Volume 30, Issue 1-2

The remelting of automobile scrap, containing galvanized steel, in an electric arc furnace (EAF) results in the generation of a dust, which contains considerable amounts of zinc and other metals. Typically, the amount of zinc is of significant commercial value, but the recovery of this metal can be hindered by the varied speciation of zinc. The majority of the zinc exists as zincite (ZnO) and zinc ferrite (ZnFe 2 O 4 ) or ferritic spinels ((Zn x Mn y Fe 1– x–y )Fe 2 O 4 ), but other zinccontaining species such as zinc chloride, zinc hydroxide chlorides, hydrated zinc sulphates and zinc silicates have also been identified. There is a scarcity of research literature on the thermodynamic aspects of the formation of these zinc-containing species, in particular, the minor zinc-containing species. Therefore, in this study, the equilibrium module of HSC Chemistry ® 6.1 was utilized to calculate the types and the amounts of the zinc-containing species. The variables studied were: the gas composition, the temperature and the dust composition. At high temperatures, zincite forms via the reaction of zinc vapour with oxygen gas and the zinc-manganese ferrites form as a result of the reaction of iron-manganese particles with zinc vapour and oxygen. At intermediate temperatures, zinc sulphates are produced through the reaction of zinc oxide and sulphur dioxide gas. As room temperature is approached, zinc chlorides and fluorides form by the reaction of zinc oxide with hydrogen chloride and hydrogen fluoride gases, respectively. Zinc silicate likely forms via the high temperature reaction of zinc vapour and oxygen with silica. In the presence of excess water and as room temperature is approached, the zinc sulphates, chlorides and fluorides can become hydrated.

An electron beam melting technique under high vacuum is known to be effective for the removal of phosphorus from silicon, however, the rate of removal is not yet adequate. In order to improve the removal rate, the effects of four experimental factors on this rate were investigated. Raising temperature of the surface of molten silicon provide effective, neither residual gas pressure in a vacuum chamber nor stirring molten silicon improve the rate, while supplying reactant gas to molten silicon had some effect.

In this work, the feasibility of using an industrial fluidized bed furnace to perform low temperature thermochemical treatments of austenitic stainless steels has been studied, with the aim to produce expanded austenite layers with combined wear and corrosion resistance, similar to those achievable by plasma and gaseous processes. Several low temperature thermochemical treatments were studied, including nitriding, carburizing, combined nitridingcarburizing (hybrid treatment), and sequential carburizing and nitriding. The results demonstrate that it is feasible to produce expanded austenite layers on the investigated austenitic stainless steel by the fluidized bed heat treatment technique, thus widening the application window for the novel low temperature processes. The results also demonstrate that the fluidized bed furnace is the most effective for performing the hybrid treatment, which involves the simultaneous incorporation of nitrogen and carbon together into the surface region of the component in nitrogen and carbon containing atmospheres. Such hybrid treatment produces a thicker and harder layer than the other three processes investigated.

In this study, the effects of density profile and hot press diagram on the technological properties of particleboard were analyzed. Physical and mechanical properties of particleboards were evaluated. Density profile was found a main parameter affecting quality properties of particleboard. While increasing entrance pressure improved the modulus of rupture and elasticity, and thickness swelling of the panels, increasing exit pressure was found to be effective on the bonding strength and thickness swelling. Exit pressure did not statistically affect the bending properties. Decreasing feeding speed of the hot press significantly improved all of the properties. While high surface density improved the modulus of rupture and elasticity, and thickness swelling, high core density caused better internal bond strength and thickness swelling. Entrance pressure was found to be effective on the surface density of particleboard. Exit pressure did not statistically affect the surface density, however, increased the core density.

In this study, the effect of cooling rate and heat treatment on the microstructural and mechanical characteristics such as microhardness of low-carbon microalloyed steel was investigated by means of optical microscopy and Vickers hardness tests. The cooling rates were controlled by introducing air-cooling, furnace-cooling, water-quenching and liquid nitrogen quenching. The obtained results showed that the difference of cooling rates and the heat treatments significantly affect the microstructure and mechanical properties of steels. These tendencies were dominant in liquid nitrogen cooled for 1073 K at 4 h and 1273 K heat treatment processes.

