Gd Ag Research Articles

The interface and lamellar structures in Mg–Gd–Ag alloys investigated by experiment and first principles

The interface and lamellar structures in Mg–Gd–Ag alloys investigated by experiment and first principles

Application of Synchrotron-Radiation Diffraction Techniques for Optimizing the Sintering Trajectory of Al2O3–Ce:(Y,Gd)AG Composite Ceramics

Application of Synchrotron-Radiation Diffraction Techniques for Optimizing the Sintering Trajectory of Al2O3–Ce:(Y,Gd)AG Composite Ceramics

Luminous output improvement in chip scale packaged Ce3+:YAG-based ceramic phosphors-converted white LEDs via laser assistance for application in automobile headlights

In this study, two kinds of composite ceramic phosphors, Ce3+:YAG/Al2O3 and Ce3+:Y(Gd)AG/Al2O3 were prepared via solid state reaction sintering in flowing pure oxygen at atmospheric pressure. The ceramic phosphors were packaged into chip-scale white light emitting diodes (w-LEDs), and laser assisted w-LED automobile headlight prototypes were assembled. The luminous flux output of the w-LEDs was significantly improved through additional blue diode laser excitation. Notably, the Al2O3 phase is able to impart an improvement in the luminescence saturation exhibited by Ce3+:Y(Gd)AG, which typically reaches saturation prior to Ce3+:YAG.

Revealing the tensile anisotropy, tension–compression asymmetry, and strain-hardening behavior of a high-performance Mg–Gd–Ag alloy

Abstract Mg–Gd–Ag-based alloys have attracted considerable attention in recent years owing to their high strength. However, their characteristic mechanical behavior remains unclear. Herein, the tensile anisotropy, tension–compression asymmetry, and strain-hardening behavior of a high-performance Mg–10.6Gd–2Ag (wt%) alloy fabricated by equal-channel angular pressing (ECAP) were systematically investigated and correlated with the evolution of microstructure and texture. The ECAP alloy exhibited synchronously enhanced tensile strength and ductility along all three directions compared with the as-cast alloy as well as improved compressive strength along the extrusion direction (ED) accompanied by slightly decreased ductility. In contrast to the pronounced reversed yield asymmetry for the as-cast alloy, the ECAP alloy exhibited a weak direct yield asymmetry along the ED. After aging, the tensile and compressive yield strengths of the ECAP alloy increased to 409 and 402 MPa, respectively, owing to the coprecipitation of basal γ'' and prismatic β' nanoplates, manifesting a near-symmetric yield response. Moreover, two strain-hardening stages (stage I and stage III) were detected in tensile deformation for all the investigated alloys, while all three stages were observed in compressive deformation. Both the strain-hardening ability and strength in the ECAP alloy before and after aging decreased slightly in the following order: ED > transverse direction (TD) > normal direction (ND), representing low anisotropy. In short, the present ECAP Mg–10.6Gd–2Ag alloy exhibited the advantages of high strength and ductility, near-symmetric yield response, and low anisotropy.

Some approaches for residual porosity estimating

Several approaches for materials residual porosity assessment are presented in this paper. Importance of development of accurate model is shown based on Al2O3–Ce:YAG and Al2O3–Ce:(Y,Gd)AG ceramic phosphors taken as model objects. The evaluated difference in the outcomes of different methods applied for estimating porosity has been shown to be as high as ∼40%. The obtained results become applicable to another types of inclusions within the studied volume of a material as in the models under consideration the main role is given to a geometrical perspective of the problem.

Polycrystalline and Single‐Crystalline Edge Layer of Mg–Gd–TM (TM=Ni, Ag) Alloys Prepared by Ion Thinner

The different segregation and lattice structure in the sample edge layer (SEL) of Mg–Gd–TM (TM: solute element, mainly Ni or Ag) alloys prepared by ion thinner have been investigated in this study. The result displays that the polycrystalline phase, Mg2GdNi9, is found in the SEL zone of Mg–Gd–Ni alloys, and the single‐crystalline phase, MgGdAg2, is found in the SEL zone of Mg–Gd–Ag alloys. The investigation of different lattice structures contributes to the distinguishment and analysis of the illusionary phases in the SEL zone of Mg–Gd–TM ternary alloys by electron microscopy sampling.

