Volume 101, Issue 7

By means of the CALPHAD (CALculation of PHAse Diagram) technique, the Pt–Zr system was critically assessed. The solution phases (liquid, bcc, fcc and hcp) are described with the substitutional model. The intermetllic compounds Pt 4 Zr, Pt 4 Zr 3 , αPtZr and Pt 3 Zr 5 are treated as the formula (Pt,Zr) m (Pt,Zr) n by a two-sublattice model with the elements Pt and Zr on the first and the second sublattices, respectively. A two-sublattice model (Pt,Zr) 0.5 (Pt,Zr) 0.5 is applied to describe the compound βPtZr with CsCl-type structure (B2) in order to cope with the order–disorder transition between bcc solution (A2) and βPtZr (B2). Another two-sublattice model (Pt,Zr) 0.75 (Pt,Zr) 0.25 with Ni 3 Ti-type structure (D0 24 ) is applied to describe the compound Pt 3 Zr in order to cope with the order–disorder transition between hexagonal close-packed (A3) and Pt 3 Zr (D0 24 ). The compound Pt 10 Zr 7 is treated as a stoichiometric compound. A set of self-consistent thermodynamic parameters of the Pt–Zr system was obtained.

Optimized thermodynamic data, successfully used for phase diagram calculations of constitutive binary systems, were used for prediction of phase equilibria in the ternary Ga–Sb–Sn system. The projection of the liquidus surface, invariant equilibria and three vertical sections with molar ratios Sb:Sn = 1, Ga:Sn = 1 and Ga:Sb = 1 of the Ga–Sb–Sn ternary system were calculated using the CALPHAD method. Alloys, situated along three selected vertical sections, were investigated using differential scanning calorimetry. The experimental phase equilibria data from this work and literature were compared with calculation results.

The viscosity of the ternary Ag–Au–Sn system has been calculated using two different semi-empirical models which apply universal parameters valid for all metals. Experimental values of the integral enthalpy of mixing were used as inputs. The theoretical results are represented as iso-lines of the excess viscosity. Additional calculations based on a geometrical model fitted to the experimental viscosities of the binary systems were applied in order to discuss the physical significance of the results predicted for the ternary system.

Tin–bismuth alloys are under intense consideration as favourable lead-free solders for consumer electronics and telecommunications. The electrical and thermal conductivity, viscosity, surface tension and density were studied in a wide temperature range above the liquidus. The scaling relations have been proposed. A comparison with data available in literature is given.

Transition metal dichalcogenides have a layered structure and are therefore promising self-lubricating films. They can be considered as potential substitutes for carbon based films in various environmental conditions. In this work, a comparative atomic force microscopy study of co-sputtered Mo–Se–C and W–S–C films is performed to evaluate their nanotribological performances. Both films are alloyed with carbon. The microstructural features of these films are characterised using scanning electron microscopy and X-ray diffraction. The hardness and elastic modulus of these films are measured employing nanoindentation. The topography, friction forces and pull off forces of the films are evaluated by means of atomic force microscopy and force spectroscopy. The results show that the roughness parameters of Mo–Se–C films are lower than that of W–S–C films at high carbon content whereas the reverse is true at low carbon content. Adhesion forces of these films based on pull-off force measurements show that Mo–Se–C films have higher pull off forces than W–S–C films. An atomic force microscopy technique is developed to estimate microscopic values of friction coefficients and to characterise the nature of surface changes due to nanotribological experiments. The friction coefficient of Mo–Se–C films is higher than that of W–S–C films at low carbon content and these friction coefficients are comparable at high carbon content.

Fe-substituted ZnWO 4 as a possibleopticalmaterialhas someinteresting properties. We report a comparison of luminescence properties of pure ZnWO 4 and Zn 0.99 Fe 0.01 WO 4 powders synthesized with aqueous salt metathesis reaction in this work. The experimental results indicated that the Fe-substitution results in decreases in the crystallinity and grain size. In comparison with the pure ZnWO 4 , the Zn 0.99 Fe 0.01 WO 4 powder shows a small intensity of blue-green emission band, significantly smaller intensity of emission peaks at longer wavelength, large half-widths of the emission bands, and a red emission band at a range of 590–680 nm. The results clearly indicate that the red emission band is related to the Fe 3+ cation.

Intermittent electromagnetic radiation (EMR) emissions from metals and alloys during deformation under unrestricted quasi-static compression are reported in this paper. The end surface conditions of the compressing platens, whether lubricated or unlubricated, influence the EMR emission characteristics. The EMR emissions under compression show shape anisotropy. The first EMR emission invariably occurs near the yield. The EMR emission characteristics are also influenced by the crystal structure. During axial compression, dead metal zones formed on the top and bottom portions of the specimens possibly generate a climbing motion of edge dislocations in the radially outward mid-regions. During the climbing motion, these edge dislocations form accelerated electric line dipoles and emit electromagnetic radiation. These EMR emissions can be used to evaluate the degree of damage in metallic components under compression.

TiC particle reinforced Fe 3 Al composites were produced with varying volume fraction of TiC powders. The effect of the TiC fractions and distribution on the properties of the composites was investigated. The composite containing 30 vol.% TiC had hardness and bending strength values of 86 HRA and 1340 MPa, which were 10% and 57% greater than those of the unreinforced Fe 3 Al, respectively. Microscopic examination of the composite showed TiC particles with grain size ranging from 50 to 100 nm were homogeneously dispersed in Fe 3 Al matrix, the larger TiC particles with sub-micrometer size were mainly located at grain boundaries and the smaller ones were within matrix grains.

