phase transition temperature and so on. However, microstructure and properties of rapidly solidified strips could be influenced by the composition of alloy. In this work, the effects of added Dy element on microstructures and properties of Nd-Fe-B rapidly solidified strips have been investigated. The strips shad a pronounced texture of the tetragonal T1(2 ∶14 ∶1) phase as shown by the prominent (00l) peaks at wheel surface. The alignment coefficient of the strips was the highest when Dy content ranged from 1 to 2at%. This is the result of the microstructure of strips being optimized through an appropriate amount of Dy addition. At the same time, the volume fraction of isotropic crystal decreased as Dy content increased. It revealed that the oxidation speed decreased with increasing Dy content.

Studies on ferromagnetic shape memory Ni–Mn–Ga alloys with Fe and rare-earths additives

The effect of Fe and rare-earths (Tb&Dy) addition on the martensitic transformation, magnetic and mechanical properties of the Ni 50Mn 30Ga 20 (at%) ferromagnetic shape memory alloy was investigated. The results show that the rare-earths exhibit negligible solubility in the Ni–Mn–Ga–Fe matrix phase and formed grain boundary phase. The grain boundary precipitate enhances the compressive ductility of the alloys. The martensite transformation temperature was found to be increased by the addition of rare-earths, while, Fe increased the Curie temperature of the Ni–Mn–Ga alloy. However, with increase in Fe content, an additional (Ni,Fe) 3(MnGa) precipitate is formed, leading to decrease in martensite transformation temperature and compressive ductility.

CYCLIC OXIDATION BEHAVIORS OF EB-PVD Dy DOPED β-NiAl COATINGS AT 1100°C

β- NiAl as a promising oxidation resistant coating material due to it high melting point and good oxidation resistant, however it reveals poor cyclic oxidation performance. In this paper, reactive element Dy doped β- NiAl coatings were prepared by electron beam physical vapor deposition (EB-PVD). Dy doping led to the grain refinement microstructure and Dy segregated mainly at grain boundaries. Cyclic oxidation behaviors of the coatings at 1100°C were investigated. The 0.05at.% Dy and 0.1at.% Dy doped coatings exhibited lower oxidation rate and better cyclic oxidation performance, as compared to the undoped coating. The effects of Dy addition on the morphologies and growth mechanism of the oxide scale were discussed.

Low-field magnetocaloric effect in (Gd 1− xDy x) 3Al 2 alloys

The effects of Dy substitution on the magnetic properties and magnetocaloric effect of (Gd 1− x Dy x ) 3Al 2 ( x = 0–0.5) alloys have been investigated by X-ray diffraction and magnetization measurements. It was found that Dy substitution decreased the cell volume as well as the magnetic transition temperature. The maximum magnetic entropy change for a magnetic field change from 0 to 1 T almost keep constant with values of −2.2 to −2.5 J/kg K, while the refrigerant capacity (RC) decreases with Dy addition. The adjustable Curie temperature, moderate magnetic entropy change, and large RC make these alloys potential candidates as magnetic refrigerant.

Formation and magnetic properties of Fe–Si–B–Dy amorphous alloy

Multi-component alloy ribbons with compositions of (Fe 0.75Si 0.10B 0.15) 100−xDy x ( X = 0, 0.5, 1 and 2 at.%) are prepared by single roller melt-spinning method. The structure is fully amorphous as demonstrated by XRD investigation. When Dy addition is above 1 at.%, the glass transition temperature ( T g) appears in DSC curves and has a large supercooled liquid range (Δ T x) up to 51 K. The amorphous alloy ribbons exhibit good soft magnetic properties with Curie temperature ( T C) between 700 K and 653 K, high saturation magnetization ( M S) between 1.58 and 1.50 T, and coercive force ( H C) of 27.77–22.28 A/m. In this study, it is shown that as little as 2 at.% of Dy addition to Fe–Si–B alloys is very effective in improving glass-forming ability and still maintains good soft magnetic properties.

Effect of Rare-Earth Elements Y and Dy on the Deformation Behavior of Mg Alloy Single Crystals

Effect of rare-earth elements (Y and Dy) on the mechanical properties of Mg solid solution single crystal is investigated. Comparing with the effect of other elements reported by previous studies, the solid solution strengthening by Y and Dy are much higher than that of other additives such as Zn for basal slip operation, while the isotropic strain by Zn atoms is higher than those of Y and Dy. Strain-rate changing tests were conducted for a further understanding of the dislocation motion and it revealed that the activation volumes estimated for Mg alloys with Y and Dy are much smaller than that of Zn-added alloy, while the activation enthalpy is almost the same. It was confirmed that the high strengthening effect by Dy addition is also found by Y addition, while the elastic interaction based on neither isotropic or anisotropic distortion are sufficient to explain the origin of the strengthening effect by Y and Dy addition.