Band 107, Heft 10

A method is proposed for calculation of the pseudobinary phase diagram associated with the dynamic transformation of austenite to ferrite. Here the driving force is taken as the difference between the austenite flow stress at the moment of initiation and the yield stress of the fresh Widmanstätten ferrite that takes its place. The energy opposing the transformation consists of the Gibbs energy difference between austenite and ferrite at temperatures above the A e 3 and the work of accommodating the shear displacements and dilatation associated with the phase change. A metastable phase diagram is calculated for a 0.30 wt.% Mn-0.01 wt.% Si steel by balancing the driving force against the three obstacles. The results show that, under dynamic conditions, the ferrite phase field extends all the way from room temperature to that for the formation of delta ferrite.

The phase equilibria of the Co–Ni–Zr ternary system at 1 000 °C, 1 100 °C and 1 200 °C were experimentally investigated by means of back-scattered electron imaging, electron probe microanalysis and X-ray diffraction on the equilibrated ternary alloys. In this study, no ternary compound is found. The (αCo, Ni) phase region extends from the Ni-rich corner to the Co-rich corner with small solubility of Zr at three sections. At 1 000 °C and 1 100 °C, Ni 5 Zr, Co 2 Zr and Ni 10 Zr 7 phases have large solid solution ranges, but Ni 10 Zr 7 phase disappears at 1 200 °C. The Ni 7 Zr 2 , NiZr, Co 11 Zr 2 , Co 23 Zr 6 and CoZr phases exhibit nearly linear compounds in the studied sections, and have large composition ranges. Additionally, some differences in phase relationship exist among the above three isothermal sections.

The phase equilibria of the Ni–Sb–Zn ternary system at 600 °C have been experimentally investigated using X-ray diffraction and scanning electron microscopy coupled with energy/wavelength dispersive X-ray spectroscopy. Four ternary compounds, NiSbZn (τ 1 ), Ni 2 SbZn 2 (τ 2 ), Ni 3 Sb 2 Zn (τ 3 ) and Ni 4.6 SbZn (τ 4 ), were identified and thirteen three-phase regions were confirmed in the present work. Moreover, the maximum solubilities of Zn in NiSb and NiSb 2 were determined to be 2.0 and 1.0 at.% at 600 °C, respectively; and those of Sb in β 1 and γ were measured up to 11.8 and 5.3 at.%, respectively.

Three Mg–Al–Zn alloys, namely AZ31, AZ63 and AZ91, were subjected to high frequency cyclic loading with the aim of revealing their fatigue behaviour. AZ63 and AZ91 alloys contained discontinuous and continuous precipitates and also the intermetallic compound Mg 17 Al 12 . Samples were loaded step by step at increasing stress amplitudes at room temperature. Three characteristics of the cycled samples were investigated: the sample surface, the fatigue fracture surface and the fracture surface after the static fracture of samples. Details of the fatigue and fracture behaviour were examined using scanning electron microscopy. The significant roles of twinning and dislocation movement during the high frequency cycling are discussed. The limited plasticity of alloys estimated during the high frequency cycling is due to a decrease in the moving dislocation density entering into the thermally activated process.

This paper treats the influence of auxetic foam on the crush response and energy absorption response of square-section tubes when subjected to uniaxial quasi-static loading. The study aims at quantifying the energy absorption capability of auxetic foam-filled square tubes for variations in wall thickness, initial height, aspect ratio and slenderness ratio of the tube. The capability of simulating the crush response of auxetic foam-filled tubes using the validated numerical models is also presented. Based on the experimental results, the influence of the auxetic foam in the thin-walled square tubes was quantified in terms of energy absorption capacity, specific energy absorption and crush force efficiency. It is evident that a thicker tube filled with auxetic foam is preferable if the energy absorption level is the primary goal, yet this compromises the crush force efficiency. The outcome of this present study is the establishment of empirical models for estimating the quasi-static crushing response of auxetic foam-filled tubes with varying slenderness ratio and aspect ratio.

