Volume 104, Issue 5

The influence of the chemical composition and the grain size of retained austenite in an ultra-fine grained medium manganese steel on the martensite transformation kinetics was investigated by means of dilatometry. A modified Koistinen–Marburger type exponential function was developed for the martensite transformation kinetics, which includes the influence of the size and the composition of the austenite. Whereas the ultra-fine grained retained austenite had a remarkably low M s temperature, the kinetics of its transformation to martensite was accelerated.

Microstructural changes resulting from isothermal decomposition of the β-phase have been studied in Cu-rich binary Cu-Al and ternary Cu-Al-Sn alloys containing up to 3 at.% Sn at temperatures from 873 to 673 K. Results are presented as TTT diagrams. The decomposition occurs in several stages, each of which involves the establishment of metastable equilibrium between β and one or more of the product phases α β 1 and γ 2 . Addition of Sn has been shown to increase the stability of the ordered β 1 -phase in relation to β. In alloys containing more than 2 at.% Sn, the β 1 emerges as a stable phase. At low Sn concentrations β 1 is metastable. An important new finding is the existence of three-phase equilibrium microstructure containing α β 1 and γ 2 . Increasing addition of Sn alters the morphology of β 1 from rosettes to dendrites and finally to Widmanstätten needles.

A comparison of the coarsening of nitrogen-rich vanadium precipitates and the coarsening of carbon-rich vanadium precipitates is presented. The precipitate phases are studied experimentally, via fabrication of model alloys, and theoretically, via simulations utilizing the DICTRA software. The experimental investigations indicate that the nitrogen-rich precipitates exhibit a slower coarsening behaviour than the carbon-rich precipitates. Analysis using thermodynamic and kinetic modelling shows that this can be explained by the higher thermodynamic stability of the nitrogen-rich precipitate compared to the carbon-rich precipitate. The calculated coarsening rates are compared with the measured rates, and found to be in satisfactory agreement using reasonable values for the interfacial energies. The investigations are motivated by the fine precipitate size distribution of nitrides and carbonitrides characteristic for high nitrogen alloyed tool steels produced by means of powder metallurgy.

The results of phase diagram investigation and characterization of the Ag-In-Sn-Cu system are presented in this paper. Samples at the In : Ag : Cu = 7 : 2 : 1 vertical section were measured with differential scanning calorimetry, and the obtained transition temperatures were compared with calculated values. From Calphad-type calculation, the phase diagram for Sn-In x Ag y Cu z (molar ratio x : y : z = 7:2:1) section is constructed. In order to obtain the microstructure of investigated alloys, scanning electron microscopy with energy dispersive X-ray spectroscopy was used.

Equal channel angular pressing of low-carbon steel produces an ultrafine-grained microstructure with an average (sub-)grain size of 325 nm and both coarse and fine carbides, a microhardness of 330 HV and 0.2 % offset yield strength of σ 0.2 = 815 MPa. The average (sub-)grain size and the mechanical properties of the steel after equal channel angular pressing were found to be stable up to 500 °C. The composition of the carbides, their sizes and their distribution in the microstructure were analyzed in order to understand their contribution to the mechanical properties and the thermal stability of the steel. Both the high strength and the thermal stability of the steel after equal channel angular pressing are associated with the grain refinement, the substructure strengthening, and precipitation hardening.

This paper presents experimental results of a range of thermophysical properties of pure polycrystalline palladium samples over a wide temperature range. Specific heat capacity was measured from 250 to 1 770 K, specific electrical resistivity from 250 to 1 800 K, hemispherical total emissivity from 1 100 to 1 800 K, normal spectral emissivity from 1 340 to 1 720 K, and thermal diffusivity in the range from 200 to 1 540 K. From the measured data, the thermal conductivity and Lorentz function were computed in the range from 250 to 1 540 K. Specific heat capacity, electrical resistivity, and both emissivities were measured by means of subsecond pulse calorimetry, while the thermal diffusivity was obtained using the laser flash technique. The first method used specimens in the form of a thin rod, of about 2 mm in diameter and 200 mm in length, and the second disk specimens of about 3 mm in thickness and 10 mm in diameter. For necessary corrections, literature data on thermal linear expansion have been used. All the results are compared with available literature data and discussed.

Nd-Fe–Al–Co alloys with thickness of 0.05–4 mm were prepared by means of rapid solidification methods, suction-casting and melt-spinning, and investigated using X-ray diffraction, electron microscopy and magnetization measurements. With appropriate composition and quenching rate, the alloys behave as single-phase hard magnetic materials. Coercivity of the alloys can reach 7.6 kOe at room temperature and exceed 30 kOe at 100 K. When the thickness of the alloys is increased, multi-magnetic phase behavior is clearly performed and Nd 2 Fe 15 Al, NdAl 2 , Nd 3 Al and Nd phases are further crystallized. The optimal hard magnetic properties of the alloys closely related to a microstructure which consists of nanocrystallites with size of 10–30 nm dispersed in an amorphous matrix. The hard magnetic phase in the alloys belongs to the amorphous phase. The nanocrystallites, whose total volume fraction is very small in comparison with that of the amorphous phase, probably act as pinning centers, resulting in high coercivity behavior of the alloys.

