Mechanical Properties Of Zr Research Articles

Effect of Temperature on the Structure and Mechanical Properties of Zr–2.5% Nb Alloy Processed by Rotary Forging

Effect of Temperature on the Structure and Mechanical Properties of Zr–2.5% Nb Alloy Processed by Rotary Forging

Structural transitions and mechanical properties of Zr2C under ambient and high-pressure conditions

Transition metal carbides have attracted considerable attention and are widely used in machining tools, hard coatings and aerospace components, owing to their excellent mechanical and thermal properties. The Zr–C system is a typical refractory and hard transition-metal carbide, and its structural integrity and stability under extreme conditions are critical for practical applications. Here, a computational study focusing on the structural stability and crystal evolution pattern of Zr2C under ambient and high-pressure conditions was performed using a particle-swarm optimization algorithm, in combination with first-principles calculations. The calculations identified seven viable stable or metastable crystalline phases of Zr2C, exhibiting Fd 3 m, R 3 m, Cmcm, Cmca, Pbcn, Pnma and I4/mcm symmetries; further, a series of structural phase transitions were determined as the pressure increased: Fd 3 m → R 3 m → Cmcm → Cmca. In addition, the mechanical and dynamical stabilities of these phases were verified, and their structural properties were investigated. Overall, this work reveals valuable information concerning the structural, mechanical and electronic properties of Zr2C, providing key insights into the mechanisms underlying its crystal evolution behavior.

Effect of Prolonged Thermal Exposure on Microstructure and Mechanical Properties of Zr – 1 wt.% Nb and Ti – 45 wt.% Nb Ultrafine-Grained Bioinert Alloys

The results on thermal stability of the microstructure and mechanical properties of Zr – 1 wt.% Nb and Ti – 45 wt.% Nb ultrafine-grained alloys subjected to long-term thermal annealing at a temperature of 400°С are presented. It is shown that in a Zr – 1 wt.% Nb ultrafine-grained alloy an increase in the annealing duration from 5 to 360 hr leads to a growth of the structural elements (grains, subgrains, fragments) of the α-Zr matrix phase and β-Nb particles. This is a consequence of the recrystallization processes, which gives rise to softening of the alloy and a decrease in their microhardness and yield stress. It is found out that an annealing treatment for as long as 360 hr does not affect the structural element size of β-phase in the Ti – 45 wt.% Nb alloy but favors a noticeable grain growth in α- and ω-phases. It is demonstrated that disordering of the Ti – 45 wt.% Nb alloy and a decrease in its mechanical characteristics are due to the recovery processes at the grain boundaries, an increase in the nanosized grains of α- and- ω-phases, and their decreased contribution to dispersion hardening.

Microstructure and mechanical properties of Zr–Co–Al alloys prepared by rapid solidification

Abstract

Effect of low-temperature annealing on the structure and mechanical properties of Zr–Cu metallic glasses

The changes in the atomic structure and mechanical properties of Zr–Cu metallic glasses caused by low-temperature annealing were studied by X-ray diffraction synchrotron radiation and nanoindentation. Results show that the nanohardness, wear resistance, and uniformity were improved by low-temperature annealing, which indicated that annealing plays a significant contribution. Diffractions patterns showed that the content of high-strength Zr–Cu pairs was increased whereas those of Zr–Zr and Cu–Cu pairs were decreased after low-temperature annealing. Thus, the process improvement was achieved by increasing the proportion of Zr–Cu pairs.

Influence of plasma immersion titanium implantation on hydrogenation and mechanical properties of Zr–2.5Nb

This paper describes the effect of plasma immersion ion implantation (PIII) of titanium on hydrogenation behavior and mechanical properties of Zr–2.5Nb alloy. Surface morphology and depth distribution of elements in the surface layer of the samples were analyzed by scanning electron (SEM) and atomic force microscopy (AFM), and glow-discharge optical emission spectroscopy (GDOES). Hydrogenation was performed at 673K temperature and 2atm pressure. It was found that after titanium implantation a diffusion barrier is formed, accumulating hydrogen and preventing hydrogen penetration in the sample volume. The microdroplet content significantly influences the hydrogenation behavior of the zirconium alloy. Hydrogen sorption rate decreased 18.3 times and 4.3 times using filtered and unfiltered PIII, respectively. The mechanical properties of titanium-implanted zirconium layer were improved. The degradation of the mechanical properties after hydrogenation was revealed.