Al2O3–Ce:YAG and Al2O3–Ce:(Y,Gd)AG composite ceramics for high brightness lighting: Effect of microstructure

The paper studies efficient Al2O3–Ce:YAG and Al2O3–Ce:(Y,Gd)AG composite ceramic phosphors produced by reactive vacuum sintering. As one of the possible routes for microstructure optimization, effect of isothermal holding time was considered. The correlation between microstructural parameters (the ratio of average grain size of the matrix and thermally stable phase, residual porosity, grain and pore size distributions) and photoluminescent properties of sintered composite ceramics after combining them with a blue light-emitting diode was identified. The differences in thermal quenching behavior between Ce-doped and Ce,Gd-codoped systems were also discussed. The highest luminous efficiency of almost 151 lm/W (4526 K) and 133 lm/W (3808 K) was obtained for Al2O3–Ce:YAG, Al2O3–Ce:(Y,Gd)AG phosphors with garnet/alumina size ratio of 2.1 and 1.6, residual porosity of P = 0.0065 and 0.0047 vol%, respectively.

Tuning texture and precipitation using Y/Gd atomic ratio in iso-concentration Mg–Y–Gd–Ag–Zr extruded alloys

Three Mg–Y(–Gd)–Ag–Zr alloys with an iso-concentration of total alloying elements but different Y/Gd atomic ratios were hot extruded at 350 °C and their microstructures and mechanical properties were comparatively studied. Extruded Mg–2.4Y–0.4Ag–0.1Zr (at.%) base alloy shows a bimodal-grained structure composed of fine equiaxed recrystallised grains and coarse elongated unrecrystallised grains and has a 011¯0//ED (extrusion direction) texture. In contrast, when Y is partially replaced with Gd, extruded Mg–1.6Y–0.8Gd–0.4Ag–0.1Zr (at.%) and Mg–0.8Y–1.6Gd–0.4Ag–0.1Zr (at.%) alloys with the Y/Gd atomic ratio of 2 and 0.5, respectively, exhibit a near fully recrystallised structure and have a [0001]//ED texture. While basal γ″ precipitates dominate but few β′ precipitates form in Mg–2.4Y–0.4Ag–0.1Zr alloy, a large number density of both β′ and γ″ precipitates form in Mg–1.6Y–0.8Gd–0.4Ag–0.1Zr and Mg–0.8Y–1.6Gd–0.4Ag–0.1Zr alloys after post-extrusion ageing. Precipitation in the Gd-containing alloys is considerably enhanced by partial substituting Y with Gd. The peak-aged Mg–1.6Y–0.8Gd–0.4Ag–0.1Zr alloy keeps a relatively good balance between grain boundary strengthening, dispersion strengthening and precipitation hardening and thus obtains a good combination of strength and ductility, whose room temperature tensile yield strength, ultimate tensile strength and elongation are 377 MPa, 479 MPa and 8.0%, respectively.

Achieving ultra-high strength in Mg–Gd–Ag–Zr wrought alloy via bimodal-grained structure and enhanced precipitation

Mg–13.1Gd–1.6Ag–0.4 Zr (wt%) alloy was either iso-thermally extruded at 350 °C or differential-thermally extruded with respectively pre-heated billet at 500 °C and die at 350 °C. The iso-thermal extrusion leads to a near fully recrystallized structure and a [0001]//ED (extrusion direction) texture. In contrast, the differential-thermally extruded alloy develops a bimodal-grained structure composed of fine equiaxed recrystallized grains and coarse elongated unrecrystallized grains with a 011¯0//ED texture. The differential-thermally extruded alloy has a higher number density of precipitates after post-extrusion ageing than that of the iso-thermally extruded counterpart. Moreover, precipitation in the differential-thermally extruded alloy is further enhanced with cold rolling before ageing. Finally, the alloy obtains room temperature tensile yield strength of 421 MPa and ultimate tensile strength of 515 MPa via differential-thermal extrusion, cold rolling and ageing, mainly ascribed to the coupled strengthening from the bimodal-grained structure and enhanced precipitation. Strength of the alloy is noticeably higher than those of Mg–Gd(–Y)–Ag extruded alloys with similar compositions reported previously and is comparable to those of other high-strength Mg wrought alloys. The findings suggest that differential-thermal extrusion plus strain ageing is a suitable approach for achieving high strength in age-hardenable Mg alloys.

Tunable blue/yellow emission in high-power white LED devices packaged with Ce:(Y, Gd)AG transparent ceramics

Abstract White LEDs have been widely used in various lighting applications. However, applying them to high lumen density systems remains a challenging issue due to the aging of the organic packing materials. In this paper, Ce:(Y, Gd)AG transparent ceramics with different Gd3+ substitution concentrations were fabricated via solid-state reaction method under different sintering temperatures and used to construct high-power white LED devices to evaluate their optical, luminescence, and thermal properties. The energy band structure of Ce3+ was effectively tailored by the energy level compressing and orbital hybridisation effects, resulting in the tunability of the blue/yellow emission of the devices and the luminescence redshift of Ce:(Y, Gd)AG ceramics. The transmittance of Ce:(Y, Gd)AG transparent ceramics had almost no impact on the photoluminescence spectra yet exhibited strong dependence on the Gd3+ substitution concentration. The emitted light of LED devices packaged with the ceramics changed from blue-white to yellow-white while increasing Gd3+ concentrations from 0.0 to 30.0 at.%. The as-assembled white LED devices exhibited excellent heat dissipation performance, uniform intensity distribution, and strong intensity in the forward direction. The industrialisation of Ce:YAG transparent ceramics-based LED devices can be accelerated especially in high-power lighting.

