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A novel approach was developed to fabricate low - oxygen powder metallurgy Ti–6Al–4 V (wt.%) titanium alloy with a highly desirable combination of ultrahigh tensile strength and good ductility. Using clean and unpassivated TiH 2 based powder compact, together with cleaning effect of in-situ dehydrogenation during heating the powder compact resulted in a low oxygen content of 0.26% in final extrusion consolidated alloy. The nature of cleaning effect during sintering was proved to be a reduction reaction of TiO 2 + 4[H] = Ti + 2H 2 O (g). Besides, solution & aging treatment produced a unique composite lamellar microstructure, which mainly consists of fine α platelets and β-transformed structures containing high number density of ultrafine acicular α precipitates. Such composite lamellar microstructure gave rise to extra geometrically necessary dislocations during tensile deformation and brought about significant dislocation hardening together with high global strain. Consequently, this Ti–6Al–4 V alloy exhibited a superior ultimate tensile strength of up to 1320 MPa and meanwhile a high elongation to fracture of not less than 12.5%. [ABSTRACT FROM AUTHOR]

The dependence of tensile properties and deformation behavior on microstructures of a near alpha titanium alloy Ti–3Al–2Zr–2Mo (wt.%) were investigated systematically. The positive roles of ultrafine α aciculae strengthened β-transformed (β t) domains on simultaneous enhancement of tensile strength and ductility of equiaxed and in particular bi-lamellar microstructures were explained. Compared with regular lamellar α/β microstructure, bi-lamellar microstructure consisting α/β t structures brought about a remarkable heterogeneous deformation introduced (HDI) strengthening and a much higher work hardening rate, which lead to enhanced strength and ductility. Only slip systems were found to operate in the equiaxed and fully lamellar microstructures, while multiple systems including and slips were activated in bi-lamellar microstructure. Besides, the fracture modes of tensile samples with different microstructures were discussed in detail. It is suggested that introducing β t domains is feasible to simultaneously enhance tensile strength and ductility of near α titanium alloys. • Near α-Ti alloy modified by β-transformed (βt) domains is suggested. • Strengthening contribution of βt domains is quantified in near α-Ti alloy. • Mechanism of simultaneously enhancing strength and ductility by βt is revealed. [ABSTRACT FROM AUTHOR]

This study investigated microstructures and mechanical behavior of a powder metallurgy (PM) Ti–3Al–2Zr–2Mo marine titanium alloy. This PM alloy was prepared by a fast sintering and immediately followed hot extrusion of TiH 2 -based powder compact. Most of the β-phase strips in as-extruded sample were found to become discontinuous via a dehydrogenation reaction of β (H) → α + β + H 2 during vacuum annealing. Such annealing rendered this alloy an excellent ultimate tensile strength up to 1080 MPa and a superior elongation to fracture of 14.0%. Further, a common annealing of 920 °C/1 h/AC brought about a lamellar microstructure consisting of coarsened α laths and β-transformed structures. Consequently, the ultimate tensile strength decreased slightly, the elongation decreased to 9.50%. It was noteworthy that the present PM alloy samples exhibited a satisfying combination of superior tensile strength and excellent ductility, which was ascribed to the reasonable oxygen solution and particular lamellar microstructures containing high content of β-transformed structures. Work hardening behavior of the present alloy was investigated, in order to explain the reason for the highly promising mechanical properties. [ABSTRACT FROM AUTHOR]

Structural distortions arising from the condensations of two essential kinds of phonon modes: the triply degenerate rotational modes (ϕx,ϕy,ϕz) of MnO6 and the doubly degenerate Jahn–Teller active modes (Q1,Q2) have been systematically investigated in the perovskite manganites. Microstructural features associated with certain types of distortions have been observed by transmission electron microscopy (TEM). In RMnO3 and La(Sr)2NiO4, we characterize the local structure, charge ordered states and orbital ordering by means of low-temperature TEM. We present direct evidence that the stripe modulation in La(Sr)2NiO4 is indeed one-dimensional within each NiO2 plane. Several typical kinds of defect structures, including antiphase boundaries and the 90°-twin domains, appear commonly in the charge-ordered states. [Copyright &y& Elsevier]

