Minor Additions Of Zr Research Articles

Design and Development of Stable Nanocrystalline High-Entropy Alloy: Coupling Self-Stabilization and Solute Grain Boundary Segregation Effects.

Grain growth is prevalent in nanocrystalline (NC) materials at low homologous temperatures. Solute element addition is used to offset excess energy that drives coarsening at grain boundaries (GBs), albeit mostly for simple binary alloys. This thermodynamic approach is considered complicated in multi-component alloy systems due to complex pairwise interactions among alloying elements. Guided by empirical and GB-segregation enthalpy considerations for binary-alloy systems, a novel alloy design strategy, the "pseudo-binary thermodynamic" approach, for stabilizing NC-high entropy alloys (HEAs) and other multi-component-alloy variants is proposed. Using Al25Co25Cr25Fe25 as a model-HEA to validate this approach, Zr, Sc, and Hf, are identified as the preferred solutes that would segregate to HEA-GBs to stabilize it against growth. Using Zr, NC-Al25Co25Cr25Fe25 HEAs with minor additions of Zr are synthesized, followed by annealing up to 1123K. Using advanced characterization techniques- in situ X-ray diffraction (XRD), scanning/transmission electron microscopy (S/TEM), and atom probe tomography, nanograin stability due to coupling self-stabilization and solute-GB segregation effects is reported in HEAs up to substantially high temperatures. The self-stabilization effect originates from the preferential GB-segregation of constituent HEA-elements that stabilizes NC-Al25Co25Cr25Fe25 up to 0.5Tm (Tm-melting temperature). Meanwhile, solute-GB segregation originates from Zr segregation to NC-Al25Co25Cr25Fe25 GBs; this results in further stabilization of the phase and grain-size (≈14nm) up to ≈0.58 and ≈0.64Tm, respectively.

Improving microstructure and deformation surface quality of novel Al-Mg-Zn-Zr alloy by varying homogenization regimes

Al-Mg-Zn-based alloys are newly developed high-performance age-hardenable 5xxx series alloys. However, they suffer from poor surface quality due to the Lüders bands and the Portevin-Le-Chatelier (PLC) effect during plastic deformation, and the elongation (EL) is impaired by the large constituent particles. In this work, various homogenization regimes combined with minor addition of Zr were employed to manipulate the microstructural evolution of Al-7Mg-2Zn-0.15Zr alloy and thus the deformation characteristics. The results demonstrate that a two-step homogenization treatment of 400 °C/12 h + 465 °C/12 h can sufficiently dissolve the constituent phase and eliminate the micro-segregation, as well as achieve a fine and uniform distribution of Al3Zr dispersoids, which results in the enhanced yield strength (YS) of 201 MPa and ultimate strength (UTS) of 376 MPa after rolling and annealing. Most importantly, it has been revealed that the dispersed Al3Zr formed via two-step homogenization is favorable to impede the movement of dislocations, which extends the waiting time, increases the stress amplitude, and thus diminishes the number of PLC bands. Moreover, the dislocation network induced by dispersed Al3Zr can further inhibit the movement of active dislocations, which inhibits the formation of Lüders bands. This study provides a simple and effective homogenization regime to optimize the mechanical response and surface quality of alloys with high-Mg contents.

Effects of Heterogenization Treatment on the Hot-Working Temperature and Mechanical Properties of Al-Cu-Mg-Mn-(Zr) Alloys.