Increase of Lie Detection Accuracy through Integrated Measurement of Pupil Dilation and Polygraph

(Y, Gd)3Al5O12: Ce ((Y, Gd)AG: Ce) ceramic solid solutions with Gd3+ ions contents from 0 to 30 at% and Ce3+ ions content of 0.01 at% were successfully fabricated using a solid-state sintering method under vacuum. The microstructure evolution and optical quality as a function of Gd2O3 substitution in (Y, Gd)AG: Ce ceramic solid solutions were studied systematically. The as prepared ceramic solid solutions provided a dense structure (above 99.0%), with an optical transmittance of 66.7% at 1064 nm, and exhibited a white light (0.3216, 0.3437) emission. It was found that moderate amount of Gd2O3 could inhibit the grain growth while promote the densification of ceramic solid solutions, whose function was similar as sintering additive.

Gd2O3 assisted densification of high quantity (Y, Gd)AG: Ce ceramic solid solutions and their luminescence characteristics

(Y, Gd)3Al5O12: Ce ((Y, Gd)AG: Ce) ceramic solid solutions with Gd3+ ions contents from 0 to 30 at% and Ce3+ ions content of 0.01 at% were successfully fabricated using a solid-state sintering method under vacuum. The microstructure evolution and optical quality as a function of Gd2O3 substitution in (Y, Gd)AG: Ce ceramic solid solutions were studied systematically. The as prepared ceramic solid solutions provided a dense structure (above 99.0%), with an optical transmittance of 66.7% at 1064 nm, and exhibited a white light (0.3216, 0.3437) emission. It was found that moderate amount of Gd2O3 could inhibit the grain growth while promote the densification of ceramic solid solutions, whose function was similar as sintering additive.

Erratum to: Thermal stability, mechanical properties and corrosion behavior of a Mg–Cu–Ag–Gd metallic glass with Nb addition

By the minor addition of Nb to a Mg–Cu–Ag–Gd alloy, a Mg–Cu–Ag–Gd–Nb bulk metallic glass (BMG) with improved thermal stability and corrosion resistance as well as good mechanical properties was developed. Mg54Cu26.5Ag8.5Gd11−x Nb x (x = 0, 1) BMGs with a diameter of 2 mm were fabricated by copper-mold casting. The Mg54Cu26.5Ag8.5Gd10Nb1 BMG exhibits enlarged supercooled liquid region of 58 K. Electrochemical measurements indicate that the addition of Nb improves the corrosion resistance of the Mg-based BMG in NaCl solution evidenced by the increased corrosion potential, though no significant effect of Nb on the corrosion behavior of the BMG in NaOH solution is observed. The Mg–Cu–Ag–Gd–Nb BMG also shows high compressive strength up to 890 MPa and elastic strain of about 1.9%.

Thermal stability, mechanical properties and corrosion behavior of a Mg–Cu–Ag–Gd metallic glass with Nd addition

Thermal stability, mechanical properties and corrosion behavior of a Mg–Cu–Ag–Gd metallic glass with Nd addition

On the role of Ag in enhanced age hardening kinetics of Mg–Gd–Ag–Zr alloys

The addition of Ag to the age hardenable Mg–Gd–Zr alloy system dramatically enhances early stage age hardening kinetics. Using atom probe tomography (APT), Ag-rich clusters were detected in a Ag-containing Mg–Gd–Zr alloy immediately after solution treatment and water quenching. During subsequent isothermal ageing at 200 °C, a high density of basal precipitates was observed during the early stages of ageing. These basal precipitates were enriched with Ag and Gd, as confirmed by APT. It is posited that Ag-rich clusters in the context of quenched-in vacancies can attract Gd atoms, increasing diffusion kinetics to facilitate the formation of the Ag + Gd-rich basal precipitates. The rapid formation of Ag + Gd-rich precipitates was responsible for accelerated ageing.

