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Abstract Nine groups of wire arc additive manufacturing (WAAM) aluminum alloy walls with different layers were deposited by variable polarity cold metal transfer arc mode using ER 5183. Their microstructures were characterized by optical microscopy and electron back scattered diffraction. For the top layer, grain size increased from 37 μm to 65 μm, and then stabilized at around 41μm, in accordance with the decrease of microhardness from 98.7 HV to 76.4 HV. As the number of deposited layers increased, the anisotropy in the bottom layers was weaken, and small-angle grain boundary may cause an increment to 96.1HV in the microhardness before stabilized around 81HV due to the heat accumulation. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the effects of ZrO 2 types including YSZ and nano-ZrO 2 as well as their contents on the phase compositions, macrostructures, microstructures, physical properties, mechanical properties and biocompatibility of Ti2448-ZrO 2 composites fabricated by spark plasma sintering (SPS). The mechanical properties such as hardness and compressive yield strength of the composites have been systematically investigated. The experimental results demonstrate that the hardness and compressive yield strength of the composites all dramatically increased with increasing the content of YSZ and nano-ZrO 2 . Meanwhile the nano-ZrO 2 could be beneficial to the uniformity of microstructure and improvement in mechanical strength of the composites. The biocompatibility of the composites containing nano-ZrO 2 was found to possess better corrosion resistance. In conclusion, Ti2448-ZrO 2 composites are potentially useful in biomedical applications with their mechanical and biological properties being evaluated in this work. [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]

A novel lead-free, high dielectric constant, ultra-wide temperature stable dielectric ceramic Ba 1−x Bi x Ti 1−x −y Zn 0.75x W 0.25x+y O 3+y (0.22≤x≤0.30, y=0.015) was synthesized by the traditional solid-state reaction method. The phase composition, electric and dielectric properties of the Ba 1−x Bi x Ti 1−x −y Zn 0.75x W 0.25x+y O 3 ceramics were investigated. The P-V-L dielectric theory was introduced. And, the chemical bond energy was calculated to track the changes in micro-structure. The relationships between chemical bond energy and the macroscopic dielectric properties(ε r , dielectric stability and dielectric loss ) in Ba 1−x Bi x Ti 1−x−y Zn 0.75x W 0.25x+y O 3+y ceramics were discussed systematically. Owing to the inhomogeneous micro-structure and the diffusion in phase transition, Ba 1−x Bi x Ti 1−x−y Zn 0.75x W 0.25x+y O 3+y ceramics showed a stable permittivity (~800±15%) over a ultra-wide temperature range (−30 to 375 °C). Moreover, dielectric loss was less than 0.02 and the insulation resistance was over 10 12 Ω cm. These features suggested that the Ba 1−x Bi x Ti 1−x−y Zn 0.75x W 0.25x+y O 3+y ceramic could be considered as a promising candidate material for energy storage applications in harsh environment. [ABSTRACT FROM AUTHOR]

Two samples of an α + β Ti-4Al-4Mo-4Sn-0.5Si (wt%) alloy, one with fine prior β grains and a heterogeneous microstructure and the other with coarse prior β grains and a homogeneous microstructure were prepared by extrusion of compacts of TiH 2 /Al/Mo/Sn/Si powder blend at 1200 and 1300 °C respectively. The heterogeneous microstructure is manifested by softer Mo-rich regions with a full α/β lamellar structure containing a high number density of parallel and nanometer sized FCC δ (TiH) needles in a harder matrix with a microstructure consisting of interweaved α plates and β transformed structure (β t) domains and grain boundary α (GB α) layers. The matrix also contains a small fraction of Sn-rich regions which have the same microstructure as the matrix. The Mo-rich and Sn-rich regions form due to the limited diffusion of Mo and Sn alloying elements. This heterogeneous microstructure sustains a high tensile yield strength of 1199 MPa, a high strain hardening rate, and an excellent tensile ductility of 12.0%. In contrast, the homogeneous microstructure comprising of interweaved α plates and β t domains together with GB α layers sustains a similar high strength, but a clearly lower strain hardening rate and a significantly lower tensile ductility of 3.5%. Non-homogeneous deformation capacity, the release of energy by forming numerous microcracks and the intermittent growth of microcracks of the heterogeneous microstructure suggest that this microstructure has a high plasticity and high resistance to the growth of microcracks. • The α + β titanium alloy fabricated has a heterogeneous microstructure and fine prior β grains. • The heterogeneous microstructure encompasses softer Mo-rich regions in a matrix of α/β t microstructure. • This alloy exhibits a superior combination of high strength (YS: 1199 MPa and excellent ductility (12.0%). • This is attributed to the compatible deformation and high microcrack growth resistance of the microstructure. [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]

Low-loss (Zn 1- x Ni x )ZrNbTaO 8 (0.02 ≤  x  ≤ 0.10) ceramics possessing single wolframite structure are initiatively synthesized by solid-state route. Based on the results of Rietveld refinement, complex chemical bond theory is used to establish the correlation between structural characteristics and microwave performance in this ceramic system. A small amount of Ni 2+ ( x  = 0.06) in A-site with the fixed substitution of Ta 5+ in B-site can effectually raise the Q  ×  f value of ZnZrNb 2 O 8 ceramic, embodying a dense microstructure and high lattice energy. The dielectric constant and τ f are mainly affected by bond ionicity and the average octahedral distortion. The (Zn 0.94 Ni 0.06 )ZrNbTaO 8 ceramic sample sintered at 1150 °C for 3 h exhibits an outstanding combination of microwave dielectric properties: ε r = 27.88, Q × f  = 128,951 GHz, τ f = –39.9 ppm/°C. Thus, it is considered to be a candidate material for the communication device applications at high frequency. [ABSTRACT FROM AUTHOR]