Jelena Stasic

The influence of applying the additional continuous laser on the synthesis of silicon-based nanoparticles by picosecond laser ablation in liquid

Silicon-based nanoparticles are synthesized by picosecond laser ablation in liquid using silicon single-crystal plates as targets. We demonstrated that applying the additional continuous laser immediately prior to and during the ablation changed the size distribution and oxygen content of the nanoparticles produced. This opens up the possibility of using the continuous laser as a simple tool for tailoring nanoparticle properties.

The influence of microstructural characteristics and contaminants on the mechanical properties and fracture topography of low cost Ti6Al4V alloy

Abstract Low cost titanium alloy compacts were produced via the powder metallurgy approach through the hydride – dehydride process and hot consolidation (hot pressing and hot isostatic pressing). The conditions of the reversible hydride – dehydride process were determined by X-ray and scanning electron microscopy characterisation of powders. Powders were consolidated both above and below the β transformation temperature. The morphology of the microstructure, and the presence of open and closed pores, as well as residual particles of hydrides and oxides have a direct influence on the mechanical properties of compacts (tensile properties and impact toughness).

Size of silver nanoparticles determines proliferation ability of human circulating lymphocytes in vitro.

In this work we present biological effects of silver nanoparticles (AgNPs) synthesized by picosecond laser ablation of silver in deionized water. We examined induction of chromosomal aberrations, lymphocyte micronuclei, appearance and recovery of double strand breaks (DSBs) of DNA, cell proliferation potential, concentration of lipid peroxidation products and insulin-like growth factor 1 (ILGF-1). We found that AgNPs sized from 3 nm to 8 nm induce cell cytostasis, which is accompanied with its clastogenic action on DNA, while AgNPs, sized 2 nm behaves contrary stimulating cell proliferation by enhancing ILGF-1 concentration.

Continuous wave laser for tailoring the photoluminescence of silicon nanoparticles produced by laser ablation in liquid

Silicon nanoparticles (SiNPs) are attracting attention for applications in various fields, from energy storage to bio-imaging. One of their main advantages is good photoluminescence (PL) properties combined with the relatively high bio-compatibility. Here, we fabricated SiNPs by the laser ablation of silicon single crystal in de-ionized water, employing simultaneously the picosecond pulse laser (150 ps, 1064 nm, 7 mJ/pulse) and a continuous wave (CW) laser (532 nm, 270 mW). TEM analysis (bright field TEM, HRTEM, HAADF, EDS) clearly shows that the introduction of the CW laser significantly increases the crystallinity of the produced nanoparticles, which may be crucial for many optical and electronic applications. The obtained SiNPs exhibit good blue photoluminescence properties, and the introduction of the CW laser into the fabrication process leads to the considerable increases in the photoluminescence. Additionally, we conducted a detailed analysis on the aging-time dependence and the excitation waveleng...

Synthesis and characteristics of precipitation hardened Cu–Cr alloy and multiply hardened Cu–Cr–Al2O3 nanocomposite obtained using powder metallurgy techniques

Abstract The hardening of copper alloy by using powder metallurgy techniques and analysis of its effects on the strength of obtained material are discussed. Prealloyed Cu-0.5 wt.% Cr powder and mechanically alloyed Cu-0.5 wt.% Cr-3 wt.% Al2O3 powder were consolidated by means of hot pressing. Optical microscopy, scanning electron microscopy and transmission electron microscopy were used for microstructure characterization of compacts. Hardness and electrical conductivity of both compacts were compared. High strengthening of the Cu–Cr compacts is achieved by aging as a consequence of the influence of precipitation particles rich in chromium. In the case of the Cu–Cr–Al2O3 composite it is a consequence of precipitation of particles rich in chromium and the presence of Al2O3 dispersoid nanoparticles.