Microstructure, thermal stability and mechanical properties of Zr–Cu–Al–Sn bulk metallic glass

Novel (Zr0.46Cu0.46Al0.08)100−xSnx bulk metallic glasses (BMGs) were prepared by copper mold casting. The microstructure, thermal stability and mechanical properties of the BMGs were investigated. The results reveal that the thermal stability of the BMGs trends to decrease with the Sn content. The plasticity and the fracture strength are however found to be enhanced with the Sn addition. Notably with an appropriate amount of Sn addition, nano-scale phase separation with the formation of Cu–Al-rich and Zr–Sn-rich glassy phases takes place during solidification, which improves the mechanical properties of the alloys effectively.

Novel compounds in the Zr-O system, their crystal structures and mechanical properties.

With the motivation of exploring new high-strength ceramics, ab initio evolutionary simulations are performed to search for all the stable compounds in the Zr-O system. We have found that not only the traditional compound ZrO2, but also the ordered suboxides R3̅-Zr6O, R3̅c-Zr3O, P3̅1m-Zr2O and P6̅2m-ZrO are stable at zero pressure. The crystal structure of semimetallic P6̅2m-ZrO consists of Zr-graphene layers and can be described as an intercalated version of the ω-Zr structure. An interesting massive Dirac cone is found in the three-dimensional (3D) band structure of P6̅2m-ZrO at the Γ-point. The elastic properties, the hardness and the correlation between the mechanical properties of Zr-O compounds and the oxygen content have been systematically investigated. Surprisingly, the hardest zirconium oxide is not ZrO2, but ZrO. Both P6̅2m-ZrO and P3̅1m-Zr2O exhibit relatively high hardness values of 14 GPa and 10 GPa, respectively. The anisotropic Young's modulus E, torsion shear modulus Gt and linear compressibility β have been derived for P6̅2m-ZrO and P3̅1m-Zr2O. Further analyses of the density of states, the band structure and the crystal orbital Hamilton population indicate that the electronic structure of Zr-O compounds is directly related to their mechanical properties. The simultaneous occurrence of the 3D-framework of Zr-O and the strong Zr-Zr bonds in P6̅2m-ZrO explains its high hardness.

Mechanical properties of Zr–2.5%Nb pressure tube material subjected to heat treatments in α + β phase field

Heat treatment studies from α+β phase field were carried out on Zr–2.5wt%Nb alloy pressure tube (PT) material using quenching dilatometry. The effects of cooling rate and soaking temperature on the nature of β phase transformation and the morphological changes in the transformed products were studied using electron microscopy. The mechanical property variations in these heat-treated dilatometry specimens were studied using miniature specimen testing techniques such as Small Punch Test (SPT) and the Automated Ball Indentation (ABI) tests at room temperature. The effects of cooling rate and the soak temperature on the mechanical properties has been correlated with the microstructural features such as size and distribution of transformed products and their morphological characteristics. The present study has established that SPT and ABI techniques are sensitive to the microstructural changes resulting from different thermomechanical treatment and hence can be adopted to characterise the mechanical properties of pressure tube at various stages of manufacturing.

First principle study of electronic structure and mechanical properties of Zr doped Al2Cu

First principle calculations are adopted using the pseudopotential plane wave method scheme to investigate the electronic structure and mechanical properties of Zr doped Al–Cu intermetallic compounds Al2Cu. Replacing an Al atom or a Cu atom with a Zr atom, this compound forms the crystal structure of Al15Cu8Zr or Al16Cu7Zr. The results show that the structural stability and alloying ability of doped structures are larger than Al2Cu. Moreover, the structural stability and alloying ability of Al15Cu8Zr are higher than that of Al16Cu7Zr. This indicates that Zr is preferred to replace the position of Al. The mechanical properties of doped structures are increased, such as stiffness and plasticity. However, the ductility decreases, and the corresponding room temperature brittleness becomes larger. Theoretical analysis reveals that these two compounds have strong hybridisation between Al s, p states and Zr d states, which leads to intensify the atomic interaction. Therefore, chemical bonds show a character of covalent bond, and the ductility reduces.

Study of thermal stability and mechanical properties of amorphous Zr19W18N63 coatings deposited by DC/RF reactive magnetron sputtering

Thermal stability and mechanical properties of Zr–W–N films have been studied. Zr–W–N films of various structure have been deposited on Si substrates by DC/RF reactive magnetron sputtering at various substrate temperatures Ts (100°–600°C) and at constant N2 partial pressure (0.27Pa). For 100°C≤Ts≤300°C, X-ray diffraction patterns show an amorphous structure of the films which is further confirmed by transmission electron microscopy measurements. For 400°C≤Ts≤600°C, a crystalline fcc phase with (111) and (200) orientation has been observed. Maximum wear resistance (H/Er~0.22) and maximum resistance to fatigue fracture (H3/Er2~1.1GPa) have been obtained for the amorphous films deposited at Ts=200°C. Post annealing of films deposited at 200°C has been carried out in air from 100° to 600°C. Oxygen starts to be incorporated in the films at 300°C annealing temperature (Tn) and its content increases with increasing Tn. No crystalline oxide phases are observed up to Tn=600°C. The hardness of the annealed films decreases with increasing oxygen incorporation.

