Gd Alloys Research Articles

Creep Behavior of Squeeze-Cast Mg–15Gd Alloy

The creep behavior of a binary Mg-15 wt.% Gd alloy was investigated over the temperature range from 523 K to 743 K, i.e., in both the single-phase region (the hexagonal close-packed solid solution of Gd in Mg) and the two-phase region (the solid solution plus Mg5Gd precipitates). The alloy was prepared by the squeeze casting technique. In the higher temperature range, at 723 and 743 K, the specimens were solution treated by in situ annealing prior to testing. At the temperature of 673 K and below, the alloy was tested in the cast state. In the higher temperature range, the behavior was interpreted in terms of the viscous glide, where the dislocation motion was constrained by the presence of solute atmospheres. The dislocation motion was controlled by the rate of the cross slip from the basal to the prismatic planes. At the temperatures of 623 K and 673 K, the creep behavior was rationalized by introducing the threshold stress concept. At the temperatures of 523 K and 573 K, the stresses required to achieve experimentally measurable creep rates were such that dislocations broke away from the atmospheres of foreign atoms. Comparison with a series of magnesium alloys prepared by squeeze casting and creep-tested by the same technique showed that gadolinium can be a favorable creep-resistance enhancing element.

The effect of Gd on the microstructure evolution and mechanical properties of Mg-4Zn-0.6Ca alloy

In this work, the effect of Gd on the microstructure evolution and mechanical properties of Mg–4Zn–0.6Ca–xGd (x = 0, 0.3, 0.6 and 1, wt%) alloys were investigated systematically. The results show that Mg-4Zn-0.6Ca alloy was composed of α-Mg, Mg7Zn3 and Ca2Mg6Zn3 phase. The W-phase (Mg3Zn3Gd2) was synthesized after addition of Gd. The dynamic recrystallization was restrained and the average grain size decreased after 0.6 wt% Gd addition, causing the increase of unrecrystallized region. In addition, the volume fraction of second phase increased with increasing Gd content up to 1 wt%, and the effect of particles stimulated nucleation (PSN) was enhanced, resulting in a decrease in unrecrystallized region. The addition of Gd promoted the occurrence of the overall texture split and TD-split texture component, causing decreased basal texture intensity. An optimal mechanical property of Mg–4Zn–0.6Ca–1Gd alloy, with the yield and ultimate tensile strength of 240 MPa and 297 MPa, respectively, was achieved. The values were increased by 82 MPa and 37 MPa, respectively, compared with that of Mg–4Zn–0.6Ca alloy. In initial deformation stage, strain-hardening rate of alloys decreased with increase of Gd content. Mg-4Zn-0.6Ca-0.6Gd alloy possessed the lowest strain-hardening rate because of fine grain size. However, strain-hardening rate was increased when Gd content was increased to 1 wt%, which may be related to decreased texture intensity and presence of many second phases. This work reveals the effect of co-addition of minor Ca and Gd on the microstructure evolution and mechanical properties of Mg-Zn alloys, which provides theoretical basis for the development of high strength Mg alloy.

Investigation of Microstructure and Texture Evolution in an AZ31/Mg–Gd Alloy Hybrid Metal Fabricated by High‐Pressure Torsion

High‐pressure torsion (HPT) processing is successfully applied to fabricate a novel hybrid material from separate discs of AZ31 (Mg–3Al–1Zn, wt%) and Mg–0.6Gd (wt%) alloys by straining through numbers of rotations, N, of 1/4, 1/2, 5, 10, and 20 turns at room temperature. The microstructure and texture are investigated near the bonding interface through the disc diameter using electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The microstructure exhibits two grain refinement regimes with the first occurring during an equivalent strain range, εeq, of ≈0.3–72 and the second during εeq from ≈72 to 517. The general texture changes from B‐fiber to Y‐fiber and C2‐fiber through the HPT processing. The resultant microstructures and textures of this hybrid alloy are examined separately for the AZ31 and Mg‐0.6Gd alloys and found controlled by the presence of twinning, slip systems, and second phases and the occurrence of different dynamic recrystallization mechanisms.

