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Microstructure, mechanical properties as well as phase transformation behavior of newly developed Ni 49 Ti 36 Hf 15-x Ta (x=0, 3, 6, 9, 12) high temperature shape memory alloys has been investigated. Ni 49 Ti 36 Hf 15 alloy consists of (Ti,Hf) 2 Ni phase which is brittle and incoherent with the martensite matrix. However, addition of Ta in place of Hf suppresses the brittle (Ti,Hf) 2 Ni phase formation with white Ta rich phase. More than 70% reduction in area has been observed in Ta added Ni 49 Ti 36 Hf 15 high temperature shape memory alloys. The austenitic transformation temperature is well above 200 °C (473 K) for lower Ta concentrations with up to 6 at. %; however; at higher Ta concentrations (i.e. above 9 at. %) decreases significantly. Overall, the addition of Ta greatly influences the hot deformation behavior and high temperature shape memory properties of Ni 49 Ti 36 Hf 15 alloy. The present paper discusses the detailed investigation on Ni 49 Ti 36 Hf 15-x Ta (x=0, 3, 6, 9, 12) high temperature shape memory alloys. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the effect of laser polishing at different treatment times on the surface roughness and corrosion resistance of a biliary nickel-titanium (NiTi or Nitinol) stent. A specific area of the stent wire surface was checked for changes in roughness by scanning electron microscopy (SEM) and a noncontact profilometer. The corrosion resistance was assessed by potentiodynamic polarization test and electrochemical impedance spectroscopy. The surface characterization revealed that laser polishing reduced the surface roughness of stent by 34-64% compared to that of the as-received stent surface condition depending on the treatment time (i.e., 700-1600 μm). Measurements using potentiodynamic polarization in simulated body fluid solution showed better anti-corrosion performance of laser-polished stent compared to magnetically-polished stent and has comparable corrosion resistance with the as-received stent condition. In this paper, we have shown a preliminary study on the potential of laser polishing for the improvement of surface roughness of stent without affecting much its corrosion resistance. [ABSTRACT FROM AUTHOR]

Highlights: [•] Flow softening of Ti–6Al–4V with a lamellar microstructure was modeled. [•] Flow softening originated from colony rotation and alpha particle coarsening. [•] The model provided an accurate prediction of the flow response during hot working. [ABSTRACT FROM AUTHOR]

Abstract: The low-temperature superplasticity and dynamic coarsening behavior of Ti–6Al–2Sn–4Zr–2Mo–0.1Si were established and interpreted in the context of inelastic-deformation theory. The starting microstructure with an equiaxed-alpha particle size of 13μm was refined to 2.2μm by a treatment comprising beta annealing/water quenching followed by warm rolling at 775°C. A series of tension and load-relaxation tests were carried out for the coarse and fine microstructures at strain rates of 10−4 to 10−2 s−1 in the temperature range of 650–750°C. The fine microstructure exhibited enhanced superplasticity (382–826% elongation) compared to that of the coarse microstructure (189–286% elongation); this trend was attributed to a larger fraction of boundary sliding and lower friction stress for the finer material. With respect to microstructure evolution, the coarsening rate of the alpha particles during deformation was ∼12 times faster than that during static coarsening. Furthermore, both the static and dynamic coarsening rates for the Ti–6Al–2Sn–4Zr–2Mo–0.1Si were 2.7–4.7 times lower than those for the Ti–6Al–4V, a trend attributable to the lower diffusivity of Mo compared to that of V at a given test temperature. The plastic flow behavior of the coarse and fine microstructures was rationalized in terms of microstructure evolution during deformation. [Copyright &y& Elsevier]

Abstract: This study aimed to achieve enhanced mechanical compatibility of Ti–13Nb–13Zr alloy by producing submicrocrystalline microstructure without imposing severe strains. In order to find the optimum processing conditions, a series of compression tests was performed for initial martensite microstructure in strain ranges up to 0.8 and 1.4, the strain rate range of 10−3 to 1s−1 and the temperature range of 500–700°C. Based on the microstructural analysis, the submicrocrystalline (∼0.4μm) alloy consisting of high-angle grain boundaries was produced via dynamic globularization at temperature of 600°C, equivalent strain rate of 10−1 s−1 and strain of 1.4, which showed about 25% enhanced mechanical compatibility as compared to the conventionally produced ones. The formation of submicrocrystalline microstructure at relatively low strain was investigated by examining the microstructure before and after dynamic globularization. [Copyright &y& Elsevier]