Mechanical behavior of carbon nanotube-reinforced Mg–Cu–Gd–Ag bulk metallic glasses

Carbon nanotube (CNT)-reinforced Mg59.5Cu22.9Gd11Ag6.6 bulk metallic glass (BMG) composites were successfully processed using the approach of differential pressure casting in copper molds. The approach allowed CNTs to maintain their tubular morphology in the glassy matrix, in spite of some reaction of CNTs with the metallic elements that led to the formation of crystalline phases. The presence of CNT in the amorphous matrix enhanced the compressive strength and fracture strain, and the compressive strength and fracture strain of composite with 3vol% CNT approached ~1007MPa and 0.42%, respectively. In composites with less than 3vol% CNT, the glass-forming ability (GFA) was similar to the undoped BMG. The study underscores that CNT reinforced Mg-based amorphous composites exhibit the potential to be the next generation engineering materials.

Experimental investigation and thermodynamic assessment of the Mg–Gd–Ag system focused on Mg-rich region

Phase equilibria of the ternary Mg–Gd–Ag system focused on Mg-rich region at 400°C and 450°C are experimentally studied through evaluation of six selected compositions under the long annealed states. Analysis techniques, such as SEM/BSE, TEM and EPMA are employed for phase identification and chemical investigation. A previously unreported ternary compound, designated as X, is detected in the microstructures of all the samples. The crystal structure of this phase is determined as diamond-cubic structure with the lattice parameter of a=1.59±0.01nm. Extensive solubility of the Mg5Gd phase along the direction parallel to the Gd–Ag binary in the ternary field is observed. Based on the thermodynamic descriptions of the three constituent binaries and the ternary experimental data obtained in the present study, a thermodynamic description for the Mg–Gd–Ag system is developed by using CALPHAD technique. Reasonable agreement between the calculated and experimental results is achieved.

Cast defects induced sample-size dependency on compressive strength and fracture toughness of Mg–Cu–Ag–Gd bulk metallic glass

In this work, Mg59.5Cu22.9Ag6.6Gd11 bulk metallic glass (BMG) is selected to investigate the specimen-size dependency of the compressive fracture strength and notch toughness. As the diameter of cylindrical sample increases, apparent fracture strength is reduced by 25% from ∼950MPa at 1-mm down to ∼710MPa at 10-mm sample, which is associated with the population and size of as-cast porosity in the BMG rods as indicated by X-ray computed tomography (CT). Meanwhile, it is inappropriate to describe the size dependence of fracture strength using Weibull or Gumbel statistics owing to the inhomogeneous distribution of cast defects in different sized rods. Similar to the compressive fracture strength, cast defects in Mg59.5Cu22.9Ag6.6Gd11 BMG also yield specimen-size dependency of the measured notch toughness, when the plate-specimen thickness varies within the range of 1–8mm. With three-parameter Weibull analysis, threshold toughness Kμ of as-cast Mg59.5Cu22.9Ag6.6Gd11 BMG can be estimated, which represents a minimum toughness value below which the cracks arrest. Using finite element analysis, it is confirmed that the specimen-thickness dependency of notch toughness does not result from the transition from plane-stress to plane-strain in the specimen, but from the extrinsic flaws.

Mg–Ni–Gd–Ag bulk metallic glass with improved glass-forming ability and mechanical properties

The improvement of glass-forming ability (GFA) and mechanical properties by using Ag to substitute Mg in the Mg–Ni–Gd bulk metallic glass (BMG) were studied. The Mg 69Ni 15Gd 10Ag 6 bulk metallic glass (BMG) could be cast into glassy rod up to 7 mm. The activation energies of Mg 69Ni 15Gd 10Ag 6 metallic glass were calculated by the Kissinger’s method to be E g = 2.24 eV, E x = 1.65 eV, E p1 = 1.36 eV, E p2 = 1.59 eV, E p3 = 1.26 eV and E p4 = 1.99 eV. The compressive fracture strength and the plastic strain of Mg 69Ni 15Gd 10Ag 6 BMG reached 846 MPa and 0.37% respectively.

Ca14Au46Sn5: a “Colored” Gd14Ag51-Type Structure Containing Columns of Well-Differentiated Hexagonal Gold Stars

A novel hexagonal phase discovered near the Ca(15)Au(60)Sn(25) quasicrystal and its cubic approximants (ACs) was synthesized by means of high-temperature solid-state reactions. Single-crystal structural analyses show that this is a Gd(14)Ag(51) isotype with composition within the range Ca(14)Au(45.56(4)-46.67(4))Sn(5.14(3)-4.14(3)), space group P6/m (No. 175), and lattice parameters a = 12.763(3)-12.879(3) Å and c = 9.326(3)-9.3815(4) Å. In this phase, Sn mixes with Au in two of seven anionic sites to give a strong coloring that generates a narrow honeycomb-like Au/Sn template, in which sizable columns of hexagonal Au stars are confined. This phase transforms into the cubic 2/1 AC phase through a peritectic reaction at ∼678 °C. The valence electron count per atom (e/a) of the present phase is in the range 1.41-1.45. However, it does not appear to follow a Hume-Rothery mechanism.