Effect of laser fluence on surface, structural and mechanical properties of Zr after irradiation in the ambient environment of oxygen

The laser irradiation effects on surface, structural and mechanical properties of zirconium (Zr) have been investigated. For this purpose, Zr samples were irradiated with Excimer (KrF) laser (λ ≈ 248 nm, τ ≈ 18 ns, repetition rate ≈ 30 Hz). The irradiation was performed under the ambient environment of oxygen gas at filling pressure of 20 torr by varying laser fluences ranging from 3.8 to 5.1 cm-2. The surface and structural modification of irradiated targets was investigated by scanning electron microscope (SEM) and X-ray diffractometer (XRD). In order to explore the mechanical properties of irradiated Zr, the tensile testing and Vickers micro hardness testing techniques were employed. SEM analysis reveals the grain growth on the irradiated Zr surfaces for all fluences. However, the largest sized grains are grown for the lowest fluence of 3.8 J cm−2. With increasing fluence from 4.3 to 5.1 J cm−2, the compactness and density of grains increase whereas their size decreases. XRD analysis reveals the appearance of new phases of ZrO2 and Zr3O. The variation in the peak intensity is observed to be anomalous whereas decreasing trend in the crystallite size and residual stresses has been observed with increasing fluence. Micro hardness analysis reveals the increasing trend in surface hardness with increasing fluence. The tensile testing exhibits the increasing trend of yield stress (YS), decreasing trend of percentage elongation and anomalous behaviour of ultimate tensile strength with increasing fluence.

Study of microstructure, texture and mechanical properties of Zr–2.5Nb alloy pressure tubes fabricated with different processing routes

Abstract Different fabrication trials involving the variation in three important stages of Zr–2.5Nb pressure tube were undertaken. The variations were with respect to the mode of breaking the cast structure of the ingot (forging vs extrusion), the hot extrusion ratio and the number of subsequent cold work stages to produce the finished tube. It was observed that the forging process resulted in superior performance in breaking the cast structure. Higher extrusion ratios resulted in more favorable texture and microstructure. More continuity of the beta phase was observed in the final microstructure for the route involving the single cold work step subsequent to hot extrusion.

Effects of Re microalloying on glass formation and mechanical properties of Zr–Cu–Al alloys

The effect of microalloying with rhenium on a metallic glass-forming alloy (Cu46Zr46Al8)100− x Re x (x = 1, 2) was investigated. Re possesses a positive enthalpy of mixing within the Cu–Re terminal system. Splat quenched foils of ≈40 µm in thickness display an amorphous structure. Their crystallisation temperature increases from T x = 504 to 513°C with addition of Re at nearly constant glass formation temperature T g = 445°C for the amorphous samples. In contrast, injection cast rods consist of B2-CuZr type phase dendrites, minor fractions of a cubic phase CuZrAl, and randomly distributed small particles of a Re-rich phase. This represents a novel concept in microalloying where Re-rich precipitates trigger the B2 phase formation. It leads to a unique combination of mechanical properties for as-cast rods, which display high strength at sizeable plastic deformation up to ε p ≈ 4% and an extended range of work-hardening prior to failure.

Effects of Ag addition on crystallization, microstructure and mechanical properties of Zr–Cu–Ni–Al–Ag bulk metallic glasses

The composition dependences of crystallization, microstructure and mechanical properties have been investigated. When the Ag content is in the range of 0–8at%, the BMGs with two or three-step of crystallization process exhibit remarkable plasticity, of which primary phase is an icosahedral phase. However, when the Ag concentration reaches 12–16at%, the BMGs with single-step of crystallization mode display relatively limited plasticity, whose precipitation phase is Zr2Cu and/or Zr2Ni intermetallic compounds. Structural analyses reveal that the presence of icosahedral medium-range order clusters, which, in turn leads to the heterogeneity of free volume distribution, is responsible for the improvement of plasticity. The present results suggest that, under appropriate microstructural design by the introduction of icosahedral medium-range order clusters, BMG has extensive application prospect as structural material.

Simple approach to the mechanical anisotropy of cold-rolled zirconium alloys

The anisotropy for the mechanical properties of Zr was revisited using the developed modeling approach based on the physical constraints of the hexagonal close-packed lattice structure. The current approach successfully reproduced the anisotropy for the mechanical properties depending on the cold-rolling directions. It is suggested that the reversing behavior of the tensile strength and the yield strength with respect to the rolling and transverse directions is highly correlated with the structural characteristics of the hexagonal close-packed lattice.

