Volume 97, Issue 8

The anelasticity of binary Fe –Al and ternary Fe –Al –Me (Me = Co, Cr, Ge, Mn, Nb, Si, Ta, Ti, Zr) alloys has been studied by mechanical spectroscopy in the Hz and kHz ranges. Relaxation peaks due to point defects – Snoek effect (S) with carbon interstitial jumps, carbon-vacancy complexes (X peak), Zener effect (Z), dislocations (D), and grain boundaries (GB) – are observed and their changes with addition of the third element are used to corroborate the respective proposed relaxation mechanisms, taking account of the changes of structure and order in the alloys which contain up to 5Co, 25Cr, 25Ge, 5Mn, 0.3Nb, 25Si, 6Ta, 4Ti, and 15Zr (all in at.%), respectively. In addition, some data of ordering temperatures, Curie temperatures, and hardness are provided for several alloys.

In the present work we study the phase transformation reaction of a Cu-20Zn-7Al (wt.%) alloy by isothermal and nonisothermal in situ X-ray diffraction. An effective activation energy for each phase is obtained for the range between 275 and 395 °C. The experimental data are also adjusted with the JMA equations. Finally, we present the TTT (time – temperature – transformation) diagram corresponding to the precipitation of alpha and gamma for the lower temperatures. Below 340 °C, we found for this alloy that the gamma phase precedes the formation of alpha.

Although some investigations of the integral enthalpy of mixing of the binary Cu–In system have already been done, there is a lack of conformity of these data within the literature. Therefore the integral enthalpy of mixing was determined with a Calvet-type calorimeter. The measurements were performed at four different temperatures to determine the temperature dependence of the integral enthalpy of mixing.

The partial Gibbs energies of zinc in the liquid Cu– In–Zn system as a function of temperature and concentration were measured in the temperature range between the melting points of the alloys and 1073 K using an EMF method with a liquid electrolyte. The thermodynamic properties were determined for 30 alloys at three different constant ratios of Cu : In of 1 : 2, 1 : 1, and 2 : 1 with zinc added in the concentration range between 5 and 90 at.%. The integral Gibbs free energy and the integral enthalpy of mixing of the ternary system were calculated with the Gibbs Duhem equation.

In an effort to better determine the thermodynamic properties of Al(g) and Al 2 O(g) the vapour in equilibrium with Al(l) + 4 at.% yttria-stabilized zirconia (YSZ) was compared to the vapour in equilibrium with Al(l) + Al 2 O 3 (s) over the temperature range 1197 – 1509 K. This comparison was made directly by Knudsen effusion-cell mass spectrometry with an instrument configured for a multiple effusion-cell vapour source ( multi-cell KEMS ). Second-law enthalpies of vaporization of Al(g) and Al 2 O(g) together with activity measurements show that Al(l) + YSZ is thermodynamically equivalent to Al(l) + Al 2 O 3 (s), indicating that Al(l) remained pure and Al 2 O 3 (s) was present in the YSZ-cell. Subsequent observation of the Al(l)/YSZ and vapour/YSZ interfaces revealed a thin Al 2 O 3 -layer had formed, separating the YSZ-cell from Al(l) and Al(g) + Al 2 O(g), effectively transforming it into an Al 2 O 3 effusion-cell. This behaviour agreed with observations made for β-NiAl(Pt) alloys measured in YSZ effusion-cell.

The high-temperature mechanical properties of both Ti 3 AlC 2 and Ti 3 AlC 2 /10 vol.%Al 2 O 3 composite, including compressive strength, bending strength, and fracture behavior, were investigated. The strengthening effect caused by Al 2 O 3 strongly depended on the mode of failure: significant enhancement in strength was only observed under the brittle mode of failure; whereas under the ductile mode of failure the strengthening effect was impaired due to Ti 3 AlC 2 matrix softening and stress relaxation.

In this work, Cu-graphite composites were prepared by electroforming technology in an acidic copper sulfate bath with graphite particles in suspension. The factors affecting the codeposition of graphite particles with copper were studied. At a particle concentration of 20 g l –1 , a current density of 3 A dm – 2 and a stirring rate of 100 min –1 graphite content in the composites was 21.7 vol.%.Microhardness and friction coefficient of the composites decreased with increasing graphite content. However, wear mass-loss decreased, but increased with graphite content above 21.7 vol.%. The wear mechanisms of pure Cu and Cu-graphite composites were adhesive wear and delaminating wear, respectively.

A high-carbon metastable austenite phase was quenched in liquid nitrogen to obtain fresh athermal martensite. Different ageing treatments were performed in order to study the transformation of the martensite phase and the formation of carbides. Neutron diffraction experiments give detailed information on the transformations during the annealing treatment itself. The tetragonal athermal martensite transformed immediately, i. e. during the heating to the ageing temperature, to cubic martensite. Ageing at 400 °C resulted in the decomposition of the austenite in ferrite and carbides and the formation of bainite. Those carbides could be determined as η-carbides transforming in χ-carbides after extended annealing times. As was expected, ageing at 170 °C resulted in the formation of a small amount of η carbides while the austenite phase remained stable.

