Concentration fluctuation and cooperative chain mobility of hyperbranched poly(ε-caprolactone)s investigated by photon correlation spectroscopy

Concentration fluctuation and cooperative chain mobility of the hyperbranched poly(ε-caprolactone)s (HPCLs) as well as that of the linear poly(ε-caprolactone) (LPCL) in their concentrated solutions in tetrahydrofuran (C_polymer=1.0 g/mL) were systematically characterized using photon correlation spectroscopy (PCS). The results were interpreted in conjunction with the architectural characteristics of the HPCLs that are the different lengths of the linear segments and the different branching structures. The HPCLs were synthesized to incorporate the different lengths of the linear segments consisting of 5, 10, and 20 ε-caprolactone units on their backbone chains, and thereby referred to as HPCL-5, -10, and -20, respectively. The relative degrees of branching (DB) of the HPCLs, which is obtained by branching ratio values, were found to be in the order of HPCL-5>-10>-20. From the narrow distribution of relaxation times and q²-dependence of relaxation rates, it was verified that the relaxation processes concerned in this study were due to the concentration fluctuations caused by cooperative chain diffusion. The correlation times, τ_c's, and the corresponding apparent activation energies, E_a's, which provide a direct evaluation for the molecular mobility, were determined by non-linear curve fittings of measured correlation functions with Kohlrausch-Williams-Watts (KWW) equation and by the Arrhenius fits of temperature dependences of τ_c's, respectively. As a result, cooperative chain mobility of the HPCLs in the concentrated solution state was found to be higher than that of the LPCL, and was enhanced with the shorter linear segments and with the higher relative DBs of the HPCLs.     

Effect of Mn addition and refining process on Fe reduction of Mg−Mn alloys made from magnesium scrap

The Fe reduction, microstructure evolution and corrosion susceptibility of Mg−Mn alloys made from magnesium scrap refining with Mn addition were investigated. The results show that significant Fe content change occurs during near-solid-melt treatment (NSMT) process even in the absence of Mn, because of the high saturation of Fe in the melt. Furthermore, in the NSMT process, even a small amount of Mn addition can lead to a sharp deposition of Mn atoms. The NSMT process can increase the growth rate of the Fe-rich particles, and then accelerate their sinking movement. Nevertheless, the addition of Mn hinders the coarsening process of Fe-rich particles. Besides, the corrosion susceptibility of the alloys is mainly affected by the solubility of Fe, which can be significantly reduced by Mn addition. Moreover, the presence of more Fe-rich particles does not necessarily increase the corrosion susceptibility of the alloy. Consequently, in the refining process of Mg−Mn alloys made from magnesium scrap, on the basis of NSMT process and adding an appropriate Mn content (about 0.5 wt.%), the purity of the melt can be improved, thereby obtaining an alloy with excellent corrosion resistance.     

Microstructural analysis of friction stir welded ferritic stainless steel

High-quality, defect-free welds were successfully produced in 409 ferritic stainless steel by friction stir welding. A remarkably fine-grained microstructure was observed in the stir zone, and the fraction of low angle grain boundary in the stir zone significantly increased as compared to that in the base material. An increase in plunging depth led to an increase of the fraction of low angle grain boundary, a decrease in grain size, and an increase in hardness in the stir zone.     

Nanocrystalline Nickel Deposition on the Titanium Alloys Using High Solution Flow Velocity

An innovative process has been developed for electroplating of nickel on titanium surface using fast solution flow technique. Nickel was directly deposited on a titanium alloy without using any pre-treatment process. Level of adhesion was determined using quantitative peel test and characterization of the deposition was performed by scanning electron microscopy. Results showed that the rate of nickel deposition at 60 °C was higher than that of the rate of nickel deposition at 40 °C. Moreover, Watts solution provided higher rate of nickel deposition compared to the sulfate-based nickel solution. The rate of deposition increased with increasing the solution flow velocity from 1.5 to 3 m/s and raising current density from 0.4 × 10⁴ to 1.6 × 10⁴ A/m² for both solution baths. Adhesion test indicated good level of adhesion between the deposited nickel and titanium surface. The bonding toughness increased to 4 J/m² for 1.2 × 10⁴ A/m² as a result of higher deposition rate. However, the mechanism responsible for the coating process was discussed in detail.     

Microstructural characteristics of a cast IN718 superalloy bonded by isothermal solidification

Isothermal solidification is a key feature of transient liquid phase bonding which prevents the formation of deleterious intermetallic phases in the joint centerline and results in bonds with improved mechanical performance. This paper discusses the metallurgical characteristics and mechanical properties of an as-cast IN718 superalloy bonded by diffusion-induced isothermal solidification of Ni-7Cr-4.5Si-3.2B-3Fe (wt%) filler metal. After transient liquid phase bonding of as-cast IN718 at 1000 °C for 60 min, a bond exhibiting a solid solution microstructure with joint efficiency of 72% in terms of shear strength was obtained. The joining process was effectively able to prevent the formation of hard and brittle nickel and chromium borides, which typically lead to critical problems in brazing. The formation of Nb-rich Laves phase, which is well known as a major issue in the fusion welding of IN718, was not observed. The bonding time, which governs the extent of isothermal solidification, was a critical parameter for controlling the mechanical properties of the joints in terms of shear strength and hardness distribution across the bond.     

Simple synthesis and characterization of SrSnO3 nanoparticles with enhanced photocatalytic activity

SrSnO₃ nanoparticles with peanut-like morphologies were synthesized by a simple wet chemical reaction. These peanut-shaped SrSnO₃ were formed by the fusion of two or more nanoparticles with an average size of 45 nm. The resulting powders were characterized in detail using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Moreover, the photocatalytic activity for hydrogen evolution from pure water was investigated under UV light irradiation. The peanut-shaped nanoparticles exhibited a much higher photocatalytic activity compared to SrSnO₃ powder synthesized by a solid-state reaction. This was attributed to their higher structural order, caused by the formation of a carbonate-free pure phase, as well as their higher surface area resulting from the decrease in the particle size.     

Analytical solution for bending of moderately thick radially functionally graded sector plates with general boundary conditions using multi-term extended Kantorovich method

An analytical solution for bending of radially functionally graded (RFG) sector plates is presented using multi-term extended Kantorovich method (MTEKM). Utilizing the principle of minimum total potential energy the governing equations are derived based on a first-order shear deformation theory and converted into two sets of coupled ordinary differential equations (ODEs) using MTEKM. Next, the derived sets of ODEs are solved analytically by the application of state-space method. Various examples are investigated by the present method and also solid sector plates are studied as special cases. Results of the present method are compared to those obtained by finite element method (FEM) and also available published works in the literature. It is found that the method proposed here exhibits a high convergence rate as well as presenting accurate results in all cases.     

Subsolidus Phase Relationship in the CaO–CuO–TiO2 Ternary System at 950°C in Air

The subsolidus phase relationship in the CaO–CuO–TiO₂ ternary system at 950°C in air was investigated. Total 26 samples having various nominal compositions were prepared by the solid‐state reaction at 950°C in air, and their equilibrium phases were analyzed by powder X‐ray diffraction (XRD). The CaCu₃Ti₄O₁₂ phase exhibits variable stoichiometry and forms as the Ca_1?xCu_3+xTi₄O₁₂‐type (?0.019 ≤x ≤0.048) solid solution at 950°C in air. On the basis of our results and previous reports on the binary phase diagrams, the subsolidus phase diagram of the CaO–CuO–TiO₂ ternary system could be constructed at 950°C in air.