Volume 105, Issue 12

Triple lines are the lines of intersection of three interfaces, either external interfaces or internal interfaces of a bulk material. They have been recognized as important microstructural features with specific kinetic and thermodynamic properties. Utilizing atomic force microscopy, the line tensions, i.e. the energy of grain boundary-free surface triple lines and grain boundary triple junctions for different crystallographic systems in copper were determined. The line tension of grain boundary triple junctions in copper was found to be positive and of the order of 10 −9 J m −1 . Junctions including low energy boundaries, twin boundaries and low angle boundaries revealed a substantially lower line tension than triple junctions comprised only of random high angle boundaries. A simple model based on a constant grain boundary energy density is proposed to account for the orientation dependence of triple line energy.

(Mg 24 Ni 10 Cu 2 ) 100– x Nd x ( x = 0, 5, 10, 15, and 20) alloys with nanocrystalline and amorphous structures were prepared by melt-spinning. X-ray diffraction and high-resolution transmission electron microscopy reveal that the as-spun Nd-free alloy displays an entirely nanocrystalline structure, whereas the as-spun Nd 15 alloy, differing from Nd 0 alloy, exhibits nanocrystals embedded in an amorphous matrix. This suggests that the addition of Nd facilitates the amorphous formation ability of the alloys. Melt spinning significantly improves the gaseous and electrochemical hydrogen storage kinetics of the alloys. Furthermore, melt spinning enhances the diffusion ability of hydrogen atoms in the alloy, but it impairs the charge-transfer reaction on the surface of the alloy electrode, which gives rise to the high-rate dischargeability of the alloy electrode, first mounting up and then going down with the increase in spinning rate.

A binary alloy of iron containing 0.17 wt.% of phosphorus has been heat treated under a variety of conditions in order to see whether the segregation of phosphorus to grain boundaries can be controlled. The alloy transforms fully into ferrite. It is found that the majority of solute found at the ferrite grain boundaries has its origins in the temperature range where phase transformation occurs, in other words, phosphorus that is accumulated and dragged with the growing ferrite–austenite transformation front. As a consequence, it cannot be suppressed using cooling rates as high as 400 K s −1 .

The aim of the present work is to investigate the effects of low temperature aging and thermomechanical treatments on the transformation and deformation behavior of an Ni-rich NiTi alloy. One sample of solution treated Ti-51.5 at.% Ni shape memory alloy was aged at 300°C for 1 hr. The other solution annealed sample, was firstly cold rolled to a reduction of 20% and then aged at 300°C for 1 hr. Applying these treatments, samples showed R-phase transformations in the absence of B19′ phase formation according to differential scanning calorimetry curves. By applying 20% cold reduction in area prior to aging, almost complete recovery of strain was observed and pseudoelasticity improved significantly compared to the conventional aged sample. Results of thermal analysis and tensile tests suggest that the observed pseudoelasticity for the thermomechanically treated sample can be due to stress-induced formation of R-phase. It is proposed that if stress-induced transformation of B19′ phase does not take place, stress-induced transformation of R-phase can extend to higher than 1% strain. Hence, pseudoelastic behavior due to this transformation can be observed.

The phase equilibria in the Co-rich corner of the Co–Mn–Ta system were investigated by means of optical microscopy, electron probe microanalysis and X-ray diffraction. Six isothermal sections in the Co-rich corner of the Co–Mn–Ta ternary system at 1300°C, 1200°C, 1100°C, 1000°C, 900°C, 800°C were experimentally determined. On the basis of previous and present experimental data of the phase equilibria, the thermodynamic assessments of the Mn–Ta binary and Co–Mn–Ta ternary systems were carried out by using CALPHAD. The thermodynamic parameters of the Mn–Ta binary and the Co–Mn–Ta ternary systems have been optimized for reproducing the experimental results in each system. An agreement between the calculated results and experimental data is obtained.

The 800°C isothermal section of the Co–Cr–Mo–Si quaternary system with the Co content fixed at 70 at.% and different contents of Cr, Mo and Si was determined by means of X-ray diffraction and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. Twelve different phase regions could be identified; one of them being a wide (Co) + Co 3 Mo 2 Si phase field, but only one four-phase region consisting of (Co) + Co 3 Mo +Co 7 Mo 6 + Co 3 Mo 2 Si was experimentally confirmed. The measured solubility of Si in the Co 3 Mo phase is rather limited but could reach up to 15.1 at.% in Co 7 Mo 6 . The solubility of Cr in Co 3 Mo and Co 7 Mo 6 was measured to be as high as 13.4 and 23.3 at.%, respectively, and the maximum solubility of Cr in (Co), αCo 2 Si and Co 3 Mo 2 Si could reach 26.9, 5.6 and 12.5 at.%, respectively.

