Peculiarities of changes of some physicomechanical characteristics of monoisotopes B, B and natural β-boron

Real structure and some physicomechanical characteristics of the samples of natural beta-rhombohedral boron B as well as of its ¹⁰B and ¹¹B monoisotopes have been studied. It was shown that the influence of ¹⁰B and ¹¹B isotopes on physicomechanical properties of boron had a different character. In particular, the samples enriched with ¹¹B had high values of microhardness, shear modulus (SM) and elastic limit if compared to those of boron, while the samples enriched with ¹⁰B monoisotopes were characterized with high values of thermal expansion coefficient (TEC) and thermal conductivity; lattice parameters a and c increased by the sequence: ¹¹B, B, ¹⁰B. It was established that TEC, thermal conductivity, microhardness, SM and shear elastic limit increased in all samples at annealing for 5 h at 1500 °C regardless of isotope content.     

Experimental studies on the microstructure and hardness of laser-treated steel specimens

An experimental investigation with 5 kW CW CO₂ laser system was carried out to study the effects of different laser and process parameters on the microstructure and hardness of carbon steel specimen with varying carbon percentage. The laser beam is allowed to scan on the surface of the work piece varying the power (1.1–2.5 kW) and traverse speed (6–15 mm/s) at two different spot sizes using TEM_01* mode laser beam. The most hardenable microstructure achieved in case of three grades of carbon steel and the most influencing parameter on the value of hardness are reported. Besides the above study, some multipass operations are also carried out to recommend an appropriate gap between consecutive passes.     

Influence of processing methods on starch properties

Native potato starch was prepared using different processing methods. The samples were characterized by wide-angle X-ray scattering (WAXS), optical microscopy, differential scanning calorimetry (DSC), and microhardness. Compression molding of the starch granules led to sintered relatively brittle materials. Here, the amylopectin crystals of the native powder remained grossly preserved. Preparation of dry films from aqueous gels resulted in disintegration of the structure of the native starch granules and in the formation of a new semicrystalline structure comprised of crystallized amylose molecules. Injection molding of native starch was found to be a processing method that gives rise to amorphous materials with superior mechanical properties.     

Growth, optical, mechanical and dielectric studies on NLO active pure and metal ion doped single crystals of bis-thiourea zinc chloride

Good quality single crystals of pure and metal ion (Ni²⁺) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals the crystalline perfection and the EDAX spectrum confirms the presence of dopant in the lattice of the parent crystal. The DRS UV-visible spectral study reveals improved transparency for the doped crystal, ascertaining the inclusion of metal ion in the lattice. The optical band gap of the pure and doped crystals was calculated to be 4.8 and 5.2 eV respectively from the UV transmission spectrum. The vickers hardness test brings forth higher hardness value for Ni²⁺doped BTZC as compared to pure BTZC crystal. The dielectric measurement exhibits very low dielectric constant and dielectric loss at higher frequencies for both the pure and Ni²⁺doped BTZC. The existence of second harmonic generation signals in the crystal also has been confirmed by performing the Kurtz powder test.     

Effect of surface nanocrystallization induced by fast multiple rotation rolling on hardness and corrosion behavior of 316L stainless steel

A nanostructured layer was fabricated by using fast multiple rotation rolling (FMRR) on the surface of 316L stainless steel. The microstructure in the surface was characterized by transmission electron microscopy and X-ray diffraction. The effects of FMRR on the microhardness, surface roughness and corrosion behavior of the stainless steel were investigated by microhardness measurements, surface roughness measurements, potentiodynamic polarization curves and pitting corrosion tests. The surface morphologies of pitting corrosion specimens were characterized by scanning electron microscopy. The results show that FMRR can cause surface nanocrystallization with the grain size ranges from 6 to 24 nm in the top surface layer of the sample. The microhardness of FMRR specimen in the top surface layer remarkably increases from 190 to 530 HV. However, the surface roughness slightly rises after FMRR treatment. The potentiodynamic polarization curves and pitting corrosion tests indicated that the FMRR treated 316L stainless steel with a surface nanocrystallized layer reduced the corrosion resistance in a 3.5% NaCl solution and enhanced the pitting corrosion rate in a FeCl₃ solution. Possible reasons leading to the decrease in corrosion resistance were discussed.     