The oxidation behavior has been studied under both dry and wet oxidation atmosphere at 873 K to 1073 K. In dry atmosphere the oxidation resistance of these alloys has been described by the formation of a protective oxide FeCr 2 O 4 at 873 K to 973 K. At 1073 K, the kinetics are parabolic with fast growing oxide leading to spalling of oxide for P92 alloy. Oxide scale formed in air was protective with a chromium rich scale at 873–973 K, while double layered oxides were formed at 1073 K with iron oxide an outer layer and inner Cr-rich spinel FeCr 2 O 4 . In wet atmosphere oxide scale was reasonably different. The oxide layer showed porous in wet atmospheres where as dense oxide layer formed during dry oxidation. The oxidation rate of P92 alloy is about 3, 2 and 1 orders of magnitude higher than the P9, P91 and E911 alloys in wet atmospheres.

Magnesium and its alloys are attractive materials for use in automotive and aerospace applications because of their low density and good mechanical properties. However, difficulty in forming magnesium and the limited number of available commercial alloys limit their use. The present work reviews the efforts to improve the attractiveness of magnesium through non-traditional processing, and presents the results of producing AZ31 magnesium alloy via powder metallurgy P/M. P/M can be used to alleviate the formability problem through near-net-shape processing, and also allows unique chemical compositions that can lead to the development of new alloys with novel properties. The feasibility of producing magnesium powder metallurgy products utilizing the industrially dominant process of mixed powder blending, uni-axial die compaction and controlled atmosphere sintering was investigated. An alloy composition based on the commercial Mg alloy AZ31 (3 mass % Al, 1 mass % Zn) was used to facilitate the comparison to similar wrought product. The optimal processing conditions (compaction pressure, sintering time and temperature) were found to maximize sintered density and mechanical properties. Results show that sintering temperature is one of the major variables that has an appreciable effect on the final properties of the samples, and that the effects of compaction pressure and sintering time were insignificant. The material showed poor tensile properties, with a maximum tensile strength of 32 MPa due to lack of sufficient densification. The latter was related to the lack of liquid phase formed during sintering of Al/Zn magnesium alloys and the barrier to diffusion due to the presence of the stable magnesium surface layer.

Compression tests of magnesium alloy Mg-3Al-1Zn (AZ31) at different temperatures and strain rate were made on plastometer Gleeble 3800. Deformation behaviour and particularly shape of stress-strain curves of the alloy AZ31 differ significantly at low and high values of Zener–Hollomon parameter Z . The border between these areas was determined mathematically as Z = 2.9E+13 s –1 . While the calculated activation energy Q was for both these areas practically identical (157 or 155 kJ mol –1 ), mathematical description of coordinates of the peak stress differs considerably. Regression and statistical analysis of experimental data have confirmed unequivocally, that it was impossible to describe by a uniform equation the whole set of data (i.e. traditional stress-strain curves, as well as those with atypical initial stage, given by the massive twinning). That's why two mathematical models were developed enabling prediction of the flow stress of investigated magnesium alloy in dependence on temperature, strain and strain rate, with inclusion of the influence of dynamic recrystallisation.

The corrosion behavior of the alloy NF616 covered with a film of molten 0.55ZnCl 2 -0.45KCl (mole fraction), similar to that found in waste incineration plants, was examined in air at 673 K by the electrochemical-impedance spectroscopy (EIS) technique. For comparison, the corrosion of the same material immersed in the deep salt was also studied. The electrochemical impedance spectra for the corrosion of NF616 beneath a film of fused salt consisted of a semi-circle at high-frequency port and a line at low-frequency port indicating a diffusion-controlled reaction. Contrary to the corrosion beneath salt film, the corrosion of the alloy in deep molten salt presented the characteristics of two capacitive loops during all the duration of the experimental test. This different EIS features under two corrosion conditions may be related to the different supply of oxygen amount. In this paper, suitable equivalent circuits representing the corrosion of the alloy under the two different corrosion conditions are proposed to fit the corresponding impedance spectra and electrochemical parameters in the equivalent circuits are also calculated.

Two new samples of polyamide-montmorillonite reinforced nanocomposites based on 4,4′-azodibenzoic acid were prepared by a convenient solution intercalation technique. Polyamide (PA) 4 as a source of polymer matrix was synthesized by the direct polycondensation reaction of 4,4′-azodibenzoic acid 2 with 4,4′-diamino diphenyl sulfone 3 in the presence of triphenyl phosphate (TPP), CaCl 2 , pyridine and N-methyl-2-pyrrolidone (NMP). Morphology and structure of the resulting PA-nanocomposite films 4a and 4b with 10 and 20% silicate particles were characterized by FTIR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of clay dispersion and the interaction between clay and polymeric chains on the properties of nanocomposite films were investigated by using Uv-vis spectroscopy, thermogravimetric analysis (TGA) and water uptake measurements.

