Lubomir Caplovic

Influence of atomisation on solidification microstructures in the rapidly solidified powder of the Cr–Mo–V tool steel

The paper deals with the analysis of microstructure formation in the tool steel of ledeburite type under quasi-equilibrium and non-equilibrium conditions. The quasi-equilibrium solidification behaviour was investigated by differential thermal analysis. The rapidly solidified powder was produced by the nitrogen gas atomisation. Three main types of solidification microstructures were observed in all granulometric fractions of rapidly solidified powder: dendritic, grain refined and compound (a mixture of dendritic and grain refined). Mechanism of microstructure transition from dendritic to non-dendritic was described.

Formation of Fe(0)-Nanoparticles via Reduction of Fe(II) Compounds by Amino Acids and Their Subsequent Oxidation to Iron Oxides

Iron nanoparticles were prepared by the reduction of central Fe(II) ion in the coordination compounds with amino acid ligands. The anion of the amino acid used as a ligand acted as the reducing agent. Conditions for the reduction were very mild; the temperature did not exceed 52°C, and the optimum pH was between 9.5 and 9.7. The metal iron precipitated as a mirror on the flask or as a colloid in water. Identification of the product was carried out by measuring UV/VIS spectra of the iron nanoparticles in water. The iron nanoparticles were oxidized by oxygen yielding a mixture of iron oxides. Oxidation of Fe(0) to Fe(II) took several seconds under air. The size and properties of iron oxide nanoparticles were studied by UV/VIS, TEM investigation, RTG diffractometry, Mossbauer spectroscopy, magnetometry, thermogravimetry, and GC/MS.

XRD, SAXS, and PALS investigations of three different polymers reinforced with tetraoctylammonium exchanged montmorillonite

ABSTRACT Three different polymer nanocomposites were prepared using clay modified with tetraoctylammonium (4C8) surfactant. The dispersion of clay silicate layers was studied using X-ray diffraction and small-angle scattering. Free-volume cavity sizes were studied with positron annihilation lifetime spectroscopy. Scattering methods confirmed disruption of all polymer lamellae organization upon organoclay addition and the creation of partially intercalated systems for polyamide and polycaprolactone. The presence of organoclay in the polymers enlarges the lower value of average positronium lifetime τ3 of polyamide and reduces the higher value of τ3 for polycaprolactone and polyethylene.

Microstructure of Cr2N-11Ag Nanocomposite Thin Film Deposited on Vanadis 6 Tool Steel

Cr2N-Ag nanocomposite thin films, containing 11 wt.% Ag solid lubricant, were deposited on substrates made of Cr-V ledeburitic tool steel Vanadis 6 by reactive magnetron sputtering at a deposition temperature of 500 °C, using pure Cr and Ag targets, in a composite low pressure Ar/N2 atmosphere. The films are composed of Cr2N-matrix and Ag particles. The films have an average thickness of 4.7 μm. They grew in a columnar manner, but, individual silver agglomerates were visible along the columnar crystals, also. The average size of silver agglomerates lies well below 50 nm. Annealing of the films at temperatures below the deposition temperature do not changed composition of films, but induce higher precipitation of silver particles on the surface of films at the temperatures 300 and 400°C. On the other hand, film annealed at 500°C manifested more remarkable Ag-redistribution, being represented by the decrease in population density of Ag-particles on the surface. The key parameter for transport Ag lubricants from Cr2N matrix to the surface is the working temperature. Cr2N-Ag films could be used for specific tribological applications through proper investigation of the working temperature and conditions.

Microstructure and Properties of CBN Diffusion Coating on High-Speed Steel

CBN diffusion coating on the ball nose end mills made of AISI-M35 high speed steel (HSS) has been produced thermo-chemically. The microstructure and component depth profiles of the CBN diffusion layer have been studied by scanning electron microscopy and energy dispersive X-ray spectrometry. The results on laboratory cutting tests of ball nose end mills made of AISI-M35 HSS with and without complex CBN diffusion coating are also introduced in the paper. The relationship between wear kinetics and tool life has been established. It was shown that under the used cutting conditions the tool life of the mills with the coating was a factor of 1.6 higher than that of the mills without the coating. The higher tribological stability of the coating in cutting process was supported by metallographic observations of the worn surfaces using scanning electron microscopy.

Evaluation of Properties of Selected Coatings on Aisi Grade 18Ni (250) Maraging Steel in Terms of their Use in Gears

The paper deals with the evaluation of selected properties of thin hard coatings on the AISI Grade 18Ni (250) Maraging Steel substrate. The paper describes their tribological properties and, based on critical evaluation, a thin hard coating is designed applicable to the maraging steel for the case of its use for the production of gears, in order to increase the surface resistance of tooth flanks of gears made of this material.

Characterisation of C-B-N Diffusion Layers Developed on High-Speed Steel Substrate

C-B-N diffusion layers on the samples of wrought and as-cast high-speed steels of AISI M2 grade have been developed thermo-chemically. Thermo-chemical treatment was carried out after full heat treatment and included holding for 1 and 3 h at 550°C in order to produce different C-B-N diffusion layers. The microstructure and component depth profiles in the C-B-N diffusion layers were studied by scanning electron microscopy and energy dispersive X-ray spectrometry. It was shown that well adhered (diffusion controlled) carbon-boron-nitrogen layers with nanosized microstructure can be thermo-chemically developed at 550°C for 1 h on the wrought and as-cast M2 high-speed steel substrates. In the samples made of the wrought M2 high-speed steel and held at 550°C for 3 h the C-B-N diffusion layer develops in the fiber-like morphology.

Microstructure and Properties of Diffusion Boride Layer on Die Steel

Diffusion boride layer has been produced on the surface of a hot work tool steel. The microstructure and elemental spectra as well as depth profiles of the elements in the boride layer have been studied by scanning electron microscopy, X-ray diffraction analysis and energy dispersive X-ray spectrometry. Micro-hardness measurement was carried out using the Vickers micro-hardness test. The results showed that the boride layer is formed by boron compound Fe2B. Additionally, boron carbide B4C has been revealed embedded in the bulk of the boride layer.

Mechanochemical-molten salt synthesis of Na{sub 2}Ti{sub 6}O{sub 13} nanobelts

A novel route for the preparation of Na{sub 2}Ti{sub 6}O{sub 13} nanobelts by mechanochemical treatment of the TiCl{sub 4}-Na{sub 2}SO{sub 4}.10H{sub 2}O-Na{sub 2}CO{sub 3} mixture for 5 min followed by molten salt synthesis is described. The mixture of the amorphous TiO{sub 2} and NaCl-Na{sub 2}SO{sub 4}.xH{sub 2}O-Na{sub 2}CO{sub 3} salt matrix was generated during milling. The molten salt synthesis of the Na{sub 2}Ti{sub 6}O{sub 13} nanobelts with lengths up to 0.5-2 {mu}m and with a width in the range of 20-250 nm was carried out in the temperature range of 700-800 {sup o}C for 1 h. The partial formation of titanate nanotubes was observed after annealing at 600 {sup o}C and washing procedure. X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential thermal analysis (DTA) were used to characterize the formation and structure of Na{sub 2}Ti{sub 6}O{sub 13} nanobelts.