Abstract: This study aimed to determine the optimum processing conditions for dynamic globularization of Ti–6Al–4V alloy having martensite microstructure, and to achieve enhanced superplasticity. A series of isothermal compression tests was carried out for martensite microstructure in the strain range of 0.6–1.4, the strain rate range of 10−3 s−1 to 1s−1 and the temperature range of 973–1223K. At each test condition, a quantitative analysis was made to measure the fraction of dynamic globularization associated with fragmentation of initial lamellar structures. It was found that the dynamic globularized fraction increased with increasing strain and with decreasing strain rate and/or temperature tested. Based on the processing map and microstructural analysis, the optimum processing condition to obtain the finest equiaxed microstructure was determined. A very high elongation over ≈1000pct was achieved at relatively high strain rate superplasticity regime (>10−2 s−1). The present enhanced superplasticity was rationalized by examining the microstructures of the alloy associated with dynamic globularization. [Copyright &y& Elsevier]

Ultrafine-grained (UFG) structure is beneficial for overcoming the strength-ductility trade-off and enhancing the superplasticity of two-phase Ti alloys. Recently, it has been demonstrated that compression with decreasing temperatures is effective for producing UFG two-phase Ti alloys initially with lamellar microstructures. However, the effect of lamellar thickness on the microstructural evolution during this process has not yet been fully elucidated. In this study, Ti-6Al-4V alloys with different lamellar thicknesses were compressed while the processing temperature was decreased from 800°C to 600°C. The thinner lamellar microstructure was preferable for preventing void/crack formation, while accelerating the continuous dynamic recrystallisation, thus providing a fully UFG structure at a relatively low strain of 1.4. In addition, the origin of different plastic flows in each sample was analysed in detail by analysing the microstructural evolution. These findings demonstrate that the processing method is effective for reducing the grain size of a two-phase Ti alloy without severe plastic deformation techniques, which require large strain (≥4). A reduction in the strain required to achieve the UFG structure would be beneficial because conventional metal-forming processes, i.e. rolling, extrusion, or forging, which are suitable for mass production, could be used. [ABSTRACT FROM AUTHOR]

The phase stability of near/metastable β-type Ti–Cr-(Mn) alloys with 4.06–13.46 wt% molybdenum equivalent fabricated by rapid solidification process were evaluated using several parameters, i.e. bond order, metal d -orbital energy level and molybdenum equivalent. The microstructural evolution of the near/metastable β-type Ti–Cr and Ti–Cr–Mn alloys was systematically investigated by using optical and transmission electron microscopies. With increasing molybdenum equivalent value in the Ti–Cr-(Mn) alloys, α" martensitic transformation and precipitation of athermal ω phase were strongly suppressed during rapid cooling. Based on microstructural investigation, the β phase stability of the alloys was evaluated using the phase stability index diagram using bond order, metal d -orbital energy level parameters. Moreover, the microstructural evolution depending on the phase stability of Ti–Cr-(Mn) alloys strongly affected to mechanical properties and trade-off behavior between strength and plasticity. Based on these microstructural evolutions and mechanical properties of the Ti–Cr-(Mn) alloys, the phase stability and a relationship between phase stability and mechanical properties of near/metastable β-type titanium alloys were systemically investigated. Image 1 • Phase stability of Ti–Cr-(Mn) alloys was evaluated by theoretical parameters and systematic investigation. • β phase stability strongly affected martensitic transformation and microstructure. • Additional phase boundaries for α" and ω ath phases were added in B o ‾ − M d ‾ phase stability index diagram. • Ti–Cr(Mn) alloys revealed large trade-off behavior on mechanical properties. • Linear relationship between yield strength and [Mo] eq value was identified. [ABSTRACT FROM AUTHOR]