Abstract Prior particle boundaries (PPBs), microstructural heterogeneity and hot workability of Ti-44Al-6Nb-1Mo-0.3 (B, Y) (at%) alloy fabricated via SPS of its prealloyed powder were investigated systematically. It was found that, during SPS consolidation below α-transus temperature, the original α 2 dendrites and martensites within prealloyed powder decomposed towards an equilibrated α 2 + γ + B2/β triphase structures. However, at early SPS stage, PPBs and two types of microstructural heterogeneities took place, and PPBs trended to generate at triple junctions of particle contact. The circular network, which was actually α 2 /γ lamellar colonies concentrated structures at interparticle contact positions, was proved to be induced by powder surface oxygen contamination. And the other microstructural heterogeneity, existing between individual domains of former powder particles, was ascribed to non uniform solidification microstructures of initial powder. Besides, PPBs were proved seriously detrimental to both high-temperature strength and ductility. Therefore, SPS with sufficient sintering time at 1240 °C was proposed to completely eliminate PPBs and produce uniform fine-grained α 2 + γ + B2/β microstructure, in order to obtain excellent hot workability. [ABSTRACT FROM AUTHOR]

The previous study has indicated that a near alpha titanium alloy of an equiaxed microstructure could hardly exhibit a desirable ductility at 20 K. This study aimed at achieving a promising balance of superhigh strength and excellent ductility of a Ti−3Al−3Mo−3Zr (wt%) alloy in cryogenic temperature field. Temperature dependence of tensile properties and deformation behavior was investigated systematically. It was found that the ultimate tensile strength (UTS) and elongation-to-fracture (EI) jumped from 730 MPa and 19.0% at 298 K to 1300 MPa and 23.0% at 77 K, respectively. Ultrahigh UTS up to 1600 MPa and an acceptable EI of 13.5% were achieved at 20 K. The ultrahigh UTS at 77 and 20 K was considered to be attributed to the sharp increase of CRSS of slip and the Hall-Petch effect of {10 1 ̅ 2}< 10 1 ̅ 1 ̅ > twinning. The enhanced ductility at 77 K was owing to the improved strain hardening ability from large-scale twinning and prismatic and basal slips. Besides, a serrated plastic flow took place at 20 K, which was essentially because the intermittent start of twinning brought about alternate stress jump and cliff-like drop. A fully-lamellar microstructure is suggested to synchronously enhance the strength and ductility of a near-alpha titanium alloy at extra-low temperatures. • Excellent strength-ductility synergy at 77 and 20 K is achieved for a fully-lamellar structured near α-Ti alloy. • Activation of widespread twinning and multiple slips contributes to toughening at 77 and 20 K. • Prismatic and basal slips, plus {10 1 ̅ 2} twinning dominate the cryogenic deformation. • Serrated deformation at 20 K is essentially attributed to the intermittent activation of twinning. [ABSTRACT FROM AUTHOR]

Different from previous research works on cryogenic titanium alloys with a lamellar microstructure, this study focused on cryogenic tensile properties and the related deformation mechanism of a fine-grained near alpha titanium alloy of equiaxed microstructure. The fine-grained equiaxed Ti–3Al–3Mo–3Zr alloy exhibited a remarkably enhanced cryogenic tensile strength until 20 K, but cryogenic ductility decreased sharply as temperature drops. Ultimate tensile strength jumped from 740 MPa at 298 K to 1290 MPa at 77 K and to 1535 MPa at 20 K, while elongation-to-fracture dropped from 20.0% to 12.5% and to 4.0%, respectively. Sharp decline of cryogenic ductility was considered to be directly influenced by the high-angle misoriented equiaxed α-Ti grains. Because dislocation motion got much difficult and twinning could not operate extensively in the fine equiaxed microstructure at cryogenic temperatures. Besides, slip and twinning could not transfer across α-Ti grain boundaries or α/β phase interfaces, resulting in premature cracking. Different from deformation of traditional counterpart with a lamellar microstructure, prismatic and basal slips invariably dominated at 298, 77 and 20 K. Only in certain α-Ti grains whose <0001> parallel to loading direction, {10 1 ‾ 2} type tension twins operated at 77 and 20 K. The present fine-grained near α-Ti alloy with an equiaxed microstructure is suggested to be applied at temperature not lower than 77 K. • Fine-grained near α-Ti alloy of equiaxed structure exhibits satisfying ductility until 77 K. • Low ductility at 20 K is due to the enhanced difficulty of slip and insufficient twinning. • Prismatic and pyramidal slips dominate tensile deformation at 77 and 20 K. • {10 1 ‾ 2} twins prefer to occur in <0001> oriented α-Ti grains and promote slip deformation. [ABSTRACT FROM AUTHOR]