Atmospheric reactive plasma sprayed Fe-Al2O3-FeAl2O4 composite coating and its property evaluation

In the present study, Fe-Al₂O₃-FeAl₂O₄ composite coatings were successfully deposited by reactive plasma sprayed Al/Fe₂O₃ agglomerated powder. Phase composition and microstructure of the coatings were determined by XRD and SEM. The results indicated that the composite coatings were principally composed of three different phases, i.e. FeAl₂O₄ phase as main framework, dispersed ball-like Fe-rich phase, and small splats of Al₂O₃ phase, and it was thought that the in situ synthesized metal phase was helpful to toughen the coating matrix. According to the results of the indentation and frictional wear tests, the composite coating exhibited excellent toughness and anti-friction properties in comparison with conventional Al₂O₃ monophase coating, though its microhardness value was a little lower than that of Al₂O₃ coating. The formation mechanism and the toughening mechanism of the composite coating were clarified in detail.     

Ion implantation effects on the microhardness and microstructure of GaN

We study the effect of N⁺ and O⁺ implantation on the microhardness and the microstructure of epitaxially grown GaN. The microhardness is measured using a Knoop diamond indenter while information on the effect of implantation on the surface morphology, microstructure and electronic structure is provided by atomic force microscopy, cross-section transmission electron microscopy and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. It is demonstrated that implantation increases the surface microhardness. A possible mechanism for the surface hardening effect is based on the formation of N interstitials that pin the dislocations and prohibit the plastic deformation. In addition to the hardening effect, the implantation induced N interstitials introduce a characteristic resonance in the NEXAFS spectra, at 1.4 eV below the absorption edge.     

Microstructure and corrosion properties of thick WC composite coating formed by plasma cladding

The thick Ni-coated WC coatings, in a matrix of Nickel-based alloys, were prepared on AISI 1045 steel using plasma cladding equipment. A pre-placed layer of uniform mixture, with different weight fractions of Ni-coated WC powder and Nickel-based alloy powder, on the steel substrate was melted at the high temperature of the plasma jet. The coating composition, microstructure and microhardness were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS) and microhardness testing. The experimental results show that the metallurgical bond was formed between the coating and substrate. The XRD results show that the coatings contain γ-Ni, carbides (such as M₂₃C₆ and M₇C₃) and boride (such as Fe₂B, Fe₃B phases). SEM shows that all the coatings are crack-free with lower porosity (<1%). It is found that the microhardness and the electrochemical behavior of the coatings are depended on the content of Ni-coated WC powder. The corrosion mechanism for the coatings may be due to the microgalvance corrosion between the phases in the cladding coatings.     

Effect of shot peening on the microstructure of laser hardened 17-4PH

In order to investigate the influence of shot peening on microstructure of laser hardened steel and clarify how much influence of initial microstructure induced by laser hardening treatment on final microstructure of laser hardened steel after shot peening treatment, measurements of retained austenite, measurements of microhardness and microstructural analysis were carried out on three typical areas including laser hardened area, transitional area and matrix area of laser hardened 17-4PH steel. The results showed that shot peening was an efficient cold working method to eliminate the retained austenite on the surface of laser hardened samples. The surface hardness increased dramatically when shot peening treatments were carried out. The analyses of microstructure of laser hardened 17-4PH after shot peening treatment were carried out in matrix area and laser hardened area via Voigt method. With the increasing peening intensity, the influence depth of shot peening on hardness and microstructure increased but the surface hardness and microstructure did not change when certain peening intensity was reached. Influence depth of shot peening on hardness was larger than influence depth of shot peening on microstructure due to the kinetic energy loss along the depth during shot peening treatment. From the microstructural result, it can be shown that the shot peening treatment can influence the domain size and microstrain of treated samples but laser hardening treatment can only influence the microstrain of treated samples.     

Electrodeposition and properties of Zn-nanosized TiO2 composite coatings

Nanosized TiO₂ particles were prepared by sol-gel method. The TiO₂ particles were co-deposited with zinc from a sulphate bath at pH 4.5 using electrodeposition technique. The corrosion behavior of the coatings was assessed by electrochemical polarization, impedance, weight-loss and salt spray tests. Wear resistance and microhardness of the composite coating was measured. The smaller grain size of the composite coatings was observed in the presence of TiO₂ and it was confirmed by the images of scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques.