Volume 109, Issue 6

The deformation behavior and dynamic recrystallization (DRX) mechanism of lean duplex stainless steel 2101 under hot compression were studied by means of optical microscopy and electron backscatter diffraction. Hot compression tests were performed at a temperature of 1 100 °C and strain rate of 0.01 s −1 , and also at a temperature of 1 000 °C and strain rate of 30 s −1 . The flow curves exhibit typical DRX characteristics, and the flow stress increases to a peak stress followed by work softening at higher strains. When the alloy was deformed at 1 000 °C and the strain rate of 30 s −1 , new ferrite grains formed through a distinct DRX mechanism occurring in the vicinity of the δ/γ interface. When the alloy was deformed at 1 100 °C and strain rate of 0.01 s −1 , a small number of fine γ phase grains distributed both in the δ ferrite matrix and at δ/γ interfaces. The refinement of γ phase was expected to form by dynamic strain induced δ to γ transformation and discontinuous dynamic recrystallisation (DDRX) mechanisms.

Two heat-resistant ferritic cast steels, 1.4476 and 1.4777 with a similar high Cr concentration, have been analyzed regarding their microstructures, mechanical properties, corrosion resistance and aging behavior. The differences observed between the grades are related to their different C contents. A higher C concentration ensures a higher mechanical resistance, in particular at high temperature (850°C) and also a better high-temperature (850°C) corrosion resistance. This is related to the formation of numerous carbides. However, this study also reveals that the microstructure of these steels is greatly affected by aging. In particular, the precipitation of the sigma phase and the formation of nitride precipitates could lead to failure during service at high temperature.

Experiments for ultrasonic-assisted pulsed-laser surface irradiation and pulsed-laser surface irradiation were conducted based on an Nd:YAG pulsed-laser machine in order to study the effects produced by ultrasonic vibration on the AISI 1045 steel surface. In addition, the effects of the ultrasonic vibration on the AISI 1045 steel surface are discussed. The results show that larger tensile residual stress is induced at the pulsed-laser surface irradiation area, and the resultant surface 3D morphology is a noticeable sink mark owing to the temperature effect and the tensile residual stress effect. The surface integrity of AISI 1045 steel subjected to pulsed-laser surface irradiation can be improved with the aid of the extra acoustic field. The findings confirm that the acoustic field can be introduced to high-power laser processing technology to improve the surface integrity of the treated materials.

DyNi 2- x Co x ( x = 0, 0.4, 0.6 and 0.8) absorbing powders were prepared using a non-consumable vacuum melting furnace and a high energy ball milling method. The effects of Co content on the microstructure and the absorbing properties of DyNi 2 powders were investigated by X-ray diffraction, scanning electron microscopy and vector network analysis. The absorbing properties of DyNi 2 powders were optimized, but did not affect the composition of DyNi 2 alloy with increasing Co content. With the addition of Co, the ∊ ″ formant frequency, μ ″ formant frequency and reflection loss peak frequency of the powders shifted to higher values. The minimum reflection loss peak of DyNi 1.4 Co 0.6 powder is about −30.65 dB with a coating thickness of 1.8 mm, and a bandwidth where R < −10 dB is 1.9 GHz.

Pulse-reverse power modes are used in galvanotechniques in order to obtain coatings with better characteristics in terms of gloss, adhesion, tracking sharp edges and uniform distribution of deposits on complex shape objects, compared with the coatings produced by constant current modes. Pulse-reverse modes also allow the use of a higher current density, and thus the production speed of electroplating cells increases. Systems for standard electroplating of copper, silver and gold are optimised by the suitable choice of duration and intensity of the pulses. It is shown that coatings with satisfactory quality can be deposited using higher current density, different modes of pulsed current in a very short period of time, without expensive and often dangerous additives in the electrolyte. Parameters of the model for certain electrochemical systems were determined by modelling and computer simulation, so the system behaviour under different circumstances becomes predictive.

In this study, the electrochemical behavior of 304L SS stainless steel in various nitric acid/chloride ratios was investigated. The characteristics of the passive film, formed at the open circuit potential (OCP) and at the passive potential (0.65 V vs SCE) were also compared. OCP results show that a stable passive film formed over the surface with higher nitric acid/chloride ratios. Potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) measurements showed that with higher nitric acid/chloride ratios, the film resistance increases ( R 1 ) for OCP, passive potential, and the critical current density ( i crit ) and corrosion rate ( i corr ) decreases. Mott–Schottky analysis revealed that the film formed at OCP shows n-type behavior for 0.01 N and 1 N concentration and shows p-type behavior for 0.1 N nitric acid concentration. At 0.65 V (vs. SCE) of film formation potential, the film formed in 1 N concentration shows n – type behavior. In 0.01 N and 0.1 N acid concentration, p-type behavior has been observed. Also, according to Mott–Schottky analysis, it was found that a lower defect density was found in 0.1 N nitric acid, for both the potentials. X-ray photoelectron spectroscopy spectra show evidence that the surface contains Fe and Cr as major elements. However, at OCP, Fe 2 O 3 was the main constituent of the passive film, whereas the passive potential film was rich in Cr 2 O 3 . In addition, nitrogen and chloride were adsorbed in the passive film at passive potential.