Quasicrystal phase evolution and mechanical properties of Mg-3.5Zn-0.6Gd alloy processed by high-pressure torsion

To explore the effect of high-pressure torsion (HPT) on the icosahedral quasicrystal phase (I-phase), the microstructure evolution and mechanical property of extruded Mg-3.5Zn-0.6Gd alloy after HPT were investigated in detail. The results showed that a large density of twins and dislocation were generated during HPT, which effectively promoted the microstructure refinement. The block-shaped I-phase was broken into chain structure and gradually evolved into granular I-phase with the increasing strain. The block and granular I-phase through HPT exhibited a more evenly distribution. After HPT for 7 turns, the average grain size was refined to round about 89 nm and microhardness reached to a maximum value about 119 HV. The 2-fold symmetry of icosahedral quasicrystal phase (I-phase) was unveiled by TEM. According to the HRTEM and IFFT, the [11 2‾ 0]Mg//[2-fold]I-phase and (0002)Mg//(2-fold)I-phase can be identified in the Mg-3.5Zn-0.6Gd alloy. The dislocation and defect with an angle nearly 135° were also observed after HPT for 9 turns. With the further increase of strain, the microhardness appeared to decrease due to the dissolution of granular I-phase. The modified strength mechanism was constructed to distinguish the contribution of grain boundary, dislocation and precipitates.

Hot deformation and constitutive equation for ultrasonic treated Nb-Si-Ti-Gd refractory alloy

The variations in flow stress at elevated temperature for Nb-20Ti-16Si-0.5Gd alloy are studied by thermal simulation experiment, in temperature ranging from 1050 to 1250 °C, at strain rate from 10−1 to 10−4 s−1 and the deformation degree of 30%. The results show that flow stress decreases with the increase of deformation temperature, on the contrary, increases with the increase of strain rate. The constitutive equation of the investigated alloy is derived through Arrhenius hyperbolic sine function, which fits accurately on the relationship between strain rate, stress and temperature.

Microstructure and mechanical properties of Mg–Ni–Gd alloy synthesised by powder metallurgy

ABSTRACT The hexagonal close-packed structure renders magnesium weak at room and high temperatures for structural applications despite its low density. Inducing thermally stable and coherent second phases would enhance/retain the strength of Mg-based alloys even at high temperatures. This paper aims to develop a high-strength Mg-based nanocomposite. A master alloy composed of Ni and Gd was cast and the composition of Mg97.56Ni1.22Gd1.22 (at.-%) was prepared using ball milling for 150 h. XRD plots of the as-milled powder having nano-size crystallites confirm the partial dissolution of the master alloy. Consolidation through sintering with 5, 7 and 9 h of exposure at 550°C and extrusion at 500°C resulted in the formation of Mg5Gd, Mg2Ni, Gd2O3 and MgO phases. The extruded samples possessed a high strength of 804 MPa, which can be attributed to ultra-fine grains and dispersoid strengthening by homogeneously distributed second-phase particles in the 100–200 nm range.

Deformation behavior of the Mg–Zn–Zr–Nd–Gd alloy

Gd and Nd added Mg–Rare Earth (Mg–RE) alloys have attracted high-temperature applications due to their excellent combinations of high specific strength, high specific stiffness, good damping capacity, and better creep life. Despite these advantages, such Mg–RE alloys have attracted applications only in the cast form, owing to the difficulty in hot workability. Therefore, to understand the hot deformation behavior of Mg–Zn–Zr–Nd–Gd alloy, the present study correlates the results of hot compression studies with microstructure and texture. Serrated flow behavior is observed due to the dynamic strain aging. Maximum strain rate sensitivity is achieved between 580 K–650 K at lower strain rates 0.001 s−1–0.01 s−1. Dynamic recovery is predominantly active within this range of temperature and strain rate. Dynamic precipitation produces ultra-fine precipitates and leads to the suppression of dynamic recrystallization behavior. All deformed samples develop a relatively weak basal texture with the [0 0 0 1] axis parallel to the compression direction.

Mechanistic origin of the enhanced strength and ductility in Mg-rare earth alloys

Magnesium (Mg) alloys with low concentrations of rare earth additions are known to exhibit strengths and ductility that are significantly higher than those obtained in traditional Mg alloys. However, the mechanisms that underlie these improvements are still open to debate. We assessed these mechanism(s) by carrying out in-depth analysis of the deformation behavior in single crystals of pure Mg and a homogenized Mg-0.75 at.% Gd alloy oriented for twinning, pyramidal- and basal-slip. We observed a fivefold increase in basal CRSS, an eightfold increase in twinning CRSS and a fourfold decrease of the pyramidal/basal CRSS (P/B) ratio due to Gd addition. We also observed that while twinning and pyramidal slip activities were similar in the two material systems, basal slip was radically different. Specifically, basal slip was planar in the alloy but wavy in pure Mg. Our work reveals that these observations are a consequence of Gd-rich short-range ordered (SRO) clusters in the alloy. We show that interactions between dislocations and the SRO clusters would lead to significant increases in strength and 〈c+a〉 slip activity, and consequently, ductility improvements in homogenized polycrystalline Mg-Gd alloys.