This study investigated the effects of a minor Zr addition (0.15 wt%) and heterogenization treatment (one-stage/two-stage) on the hot-working temperature and mechanical properties in Al-4.9Cu-1.2Mg-0.9Mn alloy. The results indicated that the eutectic phases (α-Al + θ-Al2Cu + S-Al2CuMg) dissolved after heterogenization, retaining θ-Al2Cu and τ1-Al29Cu4Mn6 phases, while the onset melting temperature increased to approximately 17 °C. A change in the onset melting temperature and evolution of the microstructure is used to assess an improvement in hot-working behavior. With the minor Zr addition, the alloy exhibited enhanced mechanical properties due to grain growth inhibition. Zr-added alloys show 490 ± 3 MPa ultimate tensile strength and 77.5 ± 0.7 HRB hardness after T4 tempering, compared to 460 ± 2.2 MPa and 73.7 ± 0.4 HRB for un-added alloys. Additionally, combining minor Zr addition and two-stage heterogenization resulted in finer Al3Zr dispersoids. Two-stage heterogenized alloys had an average Al3Zr size of 15 ± 5 nm, while one-stage heterogenized alloys had an average size of 25 ± 8 nm. A partial decrease in the mechanical properties of the Zr-free alloy was observed after two-stage heterogenization. The one-stage heterogenized alloy had 75.4 ± 0.4 HRB hardness after being T4-tempered, whereas the two-stage heterogenized alloy had 73.7 ± 0.4 HRB hardness after being T4-tempered.

Improving the Corrosion Resistance of NiNb-Based Bulk Metallic Glass through the Hot Compression

This paper aims to study and evaluate the corrosion resistance of Ni55Nb45 and Ni55Nb35Co5Zr5 bulk metallic glasses (BMGs) in an environment similar to proton exchange membrane fuel cells. Moreover, the hot compression process was carried out to find the effects of a thermomechanical treatment on the corrosion resistance. The X-ray diffraction (XRD) test indicated that the hot compression process led to formation of crystalline species in both samples; however, it was more pronounced in the Ni55Nb35Co5Zr5 alloy. It is suggested that the minor addition of Zr and Co facilitated the crystallization in the material. The polarization test unveiled that the hot compression deteriorated the corrosion resistance of the Ni55Nb45 alloy through the introduction of anomalous chemical interfaces. On the other hand, the hot deformation affected the Ni55Nb35Co5Zr5 alloy in a positive way, so that the corrosion behavior improved compared with its fully glassy state. It is suggested that the hot deformation induces some NiNb crystalline constituencies in the microstructure of Ni55Nb35Co5Zr5 BMG, leading to the enrichment of glassy matrix from Zr/Co constituencies and the enhancement of corrosion resistance.

Molecular dynamics simulation of minor Zr addition on short and medium-range orders of Cu-Zr metallic glass.

The compositional dependence of the atomic structure and glass-forming ability (GFA) was systematically studied in a binary alloy series Cu100-xZrx (x = 0.5, 1.0, 2.0, 3.0, 5.0, 7.0, 10.0) by molecular dynamics simulations. Several structural analysis techniques are adopted to find a direct relationship between the atomic structures and GFA by minor Zr addition. The simulation results confirm that the difference among the critical cooling rates proves the enhancement of GFA. It is found that the Zr addition can enhance the icosahedra short-range order (SRO). From another side, in terms of MRO, the addition of Zr can enhance interpenetrating icosahedra connection which will give rise to the Bergman-icosahedra medium-range order, resulting in a more stable, more compact, and more complex structures, which is responsible for the enhanced GFA in CuZr alloys. Furthermore, the five-fold symmetry governs the formation of the amorphous state and may behave as a principal indication of the formation of the glass state during the cooling process. We also found a critical Zr content of 3%, below which the effect of Zr on the structures is not obvious. However, when the Zr content is higher than 3%, the Zr can rapidly change the structures of the liquid and glassy structure. These results are helpful for understanding the GFA of CuZr alloys.

High Strain Rate Superplasticity in Al-Zn-Mg-Based Alloy: Microstructural Design, Deformation Behavior, and Modeling.

