Textural changes during β→α and α→β→α transformations in a near-α titanium alloy

The near-α titanium alloy Ti-6Al-5Zr-0.5Mo-0.25Si has been rolled in the β- and (α+β)-phase fields. Texture studies have been performed on each of these materials in the as-rolled condition after air cooling from the finish rolling pass, with a view to examining the transformation texture β/(α+β)→α. One of the materials from each of the β and (α+β) rolled conditions has been heat treated in the β-phase field and air cooled (AC) to α phase in order to study the nature of the α → β → α transformation texture. Results indicate that transformation textures of the α phase are significantly different for both the β as well as the (α+β) rolling conditions. Heat treatment of secondary (transformed) α in the β-phase field and its further cooling to α phase leads to relatively weak texture for the β rolled materials. The results have been discussed in relation to the microstructural features and consequent variant selections and have been correlated with those observed in titanium and its alloys.     

Bidirectional active control of structures with type-2 fuzzy PD and PID

Proportional-derivative and proportional-integral-derivative (PD/PID) controllers are popular algorithms in structure vibration control. In order to maintain minimum regulation error, the PD/PID control require big proportional and derivative gains. The control performances are not satisfied because of the big uncertainties in the buildings. In this paper, type-2 fuzzy system is applied to compensate the unknown uncertainties, and is combined with the PD/PID control. We prove the stability of these fuzzy PD and PID controllers. The sufficient conditions can be used for choosing the gains of PD/PID. The theory results are verified by a two-storey building prototype. The experimental results validate our analysis.     

Synthesis of gold nanorods in organic media

A seed mediated approach for the synthesis of anisotropic rod shaped gold nanoparticles in organic media (toluene) is demonstrated. Pre-formed gold nanoparticles stabilized in toluene by 4-hexadecylaniline (HDA) are used as seeds. These when reacted with 1-octadecylamine (ODA) hydrophobised chloroaurate ions in toluene lead to the formation of gold nanorods. ODA or alkylamines of different chain lengths which are the chloroaurate ion phase transfer agent have been found to play a key role in the formation of the nanorods. The gold nanorods that have a five-fold symmetry evolve from multiply twinned particles and are bound at the tips by [1 11] faces and at the sides by [100] faces. The gold nanorods have been shown to grow under the shape directing effect of the alkylamines which stabilize the high energy [100] faces. The concentration of the alkylamines has been found to play a critical role in the formation of the gold nanorods. Higher concentrations of the alkylamines lead to formation of spherical particles, at times of narrow size distribution.     

Grain growth and crack formation in NiO thin films by swift heavy ion irradiation

NiO thin films grown on Si(1 0 0) substrates by electron beam evaporation and sintered at 700 °C, were irradiated by 120 MeV Au⁹⁺ ions. Though irradiation is known to induce lattice disorder and suppression of crystallinity, we observe grain growth at some fluences of irradiation. Associated with the growth of grains, the films develop cracks at a fluence of 3 × 10¹² ions cm⁻². The width of the cracks increased at higher fluences. Swift heavy ion irradiation induced atomic diffusion and strain relaxation in nanoparticle thin films, which are not in thermodynamic equilibrium, seem to be responsible for the observed grain growth. This phenomenon along with the tensile stress induced surface instability lead to crack formation in the NiO thin films.     

Microstructure and Texture Evolution During Sub-Transus Thermo-Mechanical Processing of Ti-6Al-4V-0.1B Alloy: Part II. Static Annealing in (α + β) Regime

The first part of this study describes the evolution of microstructure and texture in Ti-6Al-4V-0.1B alloy during sub-transus rolling vis-à-vis the control alloy Ti-6Al-4V. In the second part, the static annealing response of the two alloys at self-same conditions is compared and the principal micromechanisms are analyzed. Faster globularization kinetics has been observed in the Ti-6Al-4V-0.1B alloy for equivalent annealing conditions. This is primarily attributed to the α colonies, which leads to easy boundary splitting via multiple slip activation in this alloy. The other mechanisms facilitating lamellar to equiaxed morphological transformations, e.g., termination migration and cylinderization, also start early in the boron-modified alloy due to small α colony size, small aspect ratio of the α lamellae, and the presence of TiB particles in the microstructure. Both the alloys exhibit weakening of basal fiber (ND||〈0001〉) and strengthening of prism fiber (RD||〈 $ 10\bar{1}0 $ 〉) upon annealing. A close proximity between the orientations of fully globularized primary α and secondary α phases during α → β → α transformation has accounted for such a texture modification.     

Effect of Texture and Grain Size on Bio-Corrosion Response of Ultrafine-Grained Titanium

The bio-corrosion response of ultrafine-grained commercially pure titanium processed by different routes of equal-channel angular pressing has been studied in simulated body fluid. The results indicate that the samples processed through route B_c that involved rotation of the workpiece by 90 deg in the same sense between each pass exhibited higher corrosion resistance compared to the ones processed by other routes of equal-channel angular pressing, as well as the coarse-grained sample. For a similar grain size, the higher corrosion resistance of the samples exhibiting off-basal texture compared to shear texture indicates the major role of texture in corrosion behavior. It is postulated that an optimum combination of microstructure and crystallographic texture can lead to high strength and excellent corrosion resistance.     

Retardation of Small Creep–Fatigue Crack in Gr. 91 Steel Through the Combined Effects of Stress Relaxation,Microstructural Evolution,and Oxidation

Metallurgical and Materials Transactions A - This investigation reports an unusual effect of hold time (up to 10 seconds) on retardation in the growth of creep–fatigue small cracks...     

Optical and structural properties of pulsed laser deposited Ti:Al2O3 thin films

Spectrally selective solar absorber coatings using metal–dielectric composites offer a high degree of flexibility since their solar selectivity can be optimized by the proper choices of constituents, coating thickness, metal particle concentration, size, shape, and orientation. In this article, Ti:Al₂O₃ composite films of various Ti contents were prepared by the pulsed laser deposition technique, and their structural and optical properties were investigated by scanning electron microscope, X-ray photoelectron spectroscope, and X-ray diffraction methods. The results demonstrate promising solar spectrally selective behavior indicating Ti:Al₂O₃ composite as an excellent choice for solar thermal applications.