• The relaxation enthalpy displayed a monotonic decreasing trend with the extension in annealing time. • The precipitation of nanocrystals with the size of about 5 nm improved the plasticity of 1.0-h-annealed specimen. • The 1.0-h-annealed specimen possesses the lowest average stress drop and shear band formation energy. • The stress drop distribution of the 1.0-h-annealed specimen presented a well characteristic of power law distribution. In this study, the effects of sub- T g isothermal annealing on the microstructure, mechanical and serrated flow behaviors of Ti 33 Zr 30 Cu 9 Ni 5.5 Be 22.5 bulk metallic glass (BMG) were investigated. The change in free volume content of the BMG was characterized according to the structural relaxation enthalpy δH r and the onset structural relaxation temperature T r , with the results indicating a monotonic decreasing trend of the free volume content with the extension in annealing time. A number of nanocrystals with a size of approximately 4 nm were precipitated on the glassy matrix when the annealing time was extended to 1.0 h, and then the size of these nanocrystals increased with further prolongation of the annealing time. Meanwhile, the room-temperature compressive plasticity of the Ti 33 Zr 30 Cu 9 Ni 5.5 Be 22.5 BMG greatly improved from 1.4% to 4.2%, and the high strength was retained after annealing for 1.0 h, which can be largely attributed to the formation of the nanocrystals with the size of about 4 nm. With the extension of the annealing time, however, the further growth of the nanocrystals resulted in the degeneration of the compressive strength and the plasticity. The serrated rheology analysis revealed that the distribution histogram of the stress drop for the 1.0 h-annealed specimen represented a well characteristic of power-law distribution, whereas the 4.0 h-annealed showed a chaotic dynamics of jerk flow. Furthermore, the 1.0 h-annealed specimen possessed the lower average stress drop (12 MPa), formation energy per unit shear band (254.9 J/m2) and average shear band velocity (1.21 × 10−5 m s−1). [ABSTRACT FROM AUTHOR]

• Thermally-deformed specimens have a denser structure and higher characteristic temperature than the annealed specimens. • Thermally-deformed and annealed specimens precipitated some nanocrystals with the size of approximately 10 nm at 648 K. • The yield and fracture strengths of the thermally-deformed specimen are higher than that of the annealed specimen. • Both the 648 K-deformed and 648 K-annealed specimens exhibited brittle fracture characteristics. The effects of deformation and isothermal annealing in supercooled liquid region on the microstructure and room-temperature mechanical properties of the Ti 33 Zr 30 Cu 9 Ni 5.5 Be 22.5 bulk metallic glass were systematically investigated. The results indicated that the thermally-deformed specimens exhibited denser structures and higher characteristic temperatures (T g and T x) than the annealed specimens at the corresponding temperature; however, this difference gradually decreased as the experimental temperature increased. Further, the thermally-deformed specimens exhibited higher yield and fracture strengths than the annealed specimens, whereas they exhibited similar plasticity. The deformed and annealed specimens precipitated some nanocrystals with a size of approximately 10 nm when the experimental temperature increased to 648 K, causing the rapid deterioration of their plasticity. [ABSTRACT FROM AUTHOR]

Abstract: A new dual-phase nanocomposite magnet, made up of the well-coupled Sm3(Fe,Ti)29N x and α-Fe nano-crystals, has been successfully fabricated by the melt-spun technique. Measurements of magnetic properties reveal that the hysteresis loop shows up the notable characteristics of single hard magnet in the well-crystallized samples. The electron microscopy investigations indicate that the grain sizes in our samples in general range from 30 to 60nm for Sm3(Fe,Ti)29N x and from 10 to 20nm for α-Fe, grain boundaries between the Sm3(Fe,Ti)29N x and α-Fe phases are clean without any impurities. These structural features are fundamentally compatible with direct exchange-coupling between these two magnetic phases. [Copyright &y& Elsevier]

• The effect of rapid cooling after continuous heating on the alloy was investigated. • Influence of crystal structures on the mechanical properties of RC450 were studied. • The strengthening and embrittlement mechanism of the crystalline phase was discussed. The effects of rapid cooling after continuous heating on mechanical properties and microstructure of Zr 50 Cu 34 Al 8 Ag 8 amorphous alloy are investigated. The microstructure of the alloy is analyzed by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. Experimental results show that the rapid cooling of the amorphous alloy after heating to 450 °C possesses the best comprehensive mechanical properties, which can be attributed to the formation of 4.65% ordered crystal structures in the amorphous matrix. When the heating temperature rises to 480 °C, a large number of hexagonal Al 2 Zr and Ag 2 Al phases precipitate in the amorphous matrix, thereby deteriorating the alloy properties. [ABSTRACT FROM AUTHOR]