Increasing the strain rate at superplastic forming is a challenging technical and economic task of aluminum forming manufacturing. New aluminum sheets exhibiting high strain rate superplasticity at strain rates above 0.01 s−1 are required. This study describes the microstructure and the superplasticity properties of a new high-strength Al-Zn-Mg-based alloy processed by a simple thermomechanical treatment including hot and cold rolling. The new alloy contains Ni to form Al3Ni coarse particles and minor additions of Zr (0.19 wt.%) and Sc (0.06 wt.%) to form nanoprecipitates of the L12-Al3 (Sc,Zr) phase. The design of chemical and phase compositions of the alloy provides superplasticity with an elongation of 600–800% in a strain rate range of 0.01 to 0.6/s and residual cavitation less than 2%. A mean elongation-to-failure of 400% is observed at an extremely high constant strain rate of 1 s−1. The strain-induced evolution of the grain and dislocation structures as well as the L12 precipitates at superplastic deformation is studied. The dynamic recrystallization at superplastic deformation is confirmed. The superplastic flow behavior of the proposed alloy is modeled via a mathematical Arrhenius-type constitutive model and an artificial neural network model. Both models exhibit good predictability at low and high strain rates of superplastic deformation.

Effect of Moist Air and Minor Zr Addition on Oxidation Behavior of Arc-Melted Multiphase Mo–Si–B Alloys in the Temperature Range of 1000 °C–1300 °C

Arc-melted multiphase intermetallic alloys, Mo76Si14B10, Mo74Si14B10Zr2, Mo79.5Si12B8.5 and Mo77.5Si12B8.5Zr2 with microstructures containing Moss, Mo3Si and Mo5SiB2 were isothermally exposed for 1 h or 24 h at 1000 °C, 1150 °C and 1300 °C in dry or moist air. The residual area fraction was found to be the highest on exposure at 1150 °C in dry air, but the least at this temperature in moist air. Examination of dry air formed oxide scales by X-ray diffraction, and scanning electron microscopy with energy-dispersive spectroscopy showed the presence of Mo, and MoO2 with a continuous, protective glassy B2O3–SiO2 top layer. Formation of Zr(MoO4)2 in the Zr-containing alloys had lowered mass loss by arresting MoO3 vaporization, and had enhanced the B2O3–SiO2 scale formation kinetics. Further, Si(OH)4, cristobalite, H3BO3 and MoO3·(H2O)2 appeared to be constituting the oxidation products formed in moist air. Alloying with Zr enhanced the kinetics of protective scale formation by lowering the Moss content, and microstructural refinement. The deterioration of oxidation resistance in moist air was conjectured to be due to longer duration required for protective scale to form, formation of β-cristobalite permitting grain boundary diffusion of oxygen anions, as well as volatile hydrated oxidation products as mentioned above. Formation of ZrSiO4 and dissolved ZrO2 in B2O3–SiO2 scale of the Mo-Si-B-Zr alloys in both dry air and moist air is considered to have contributed to the enhanced protective character of oxide scale by stabilizing the glassy scale.

Effects of minor Zr addition on the microstructure and mechanical properties of laser welded joint of Al/SiCp metal-matrix composite

Laser butt welding (LW) joints of aluminum-matrix composite with 10 vol% silicon carbide particle (SiCP) was compared between with and without the addition of zirconium (Zr). By adding zirconium (Zr) to the molten pool, ultimate tensile strength (UTS) of the joints were increased from about 65% of the UTS of the parent material (BM) to the equal UTS of BM. It was found that, by adding minor Zr into molten pool, porosity defects in welded seam zone (WM) disappeared; the residual SiC particles in WM were tightly bonded with the surrounding matrixes; generation of large size brittle phase Al4C3 was inhibited in the WM; fine ZrC precipitates with the size of 5–10 μm was generated and uniformly distributed in the WM zone. These results highlight the possibilities for strengthening fusion welded joint of Al/SiCp metal-matrix composite by taking Zr as alloying element.