Reinforcement size is an important factor that influences the mechanical and tribological properties of particulate reinforced metal matrix composites (PRMMCs). However, relatively few works have been carried out to investigate this issue. There are still many problems to be solved, on the optimum design of PRMMCs of tribological applications. In this work, copper-matrix composites reinforced with SiC particles of mono-size and hybrid-size are fabricated through a powder-metallurgy plus hot-extrusion method. The main purpose is to investigate the effect of reinforcement size hybridization on the dry sliding wear behavior of PRMMCs. The results indicate that finer particles result in a better reinforcing effect and significantly reduce the plastic flow and adhesive transfer of surface and subsurface material. The deeply embedded coarse particles bear the external applied load and resist the plowing effect of the counterpart. The different roles of the particulate components with various sizes promote the exertion of the other’s strengthening function, therefore resulting in higher wear resistance.

The strain distribution in a new generation nickel-based single crystal superalloy has been determined in the temperature range 293 K– 1598 K. Measurements have been performed using diffraction of high energy synchrotron radiation (150 keV, λ = 0.008 nm) to determine the variations with temperature of the γ/γ′ lattice mismatch and of the γ′ volume fraction. The chemical segregation at the dendrite scale and the internal stress induce a large range of values for the lattice mismatch. The measurements of the γ′ volume fraction determined by X-ray diffraction are in agreement with those obtained by atom probe tomography, image analysis or computation.

An electric-current-pulse (ECP) treatment was employed to rapidly heat a dogbone-shaped Ti-6Al-4V sheet. After the treatment, the alloy was modified from a single micrometer-sized structure to a shape-associated combinatorial counterpart. Coexisting with the original equiaxed coarsegrained α-Ti and the intergranular β-Ti, two kinds of novel ultrafine structures, nanometer-sized lamellar twins of β-Ti martensites and refined bimodal structure have been produced in the different parts of the bulk sample. Formation of the novel microstructures during the ECP treatment was systematically investigated. This work demonstrated that the ECP rapid heating treatment is a promising method to tailor the microstructures of the metallic alloys basically by designing the shape-associated distribution of the current density and offer a new possibility for improving the conventional alloys.

In this study, the effect of Ti –B (0.05 – 0.7 wt.% Ti, 0.01 – 0.13 wt.% B) and Sr additions (0.05 – 0.7 wt.%) on the hardness, ultimate tensile strength (UTS), strain and fatigue properties of the gravity cast Zn – Al-based ZA-12 alloy was investigated. While the Ti –B additions had no significant effect on the hardness of the alloys, the Sr additions lowered the hardness by a small amount. UTS and fatigue resistance of the ZA-12 alloy increased with 0.05 wt.% Ti, but the addition of 0.05 wt.% Sr to the standard alloy did not change these properties significantly. In excess of 0.05 wt.% Ti and Sr, the UTS and fatigue resistance of the alloys decreased and reached a lower value than that of the standard alloy. The failure strain only increased for the ZA-12 alloy containing 0.05 wt.% Ti, then decreased with further increase in Ti content. The failure strain values of the alloys decreased with addition of Sr. Metallographic examination indicated that the addition of Ti –B strongly modified the microstructure of the standard ZA-12 alloy, but Sr did not. Ti and Sr have also formed complexshaped intermetallic compounds, which were identified as Al 5 Ti 2 Zn and Zn 5 Al 3 Sr by X-ray diffraction and EDS analyses. It can be suggested that these particles cause a decrease in UTS, fatigue resistance, and strain to failure of the ZA-12 alloy.

The use of atomic force microscopy (AFM) in the magnetic force mode (MFM) for the determination of austenite (nonmagnetic phase) in duplex and TRIP (transformation-induced plasticity) steels is described. The influence of the sample preparation for the MFM measurements is investigated, showing that a final electropolishing stage is necessary in the case of TRIP-steels. The results of the determination of austenite in the range of 6 – 15% with AFM were compared with those obtained with electron backscattered diffraction (EBSD) and light optical microscopy. For TRIP-steels an identification of retained austenite with MFM was found to show a better resolution than classical light optical microscopy.

Prefil Footprinter, a portable pressure filtration instrument, is usually employed to detect liquid metal quality. However, no investigations have ever been done to determine overall filtration resistance and resistance of the “clean” filter media. Based on the identification of flow behaviour using the derivative methods, classic filtration equations have been effectively used to estimate total filtration resistance for the first time. The variations of overall resistance during filtration provide a new approach to understand filtration behaviour. The resistance values of the “clean” filter media have been obtained for the first time. An innovative method has been developed to obtain the resistance of the “clean”' filter media through the backward extrapolation of the overall filtration resistance versus filtrate weight or filtration time curves over the steady stages operating in incompressible cake mode.

X-ray phase analysis combined with high-resolution electron microscopy of samples taken from a genuine Damascus sabre after annealing for 24 hat 400 °C and 800 °C followed by slow cooling down to room temperature has led to a better insight into the nature of cementite nanowires, which have been discovered recently. According to the present study, nanowires remained after 400 °C annealing, but disappeared after heat treatment at 800 °C and subsequent cooling down. On the other hand, perlitic cementite has been retained qualitatively after the same treatment. Knowing that the exceptional mechanical properties of Damascene blades disappear after annealing, the present results suggest a significant influence of the nanowires upon these features.

The present study aims to analyze the effect of tin, added to zinc bath containing aluminium, on the microstructure and on the development of spangles of continuous hot-dip galvanized coatings. Different experimental conditions have been explored and the mechanism of nucleation and growth taking place during the solidification of the coating are discussed with the support of a thermodynamics approach.