Microstructure and Properties of Electrodeposited nc-TiO2/Ni–Fe and Ni–Fe Coatings

In this study, nc-TiO2/Ni–Fe composite coatings, and Ni–Fe alloys as equivalents to their matrices, were obtained from citrate-sulphate baths in the electrodeposition process using direct current and pulse current conditions. The aim of the study was to examine the effects of TiO2 nanoparticles and current conditions on the chemical composition, surface morphology, microstructure, microhardness and magnetic properties of the electrodeposited coatings. The results show that the concentration of Fe in Ni–Fe alloys is related to the current conditions and is higher in the case of pulse current electrodeposition, while such a relationship was not observed for composites. The reinforcement of composites with TiO2 nanoparticles results in a more developed surface topography with many nodule-like structures. Composites and equivalent alloys deposited in pulse current are characterized by a finer grain size than those obtained in direct current. TiO2 nanoparticles and their agglomerates, several tens of nanometres in size, are distributed randomly in the Ni–Fe matrix of composites deposited in both current conditions used. Incorporation of a high volume fraction of nc-TiO2, exceeding over a dozen percent, and decreasing the nanograin size in nc-TiO2/Ni–Fe composites electrodeposited under pulse current conditions, allow a higher hardness to be achieved than in their counterparts obtained using direct current. Magnetic measurements showed ferromagnetic ordering of pristine TiO2 nanoparticles, however, the introduction of TiO2 nanoparticles into the Ni–Fe matrix resulted in a decrease in coercivity and saturation magnetization. Graphic Abstract

Significance of the Nanograin Size on the H2S-Sensing Ability of CuO-SnO2Composite Nanofibers

CuO-SnO2composite nanofibers with various nanograin sizes were synthesized for investigating their sensing properties with respect to H2S gas. The nanograin size in the CuO-SnO2composite nanofibers was controlled by changing the thermal treatment duration under isothermal conditions. The nanograin size was found to be critical for the sensing ability of the composite nanofibers. The CuO-SnO2composite nanofibers comprised of small-sized nanograins were more sensitive to H2S than those with larger-sized nanograins. The superior sensing properties of the CuO-SnO2composite nanofibers with the smaller nanograins were attributed to the formation of the larger number ofp-CuO-n-SnO2junctions and their transformation tometallic-CuS-n-SnO2contacts upon exposure to H2S gas. The results suggest that smaller nanograins are conducive to obtaining superior H2S-sensing properties in CuO-SnO2composite nanofibers.

Investigating on the Reverse Transformation of Martensite to Austenite and Pseudoelastic Behavior in Ultrafine-Grained Fe-10Ni-7Mn (wt %) Steel Processed by Heavy Cold Rolling

Fe-10Ni-7Mn (wt. %) steel is a member of ultrahigh strength steels which shows good ductility in the solution annealed condition and excellent age hardenability. In the current research, this alloy was subjected to heavy cold rolling in which the reverse transformation of martensitic to austenite was brought about. From the XRD, DSC and dilatometric analyses, it is resulted that after 60 % cold rolling the austenite phase may be formed by displacive mechanism. Stability of austenite at room temperature is referred to the ultrafine/nanograin size of austenite after deformation which prevents the austenite to martensite transformation. The presence of ultrafine/nanoaustenite formed by displacive mechanism leads to the observation of new mechanical properties during cyclic tensile test. This behavior is known as pseudoelastic phenomenon. In this behavior, during loading-unloading tensile cycle, the shape of the specimen return to its original configuration with a hysteresis loop in its path to the zero strain point.

The 3D Kuramoto-Sivashinsky Equation for Nonequilibrium Defects Interacting through Self-Consisting Strain and Nanostructuring of Solids

It is shown that the bulk defect-deformational (DD) nanostructuring of isotropic solids can be described by a closed three-dimensional (3D) nonlinear DD equation of the Kuramoto-Sivashinsry (KS) type for the nonequilibrium defect concentration, derived here in the framework of the nonlocal elasticity theory (NET). The solution to the linearized DDKS equation describes the threshold appearance of the periodic self-consistent strain modulation accompanied by the simultaneous formation of defect piles at extremes of the strain. The period and growth rate of DD nanostructure are determined. Based on the obtained results, a novel mechanism of nanostructuring of solids under the severe plastic deformation (SPD), stressing the role of defects generation and selforganization, described by the DDKS, is proposed. Theoretical dependencies of nanograin size on temperature and shear strain reproduce well corresponding critical dependencies obtained in experiments on nanostructuring of metals under the SPD, including the effect of saturation of nanofragmentation. The scaling parameter of the NET is estimated and shown to determine the limiting small grain size.

PZT FILM GENERATOR DRIVEN BY ULTRASONIC WAVE

Energy harvesting was demonstrated in hydrothermal PZT nanocrystal films driven by ultrasound. With high temperature sintering and solution infiltration, PZT films with nanograin size was found to exhibit bulk-like properties such as large remnant polarization of 42 μC/cm2. With the bulk-like properties, a packaged PZT film device was demonstrated to be capable of converting mechanical energy carried by the ultrasonic wave into electrical energy in a reliable and efficient way. The result suggests an alternative potential solution for energy harvesting application.

Ultrahigh-pressure densification of nanocrystalline WB ceramics

Phase-pure nanostructured WB ceramics are hot pressed at ultrahigh pressures of 1.0 to 3.0 GPa and high temperatures of 700 to 1000 °C (UHPHT) for 60 min. The UHPHT samples are nanograin size from 15 to 40 nm. Our experimental observation shows that ultrahigh pressure could improve densification, and the density of WB samples could reach 99.4% of theoretical. The comparative experiments carried out at ambient pressure and temperatures of 550 to 1100 °C for 60 min indicate that the external pressure was favorable for phase-pure and highly dense WB formation. In addition, the UHPHT samples give a high hardness value of 28.9 ± 0.8 GPa.