The effect of interlayer cooling in directed energy deposition on the microstructure and mechanical properties of two titanium alloys (Ti–6Al–4 V and Ti–2.5Fe–4.5Al–0.25Si) was investigated in this study. On the one hand, the general process of directed energy deposition provided sufficient time for element partitioning, resulting in the formation of the isothermal ω. On the other hand, interlayer cooling interfered with element partitioning and isothermal ω formation. It induced the formation of the supersaturated α. The isothermal ω or supersaturated α, generated based on the fabrication conditions, significantly influenced the mechanical properties of these alloys. The higher the β-phase stability of the alloy, the greater is the change in its mechanical properties depending on the fabrication conditions. This study provides guidelines for the design of new alloys manufactured using directed energy deposition. • Two Ti alloys were used to study effect of interlayer cooling on tensile behavior. • Supersaturated α and isothermal ω strongly influences the tensile properties. • Interlayer cooling generated the supersaturated α and increased the strength. • General fabrication generated isothermal ω and decreased the ductility. [ABSTRACT FROM AUTHOR]

Abstract Bimodal grain structures are often produced in a metal by employing severe plastic deformation followed by low-homologous-temperature annealing (≤0.4 T m , where T m is melting temperature). Here, a bimodal grain structure was achieved in a Co–20Cr–15W–10Ni–C superalloy via moderate cold rolling (strain ≈0.3) and ultrahigh-homologous-temperature annealing (≥0.8 T m). During annealing, carbide-assisted heterogeneous static-recrystallization played a key role in forming the bimodal grain structure. A 40% increase in combined strength and ductility was observed. Graphical abstract Image 1 Highlights • A bimodal grain structure was achieved in a superalloy without severe deformation. • Cold rolling and ultrahigh-homologous-temperature annealing were carried out. • Carbide-assisted heterogeneous static recrystallization occurred during annealing. • The bimodal grain structure provided 40% higher σ × ε values than uniform grains. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ti-23Nb-1Ta-2Hf-O shows gum-metal-like superproperties. • Nanodomain, giant fault, and ω phase transformation were observed. • Three magic numbers were not sufficient to obtain superproperties. • Equivalent β-stabilizer content should be considered to design gum metal. Abstract The conditions needed to design gum metal were reconsidered based on the equivalent β stabilizer content required to obtain compositional/microstructural variability in a Ti-24(Nb + Ta + V)-(Zr, Hf)-O system. It was found that 90% cold-worked Ti-23Nb-1Ta-2Hf-O alloy exhibits gum-metal-like superproperties such as ultrahigh strength, ultralow elastic modulus, superelasticity, superplasticity, and Elinvar behavior. These multi-functions can be achieved even with the deformation-induced ω phase if nanodomains and giant faults exist. This suggests that not only the three electronic magic numbers, but also the equivalent β stabilizer content should be considered to attain the superproperties. [ABSTRACT FROM AUTHOR]

This study investigated the room temperature compressive deformation behavior of Cu bulk material manufactured by cold spray process. Initial microstructural observation identified a unique microstructure with grain size of hundreds of nm in the particle interface area and relatively coarse grains in all other areas. Room temperature compressive results confirmed cold-sprayed Cu to have a yield strength of 340 MPa, which is similar to materials manufactured by severe plastic deformation process such as equal channel angular press. In addition, strain softening phenomenon, which is rarely found in room temperature compressive deformation, was observed. According to such unique characteristics, continuous microstructure evolution and surface fractures according to the strain ( ε = 0.3/0.6/0.9) of the material were observed, and considerations were made for deformation and fracture behavior. Microstructural observation after compressive deformation confirmed that average grain size decreased as the strain increased, and the fraction of the low-angle boundary, which has an indirect relationship with dislocation density, showed a tendency to decrease in ε = 0.3-0.6 region where the strain softening phenomenon occurs. Based on the results described above, this study was able to identify the possibility of manufacturing cold-sprayed Cu bulk material for structural material and its room temperature deformation behavior. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) nano flowers uniformly attached to the surface of Molybdenum disulfide (MoS 2 ) sheet were successfully prepared via a simple facile one pot hydrothermal method. The morphology and microstructure of the prepared samples was characterized using field – emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and photoluminescence (PL) spectroscopy. The Brunauer-Emmett-Teller (BET) surface area was determined using physical and chemical analyzer. The characterization results showed that the flowers like ZnO micro-structures were uniformly attached to the surface of MoS 2 . The as-prepared MoS 2 /ZnO composite showed enhanced photocatalytic activity and considerable stability for the photo degradation of phenol red as compared with pure MoS 2 and ZnO under both UV and visible light irradiation. Such an enhancement of photo degradation capability was ascribed to the synergistic effect between the flowers-shaped ZnO particles and sheet-like structure of MoS 2 , which boost the migration efficiency of photo-induced electrons and hinder electron-hole recombination rate. It was also found that the amount of MoS 2 in the composite has a significant effect on the degradation activity. Moreover, the antibacterial activity test towards the gram negative Escherichia-coli showed that the MoS 2 /ZnO composite has better antibacterial properties compared to pure ZnO and MoS 2 . [ABSTRACT FROM AUTHOR]

