Formation Of Face-centered Cubic Phase Research Articles

Formation of Face-Centered Cubic Phase in Ti35 Alloy Under In Situ Heating Transmission Electron Microscopy

Formation of Face-Centered Cubic Phase in Ti35 Alloy Under In Situ Heating Transmission Electron Microscopy

Fabrication of Pt nanoparticles by nanosecond pulsed laser ablation in aqueous solution of ethanol using KrF excimer laser

The present paper presents the premiere synthesis of platinum nanoparticles (Pt-NPs) by pulsed laser ablation in aqueous ethanol solution (PLAL) using an excimer nanosecond KrF laser. The impact of the laser fluence, repetition rate (RR) and ethanol concentrations on the optical and morphological properties of the obtained Pt-NPs was investigated. The optical characteristics has been assessed by transmission spectroscopy in the UV/Vis region, and the issues associated to the volatile component’s evaporation are discussed. Detailed information on the morphological properties was acquired via High-Resolution Scanning Transmission Electron Microscopy (HR-STEM). Mean size values in the range of 1.7–2.45 nm with narrow standard deviations from ± 0.6 up to ± 1.1 nm, were established for the synthesized Pt-NPs, that showed a certain level of aggregation. The smallest mean size value, 1.7 nm, was found for the sample produced using 2.3 Jcm−2 laser fluence, 10 Hz RR in 60 % ethanol concentration. The narrowest size distribution (±0.6 nm) was achieved with the same laser fluence and RR in 80 % aqueous ethanol solution. In addition, the metallic character (Pt) of the atoms forming the NPs was confirmed by Direct Analysis in Real Time Mass Spectrometry (DART-MS). The formation of face-centered cubic phase for Pt-NPs with interplanar distances of 0.25 and 0.19 nm for (200) and (111) crystalline planes, respectively, was revealed by X-ray diffraction (XRD). These results are in good agreement with those from HR-STEM analysis, where similar interplanar distances were obtained for individual NPs.

Effect of high temperature heat treatment on microstructure and properties of FeCoCrNiAl high-entropy alloy laser cladding layer

Here, the heat treatment for FeCoCrNiAl high-entropy alloy (HEA) laser cladding (LC) layer was given at a temperature which is higher than that of the first phase transition. The effects of heat treatment on the phase transition, microstructure and mechanical properties of the LC-ed FeCoCrNiAl were studied. Meanwhile, the LC-ed sample was compared with the casting specimen. The results showed that the cladding layer had lower activation energy of phase transformation, and it had higher proportion of Fe element because of the dilution of the matrix metal, which promoted the formation of face-centered cubic (FCC) phase. Then more FCC phase structures precipitated in the cladding layer after heat treatment. However, the formation of FCC phase did not change the texture characteristics of the cladding layer. The differences in physical properties, slip system, Burgers vector and dislocation types between the two phases, as well as the serious atomic disarrangement at the two-phase interface, caused a significant increase of dislocation density. The mechanical properties of the FeCoCrNiAl-HEA were improved by the the presence of proper amount of FCC phase combined with fine grains strengthening and dislocation strengthening. Nevertheless, the excess amount of FCC phase promoted plastic deformation and weakened the strengthening effects of dislocation and fine grain strengthening. • Alloying elements and activation energies promoted phase transformations under thermal action. • Solid phase transition under heat treatment did not change the grain growth orientation in coating. • Variations in physical properties between two phases promoted the existance of dislocations. • Dislocations, fine grains and phase proportions influenced mechanical properties of FeCoCrNiAl.

Tailoring mechanical and magnetic properties of AlCoCrFeNi high-entropy alloy via phase transformation

Phase constitutions, either changed by alloying or by phase transformation, are the key factors to determine the magnetic and mechanical performances of high-entropy alloys (HEAs). Using the AlCoCrFeNi HEA as a candidate alloy, this paper demonstrates the effect of phase transformation on both the mechanical and magnetic properties in the multi-phase system. With increasing heat treatment temperature, the sigma (σ) and face-centered-cubic (FCC) phases disappeared at 1000 °C and 1200 °C, respectively. Such volume fraction changes of σ, FCC and body-centered-cubic (BCC) phases have divergent effects on mechanical and magnetic properties. The excellent strength-ductility combination will be achieved as the disappearance of σ phase and formation of FCC phase. As for the magnetic properties, the volume fraction of BCC phase plays a major role in determining its saturation magnetization. When the volume fraction change of BCC phase is not evident, the higher volume fraction of FCC phase will influence its magnetization at 2 T. Our present work might provide insights into analyzing the evolution of both mechanical and magnetic properties of HEAs caused by complex phase transformation.

