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The complexed sol-gel method has unique advantages in the preparation of multi-component functional thin films. In this paper, Bi2212 superconducting thin films were prepared by sol-gel method on SrTiO 3 (100) single crystal substrates. Glycine and glycolic acid were used as complexing agents. The thermal decomposition processes of the two sols were analyzed by contrasting thermal-thermogravimetric curves. The heat treatment processes of the different complexing agent systems were optimized to obtain films with flatter surface morphology. The phase composition of the intermediate products during the precursor heat treatment was changed by adjusting the conditions of the complexing agent and the acidity of the sol, which expanded the pure phase temperature interval of the final product. The pure phase temperature interval, morphology, surface roughness, and electrical transport properties of Bi2212 superconducting films prepared with different complexing agent sol-gel systems were investigated. When glycolic acid was used as the complexing agent, the Bi-2212 superconducting films showed the widest phase formation temperature zones of 25 K. They also had a smaller surface roughness of 10–15 nm. Other than that, all samples had good epitaxial properties, and electrical transport properties. This work provides a new idea for expanding the phase-forming temperature region of multicomponent functional ceramics. It also shows the promising potential of sol-gel method for preparing multicomponent functional films with high quality surfaces. [ABSTRACT FROM AUTHOR]

Powder metallurgy (PM) Ti–6Al–2Sn–4Zr–2Mo–0.1Si–(0, 2, 4)W (wt%) alloys were fabricated by thermomechanical consolidation of TiH 2 -based powder compacts and subsequent heat treatments. Samples of the as-fabricated alloys were also heated at 650 °C for 200 h. The addition of 2 or 4 wt%W to the base alloy changed its microstructure of parallel α/β lamellar colonies and grain boundary α (α GB) to an interwoven α/β t microstructure consisting of α GB and a network of interpenetrating α plates with β transformed structure (β t) domains comprising variants of fine α laths and β matrix. The partition of the β stabilizing W between β and α phases and the low diffusivity of W atoms limited the growth of α plates/laths, decreasing the thickness of α plates/laths and increasing the volume fraction of β. The increased hardening of the β phase and enhanced α/β interface strengthening associated with the 4 wt%W addition led to a significant increase in the tensile strength of the alloy from 1281 ± 10–1411 ± 12 MPa. However, the high flow stress and the very fine microstructure caused significant strain localization in the weak α GB , resulting in premature fracture of the α GB (intergranular fracture) and the low ductility (1.4%). Here, premature fracture meant the fracture occurred prior to the alloy reaching its ultimate tensile strength. The heating caused the β interlaths in the W-free alloy to partially dissolve and become β particles distributed along the original lines of β interlaths accompanied by the precipitation of α 2 -Ti 3 Al in the α plates. The addition of W inhibited the dissolution of β interlaths and caused the precipitation of a higher volume fraction of α 2 precipitates during heating. The microstructural changes caused by heating resulted in a slight decrease in strength and a significant decrease in ductility for the W-free alloy, but a significant increase of the yield strength of the 2 W and 4 W alloys with some sacrifice of the tensile ductility. The microstructural reasons for the effects on mechanical properties were analyzed with the assistance of detailed characterization of the dislocations in the deformed specimens. • Effects of W alloying on a PM Ti–6Al–2Sn–4Zr–2Mo–0.1Si alloy are investigated. • W refines α plates and enhances formation of β transformed structure domains. • W enhances hardening of the β phase and α/β interface strengthening. • W increases the microstructural stability and prevents the strength reduction from heating. • High W content promotes α 2 precipitation strengthening of the alloy after heating. [ABSTRACT FROM AUTHOR]

Powder metallurgy (PM) near α Ti−6Al−2Sn−4Zr−2Mo−0.1Si−0.5Y (wt.%) alloy with a low oxygen content and fabricated by thermomechanical powder consolidation of an elemental powder blend with a trace amount of Y addition was subjected to two heat treatments to obtain different microstructures which were free of grain boundary α (α GB) layers. One heat treatment (960°C/1h/AC, AC = air cooling) led to the formation of an α/β t microstructure consisting of 75.3 vol% primary α (α p) domains with globular and platelike morphologies, 21.5 vol% β transformed structure (β t) domains comprising ultrafine secondary α (α s) lamellae in a β matrix and 3.2 vol% thin β strips. The other heat treatment (960°C/1h/WQ+580°C/6h/AC, WQ = water quenching) led to the formation of a microstructure consisting of 38.2 vol% isolated α p plates, slabs, and globules dispersed in a β t matrix comprising nanometer-sized α s lamellae and residual β strips. The first microstructure rendered the alloy with high tensile strength of 1128 MPa and excellent tensile ductility of 15.6%, thanks to the activation of abundant and slips in all α grains and tensile twinning in the "hard" <0001> micro-textured α grains with the c-axis parallel to the tensile force direction which mitigated the strain localization and enhanced strain hardening. On the other hand, the harder nanostructure of the β t matrix in the second microstructure resulted in a significantly increased tensile strength of 1351 MPa while maintaining an excellent tensile ductility of 10.5%. This can be attributed to the activation of abundant and slips in thin α plates and a limited degree of tensile twinning in the "hard" α domains, as well as a large number of statistically stored dislocations (SSDs) within the micron-scaled α slabs/globules. Both microstructures rendered the alloy with favorable ductile fracture. [ABSTRACT FROM AUTHOR]