Structure, Thermal Stability and Mechanical Properties of Zr<SUB>65</SUB>Al<SUB>7.5</SUB>Ni<SUB>10</SUB>Cu<SUB>17.5</SUB> Glassy Alloy Rod with a Diameter of 16 mm Produced by Tilt Casting

Bulk glassy alloy rods with a diameter of 16 mm and a length of 40 to 45 mm were produced for Zr65Al7:5Ni10Cu17:5 alloy by a tilt casting method. The alloy specimens taken from the different sites which are away by about 10 mm, 15 mm and 30 mm from the bottom surface of the cast rod consist of a glassy phase and their thermal stability, mechanical properties and fracture mode are almost independent of the specimen sites. The glass transition temperature, temperature interval of supercooled liquid region before crystallization and heat of crystallization are about 643 K, 102 K and 55 J/g, respectively, for the specimens taken from the three different sites. Besides, Young’s modulus, yield strength, fracture strength, yield strain and plastic strain of the specimens are about 87 GPa, 1540 MPa, 1580 MPa, 0.018 and 0.005, respectively. The fracture mode consisting of shear plastic deformation along the maximum shear stress plane, followed by an instantaneous final rupture is also independent of the specimen sites. These data indicate that the cast glassy alloy rod with a diameter of 16 mm has nearly the same characteristics, though the cooling rate is significantly dependent on sample sites. The knowledge of producing the Zr-based bulk glassy alloy rod with nearly the same characteristics in the large diameter range up to 16 mm is encouraging for future applications of bulk glassy alloys as a new type of engineering material. [doi:10.2320/matertrans.MER2008127]

Formation of bulk metallic glasses in Cu 45Zr 48− xAl 7RE x (RE = La, Ce, Nd, Gd and 0 ≤ x ≤ 5 at.%)

We report a series of bulk metallic glass-forming alloys of compositions (Cu 45Zr 48− x Al 7RE x , RE = La, Ce, Nd, Gd and 0 ≤ x ≤ 5 at.%). By using a conventional copper mold sucking method, alloys with diameters ranging from 5 to 10 mm can be readily solidified into an amorphous structure without detectable crystallites. The best glass-forming ability is obtained for the alloys Cu 45Zr 46Al 7RE 2. Possible effects of RE addition on the glass-forming ability are discussed. In addition, the compositional effect on mechanical properties of Zr–Cu–Al–Gd alloys is presented.

The effect of the addition of Ta on the structure, crystallization and mechanical properties of Zr–Cu–Ni–Al–Ta bulk metallic glasses

Zr-based bulk metallic glasses (BMGs) or bulk metallic glass matrix composites (BMGCs) have been prepared by using a copper-mold casting in the Zr 65− x Ta x Cu 17.5Al 7.5Ni 10 (where x = 1–10 at%) alloy system while varying the Ta content. A monolithic amorphous phase of BMG was achieved when Ta was less than 2 at%, while amorphous matrix composites reinforced by Ta-solid solutions were obtained when Ta is 5 at% or higher. The addition of Ta also affected significantly the crystallization of the amorphous phase. A multi-step process of crystallization with a preferential formation of quasicrystals occurred in the alloys containing 2–5 at% Ta, while a single-step pathway of crystallization with the formation of stable Zr–Cu intermetallic compounds took place when Ta was beyond this range. In addition, a quasi-static compression test revealed that both fracture strength and plasticity of the base BMG were remarkably enhanced as Ta content increased. The effect of the addition of Ta on the structure; crystallization process; and deformation behavior of the Zr-based alloys is discussed.

Characterization of multiple crystallization steps in Zr 41.2Ti 13.8Cu 12.5Ni 10Be 22.5 bulk metallic glass

The effects of crystallization on the thermal and mechanical properties of Zr 41.2Ti 13.8Cu 12.5Ni 10Be 22.5 (number indicate at.%) bulk metallic glass (BMG) have been systematically studied by varying annealing times at 400 °C. An icosahedral quasicrystalline phase was identified in the specimen annealed for 30 min at 400 °C by using differential scanning calorimetry, X-ray diffraction, and (high-resolution) transmission electron microscopy. Embrittlement behavior due to nanocrystallization has also been examined by carrying out hardness and compression tests for specimens annealed for various times. The fracture strength at room temperature was found to decrease as the annealing time increased. The hardness was, on the other hand, observed to increase due to the increase in nanocrystalline volume fraction with the progress of annealing treatment.