Abstract: Eight different oxide dispersion strengthened (ODS) steels were manufactured to investigate the influence of several processing parameters including milling temperature, rotation speed, and consolidation temperature. Microstructural evolution and resulting mechanical properties were then characterized for the different manufacturing processes. As milling temperature decreases, microstructures become finer and room temperature tensile strength increases. Lowering the consolidation temperature induces an increase in tensile strength with a decrease of ductility. The microstructure becomes homogeneous as the tensile strength increases when the milling speed increases from 100rpm to 250rpm. However, the improvement seems to be less effective than the adoption of a cryomilling technique. Porosity development was considerably dependent not only on consolidation condition but also on powder quality after mechanical alloying. [Copyright &y& Elsevier]

The present work investigates the microstructural evolution of a biomedical Co-20Cr-15W-10Ni alloy during multi-pass thermomechanical processing (TMP) and clarifies its effect on the tensile properties. The results indicate that multi-pass TMP consisting of repetitive cold groove-rolling followed by annealing is attractive for fabricating the alloy rod for fine wire and mini-tube making. The multi-pass TMP provided significant grain refinement from 100 to 4 μm via five repetition and, can create bimodal grain structures consisting of fine (≈3 μm) and coarse grains (4−16 μm). The bimodal grain structure provided a superior strength-ductility combination, a yield strength of 593−738 MPa and ultimate strength of 1197−1304 MPa with a uniform elongation of 54.7−61.1%. Changing the annealing condition in the final TMP step enables to further refine the grains to 2 μm and also modify the grain size distribution and, the dispersion and fraction of nano-carbides. Thus, the mechanical properties of the Co-20Cr-15W-10Ni alloy can be further optimized, leading to a yield strength of 795−890 MPa and ultimate strength of 1328−1363 MPa with a uniform elongation of 49.4−64.0%. [ABSTRACT FROM AUTHOR]

The present study describes the influence of β stabilizers (namely Fe and Cr) on the microstructural evolution and mechanical behavior of Ti–6Al–4V alloy fabricated by direct energy deposition. As the β stabilizer content increases from 1 to 4 wt%, the coarse columnar-grained morphology typical of additively manufactured Ti–6Al–4V is significantly refined, with a columnar-to-equiaxed transition. Furthermore, reheating of the deposited layers by the deposition of overlaying layers during fabrication induces an element partitioning effect, resulting in the formation of fine-grained α and isothermal ω. Hence, the heat profile during direct energy deposition resembles conventional solution and aging treatments. In addition, increasing the amount of β stabilizer steadily increases the room temperature strength of the Ti–6Al–4V alloy. The alloy with 4 wt% Fe showed the maximum strength, of ∼1.5 GPa. • The columnar-to-equiaxed transition of microstructure was achieved in the direct energy deposited Ti–6Al–4V alloy with the addition of Fe and Cr. • The maximum room temperature strength of the Ti–6Al–4V with 4 wt% Fe alloy reaches ∼1.5 GPa. • The reheating phenomenon caused by deposition of overlying layers during direct energy deposition resembles conventional solution and aging treatments. • With an increasing amount of β stabilizer, the phase constituents in the Ti–6Al–4V alloy changed from αʹ.→ αʹ+α+ω+β → α+ω+β [ABSTRACT FROM AUTHOR]