• With an addition of 0.2 wt%Si, the Si atoms are equally in α and β phases. • Si solute atoms retard the growth of α phase, causing refinement of the α/β t lamellar structure. • Si atoms enhance solid solution strengthening and Si atoms enhanced α/β t interface strengthening. • Increasing the Si content to 0.5 wt% cause a further increase of the yield strength by 50 MPa. • With a high strength, the tensile ductility deteriorates, due to the premature fracture of grain boundary α layers. Ti-4Al-4Mo-4Sn-xSi (wt%) (x = 0, 0.2, 0.5) alloys were fabricated by hot extrusion of compacts of blends of TiH 2 , AlMo60 master alloy and other required elemental powders followed by heat treatments involving vacuum annealing, solution treatment, air cooling and aging. The microstructure of the alloys consists of α plates, lamellae of α and transformed β structure (β t), β t blocks as well as grain boundary α layers. With the addition of 0.2 wt%Si, the Si atoms exist in equal concentration in both α and β t regions as solute atoms, and they retard the growth of α phase, causing a decrease of the average thickness of α plates and lamellae and slight increase of the volume fraction of β t lamellae and blocks. The solid solution strengthening and enhanced α/β interface hardening brought by the 0.2 wt%Si cause the yield strength of the Ti-4Al-4Mo-4Sn alloy to increase significantly from 1030 to 1130 MPa with a slight decrease of the tensile ductility (7.4% vs 6.8%) and without changing the fracture behavior. With the addition of 0.5 wt%Si, the extra Si causes nanometer sized silicide (Ti 5 Si 3) precipitates to form in both α and β t regions and further microstructural refinement. The additional α/β interface hardening and precipitation hardening cause the yield strength of the alloy to increase further to 1177 MPa, but the tensile ductility deteriorates clearly with the elongation to fracture decreasing to 4.9%. The main reason for this ductility decrease is the premature fracture of grain boundary α layers caused by the higher flow stress which can induce more strain localization at the grain boundary α layers. [ABSTRACT FROM AUTHOR]

A powder metallurgy (PM) near α Ti–6Al–2Sn–4Zr–2Mo−0.1Si (wt.%) alloy was fabricated by in-situ dehydrogenation and hot extrusion of a TiH 2 -based powder compact and heat treatments. Three types of microstructures were obtained in the as-consolidated state and after different heat treatments. They are a basketweave microstructure consisting of a network of inter-penetrating α plates filled with domains of ultrafine β transformed structure (β t) (Type I microstructure), an α/β lamellar microstructure with most β layers being thin and discontinuous plus α layers at prior β grain boundaries (Type II microstructure) and an α/β t lamellar microstructure (Type III microstructure). Although the three types of microstructures render the alloy with a similar yield strength (1085–1109 MPa) and ultimate tensile strength (1217–1239 MPa) due to the balanced effects of various strengthening mechanisms, the Type II microstructure exhibits a significantly lower tensile ductility than the other two types of microstructures (elongation to fracture: 5.5% vs. 13–14%). Examination of dislocations in the tensile deformed specimens reveals that dislocations cutting through the thin β layers in the Type II microstructure during deformation. Such interactions between moving dislocations and thin β layers in the Type II microstructure are expected to be the primary reason for the clearly lower strain hardening rate, premature fracture of grain boundary α layers and low tolerance to strain localization observed in the tensile tests, fracture surface examination and DIC analysis. This correlation between the microstructures and tensile deformation behavior strongly suggests that preventing moving dislocations cutting through thin β layers by turning them into thicker and ultrafine structure strengthened β t lamellae or blocks is critically important in ensuring high tensile ductility of high strength PM near α titanium alloys. • Three types of microstructures are obtained in a PM near α titanium alloy. • All three types of microstructures render the alloy with a similar high strength. • Type II microstructure gives a much lower tensile ductility than other two types of microstructures. • The lower ductility is attributed to dislocation cutting of thin β layers in Type II microstructure. • Preventing the dislocation cutting through is key for both high ductility and high strength. [ABSTRACT FROM AUTHOR]