A comparative study of microstructure, compressive, and fracture properties of Ti3Al-based intermetallics produced via powder metallurgy, and melting and casting processes

Abstract A comparative study of the microstructure, compressive properties, and fractography of Ti3Al and Ti3Al–Nb intermetallics produced via powder metallurgy and standard vacuum melting and casting processes has been carried out. Non-porous compacts were obtained via vacuum hot pressing of powders produced by mechanical alloying. Prior to compression tests, all samples were homogenized by a solution treatment at 1050°C (α + β region), followed by water quenching. The compression tests were performed from room temperature to 500°C in vacuum at a strain rate of 2.4 × 10–3s–1. Detailed microstructural characterization was conducted using scanning electron microscopy, followed by energy dispersive X-ray spectroscopy and X-ray diffraction analysis. Values of compressive mechanical properties of compacts were higher than those of castings. Fracture topography was examined by scanning electron microscopy. A correlation between ductility and the fracture mode exists for all materials.

Effect of synthesis parameters on structural and mechanical properties of Ti 3 Al–Nb–Mo intermetallic compound obtained by powder metallurgy techniques

The influence of microstructure, heat treatment and alloying addition on mechanical and fracture properties of Ti3Al-based intermetallic at room and elevated temperatures was studied. Ti3Al–11Nb–1Mo (mole fraction, %) alloy was consolidated via powder metallurgy processing by mechanical alloying (MA) and hot pressing (HP). MA powders were characterized using XRD and SEM-EDS. Optimum MA duration was 25 h and HP conditions of 1350 °C, 2 h, 35 MPa. After HP, solution treatment at 1050 °C for 1 h and water quenching α2+β Widmanstatten microstructure is present, while subsequent aging at 800 °C during 24 h induces small content of O-phase. High fraction of β-phase is a direct consequence of Mo. Compression tests were performed from room temperature to 750 °C in vacuum. The yield strength of compacts increases with temperature up to 250 °C (pyramidal slip systems activation), after which it decreases. Ductility increases throughout the whole temperature range. The presence of O phase contributed to ductility increase in aged alloys, while negligibly lowering yield strength. Registered drop in the yield strength of aged alloys compared with non-aged ones was mostly influenced by precipitation of α″2 particles. Mixed fracture modes are operative at all temperatures.

Microstructural and mechanical properties of Cu-7vol.%ZrB2 alloy produced by powder metallurgy techniques

Abstract The Cu-7vol.%ZrB2 alloy examined in this study was consolidated via powder metallurgy (PM) processing by combining mechanical alloying and hot pressing. Powder mixture with composition: 94.78 wt.% copper, 4.1 wt.% zirconium, and 1.12 wt.% boron was used as a starting material. Mechanical alloying of powder mixture was performed at various times: 5, 10, 15, 20, 25, and 30 h. Structural changes that occur in the samples of copper alloy with 7vol.%ZrB2 after milling and during hot pressing process were studied with the use of X-ray diffraction. Scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometry (EDS) was applied to examine the morphological properties and elemental analysis of the hot-pressed samples as a function of milling times. Also, hardness of the Cu-7vol.%ZrB2 alloy was investigated, and the results showed that hardness of the samples increased as the milling time increased. The compressive properties at room temperature are correlated to the corresponding hardness results. Distribution of ZrB2 particles and presence of agglomerates in the Cu matrix directly depend on the milling time and show strong influence on compressive properties and fracture of Cu-7vol.%ZrB2 alloy.

Properties of Copper-Based Composite Reinforced with Al2O3 Particles of Different Size

Copper matrix was simultaneously reinforced with nano- and micro-sized Al2O3 particles via high-energy milling of the mixture of inert gas-atomized prealloyed Cu-1 wt.% Al powder and 0.6 wt.% commercial Al2O3 powder. At the maximum of microhardness (2400 MPa) the grain size reaches the smallest value as a result of the synergetic effect of nano- and micro-sized Al2O3 particles. The relatively low decrease in microhardness during HTE may be explained by grain growth which is retarded by Al2O3 nano-sized particles precipitated at the grain boundaries.