A comprehensive study on synthesis behavior of nanostructured Al-Zn-Mg-Cu alloy powder with and without 3 wt.% Al2O3 particles during mechanical alloying

The mechanical alloying (MA) process was applied to synthesize nanostructured Al-Zn-Mg-Cu alloy powder and its composite with 3 wt.% Al2O3 particles. Both the alloy and the composite powders were produced by simultaneous milling of the constituents for different milling times (0–50 hours), with fixed milling technical parameters. The produced powders were characterized by the X-ray diffraction (XRD) analysis to detect the generated phases. Also, a scanning electron microscope (SEM) and a transmission electron microscope (TEM) were used to observe the morphologies and measure the crystallite size of the powders, respectively. It was found that during the production of the composite powder, the size of Al2O3 particle changed which led to unexpected outcomes. In the alloy state, the average particle size and the crystallite size were lower and the microhardness values were higher than those in the composite powder. Also, the steady state was achieved after a shorter MA time in the alloy state compared to the composite state. The major reason for these results was the changes of alumina particle size in the composite powders at the first stages of the MA process due to consuming a noticeable amount of energy, which made them ineffective. In addition, the compressibility in the composite powders was lower than that of the alloy powders due to the presence of alumina particles. Moreover, in both powders, the compressibility decreased with increasing the MA time because of the increased work hardening and the reduced flow properties.

Dealloying of Cu-Mg-Ca Alloys

The chemical dealloying of Cu-Mg-Ca alloys in free corrosion conditions was investigated for different alloy compositions and different leaching solutions. For some of the precursor alloys, a continuous, pure fcc copper with nanoporous structure can be obtained by dealloying in 0.04 M H2SO4 solution. Superficial nanoporous copper structures with extremely fine porous size were also obtained by dealloying in pure water and 0.1 M NaOH solutions. The dealloying of both amorphous and partially crystalline alloys was investigated obtaining bi-phase nanoporous/crystal composites with microstructures depending on the precursor alloy state. The fast dissolution of Mg and Ca makes the Cu-Mg-Ca system an ideal candidate for obtaining nanoporous copper structures with different properties as a function of different factors such as the alloy composition, the quenching process, and leaching conditions.

Microstructure Changes and Improvement in the Mechanical Properties of As-Cast AlSi7MgCu0.5 Alloy Induced by the Heat Treatment and ECAP Technique at Room Temperature

The changes in the microstructure and improvement in the mechanical properties of as-cast AlSi7MgCu0.5 alloy induced by the heat treatment and technique of equal channel angular pressing (ECAP) were investigated. The heat treatment of as-cast alloy performed before the ECAP technique was required to increase the plasticity of the alloy. Therefore, the samples of analysed alloys were solution annealed at optimized temperature of 823 K for 4 hours to dissolve the particles of intermetallicπ(Al8FeMg3Si6) phase and to spheroidize the Si particles. Subsequently, water quenching and artificial ageing at optimized temperature of 573 K for 5 hours was used to obtain an overaged alloy state. The microstructure of alloy was consisted ofα(Al) solid solution, eutectic Si particles, and intermetallicβ(Mg2Si), Q-Al4Mg5Si4Cu,α-Al12(Fe,Mn)3Si, and/orα-Al15(Fe,Mn)3Si2phase particles. The crystal structure of present phases was confirmed by hard X-ray diffraction at Deutsches Elektronen-Synchrotron (DESY) in Hamburg and by the selected area electron diffraction (SAED) performed inside the transmission electron microscope (TEM). The heat-treated alloy was processed by ECAP at room temperature following route A. Repetitive ECAP of alloy homogenized the heterogeneous as-cast microstructure and formed the ultrafine subgrain microstructure with elongated subgrains of 0.2 µm in width and 0.65 µm in length and the high dislocation density. Microstructural changes in alloy induced by both heat treatment and ECAP led to the high strain hardening of the alloy that appeared in an improvement in strength, ductility, and microhardness of alloy in comparison with as-cast alloy state.

Homogenization of AlSi7MgCu0.5 Alloy as-Cast Structure by ECAP Processing

The homogenization of AlSi7MgCu0.5 alloy as-cast structure by using an equal channel angular pressing (ECAP) was investigated. The heat treatment of as-cast alloy applied before ECAP processing was required to increase alloy plasticity. Therefore, the samples of analyzed alloy were solution annealed at temperature of 550 °C for 4 hours and subsequently water quenched. Quenched samples were artificially aged at temperature of 300 °C for 5 hours to obtain an over-aged alloy state. The solution annealing of as-cast alloy state caused a partial spheroidization and coarsening of eutectic Si-particles. During artificial aging of analyzed alloy, the incoherent particles precipitated uniformly from α-solid solution. The ECAP technique at room temperature homogenized its heterogeneous dendritic microstructure and formed the ultra-fine grains of solid solution. A redistribution and fragmentation of the eutectic Si-particles and precipitated particles was occurred.

STUDYING THE EFFECTIVENESS OF THE NiCrN ALLOY FORGING PROCESS

Chromium- and nickel based alloys offer good mechanical properties, while keeping them also in highly corrosive environment. In addition, the introduction of the nitrogen at the level of 0.3 to 0.5% to the alloy structure, increases the plastic deformation ability of the cast alloy. This observation is fully confirmed by the results of the plastic deformation tests (performed on Gleeble), which are presented in this paper. The laboratory samples made of NiCrN wrought alloy and processed by die forging, demonstrated the significant increase of the yield stress and plastic deformation ability for the applied deformation degrees. The experiments showed about twofold increase of the resistance to cyclic loading for the forged products, when comparing it to the initial alloy state after casting. The developed technology (validated by numerical simulations) has been used to manufacture the workpiece for the propeller shaft. The results of the deformation performance for the element subjected to plastic processing have been compared with the material in its cast state.

COMPOSITION DEPENDENCE OF BULK MODULUS AND BOND LENGTH OF MgxZn1-xO(x = 0.0-1.0) ALLOY SEMICONDUCTORS

For the first time, a general viewpoint of electronegativity and chemical bond in alloy semiconductors, e.g., Mg x Zn 1-x O (x = 0.0-1.0) was proposed. The variation of bulk modulus and bond length, as well as their dependence on Mg concentration x were quantitatively simulated. The bulk moduli of Mg x Zn 1-x O alloys decrease with increasing Mg concentration x. The detailed variation of bond lengths of both Mg–O and Zn–O in Mg x Zn 1-x O alloys in the whole composition range was determined, which is less than 0.007 Å. The valence state of Mg is larger than that of Zn when x = 0.0-1.0, which leads to the increase of valence state of O with increasing Mg concentration x. The current results clearly indicate that Mg x Zn 1-x O condenses in an alloy state.

Quantitative V-L-S Growth Model and Experiments of Fe Catalyzed Si Nanowire Formation

ABSTRACTWe report the formation of Si nanowires (SiNWs) by vapor-liquid-solid (V-L-S) mechanism where Si atoms are pumped from Si wafer. This happens when a material has the large difference of activity in its pure (Si) and alloy state (Si-Fe). We developed a kinetic model to quantitatively describe the growth of the nanowires. The model predicts that the length of the nanowires increases linearly with the growth time.