The structural, magnetic and magnetocaloric properties of Gd 7 Pd 3- x Fe x compounds with x = 0, 0.2 and 0.4 were investigated. Rietveld refinement of X-ray powder diffraction shows that all the investigated samples are single phase and crystallize in a hexagonal structure with the space group P6 3 mc. The lattice parameters ( a , b and c ), and the cell volume ( v ) decrease with the increase of Fe content in Gd 7 Pd 3- x Fe x , mainly because of the difference in atomic radius between Fe and Pd. Magnetization versus temperature in a magnetic applied field of 0.05 T shows that Gd 7 Pd 3- x Fe x displays a paramagnetic (PM) – ferromagnetic (FM) transition with the Curie temperature T C decreasing from 336 K for x = 0.0 to 319 K for x = 0.4. Under a field change of 0 to 5 T, the maximum values of the magnetic entropy change (|ΔSMmax|)$\left( {|{\rm{\Delta }}S_M^{max}|} \right)$ are 5.09 J kg −1 K −1 , 4.89 J kg −1 K −1 , and 4.46 J kg −1 for x = 0, 0.2, and 0.4, and the corresponding relative cooling powers (RCP) amount to 387.6 J Kg −1 , 357.2 J · Kg −1 , and 385.5 J Kg −1 , respectively. The stable magnetocaloric effect and refrigeration capacity near room temperature reveal that the Gd 7 Pd 3- x Fe x compounds may be considered as refrigerants for magnetic refrigeration.

Composites of AZ91D magnesium alloy reinforced with fly-ash cenosphere (FAC) were prepared by a stirring method. The effects of the FAC particle size (83, 116, and 146 μm) and the test frequency (0.5, 1, and 5 Hz) on high-temperature damping capacity and dynamic Young's modulus of the composites were investigated. The results show that the FAC particles distributed homogeneously in the Mg-alloy matrix and some new phases formed. The composites with 146-μm FAC exhibited the highest damping capacity at all test frequencies at high temperatures, whereas the highest dynamic Young's modulus was exhibited by the composites with 83-μm FAC. Therefore, composites with good damping capacity and mechanical properties could be obtained through selection of reinforcement particles of an appropriate size.

The effects of extrusion parameters on the microstructural characteristics and the tensile properties of Al-10 vol.% SiC composites containing three different particle sizes of 38, 62, 82 μm were investigated. The results showed that the tensile properties of the composites were improved with the increase of extrusion ratio only up to 12 : 1 for the extrusion temperatures of 450 and 500 °C, but continued to improve at extrusion temperature of 550 °C due to the considerable reduction in porosity and appropriate alignment of reinforcing phase. Furthermore, the increased extrusion temperature resulted in improvement of elongation and tensile strength at the expense of yield strength. It was found that the extrusion treatment under the conditions of larger sized particles, lower temperature and higher ratio provided more pronounced breakage of SiC particles which could be beneficial if the broken pieces of SiC were totally embedded in the matrix.

Zn 0.8 Ni 0.2 Fe 2 O 4 nanoparticles were prepared in a three-step synthesis involving the co-precipitation of metal nano-hydroxide, coating the metal nano-hydroxide with oleic acid, and hydrothermal treatment (ferritization). The nanoparticles were analyzed using X-ray diffraction, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscopy. All samples heated at temperatures from 140 °C to 180 °C were crystalline Zn 0.8 Ni 0.2 Fe 2 O 4 with particle sizes ranging from 5–8 nm. Vibrating sample magnetometry results indicated that the coercive force and remanence of the samples were close to zero, and the saturation magnetization values were high (14.20–27.12 emu · g −1 ).

Polybutylene terephthalate (PBT) is extensively used for automobile and aircraft components, which are prone to continuous damage and, thus, are expected to have superior mechanical properties. With the aim of achieving this, carbon nanotube (CNT) reinforced polymer composites are steadily gaining importance. To address this area, the present study deals with the fabrication and characterization of PBT reinforced with multi-walled CNTs (0.1 to 0.5 wt.%) and its effect on tensile strength. The strength of the composite increased at first and later reduced marginally with increasing filler content. A study of fractured surfaces of the composites showed formation of CNT–polymer inflorescence type morphology which indicated that the nanotubes within the polymer matrix act as an anchor for carrying and distributing the load during fracture. This demonstrates appreciable interfacial bonding between polymer matrix and the CNTs.

Interdiffusion coefficients of the β single-phase in the Ti-rich portion of the binary Ti– X ( X = Al, Mo, V, Cr, Fe) systems at 1 523 K were determined by annealing infinite diffusion couples between appropriate pairs of alloys. The values were derived from the concentration profiles by electron probe microanalysis coupled with the Boltzmann–Matano method. The comparison of the interdiffusion coefficients in these binary Ti– X ( X = Al, Mo, V, Cr, Fe) systems show that the Mo diffuses the least while the Fe diffuses fastest in titanium alloys. Furthermore, the values of the interdiffusion coefficients of the Ti–Al, Ti–V and Ti–Cr binary systems were similar.

Bismuth ferrite (BiFeO 3 , or BFO) is a kind of multiferroic material with a single phase. One-dimensional nanomaterials have unique electrical, magnetic, and optical properties due to anisotropy and unique size effects. Bismuth ferrite nanowires were prepared by hydrothermal method processing at different mineralizer concentrations. X-ray diffraction results show that the increase of mineralizer concentration can inhibit the reaction to generate impurities. It can be observed from scanning electron microscopy that along with increasing of mineralizer concentration, the length of the nanowires increase. Transmission electron microscopy and UV–visible spectrophotometry results reveal that the appropriate increase of nanowires length is beneficial to enhancing the absorption of light.