The mapping of Mg 2 Si and β-AlFeSi phase fractions in the as-cast microstructure of Al–Mg–Si–Fe–Mn (6xxx series) alloys has been performed over the useful composition range (0–1.2 mass%) of the principal alloying elements Mg and Si. The calculations were based on the Scheil–Gulliver assumption of infinite diffusion in the liquid and limited diffusion in the solid state. The computed phase fractions were validated with experimental measurements of phase fractions. The mapping procedure allows the control of intermetallic phases in the as-cast microstructure, the minimization of the β-AlFeSi phase in particular, which is a significant prerequisite in obtaining enhanced extrudability, combined with high strength in this alloy series. Construction of maps for different levels of Mn has shown that addition of Mn could allow for higher alloying with Mg and Si, in order to obtain higher amounts of Mg 2 Si, without at the same time increasing the β-AlFeSi phase in the as-cast microstructure.

Al–Si–Cu casting alloys are widely used in manufacturing automotive parts. Semisolid forming of these alloys can eliminate major problems in their die casting. In this study, low superheated melt was employed to modify the microstructure and to produce non-dendritic A380 alloy. Melt was poured on a cooling slope plate at 615°C and ingots were obtained through permanent mold casting. They were thixoformed using a hydraulic press after holding at 570°C for 15 min to yield a microstructure having α-Al globules, Si particles, and modified β-phase intermetallic compounds. Image analysis showed that the size and distribution of α-Al phases and iron-bearing intermetallics were modified by using semisolid processing. The results also showed that cooling slope casting and thixoforming have improved the mechanical properties including tensile strength, elongation, and hardness of the high iron content A380 alloys.

The paper describes the effect of minor additions of scandium and zirconium on the superplastic behaviour of friction stir processed Al-5Mg based alloy. The measurements included the flow curves and tensile elongations of (in wt.%) Al-5Mg-0.1Zr, Al-5Mg-0.2Sc, and Al-5Mg-0.2Sc-0.15Zr alloys at initial strain rates ranging from 1 × 10 −3 to 1 × 10 −1 s −1 , and at forming temperatures from 350 to 500°C. The inclusion of friction stir processing at tool rotation rates of 95 and 475 rpm considerably enhanced the superplastic behaviour of the Al-5Mg-0.2Sc-0.15Zr alloy, which was reflected in elongations without failure of over 1900%. Other friction stir processed alloys, treated at lower tool rotation rates, did not achieve superplasticity due to abnormal grain growth. The results yielded by the friction stir processed alloys are compared with the superplastic behaviour of the same alloys produced conventionally by cold rolling.

In this study, the properties of vinyl ester/glass flake (VE/GF) coating on mild steel plates was investigated to determine its anti-corrosion performance. The corrosion penetration rate of VE/GF coated and uncoated mild steel was evaluated using immersion tests for 20 days. Corrosion resistance of the coating was evaluated in various corrosive environments viz. 5% HCl, 8% HCl, 5% NaOH and 7% NaOH. The mild steel plates were coated with four different thicknesses of VE/GF coating and a comparative analysis was carried out to evaluate the corrosion protection efficiency. Scanning electron microscopy was carried out before and after the immersion test to study the morphological changes and products of corrosion.

In the present paper the stabilization of Al–Pb metallic emulsion was studied. The pure liquid Pb is dispersed in liquid Al-rich Al–Sr alloy which contains dispersed Al 4 Sr precipitates. The Sr is dissolved in the Al-rich liquid and it is redistributed into the Pb phase. By the emulsification method the new Pb 3 Sr phase droplets are homogeneously dispersed in the Al-rich matrix. The Al–Pb metallic emulsion is cooled spontaneously.

In this article, a new method of synthesis of ultrafine powder solid solution (Ti,W)C by a combination of classical liquid-phase precipitation on a carbon support and low-temperature microwave heat treatment is proposed. An entire spectrum of intermediates obtained during thermolysis, reduction, and carbidization precursor to the final product has been obtained. The structure, particle morphology, phase structure and surface area values for the samples are shown.

Porous silicon nitride ceramics were fabricated without pore formers via microwave sintering. Microwave sintering at different temperatures produced unique microstructures with high porosity. The best porous silicon nitride ceramics were fabricated at 1550°C for 30 min; the resulting product had a bulk density of 1552 g cm −3 , an open porosity of 43.9%, and a flexural strength of 43.6 MPa. The mean pore channel size and the dielectric constants of the fabricated porous silicon nitride ceramics ranged from 0.1 μm to 1 μm and 2.9 to 3.4 under different temperatures, respectively.