Effects of minor Zr addition on the microstructure and mechanical properties of laser welded dissimilar joint of titanium and molybdenum

The capability to join molybdenum (Mo) and titanium (Ti) is of great interest for applications in aerospace and nuclear energy fields. Despite the importance, no effective methods have been developed to avoid the embrittlement problem of heat affected zone (HAZ) on the side of molybdenum plate to produce high strength joints. In this study, by adding zirconium (Zr) to the molten pool, ultimate tensile strength (UTS) of the joints were increased from about 350 MPa to about 470 MPa which reached more than 90% of that of the Ti base metal (BM). During this process, an ultra-fast diffusion behavior of Zr in HAZ on the side of a Mo plate (HAZMo) was observed. Electron back-scatter diffraction (EBSD) analysis revealed that diffusion distance of Zr in HAZMo was up to 0.75 mm, which was confirmed by the ZrO2 particles presented at both grain boundaries (GB) and the interior of the grains in HAZMo. Formation of ZrO2 particles not only inhibited the growth of recrystallised grains in HAZMo but also suppressed the precipitation of volatile MoO2 at GBs in HAZMo. These results highlight the possibilities for strengthening HAZ of refractory metals with intrinsic brittleness through fusion zone alloying.

Achieving better glass-forming ability and magnetocaloric effect in the minor Zr-substituted Gd50Co50 amorphous alloy

The glass-forming ability (GFA) and magnetic properties of the minor Zr-substituted Gd[Formula: see text]Co[Formula: see text] amorphous alloy were investigated. The Gd[Formula: see text]Co[Formula: see text]Zr2amorphous ribbons prepared by melt-spinning show better GFA. With increasing minor Zr addition, the Gd[Formula: see text]Co[Formula: see text]Zr2amorphous ribbons possessed higher magnetic entropy change peak ([Formula: see text]S[Formula: see text] = 3.9 Jkg[Formula: see text]K[Formula: see text], under 5 T) but lower Curie temperature (T[Formula: see text] = 231 K) than the Gd[Formula: see text]Co[Formula: see text] amorphous alloy. The mechanism for the improved GFA, magnetocaloric effect (MCE) and the decrease in T[Formula: see text] was investigated. Finally, combined with other Gd-based amorphous ribbons, the Gd[Formula: see text]Co[Formula: see text]Zr2amorphous alloy was employed to construct amorphous composites to achieve a table-like magnetic entropy change profile, which can provide optimal efficiency when utilizing an Ericsson thermodynamic cycle.

Fe-B-Si-Zr bulk metallic glasses with ultrahigh compressive strength and excellent soft magnetic properties

A series of quaternary Fe-B-Si-Zr bulk metallic glasses (BMGs) with high Fe content were prepared by minor addition of Zr into Fe-Si-B alloy using copper-mold casting method. The proper adjusting in B, Si and Zr contents leads to significant improvement in glass forming ability (GFA). The thermal, mechanical and soft magnetic properties for this kind of BMGs were investigated. The strong interactions among constituent elements render Fe77.7B15.5Si5Zr1.8 BMG ultrahigh compressive strength of 4167MPa. The BMGs with low Zr content exhibit high saturation magnetization (Ms) of over 1.5T. Especially, high Ms of 1.60T and low coercive force (Hc) of 4.3A/m have been detected in Fe77.5B15.5Si5.5Zr1.5 BMG.

Effect of minor addition of Zr on the oxidation behavior of Ti-Cu metallic glasses

The oxidation behavior of (TiCu)100-XZrX (x=3, 5, 7 at%) amorphous alloy during continuous heating up to 1073 K has been investigated. The weight-gain due to oxidation occurs in a two-step mode. The first-step oxidation (630~730 K) is associated with supercooled liquid region. The oxidation layer consists of intermixed TiO2 + ZrO2 layer at outer side and amorphous oxide layer at inner side. The oxidation rate at the second-step above 880 K becomes significantly different depending on the Zr content. In x=3 alloy, the oxidation layer consists of TiO2 layer at outer side, intermixed TiO2 + ZrO2 layer, and Ti3Cu3O layer at inner side. As the fraction of ZrO2 increases in x=5 and 7 alloys, the growth of oxide layer is accelerated due to provision of easier diffusion path in the intermixed oxide layer, forming intermixed multi-phase (TiO2 + ZrO2 + Ti3Cu3O + Cu51Zr14) oxide layer.