Bimodal grained Mg–0.5Gd–xMn alloys with high strength and low-cost fabricated by low-temperature extrusion

Obtaining high strength in Mg alloys generally requires a high alloying content, especially rare earth elements. However, as a lightweight alloy, the heavy rare-earth content has a negative impact on the density of Mg alloys and the related cost, which increases the exploration need of low rare-earth and low-cost Mg alloy. In this work, a new low-cost and high mechanical strength Mg–0.5Gd–xMn (x = 0, 0.5, 1.0, 1.5, 2.0 wt.%) alloys system was developed by the low-temperature extrusion at 250 °C. A typical bimodal grain structure was formed in as-extruded Mg-0.5Gd-xMn alloys. The results presented a gradually increased yield strength and ultimate tensile strength with the increment of the Mn content from 0 to 1.5 wt.%. The tensile yield strength and ultimate tensile strength reached 357 MPa and 364 MPa in Mg–0.5Gd–1.5Mn alloy, which was 62 MPa and 63 MPa higher than that of the Mg–0.5Gd alloy. The high performance was mainly due to the bimodal grain structure, which produced a good Hall-Petch strengthening and the back stress strengthening. The Mg–0.5Gd–xMn alloys possessed a feature of comparable high mechanical strength with heavy rare-earth content traditional Mg alloys but a much lower cost, which promotes the future application.

Effects of Minor Gadolinium Addition and T4 Heat Treatment on Microstructure and Properties of Magnesium

Mg–Gd alloys are candidates for degradable implants combining favorable mechanical and corrosion properties. Gd has a high solid solubility in Mg and an acceptable biocompatibility. The influences of different amount of Gd additions and solid solution (T4) treatment on mechanical properties and corrosion in 0.9 wt% NaCl and cell culture medium (CCM) of magnesium are systematically investigated. The effects of Gd are clarified by microstructural characterizations as well as stress and degradation analysis. It is shown that minor Gd additions to pure Mg lead to Gd solid solution in Mg (α) and the formation of Mg5Gd intermetallic particles (IMPs), which increase the hardness, tensile, and compressive strength. The GdH2 phase is found in low‐alloyed Mg–Gd alloys. The corrosion rate (CR) is increased by the addition of more Gd due to the increased kinetics of the cathodic reaction. However, the resistance to degradation is effectively improved by T4 heat treatment due to the dissolution of IMPs. The reduced susceptibility to pitting can be achieved by a minor Gd addition and T4 heat treatment. The Mg–2Gd alloy is a potential candidate for implants due to its good combination of tailorable mechanical properties and low homogeneous in vitro degradation rate (DR).

Evolutions of microstructure and texture of Mg-Gd alloy wires processed by cold drawing

High-performance Mg-4.7Gd (wt%) alloy wires were prepared by large-strain multiple-pass cold drawing process. The maximum accumulative true strain (ATS) of Mg-4.7Gd alloy reached as high as 165%, indicating an excellent formability of Mg alloy at room temperature. Evolutions of microstructure and texture as well as mechanical properties of Mg-4.7Gd (wt%) alloy wires were studied in as-extruded and as-drawn condition. A small amount of grain with nano-sizes were observed by transmission electron microscope in the microstructure of as-drawn alloy wires with large ATS. The weak texture components with ∼45° to the transverse direction (TD) drawing direction (DD) instead of the basal texture formed in as-extruded Mg-4.7Gd alloy wire, which was beneficial to the subsequent cold drawing. As ATS increased, grains rotated around the DD and gradually approached the TD. And, the non-basal texture of G4.7 gradually increased with cold drawing due to the addition of Gd, constrained inclined compressive stress, twinning and large strain. This evolution in texture leaded to the formation of <101¯0> fiber texture with <101¯0> parallel to the DD and consequently contributed an extraordinary drawing deformability to Mg alloy.