Material degradation and ageing is of particular concern for fossil fuel fired power plant components. New techniques/approaches have been explored in recent years for Residual Life assessment of aged components and material degradation due to different damage mechanism like creep, fatigue, corrosion and erosion etc. Apart from the creep, the high temperature corrosion problem in a fossil fuel fired boiler is a matter of great concern if the fuel contains sulfur, chlorine sodium, potassium and vanadium etc. This paper discusses the material degradation due to high temperature corrosion in different critical components of boiler like water wall, superheater and reheater tubes and also remedial measures to avoid the premature failure. This paper also high lights the Residual Life Assessment (RLA) methodology of the components based on high temperature fireside corrosion. of different critical components of boiler.

Wear behaviour of special brass produced through two different methods (centrifugal and sand casting) was investigated. The wear tests were carried out at sliding velocities of 0.2 ms –1 , 0.3 ms –1 , 0.4 ms –1 and 0.5 ms –1 and under 10 N, 20 N, and 40 N variable loads. The sliding distance was 600 m for all the tests. A pin-on-disc device with round specimen inserts was used to conduct friction and wear tests in which the friction coefficient, the contact temperature and the linear wear of the tribo-pairs were continuously recorded against sliding distance. Two different materials were used as the counterparts, namely ferritic ductile iron equivalent to GGG40 and pearlitic ductile iron equivalent to GGG60. The microstructures and wear scars of the brass specimens were examined by optical, scanning electron microscopy (SEM) and X-ray microanalyses by EDAX. A correlation between hardness and wear volume rate was established for the investigated centrifugally cast and sand cast brass specimens. The volume rate of specimens produced by sand casting method was generally found to be higher than those of centrifugally cast specimens. Ferritic ductile counterpart led to higher wear volume rate than pearlitic ductile counterpart for the both specimens. Severe abrasive wear scars were observed for the sand cast specimens/ferritic ductile iron pair. However, severe adhesive wear took place for the centrifugally cast specimen/pearlitic ductile iron pair.

To protect Fe-Cr-Ni based alloy from high temperature corrosion in carbon containing atmosphere at elevated temperature, alumina coating was prepared on the Fe-Ni-Cr alloy substrate by pack cementation and oxidation. Results showed that a surface FeAl layer formed after the pack cementation process, and an Al 2 O 3 coating formed by selective oxidation of the FeAl layer. The coating adhered tightly to the FeAl layer without any cracks or porous inbetween them. By the oxidation process the catalytic elements such as Fe and Ni were remarkably reduced from the surface. Further anti-coking test indicated that the alumina scale could successfully inhibit the outward diffusion of catalytic elements and showed excellent coking resistance.

The prediction of evaluation a U- and V-shaped cracks on the surface and subsurface of a continuously cast steel slab, is investigated during hot rolling. The numerical simulation is carried out by means of FE-code DEFORM 3D. Therefore, an algorithmic decision tree was developed by the C 4.5 program and applied in prediction of surface and subsurface defects behaviour during the numerical simulation of hot rolling. Cracks were selected as a transversal and longitudinal to the rolling direction. In addition to the transversal and vertical U- and V-shaped cracks on the surface; subsurface defect, referred as “circle hole”, on the side part of workpiece were evaluated. In terms of surface defects evolution, U-shaped cracks show a deteriorating influence during hot rolling. On the basis of the algorithmic decision tree established, the prediction of cracks evolution (defined before plastic deformation process) during hot rolling is examined.

The development of stabilizing oxides during foaming process has been studied. The investigation of microstructure shows that the surface oxide films on the aluminum powder particles were ruptured after compaction. Pore nucleation results in a comprehensive shearing of oxides. After complete melting of powder particles at which a continuous liquid is dominant, the oxides move through the cell walls and Plateau borders by convection, due to pore growth, and connected to each other due to their tangled shape, forming strong local clusters or networks, leading to foam stability.

In this paper an effect of different temperatures on mechanical properties and creep responses of 50CrMo4 steel were considered. Both mechanical properties and creep behavior were determined by uniaxial tests. Curves representing specimen elongations as well as reduction in specimen areas at elevated temperatures are also shown. Creep curves as the responses of the considered material subjected to uniaxial stresses at high temperatures are also demonstrated. The notch impact test was carried out using Charpy impact machine and fracture toughness was calculated. The experimentally obtained data may be of significant interest in structure design procedure.