An investigation was carried out to examine the influence of two step austempering on microstructural parameters and the wear behaviour of austempered ductile iron. Ductile iron was austenitised at 900°C for 30 min, and then austempered successively at two different temperatures. It was first austempered at 300°C for different durations from 2 min to 30 min and subsequently austempered at 400°C for 2 h, after which it was quenched to room temperature. Resulting microstructures were characterised through optical microscopy and X-ray diffraction. Mechanical properties were studied through hardness measurement and tensile testing. Wear studies were carried out using a pin-on-disc machine. Wear rate was found to decrease with increasing time at the first step temperature of 300°C. At short austempering times at 300°C, the amount of austenite was instrumental in improving the wear resistance through formation of deformation induced martensite. Wear rate was found to depend on yield strength, austenite content and its carbon content.

In this work, forming and fracture limit diagrams have been experimentally evaluated for aluminium 5052 alloy sheet annealed at four different temperatures namely 200°C, 250°C, 300°C and 350°C. With the help of these diagrams, the safe range which avoids necking and fracture during forming of aluminium 5052 alloy sheets was examined and the effect of annealing temperature on this range and other parameters namely microstructure, tensile properties and formability parameters were studied. The forming limit diagrams of aluminium 5052 alloy sheets annealed under different temperatures were also examined with respect to the crystallographic texture point of view. The crystallographic textures were then correlated with normal anisotropy of the sheet metal. It was found that the formability of aluminium 5052 alloy annealed at 350°C possessed good formability, optimal texture and high normal anisotropy value.

The main objective of this study is to investigate the suitability of fly ash and basaltic pumice as additives in the production of high quality clay fired bricks. Clay bricks with/without additives were produced adding equal amounts of fly ash and basaltic pumice, separately and together, with the rates of 5, 10 and 20 wt.%. Each sample was fired at 700, 900 and 1 050°C for 8 h. Bulk density, harmful magnesia and lime, shrinkage, water absorption, compressive and flexural strength, freezing and thawing tests were carried out. The test results were compared with the standard values and they were found to be satisfactory. Finally, it was concluded that both fly ash and basaltic pumice were suitable admixtures and could be used efficiently in fired brick production.

Huge amounts of cotton and textile ash waste are disposed of by countries all over the world. The majority of cotton wastes and textile ash wastes is expelled in such a way as to cause serious environmental problems. The present study involves experimental research investigating the potential use of cotton and textile ash wastes combination for producing a new and lightweight composite building material with good insulation properties. The results showed that the cotton and textile ash waste bricks fulfill the compressive strength and heat conductivity requirements of the ASTM and Turkish Standards. A cotton and textile ash waste brick house has been found to be superior to a concrete brick house for regulating indoor temperatures. The production process can be easily applied in conventional brick plants. The product is a light weight composite which can be used for making bricks and wall and ceiling panels with good insulation properties.

To investigate the effects of homogenizing and aging treatments on the microstructure and microhardness of an Nb-silicide based ultrahigh temperature alloy, coupons were homogenized at 1 300–1 600°C for 50 h, and then aged at 1 100°C for 50 h. The results show that the phase constituents of the heat-treated alloys are still Nb solid solution and silicides, α-(Nb,X) 5 Si 3 phase forms after heat-treatments at temperatures above 1 500°C. With the increase in heat-treatment temperature, the original big polygonal and plate-like silicides gradually break into small ones, and the amounts of retained typical lamellar and rod-like eutectic colonies reduce clearly. The variation of partitioning ratios of alloying elements between Nb solid solution and silicides causes the change in microhardness of the alloy. 1 500°C/50 h + 1 100°C/50 h is an optimum heat-treatment process.

The thermal expansion of the Fe-(30–40) wt.% Ni-(20–30) wt.% Co-(6–10) wt.% Cr alloys matches closely with yttria-stabilized zirconia, often used as electrolyte in solid oxide fuel cells. At the best fit, the difference in the thermal expansion coefficients does not exceed 0.7·10 –6 K –1 in the range from room temperature to ~500°C. Significant mismatch begins above 600°C, but the internal stresses this mismatch might cause in the metallic component of the metal/ceramics junctions remain significantly below the yield strength up to the temperatures exceeding the starting temperature of relaxation processes by ~180–240°C. The above alloys are phase stable so that no phase transformations are expected at the cell operating temperatures. Their resistance to corrosion attacks in cathodic and anodic environments is comparable to ferritic steels containing 25–30% chromium. The transfer of chromium from the alloys containing 34% Ni, 30% Co and 6–14% Cr into the La 0.6 Sr 0.4 MnO 4 cathode material occurs after 400–600 h heating at 900°C. Chromium penetrated to a depth of 20 μm at most.

The magnetic materials studied most by current international projects are based on ultrafine particles, in solid or liquid matrix. In order to design a good magnetic material based on nanoparticles, it is required to know their magnetic properties. Magnetic measurements represent a relatively difficult area of electrical engineering. In order to find the magnetic properties of nanometric magnetic powders, it is very difficult to use a traditional measurement method (e.g. using a toroidal coil). In this case, it is advisable to use compensation methods. In this paper, we present a study, based on simulation, of the compensation coil installation used to obtain the magnetisation curve of the ferrite nanometric powders of NiZn to 50 Hz. The experimental installation consists of a magnetisation circuit with two identical coils, connected in opposition, and a secondary circuit used to compensate the voltages induced in the identical probe coils, without sample. The parameters for which we obtain good secondary circuit compensation are simulated by the Electronics Workbench program – version Multisim 8.