Volume 104, Issue 12

A coherent precipitate, on growth beyond a critical size, can become semicoherent through the formation of interfacial misfit dislocations. This investigation pertains to the finite element simulation of the state of stress of a coherent precipitate, its growth and the change in state of stress on the formation of an interfacial misfit dislocation loop. Critical radii are determined from the simulations based on: (i) global energy minimum ( r *) and (ii) local force balance along the radial direction ( r c ). The concept of local force balance as existing in literature is extended to the circumferential direction, to calculate a new critical size ( r t ). Local force balance gives radii at which the interface is the stable position for the dislocation loop. Off-interface stability of the dislocation loops is also investigated. The Cu–γFe system is used as an example to illustrate the new methodology developed and validate the results of the simulation. The power of the methodology is shown by considering a configuration (precipitation in a thin disc), where standard theoretical formulations are inadequate.

This paper examines the feasibility of thixoforming two commercial aluminum–copper alloys: AA2011 and AA2014. This evaluation was performed in three steps: 1) characterization of the raw materials, including an analysis of their constituents, partial melting range temperatures, and microstructures; 2) characterization of the samples' morphological evolution during partial melting to observe their globularization at two different sets of temperatures, (solid fractions of 45 % and 60 %), and four holding times: 0, 30, 90 and 210 s; and 3) tests of the morphological behavior under the same partial melting conditions of temperature and holding times. The results indicate that, despite the difficulty of controlling the temperature of the semi-solid transition, these two alloys are suitable for thixoforming processes. Their morphology is stable in the semi-solid range and the corresponding viscosity values are lower than 10 6 Pa · s, resulting in a maximum conformational stress of 2.4 MPa.

In this study, AISI 304 (X5CrNi18-10) austenitic stainless steels were joined by means of friction stir welding. The welded joint strength of stainless steels was influenced by many factors, such as different tool rotational speeds, traverse speeds, compressive tool forces, and tool angles, etc. There is a strong interrelation among the friction stir welding design parameters. The effects of design parameters on the welded joint were analyzed using a genetic algorithm. Appropriate design parameter configurations led to fine-grained microstructures that resulted in higher tensile strength joints compared to the base material. The best design configuration that led to 1.16 times higher strength than the base material was achieved with 47.5 mm min −1 traverse speed, a rotational speed of 1 180 min −1 , compressive tool force of 7 kN and tool tilt angle of 2.0°.

Explosive cladding is a solid state welding process best suited for joining incompatible metals. The selection of process parameters viz., explosive mass ratio, stand off distance and initial angle of inclination dictate the nature of the cladding. Optimization of process parameters in explosive cladding of titanium–stainless steel 304L plates, based on two level three factorial design, is attempted to establish the influencing parameters. Analysis of variance was employed to find the linear, regression and interaction values. Mathematical models to estimate the responses-amplitude and wavelength were developed. The microstructure of the Ti–SS304L explosive clad interface reveals characteristic undulations concurrent with design expectations.

In this paper, the influence of major hot rolling process parameters on strain hardening exponent and grain size as criteria for the formability of Nb-microalloyed steel sheet was investigated and an optimum level of parameters by using Taguchi grey relational analysis has been obtained. For this purpose, parameters of roughing, finishing and coiling temperatures were chosen and four levels for these temperatures were considered. Sixteen experiments for each response were conducted based on an orthogonal array of the Taguchi method. Analysis of variance, signal to noise ratios and grey relational grade were calculated in order to optimize strain hardening exponent and grain size of Nb-microalloyed steel sheets, simultaneously. It was observed that the roughing temperature of 1 050 °C; finishing temperature of 850 °C; and coiling temperature of 700 °C are the optimum parameter values producing better formability in terms of strain hardening exponent and grain size. The validity of Taguchi grey relational analysis to process optimization was also well established by means of confirmation tests.

The work presents the X-ray photoelectron spectroscopy measurement results of LDX 2101 duplex steel surface after magnetoelectropolishing in comparison with the results obtained after a standard electropolishing in still electrolyte and in the electrolyte with moderate mixing. A considerable improvement of the steel surface was found to appear after the magnetoelectropolishing treatment concerning the general composition. The calculated ratio of chromium compounds to iron compounds Cr- X /Fe X equals 2 after magnetoelectropolishing and only 0.5 after a standard electropolishing. On the other hand, the ionic Cr 6+ content after magnetoelectropolishing was the lowest (2.77 at.%), and after a standard electropolishing it was the highest (30.3 at.%). Such results are expected to influence the corrosion behavior of the steel and increase the corrosion resistance greatly.