Effect of gadolinium addition on the corrosion behavior and oxide properties of titanium in boric acid solution at 50 °C

The purpose of this study is to investigate the electrochemical and immersion corrosion behavior of Ti-5 wt.% Gd alloy in a boric acid solution at 50 °C. The chemical states and defect densities of oxide films formed in the solution were determined using X-ray photoelectron spectroscopy and the Mott–Schottky relation, respectively. Ti-5Gd alloy revealed a higher corrosion and passive current density, and greater weight loss compared to pure Ti, which is primarily attributed to the preferential dissolution of anodic Gd-rich particles in the cathodic Ti matrix. Incorporation of Gd3+ ions into the TiO2 lattice increased oxygen vacancy concentration; therefore, the oxide films of Ti-5Gd alloy contained much more point defects that carry the charges through the films, thereby deteriorating the corrosion resistance of the alloy in regards to the properties of the films.

Modified Biodegradation Behavior Induced Beneficial Microenvironments for Bone Regeneration by Low Addition of Gadolinium in Zinc (Adv. Healthcare Mater. 21/2022)

Biodegradable Materials In article 2201184 by Yufeng Zheng and co-workers, trace amounts of gadolinium are used to modify the biodegradation behavior of zinc via refinement of the intrinsic microstructure. As a result, a Zn-0.4Gd alloy implant generates beneficial microenvironments for bone regeneration by fulfilling the favorable biological role of zinc, contributing to improved osteogenesis and osseointegration.

Tailoring the Texture and Mechanical Anisotropy of Multi-cross Rolled Mg–Zn–Gd Alloy by Annealing

Tailoring the Texture and Mechanical Anisotropy of Multi-cross Rolled Mg–Zn–Gd Alloy by Annealing

The effects of continuous and discontinuous β-Mg17Al12 on compression creep properties of Mg-8.0Al-1.0Nd-1.0Gd alloys

The microstructure evolution of β-Mg17Al12 in as-cast Mg-8.0Al-1.0Nd-1.0Gd alloy during 420 °C solution and then 210 °C aging treatment was investigated. The results indicate that the discontinuous precipitation (DP) distributes along grain boundaries, and the needle-shaped continuous precipitation (CP) with crystallographic orientation relationship (OR) of [1‾101]Mg//[334‾]β, (01‾11)Mg//(313)β, (1‾011‾)Mg//(33‾0)β are the main intragranular precipitated phases. Compression creep tests of the specimens were carried out at a stress of 60 and 90 MPa at 150 and 180 °C. The microstructure observation reveals that the considerable 86° {101‾2} tension twins assist in the creep deformation for all crept specimens. The solid solution treated alloys achieve excellent creep resistance compared with the aged alloys owing to the strong co-segregation between Nd and Gd in α-Mg and β-Mg17Al12 at 180 °C/90 MPa. However, the creep properties of the aged alloys are superior to that of the solid solution treated alloys at 180 °C/60 MPa and 150 °C/90 MPa, which can be attributed to the inhibited dislocation slipping via needle-shaped and spherical CP. In addition, increasing the CP region and reducing recrystallized grains could improve the creep resistance. Combining the micro-morphology of creep structure and creep parameters (n, Q), the dominated creep mechanism for solid solution treated alloys is grain boundary sliding (n = 1.5–1.8, Q = 32–36 kJ/mol), while the dislocation climb combined with grain boundary diffusion (n = 4–6, Q = 60–80 kJ/mol) is regarded as the controlling creep mechanism for the aged Mg-8.0Al-1.0Nd-1.0Gd alloys.

Comparative Study on Corrosion Behavior and Mechanism of As-Cast Mg–Zn–Y and Mg–Zn–Gd Alloys

Comparative Study on Corrosion Behavior and Mechanism of As-Cast Mg–Zn–Y and Mg–Zn–Gd Alloys

Chemical interactions of solute atoms during L12 cluster formation in Mg–Zn–Gd alloys with long-period stacking ordered structure

Magnesium-based alloys containing transition metal (TM) and rare-earth (RE) atoms form L12-type TM6RE8 clusters, which are regularly arranged into long-period stacking ordered (LPSO) structures. X-ray absorption spectroscopy (XAS) and ab initio calculations were performed on the solution-treated Mg97Zn1Gd2 alloy before and after aging at 673 K to understand the L12 cluster formation mechanism and the interactions between the TM and RE atoms. Ab initio simulations of Zn K X-ray absorption near edge structure (XANES) spectra showed that the sharpness of the white line depended on the number of Gd atoms. The fine spectral structure changed with the local structure around the Zn atom. The measured XANES spectrum indicated that the Zn in the solution-treated Mg97Zn1Gd2 alloy was initially dissolved in Mg3Gd and then incorporated within L12 clusters after aging. Furthermore, an analysis of the l-projected density of states showed that the sharp white line peak in the XANES spectrum resulted from the interaction of Zn p and Gd f states, which occurred with spinodal decomposition and structural relaxation of L12 clusters. This spinodal decomposition and structural relaxation, caused by the electronic interaction between the RE and TM atoms, may be one of the reasons why rare-earth elements are indispensable for forming an LPSO structure.