Dispersion strengthened materials belong into the group of composite materials, which are made mainly by powder metallurgy. Their structure has a polycrystalline matrix, in which dispersion particles are incorporated, mainly oxide, carbide and nitride type. The Al-C systems belong among modern materials designed for work at elevated temperature. This work focused on a study of the microstructure in containing 4 vol.% Al 4 C 3 . The microstructure was analyzed X-ray diffraction line profile analysis. It is a powerful and convenient method to probe the microstructural characteristics of composites materials. In this paper the development of texture and size of crystallites in composite material dependence on annealing time and temperature was examined. Texture of the experimental materials was analyzed by means texture coefficient (TC). TC for the (220) plane in Al 4 C 3 composite indicate the presence of markedly deformed texture. Size of crystallites depends on annealing temperatures and times.

Lead-free solders with copper represent possible substitution for standard lead-tin solders. For the complete definition of the properties of the ternary Bi-Cu-In system, there were performed the investigation of micro structures, hardness by Brinel, and electric conductivity of the alloys. In the range of this ternary system, numerous alloys were tested for three vertical sections, with molar ratio Sb : Cu = 1, Cu : In = 1, Sb : In = 1. The micro structures of the alloys were investigated by application of optic microscopy. By application of CALPHAD method, and software package PANDAT 8.1. there were calculated the isothermal cross sections at 298 K and 673 K. The experimentally obtained phase compositions in microstructures are in a good agreement with phases on calculated cross sections.

New poly(amide-imide)-montmorillonite reinforced nanocomposites containing Bis(4-N-trimellitylimido) diphenyl ether moiety in the main chain were synthesized by a convenient solution intercalation technique. Poly(amide-imide) (PAI) 4 was synthesized by the direct polycondensation reaction of Bis(4-N-trimellitylimido) diphenyl ether 3 with 4,4′-diamino diphenyl ether 2 in the presence of triphenyl phosphite (TPP), CaCl 2 , pyridine and N-methyl-2-pyrrolidone (NMP). Morphology and structure of the resulting PAI-nanocomposite films 4a and 4b with 10 and 20 mass% silicate particles respectively, were characterized by FT-IR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The properties of nanocomposites films were investigated by using Uv-vis spectroscopy, thermogravimetric analysis (TGA) and water uptake measurements.

In this investigation, ignition processes of the methane and the propane using a high-temperature oxidizer ( T oxi > T ai ) with a varying oxygen concentration z O2 - the HTAC (High Temperature Air Combustion) conditions, applying a constant-volume bomb (CVB) was investigated. The influence of the initial temperature of the oxidizer T oxi was analyzed and discussed. It is shown that in order to achieve an effective reaction of ignition the oxidizer temperature needn't be maximized. Detailed evolution of ignition delay time with equivalence ratio τ ig was presented. It can be concluded that increment of oxygen concentration z O2 in oxidizer results in decrease of τ ig . Trials with propane are characterizing lower values of ignition delay time τ ig in comparison with methane.

By means of the measurement of creep curves and microstructure observation, an investigation has been made into the microstructure evolution of γ ′ phase in [001] orientation single crystal nickel-base superalloy during tensile creep. Results show that, after full heat treatment, the microstructure of the single crystal nickel-base superalloy consists of the cubical γ ′ phase embedded coherently in the γ matrix, and arranged regularly along the 〈100〉 orientations. During tensile creep, the cubical γ ′ phase in the alloy is transformed into the rafted structure along the direction vertical to the applied stress axis. During steady state creep, the strain rate of the single crystal nickel-base superalloy is controlled by the climbing of dislocations in the ranges of the applied temperatures and stresses. After crept up to fracture, various morphologies of the rafted γ ′ phase are displayed in different regions of the specimen, and the coarsening and twist extent of the rafted γ ′ phase increase as the distance from the fracture decreases, which is attributed to the increment of the effective stress and strain extent in the necked region.

A method for the joining of a Ti 52 Al 46.8 Cr 1 Si 0.2 Titanium Aluminide alloy by laser powder welding is presented. The technique acts to join materials by consolidating powder with focused laser beam to form weld beads that fill a V joint. In order to avoid the occurrence of residual thermal stresses and hence cracking of the brittle material, the weld plates were heated to a temperature of 1173 K (= 900 °C) by an ohmic heating device, welded and then slowly cooled to produce pore and crack free welds.