The phase equilibria of the Al-Cr-Pr ternary system at 773 K have been experimentally determined based on results of X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray analysis. 2 ternary compounds, Al 20 Cr 2 Pr and Al 8 Cr 4 Pr, as well as 11 binary compounds, i. e. Al 7 Cr, Al 4 Cr, α-Al 9 Cr 4 , α-Al 8 Cr 5 , AlCr 2 , α-Al 11 Pr 3 , Al 3 Pr, Al 2 Pr, α-AlPr, AlPr 2 and β-AlPr 3 were confirmed. No compound was found in the Pr-Cr binary system. The isothermal section of the Al-Cr-Pr ternary system at 773 K consists of 15 three-phase regions, 30 two-phase regions and 16 single-phase regions. Homogeneity ranges of intermetallic compounds at 773 K have been determined.

Silicon carbide ceramics were fabricated using the spark plasma sintering technique without the use of additives. The sintering process was carried out at four different temperatures in the range of 2 073−2 223 K under two different pressures, 40 MPa and 80 MPa, under vacuum. The effects of different temperatures and pressures on the density, Vickers hardness, fracture toughness, and microstructure were examined. Fully dense monolithic silicon carbide ceramics with a relative density of approximately 99 % were obtained. Increasing the pressure from 40 to 80 MPa and the temperature from 2 073 to 2 223 K resulted in an increase in the relative densities of spark plasma sintered ceramics from 87 % to 97.5 % and 95.5 % to 99.7 %, respectively. The results revealed that the silicon carbide ceramic spark plasma sintered at 2 223 K while applying 80 MPa of pressure with a 5-minute soaking time under vacuum has the highest hardness and fracture toughness values of 31.9 GPa and 3.6 ± 0.3 MPa·m 1/2 , respectively.

Pure and Mn-doped barium hafnate titanate ceramics (BaHf 0.1 Mn x Ti 0.9 – x O 3 , where x = 0, 0.02, 0.05, 0.08, and 0.1) are prepared by means of a sol–gel method. The microstructures, dielectric properties and ferroelectric properties of the ceramics are investigated. X-ray diffraction patterns indicate that Mn 4 + ions enter the unit cell to maintain the perovskite structure of solid solution. Consequently, the tetragonality gradually decreases with increased Mn content. The grains of Mn-doped BaHf 0.1 Ti 0.9 O 3 ceramics become uniform and almost spherical. The diffuseness constant decreases from 1.89 to 1.48 with increased Mn content from 0 at.% to 5 at.%. Hysteresis loops can be observed in all samples from 30 °C to 90 °C, which may be due to the relaxor ferroelectric property of these ceramics.

Titanium alloys that are used as implant materials generally fail due to the occurrence of significant localized corrosion by interactions with corrosive body fluid. Implants also undergo loosening and detachment from the bone due to its poor biocompatibility. In this study, nano hydroxyapatite synthesized via a wet chemical method, using calcium oxide obtained from sea shells, was used to prepare a composite coating with polysulfone and was electrospun on to Ti-6Al-4V alloy. The controlling parameters of electrospinning were varied to study the characteristics of the coating followed by bioactivity studies, to ensure the biocompatibility of the coated material.

In this research, SiO 2 /TiO 2 /SiO 2 nanostructured thin films were deposited on glass substrates using an electron beam physical vapor deposition technique. The structure, morphology, surface composition, hydrophilic and photocatalytic properties of the thin film were investigated by means of X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, water contact angle measurements and methylene blue degradation. The results indicated that SiO 2 /TiO 2 /SiO 2 nanostructured thin film shows superhydrophilic and photocatalytic properties which greatly encourage the self-cleaning function of the film.

Manganese vanadate microtubes have been synthesized via a simple hydrothermal process using polyvinyl pyrrolidone as the surfactant. Scanning electron microscopy observation shows that polyvinyl pyrrolidone plays an essential role in the formation and phase transformation of the manganese vanadate microtubes. A polyvinyl pyrrolidone-assisted “Ostwald ripening” growth mechanism has been proposed to explain the formation process of the manganese vanadate microtubes. The electrochemical behavior of L-cysteine at the manganese vanadate microtube modified glassy carbon electrode has been analyzed. The manganese vanadate microtube modified glassy carbon electrode exhibits the performance for the electrochemical determination of L-cysteine with a detection limit of 9.2 μM and linear range of 0.01 – 2 mM.

We report the modification of the luminescent properties of ZnS nanoparticles by the adsorbed chemical species. ZnS nanoparticles were prepared via microwave-assisted synthesis. The effects of the concentrations of citrate and SO 4 2− ions on the optical properties were analyzed by means of UV-Vis and photoluminescence spectrophotometries, and Fourier-transform IR spectroscopy. ZnS nanoparticles were also analyzed by means of X-ray diffraction and transmission electron microscopy. The results confirm that the luminescent properties of the synthesized particles are affected by the adsorbed chemical species (citrate and SO 4 2− ions). ZnS nanoparticles synthesized with 30 and 45 mM Na 2 SO 4 , and 2 mM trisodium citrate exhibit higher intensity of luminescence than those synthesized with 15 mM Na 2 SO 4 . The average diameter of the ZnS nanoparticles synthesized under these last experimental conditions is about 20 nm.