Effect of gadolinium on the deformation and recrystallization behavior of magnesium crystals

Single crystals of pure Mg and Mg-0.8 wt% Gd alloy oriented for non-basal slip were deformed in plane strain compression at room and elevated temperatures to investigate activation of prismatic and pyramidal 〈c+a〉 slip in both materials. Compression along the c-axis of Mg–Gd single crystals revealed no marked improvement in room temperature ductility compared to pure Mg because there was no noticeable increase in 〈c+a〉 slip activity. At room temperature, Mg–Gd single crystals fractured along {112¯4} planes, which was the same fracture habit for pure Mg. Compression perpendicular to the c-axis, where specimens were favorably aligned for prismatic slip, exhibited cooperative extension/compression twinning and no notable increase in prismatic slip activity. Although the addition of Gd did not promote activation of non-basal slip, it had a significant impact on continuous dynamic recrystallization. It is concluded that the improved formability in polycrystalline Mg–Gd alloys must be primarily attributed to a change in recrystallization behavior and its effect on texture, rather than the activation of additional slip modes.

The effect of T4 and T6 heat treatments for dynamic impact behavior of casting Mg-Gd-based alloys

The study of dynamic impact properties of Mg–Gd alloy is important for its application in aerospace, automotive manufacturing and weaponry fields. In this work, the dynamic behaviors of the casting solid-solution (T4) and peak-aged (T6) Mg-6.5Gd-3Y-0.5Zr alloys were investigated at different strain rates by using optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), differential scanning calorimetry(DSC), X-ray diffraction(XRD), transmission electron microscopy(TEM), Vickers hardness testing, and split Hopkinson press bar(SHPB). Due to the dynamic precipitation phase during the SHPB and the residual rare earth hydride(REH) particles produce in the T4 treatment, the compressive strength of the casting T4-sample can reach 485 MPa at a strain rate of 3500 s−1. The casting T6-alloy precipitated a reinforced phase β′ and therefore exhibited an ultra-high compressive strength of 519 MPa at a high strain rate of 4500 s−1. The dynamic compressive strength of a T4 sample is unaffected by strain rates, whereas the dynamic compressive strength of a T6-sample is sensitive. Based on fracture morphology, the cracks are made up of a 45° loading direction crack on the cylindrical surface and a compressed surface crack. The fracture surface is characterized by cleavage planes and dimples. As the deformation strain-rate increases, the number of cleavage planes increases, while the proportion of dimples decreases. Under varied strain rates, it can likewise be deduced that cleavage fracture is the main fracture mechanism of the T6-alloy.

Intrinsic magnetic properties of the RFe11Ti (R = Y and Gd) alloys by Co, Zr and C doping

We present theoretical investigations on the electronic and magnetic properties of the RFe11-xCoxTiCz and R1-yZryFe11Ti (R = Y and Gd; x = 0–3, y = 0–0.1, z = 0 and 1) alloys describing the dependence of the magnetic properties (magnetic moments, magneto-crystalline anisotropy, exchange-coupling parameters and Curie temperatures) on the R/Zr and Fe/Co ratios and by C addition. According to our calculations for YFe11-xCoxTi, the total magnetic moment and magnetocrystalline anisotropy energy (MAE) are maximized for x = 1. On the other hand, Co doping enhances the MAE but reduces the total magnetic moment in GdFe11-xCoxTi alloys. The doping adding one C atom to the near-neighbour environment of Fe 8j site affects the magnetic moments of Fe changing their magnitude sequence. Also, Zr for R substitution and C addition have lower impact on MAE, compared with Co for Fe substitution in RFe11Ti-type alloys. The calculated exchange-coupling parameters show highest values between Fe 8i spins, followed by Fe 8i – Fe 8j spins for all investigated alloys. The corresponding mean-field approach estimated Curie temperatures show qualitative agreement with available experimental data.