Nano-crystalline high entropy alloys prepared by mechanical alloying

High-entropy alloys are a new class of material. In recent past, high-entropy alloys have attracted a great deal of attention from researchers due to their unique multi-element solid-solution structures and excellent properties. This paper deals with a new promising class of high entropy alloys synthesized through mechanical alloying for 15 h. The elemental powders are milled in high energy ball milling. The elemental powders are taken out at particular time intervals for the phase analysis through X-ray diffractometer. The particle morphology was scrutinized by Scanning electron microscopy. The phase analysis through X-ray diffractometer reveals the formation of face-centered cubic phase along with some Ni-Si based compounds after 15 h of mechanical alloying. An increase in crystallite size is observed with increase in milling time whereas, a decrement in lattice strain is observed with advancing milling time. To support the lattice strain increment, the dislocation density is also calculated by using the variance method. The high negative mixing enthalpy of Si and Ni results into the formation of Ni-Si based compound.

Transitory phase transformations during [formula omitted] twinning in titanium

101¯2101¯1¯ twinning presents a variety of properties that entirely depart from the classical twinning behavior. In this work, deformation of a single crystal Ti under uniaxial compression perpendicular to the c-axis was investigated by using atomistic simulations. Very interesting phase transformations between body centered cubic (BCC), hexagonal close-packed (HCP), face centered cubic (FCC) structures were observed. These phase transformations are only transitory. Before twin nucleation, HCPparent→BCC transformation occurred. The lattice transformation can be described as: (101¯0)P→(110)BCC, and (0002)P→(11¯0)BCC. Then the BCC phase transformed to HCP which satisfies 101¯2101¯1¯ twin relationship with the HCP parent. This transformation is accomplished by atomic shuffles and no shear is involved. After the BCC phase was entirely transformed, the deformation was dominated by twin growth. At the twin boundary (TB), a FCC phase was present, separating the parent from the twin. The FCC structure was transformed from the HCP parent. This transformation is also transitory and involves both shear and shuffle. Shuffling transforms the double-layered (101¯0)P plane of parent into a close-packed (111)FCC plane, and then a shear with a Burgers vector of half a Shockley partial dislocation on the (111)FCC plane generates the correct FCC structure. It was observed that the formation of FCC phase at the TB hinders twin growth. But as the strain increases, the FCC phase transformed to the HCP twin and this process involves Shockley partials on the interface. Strain accommodation was analyzed to explain the formation of the FCC phase at the TB. These transitory phase transformations during deformation twinning further corroborate that 101¯2101¯1¯ twinning completely departs from the classical twinning behavior.

Synthesis and Characterization of Co-Ni and Fe$_{3}$O$_{4}$-Pd Nanocomposites

Co-Ni needle-like and Fe3O4-Pd spherical nanoparticles were prepared by water-in-oil microemulsion (W/O). The as-synthesized nanoparticles have been encapsulated by silica (SiO2) and polyvinyl alcohol (PVA) in N2 atmosphere. Their structure and magnetic properties were evaluated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). The influence of structural modifications to the magnetic properties of nanocomposites has been investigated. Powder X-ray diffraction analysis indicated the formation of face-centered cubic phase for both Co-Ni and Fe3O4-Pd systems. The average crystallite size for the studied samples has been calculated in the range of 7-26 nm. TEM images revealed the morphology of the particles as needle-like nanoparticles for Co-Ni alloy and spherical for Fe3O4-Pd system. The magnetization curves of nanocomposites at room temperature demonstrated coercivity values between 8.2 and 15.5 kA/m for Co-Ni nanocomposites and superparamagnetic behavior of Fe3O4-Pd nanocomposites due to the small-size effect of nanoparticles.