The ternary carbonate eutectic mixture of Li 2 CO 3 , K 2 CO 3 and Na 2 CO 3 as a heat transfer and storage medium has excellent thermophysical properties, but with high viscidity as compared with some other inorganic salts such as chlorides and nitrates. The addition of chlorides or fluorides to molten carbonates may improve their fluidity, but possibly making the melt become more corrosive. In this study, the corrosion behavior of type 304, 310 and 316 stainless steels in an eutectic (Li,Na,K) 2 CO 3 melt with and without an eutectic mixture of NaCl and KCl at 973K in air have been examined. The experimental results indicated that 310 steel shows a much better corrosion resistance in molten carbonates than both 304 and 316 steels, due to the formation of a continuous LiCrO 2 scale. The addition of chlorides to carbonates melt accelerated the corrosion of the steels, especially 310 steel, producing scales with more porosity.

Arsenic removal from molten steel by the calcium iron alloy and rare earth alloy (48% Ce, mass percentage) has been exploringly studied at 1853 K. It is found that the addition of rare earth alloy makes the arsenic removal more effective. This phenomenon may originate from the facts that the addition of Ce lowers the activity coefficient of sulfur, and the low activity of sulfur restrains the reaction of calcium iron alloy and sulfur, which promotes the arsenic removal reaction. Thus more rare earth alloy addition results in the higher arsenic removal ratio. However, due to the high cost of rare earth alloy, increasing the quantity of calcium iron alloy may be a choice to improve the arsenic removal effect in molten steel. It is found that when the weight ratio of rare earth alloy/steel is fixed at 5%, the arsenic removal ratio increases with the calcium iron alloy amount increasing. When the weight ratio of calcium iron alloy/steel is 18 %, the arsenic removal ratio is 50 %. This result may be acceptable for the industrial purpose.

In this study, wear characteristics of titanium and titanium alloyed materials produced with mechanical alloying/milling (MA/MM) method were studied. In production of titanium and titanium alloyed materials, sponge titanium, gas atomised titanium powder and pre-alloyed Ti6Al4V alloy powder were used. The produced materials were characterised by scanning electron microscope, optical microscope, X-rays diffractometer (XRD) and EDS. The wear tests were carried out on a pin-on-disc type wear device under three different loads (15–30–45 N), four different sliding distances (500–1000–1500–2000 m) and a sliding speed of 1 ms –1 . The results showed that no porosity was found on the gas atomised titanium and the Ti6Al4V alloy while very low amounts of micro porosity were formed on the sponge titanium samples. EDS analysis, on the other hand, revealed some Fe contamination on the materials, arising from the milling environment. It was seen that the hardness values of the samples produced from the gas atomised titanium powder were higher either than the samples produced from the sponge titanium, or the samples produced from the Ti6Al4V alloy. The fact that the wear losses obtained for the samples produced from the TiAl4V and gas atomised titanium powders were lower when compared to the sponge titanium. This was considered as the result of porous structure of sponge titanium.

Coatings are seen a promising way to improve the corrosion resistance of relatively cheap power plant steels to enable higher steam temperatures than currently in use. In this research, 9–12% Cr steels P91 and HCM12A are coated with aluminium diffusion coating by a slurry method and exposed for 336 hours at 833 K and 883 K to atmospheres containing varying amounts of O 2 , H 2 O, HCl and SO 2 . Corrosion behaviour of the coated steels is compared to that of those steels in an uncoated condition. Characterization is performed by weighing, SEM + EDS and XRD. The results show that corrosion resistance of P91 and HCM12A is significantly improved by the aluminium diffusion coating at high temperatures in atmospheres containing HCl and SO 2 . The corrosion rate of the aluminized specimens slightly increases with increase in test temperature but remains virtually the same irrespective of the composition of the atmosphere. On the other hand, the corrosion rate of the uncoated specimens is dependent on both the atmosphere and the temperature. The steels undergo active oxidation that results in formation of non-protective, thick and layered scales in HCl containing atmospheres. SO 2 addition slightly decreases the corrosion rate although it is anyway higher than that in SO 2 containing atmosphere without HCl.

Polyvinylidene fluoride-co-hexafluoropropylene (PVdF-co-HFP) with conducting polyaniline (PAni) was studied to measure free-volume intensity ( I 3 ), orthopositronium (o-Ps) lifetime ( τ 3 ), and Doppler momentum distribution parameters (S and W) as a function of temperature varying from 273 to 373 K and PAni weight percentage varying from 1%–20% using the techniques of Positron Annihilation Lifetime Spectroscopy (PALS) and Doppler Broadening Annihilation Radiation (DBAR). It has been observed that the free-volume intensity and the o-Ps lifetime increased sharply with PAni weight percentage up to 4% after which decreased slowly. DBAR momentum distribution parameters behaved similarly as well and it's assumed that in the studied samples one-type defect was to exist. The thermal expansion coefficient also as a function of PAni weight was extracted from PALS data.