Volume 108, Issue 9

Material selection is considered an important step in the design and manufacturing of a part/product. Wrong selection of material may cause poor quality, increase in cost, early failure of the product, or any combination of them. It may also create difficulties in the manufacturing process leading to increases in manufacturing time and cost. The general rule in design is to select materials based on their properties that match with the product requirements. Hence, decision making for material selection is a crucial process, and several mathematical tools and techniques have been presented in the literature to aid this process. Those techniques have their own advantages and limitations. This paper proposes the application of the grey-based fuzzy logic approach to solve three real time material selection problems. For all the examples, the first and the last ranks of materials derived using the adopted method and those obtained by past researchers are exactly the same. This indicates that when uncertainties are involved, grey-based fuzzy logic can be employed as an efficient tool for solving complex material selection problems.

Under the same potential, the structure of Co nanowires depends on the Co 2+ concentration. While depositing in 0.391 M solution at −1.6 V, the rate of producing Co adatoms on Au surface is lower and larger Co critical clusters can form, favoring the formation of hcp Co. While depositing in 1.067 M solution at −1.6 V, the rate of producing Co adatoms on Au surface is higher and smaller Co critical clusters can form, favoring the formation of fcc Co. Therefore, the structure of electrodeposited Co nanowires can be controlled by the rate of producing Co adatoms.

The continuous cooling transformation diagram of a low carbon bainitic–martensitic steel was constructed using dilatometry and metallographic methods. It was found that as cooling rate increases, the structure changes from granular bainite to lath martensite. Three regions of different kinetic behavior were discerned for the bainitic–martensitic steel. One of the regions conformed to martensite formation and the other two comprised transformation to bainite. A non-isothermal type of Johnson–Mehl–Avrami–Kolmogorov kinetic equation of reaction rate was used to analyze the transformation behavior during continuous cooling of bainite formation. The Avrami exponent and activation energy values for different regions at cooling rates of 0.1 and 0.4 K s −1 varied from 1.5 to 4.7 and 71 to 84 kJ mol –1 respectively. Models obtained from such kinetic coefficients closely corresponded to experimental results.

The substructures and crystallographic features of martensite in 1.01C high-carbon steel were investigated using transmission electron microscopy and electron backscatter diffraction scanning electron microscopy. The results indicated that the “new” thin-plate martensite (M2), formed at cryogenic temperatures, possessed unique substructures and crystallographic features, which were quite different from the “original” large lenticular martensite (M1) formed at relatively high temperatures. Furthermore, the M1 and M2 can be distinguished and quantified using the band-contrast distributions from backscatter diffraction scanning electron microscopy.

The mechanical properties of YBCO thin film deposited on SrTiO 3 (100) substrates by magnetron sputtering were determined using Berkovich nanoindentation and scanning electron microscopy. Hardness and elastic modulus were determined via the Oliver–Pharr method from indentation load–depth curves. The hardness values of the YBCO thin film show depth dependence, i. e., indentation size effect, which arose from the surface roughness as detected by scanning electron microscopy. Multiple pop-in events were observed on the loading curves, however, no obvious pop-out takes place during the elastic recovery. In addition, an effective analytical method accommodating the indenter imperfection was proposed and validated against experimental data in terms of elastic modulus, yield stress and friction angle using the Drucker–Prager yield criterion for the YBCO thin film.

Commercially pure Al wires are severely plastic deformed by a novel method called equal channel angular torsion drawing (ECATD) up to four passes. Initial wires are drawn through an equal channel angular die and simultaneously torsion deformed by turning the ECATD die. The wires are deformed up to an equivalent strain of 1 to 4 (based on FE result) at room temperature. The microstructural evolution of the wires is investigated using optical microscopy of both longitudinal and transverse cross-sections. A grain refinement from 100 μm to a mean grain size of 1–10 μm is achieved mainly at the areas near the surface of the wires. A decreasing trend of grain refinement is observed from the edge area to the wire center due to the non-uniform strain distribution, resulting in an inhomogeneous hardness. A significant increase in hardness is obtained from ∼22 HV to ∼43 HV at the wire center and to ∼60 HV at the wire edge, this confirms simulated equivalent plastic strain. The most important advantage of this process is the ability to impose continuous large plastic deformation on wires. It can be used as an industrial method for continuous strain hardening and grain refinement of wires.

Deep cup-shaped parts were forged at 723 K from Mg-3Al-1Zn alloy extruded rods. The obtained microstructure, texture, and mechanical properties were examined by optical microscopy, X-ray diffraction, electron backscattered diffraction, and compression testing. Results indicate that the evolution of the microstructure and mechanical properties of the alloy can be divided into 2 distinct stages by the corner. For all tested specimens, the narrowest elongated grains, finest dynamic recrystallized grains, and strongest intensity of texture were obtained at the corner. Distinct differences in mechanical properties were presented both between the testing directions and among the tested locations. For the specimens tested in the same direction, yield strength increased with the texture flow. This result is consistent with the fraction of deformed grains but not with the variation in grain size or texture intensity.

The plasma electrolytic oxidation (PEO) technique was used to coat AZ31 magnesium alloy in a phosphate-based electrolyte. Effects of oxidation time on the morphology, phase structure, and corrosion resistance of the ceramic coatings were systematically investigated by scanning electron microscopy, X-ray diffraction, potentiodynamic polarization and electrochemical impedance spectroscopy testing. The main components of the resulting coatings were MgO, MgF 2 and t-ZrO 2 . It was also found that there was a significant influence of the oxidation time on the corrosion resistance of the coatings. The coating obtained under the oxidation time of 10 min exhibited a corrosion current of 3.89 × 10 −6 A cm −2 in 3.5 wt.% NaCl solution, which was a significant decrease compared with the uncoated magnesium alloy. The results of the corrosion tests indicated that the PEO coating formed at 10 min demonstrates a higher corrosion resistance compared to the samples formed at 5, 15 and 20 min.

The phase equilibria of the Ni–Nb–V ternary system at 1 000 °C and 1 200 °C were established using electron probe microanalysis, X-ray diffraction and differential scanning calorimetry. The results of the investigation revealed that: (1) The Nb solubility in (Ni) and σ′ phases was less than 10 at.%; (2) A ternary compound τ (NiNbV) was confirmed, in which V had a large solubility; (3) A new liquid region was evident at 1 200 °C, but was absent at 1 000 °C; (4) The lattice constants of Ni 3 Nb and Ni 6 Nb 7 phase decreased with increase in V content in the Ni 3 Nb and Ni 6 Nb 7 . The phase equilibria of the Ni–Nb–V ternary system will contribute to its thermodynamic assessment.

In the present work, Cu 1- x Mg x Fe 2 O 4 ( x = 0.2, 0.4, 0.6, 0.8 and 1.0) ferrites have been synthesized via a conventional solid-state reaction method. Thermal analysis and the estimation of total weight loss of the samples were performed by differential thermal analysis and thermogravimetric analysis measurements. The thermal variation of initial permeability exhibits unusual dependence with the manifestation of a broad hump followed by a Hopkinson peak attributed to the structural transformation and minimization of magneto-crystalline anisotropy energy, respectively. A decrease in resistivity is observed with increase in temperature and corresponding activation energies for conduction have been calculated. Possible explanations for the observed physical, thermal, magnetic and transport properties with temperature of the samples are discussed in the present paper.