Ir 1–x Re x (0.15 ≤ x ≤ 0.40) phases prepared under high-pressure, high-temperature conditions from nanopowders of iridium and rhenium were characterized using powder X-ray diffraction and scanning electron microscopy. Structural characteristics of the phases obtained were identical with the corresponding parameters for the solid solutions prepared by means of melting and thermal decomposition of the precursors. The data obtained make it possible to improve solid-state solubility limits in the binary Ir–Re phase diagram. As revealed, the maximum solid solubility of Ir in Re is 68 at.%, and that of Re in Ir is 20 at.%.

Fe/metal oxide nanocomposite particles were produced by means of hydrogen reduction assisted ultrasonic spray pyrolysis. Fe/Fe 0.761 Mg 0.239 O and Fe/MgO nanocomposite particles were obtained at 600 and 800 °C, respectively. The thermodynamics of the formation reactions were investigated. Increasing the reaction temperature allowed efficient reduction of the precursor to metallic iron that induces the formation of pure MgO phase. The crystallite sizes of the Fe in the composite structures slightly increased, and also the crystallite sizes of the oxides decreased with elevating temperature. The nanocomposite particles exhibited spherical morphology and their particle sizes were slightly different. All of the samples showed ferromagnetic characteristics and the results indicate that the amount of metal and metal oxide phases most affected the saturation magnetizations of the composite particles which were lower than pure iron.

Pure Ni and Ni/SiC nanocomposite layers were prepared by means of direct current electrodeposition in a sulfate–chloride nickel plating bath. The surface characteristics and properties of Ni/SiC nanocomposite layers and pure nickel coatings were comparatively investigated. The surface morphology, microstructure, topography, roughness and corrosion were characterized using scanning electron microscopy with energy dispersive X-ray spectroscopy, transmission electron microscopy, atomic force microscopy, epifluorescence microscopy and electrochemical methods. The results show that the electro-co-deposition of nano-SiC (20 nm) into a nickel matrix can significantly affect the morphology, microstructure and surface properties of Ni/SiC nanocomposite coatings. Ni/SiC nanocomposite coatings are of great interest for improving electrochemical corrosion resistance as well as resistance to bacteria attachment.

A scaffold, synthesized from bio-degradable polymers and Bombyx mori silk fibroin in the form of films and fibrous assemblies, has been used as the bio-material for in-vivo applications. In the present work, the scaffold was prepared from the fibroin of Indian eri silk via the electrospinning method. The diameter of the fibre produced was in the range of 300 to 900 nm. The scaffold was subjected to ethanol treatment to improve its dimensional stability, as there was the problem of curling and shrinking when it was treated with solutions used for the cell culture. The scaffold was characterized for surface, thermal and tensile properties. The dimensional stability of the scaffold improved and the porosity reduced, due to the treatment of the scaffold with ethanol. The average failure stress of the raw and ethanol treated scaffold was 2.34 MPa and 4.91 MPa respectively and the mean strain was 13.63 % and 7.91 % respectively. Bone marrow stromal cells were isolated from the bone marrow of Swiss albino mice, and cultured on the ethanol treated electrospun fibrous scaffold. Scanning electron microscopy of the culture was carried out to evaluate the attachment and growth of cells on the scaffold at different incubation periods. Mouse bone marrow stromal cells adhered and grew on the electrospun fibrous scaffold prepared from eri silk fibroin, and the cell density increased with increasing incubation periods.

Nanometer scale nickel phosphide particles (Ni 2 P and Ni 12 P 5 ) were synthesized via a mild hydrothermal method with red phosphor and nickel chloride as raw materials. X-ray diffraction, energy dispersive spectrometry, transmission electron microscopy, scanning electron microscopy and differential thermal analysis–thermogravimetric analysis were employed to characterize the resulting products. The results showed that the as-prepared products were well crystallized and particle sizes ranged from 10 to 40 nm. Investigation of raw material ratios and initial pH of the reaction system showed increasing P/Ni ratio did benefit the formation of Ni 2 P but went against obtaining Ni 12 P 5 and nano-particles were obtained only in an alkaline environment. Subsequent differential thermal analysis–thermogravimetric analysis indicated that Ni 2 P remained as the major phase till 500 °C in an air atmosphere.

This paper reports the synthesis and characterization of CeO 2 nanoparticles via a simple and cost-effective co-precipitation method using cerium (III) nitrate hexahydrate, ammonium carbonate, cetyltrimethylammonium bromide (CTAB) and polyvinyl pyrrolidone (PVP) as the starting chemicals. The precursor was calcined at 600 °C for 2 h to obtain CeO 2 nanoparticles. The X-ray diffraction and Fourier transform infrared spectroscopy analysis results indicated that the calcined CeO 2 sample has the fluorite structure of CeO 2 and adding surfactant increases the obtained CeO 2 amount. Transmission electron microscopy revealed that the CeO 2 samples consist of crystalline particles of 5–8 nm which are weakly aggregated and using the surfactants further decreases the agglomeration. The effects of PVP in decreasing the crystallite size and agglomeration, as well as, increasing the obtained CeO 2 amount have been greater than for CTAB.