The growth mechanism and properties of the oxide films on iron and AISI 304 stainless steel were studied in simulated acid rain ( pH 4.5) by means of electrochemical techniques and atomic absorption spectrometry. The layer-pore resistance model was applied to explain a potentiodynamic formation of surface oxides. It was found that the growth of the oxide film on iron takes place by the low-field migration mechanism, while that on the stainless steel takes place by the high-field mechanism. Kinetic parameters were determined. Impedance measurements revealed that Fe surface film has no protective properties at the open circuit potential, while the resistance of stainless steel oxide film is very high. The concentration of the metallic ions released into solution and measured by atomic absorption spectroscopy was in accordance with the results obtained from the electrochemical techniques.

This research introduces the mechanosynthesis process for CaMoO 4 nanoparticles by using MoO 3 and CaO as initial reactants. An empirical model was developed to describe the kinetics of the reaction. X-ray diffraction was used at each step of the milling to evaluate the developed model. The experimental data and the results from the model are in good agreement. The synthesized powders in this research were characterized using X-ray diffraction, electron microscopy, dynamic laser scattering, and photoluminescence spectroscopy techniques. Photoluminescence characterizations revealed that the synthesized CaMoO 4 generated two photoluminescence emissions, at 377 nm (violet) and 515 nm (green). It was also observed that further milling of the synthesized powders changed the photoluminescence properties of the product. After 12 h of milling, the synthesized CaMoO 4 generated a novel photoluminescence emission at 564 nm. The results of this research indicate that mechanical milling can be employed to control the photoluminescent properties of CaMoO 4 .

Iron oxide nanoparticles were synthesized with Fe +2 and Fe +3 precursors in a 1 : 2 ratio by using the hydrothermal method under different reaction temperatures and alkaline conditions. The iron oxide nanoparticles were characterized for structure, morphology, optical and magnetic properties. X-ray diffraction analysis confirmed that the samples prepared at different hydrothermal temperatures exhibited a magnetite structure, the increased intensity of the peaks indicates a high degree of crystallinity. The transformation of goethite to Fe 3 O 4 structure was observed with variation of the pH value. The morphological study revealed that some samples exhibited spherical particles and some others exhibited a mixed morphology of spheres and rods. The iron oxide synthesized at 190 °C exhibited better magnetic properties due to the uniform distribution of spheres with particles size in the range, 18 – 25 nm.

In the present study, zinc selenide powder was successfully sintered using spark plasma sintering. The effect of spark plasma sintering temperature and pressure on the densification, microstructure and hardness were investigated. Relative density, microstructure, hardness and crystallographic properties of specimens were evaluated by means of the Archimedes method, optical microscopy/scanning electron microscopy, micro-Vickers and X-ray diffraction, respectively. The results indicated that temperature and pressure were the most effective parameters affecting the process. The maximum relative density (99.3%) and hardness (163 kg mm −2 ) were obtained using conditions of 1100°C for 5 min under 70 MPa. The crystallographic orientation (twinning) observed by optical microscopy was confirmed by X-ray diffraction results.

Infiltration of molten metal into ceramic performs without using external force is a new fabrication method for metal-matrix composites. In this research, the kinetics of pressureless infiltration in the processing of Al/SiC composites have been investigated. In order to improve the wettability and infiltration properties, Al-6Mg (wt.%) alloy was prepared. Also, the ceramic component was coated for 15 min using electroless copper plating at a temperature of 60 – 70 °C ( pH = 12.5) and a rate of 17 – 20 μm s −1 . Infiltration of molten aluminum into the coated ceramic perform was successfully carried out in the temperature range of 850 to 950 °C under nitrogen atmosphere. Microstructural investigations indicated a well-bonded metal–ceramic joint. Kinetic studies showed that the melt infiltration into the ceramic foam follows an S-shaped curve. The infiltration rate was specified with respect to variables such as the experiment temperature and the size of the pores of the ceramic component. The results revealed that by increasing the temperature and the size of pores, the infiltration rate increases. For infiltrating molten metal into the 10 and 30 ppi foams, activation energies of 5.902 kJ mol −1 and 7.232 kJ mol −1 are required, respectively.

The increasing need for materials with light weight, high resistance to corrosion and wear, toughness and strength, machinability, high thermal capacity etc. for various applications is unending. This demand has continued to stretch the exploitation and manipulation of various functionally graded materials (FGMs) and their production methods. This study explores one of the FGM production processes called the centrifugal casting technique (CCT). The centrifugal casting process has several potential advantages over traditional casting methods. This study provides information regarding the basic functionally graded production methods and their applications and also discusses categories of CCT, evolution and process parameters.