Effect of Zr content on microstructure and mechanical properties of AlCoCrFeNi high entropy alloy

The AlCoCrFeNiZrx alloys are produced by electric arc melting and their microstructure and mechanical properties were analyzed. The alloys present two types of microstructures. One is a periodic structure consisting of the ordered BCC phase and BCC solid solution phase caused by spinodal decomposition, and the other is a mixture of the ordered BCC phase and Laves phase which nucleate and grow alternatively. The coexistence of ordering and spinodal decomposition can be attributed to the lattice strain caused by the addition of Zr element with a large atom radius. The criteria (ΔHmix and ΔR) cannot effectively predict the phases for the AlCoCrFeNiZrx alloys and the Laves phase even appears in the AlCoCrFeNiZr0.008 alloy. The compressive test shows that minor Zr addition can significantly improve the mechanical properties. The AlCoCrFeNiZr0.008 alloy has the yield strength of 1560MPa, fracture strength of 3513MPa and plastic strain of 29.5%, which are increased by 240MPa, 843MPa and 7% compared with the AlCoCrFeNi alloy, respectively. However, when the Zr content is above 0.1, the fracture strength and plastic strain decrease significantly although the yield strength of the alloys increases with the Zr content further increasing.

페라이트/마르텐사이트계 산화물 분산강화 합금의 미세조직과 인장특성에 미치는 Cr, Mo, Al, Zr, Y2O3의 영향

To develop an advanced ODS alloy for core structural materials for next-generation nuclear reactor system applications, effects of alloying elements such as Cr, Mo, Al, Zr and Y2O3 on microstructures and tensile properties of ODS ferritic/martensitic alloys were investigated. The ODS alloys were fabricated by mechanical alloying, hot isostatic pressing, and hot rolling processes. The Cr concentration revealed little effect on the tensile strength, but it affected the grain morphology as a result of phase transformation. Mo acted to increase the tensile strength at an elevated temperature. Both grain and oxide particle sizes were significantly coarsened by Al addition. These enlargements led to a decrease in tensile strength but improved the elongation. Minor addition of Zr enhanced the tensile strength, and an increase of Y2O3 addition deteriorated the elongation. These results could be very useful in optimizing the alloying element concentration of ODS alloys with superior out-of-pile mechanical properties. †(Received July 18, 2013)

Oxidation resistance in LBE and air and tensile properties of ODS ferritic steels containing Al/Zr elements

The effects of Al and Zr addition on improvement of oxidation resistance in lead–bismuth eutectic (LBE) and in air as well as the tensile properties were investigated for the oxide dispersion strengthened (ODS) steels. The 16Cr–4Al–0.8Zr–ODS steel samples were fabricated by a sol–gel method combining with spark plasma sintering technique. The tests in LBE at 600°C for 1000h indicate the good oxidation resistance comparing with the specimens without Zr/Al elements. The samples also exhibit superior oxidation resistance in air due to formation of dense and continuous aluminum oxide film. Minor Zr addition prevents the Al element induced coarsening of the oxide particles in ODS steels and significantly improves the ultimate tensile stress and total elongation of the samples.

Interaction between Zr Addition and Intensive Melt Shearing on Grain Refinement of Commercial Purity Magnesium

The interaction between Zr addition and intensive melt shearing on grain refinement of commercial purity Mg has been investigated experimentally. It was found that, without intensive melt shearing, the grain structure of Mg is changed from columnar grains to equiaxed grains with the increase in Zr concentration. However, with intensive melt shearing, the grain structure of Mg undergoes a complex change as a function of Zr concentration; for instance, the grain structure showed equiaxed grains at 0.1wt. % Zr concentration, while it was changed to columnar grains at 1wt. % Zr concentration. It was noted that, particularly, under the intensive melt shearing condition, the grain size of Mg with minor addition of Zr (0.1%) was further decreased to 134 ± 4 μm compared with that of Mg without Zr addition (217 ± 15 μm).

Effect of texture evolution on mechanical properties of near eutectic Al–Si–Mg alloy with minor addition of Zr/V during hot extrusion

Texture evolution of as-extruded near eutectic Al–Si–Mg alloy with minor addition of Zr or V was studied by electron backscatter diffraction (EBSD), and the tensile properties were tested. To some extent, addition of 0.1% Zr could impede the recrystallization operation of near eutectic Al–Si–Mg alloy during hot extrusion. Addition of 0.1% V exhibits very strong inhibitory effect on recrystallization, that the texture of 4# alloy is mainly composed of deformation texture component of Brass {110}〈112〉, which may contribute to the excellent combined properties of ultimate strength (UTS), yield strength (YS) and elongation. The impact of Zr addition on the tensile properties is not as considerable as that of V addition.

On the thermal conductivity of Cu–Zr/diamond composites

Interfaces and close proximity between the diamond and the metal matrix are very important for their thermal conductance performance. Matrix-alloying is a useful approach to greatly enhance the interfacial bonding and thermal conductivity. In this study, the copper–diamond (Cu/Dia) composites with addition of 0.8, 1.2 and 2.4wt.% zirconium (Zr) are prepared to investigate the influence of minor addition of Zr on the microstructure and thermal conductivity of the composites. The thermal conductivity of the composites is analyzed both experimentally and theoretically. It is demonstrated that moderate interfacial modification due to the Zr added is beneficial to improve the thermal conductivity of the Cu/Dia composites.

Effect of Zr on the thermal stability and magnetic properties of Fe 78Si 9B 13 glassy alloy

The (Fe 0.78Si 0.09B 0.13) 100− x Zr x ( x = 0, 1 and 2) glassy alloys have been investigated in this paper. The experimental results show that the minor addition of Zr can improve the thermal stability of the Fe-based alloy. The thermal contraction process of the ribbons is mainly dependent on the crystallization process. With increasing Zr content ( c Zr), the difference (Δ d) between the nearest neighbor distance ( d exp) deduced from the X-ray diffraction pattern and the estimated nearest neighbor distance d cal, the onset crystalline temperature ( T x), the reduced crystalline temperature ( T rx), the apparent activation energy ( E p1) for the first crystallization, and the difference (Δ α) between the expansion coefficients of amorphous ribbons ( α amor) and fully crystallized counterparts ( α cryst) of the Fe-based glassy alloys first increase and then decrease, which is opposite to the change of the saturation magnetization ( M s). The variation of these parameters can be explained by the deviation degree from the equilibrium state of the amorphous ribbons. Besides the M– T measurement, the Curie temperature ( T c) of the Fe-based glassy alloys can also be scaled by the bump and inflection temperatures ( T c,dsc and T k) in differential scanning calorimetric and dilatometric curves, respectively, showing a slight decreasing tendency with increasing c Zr.

Effect of phosphorus modification on the microstructure and mechanical properties of DC cast Al-17.5Si-4.5Cu-1Zn-0.7Mg-0.5Ni alloy

Direct chill (DC) casting of an Al-17.5Si-4.5Cu-1Zn-0.7Mg-0.5Ni alloy with minor additions of Zr, V and Ti was performed and the effect of phosphorus modification on the solidification microstructure and mechanical properties were investigated. The results show that the addition of phosphorus refines the primary Si crystals remarkably but coarsens the eutectic Si in the DC cast billets. In the samples taken in 1/2 radius region of the billets of 100 mm in diameter, the average size of the primary Si particles in the unmodified alloy is 38 μm, while that in the modified alloys range from 13 to 26 μm, depending on the melt treatment time. The AlP particles as heterogeneous nucleation sites for the primary Si crystals were observed in the center of the primary Si particles. In the modified alloy, the achieved ultimate tensile strength is 320MPa and 433MPa respectively in the as-cast state and T6 state. The size of the primary Si particles is critical for the improvement of the mechanical properties of the alloy.