J. Kusiński

Laser cladding and erosive wear of Co–Mo–Cr–Si coatings

Defect free coatings, made of Tribaloy T-400 powder, deposited by laser cladding on iron and nickel based substrates are described. The proper selection of the cladding process parameters allowed us to get coatings with low dilution of the base material. Cross-sections of such coatings have been examined to reveal their microstructure using optical, scanning electron and transmission electron microscopy, chemical analysis (EDS microanalysis), phase composition (XRD), hardness and microhardness testing methods. Compared with other deposition techniques the microstructure of the laser coatings showed a high degree of refinement and chemical homogeneity. Grain coarsening was observed in the heat-affected zones and was explained as being due to the overlapping of subsequent tracks during the coatings deposition. The erosive wear resistance of the coatings has been investigated. In general, the laser deposited coatings turned out to be susceptible to extensive erosive wear. This effect was explained by lack of feasibility of the coated material to plastic deformation during erosion.

SEM and TEM microstructural investigation of high-speed tool steel after laser melting

Abstract The microstructure of a continuous CO 2 laser-melted high-speed steel, namely M2, has been studied. The formation of the microstructure under rapid solidification conditions is described by means of scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. A very fine dendritic structure is characteristic for the microstructure formed under such rapid solidification conditions like laser melting. This structure generally consists of fine dendrites of austenite crossed by a very fine carbide network or the eutectic without the primary large carbides. The structure obtained in the surface layer after laser melting permits to get a high level of hardness and shows an improved wear resistance.

Microstructure, chemical composition and properties of the surface layer of M2 steel after laser melting under different conditions

Abstract Metallographical (optical, SEM, TEM), microprobe, wear resistance and microhardness investigations of M2 high-speed tool steel surface melted by continuous CO 2 (with different power) and Nd:YAG pulsed lasers are described. It became apparent that there was a considerable influence of the laser type, scanning velocity, gas jet atmosphere and the antireflective graphite coating on the melted zone dimensions and its as-resolidified structure. The notable differences between the microstructures of the melted zones were related to the laser type and laser power. In comparison to the uncoated specimens, laser melting of the specimens coated with a colloidal graphite layer resulted in significantly increased dimensions of the laser-affected layer and a coarser as-resolidified structure. Depletion of the Cr, V, Mn and C in the resolidified zone after treatment under oxygen atmosphere was related with the high reaction efficiency of these elements to oxygen. Hardness of the melted zone in the uncoated samples was higher than that of both the graphite-coated samples and the conventionally hardened matrix. The lathe tools treated by the Nd:YAG pulsed-laser radiation showed the longest cutting life-time.

The microstructure of plain carbon steel laser-alloyed with silicon carbide

Abstract The microstructure of mild carbon steel after laser alloying with SiC is described. The macrostructure of the alloyed layer consisted of three well-defined zones. The first zone consisted of crystals growing epitaxially on the partially remelted matrix grains, the second zone had only columnar crystals, and the third zone consisted of mixed (dendritic/acicular) crystals near the surface. The martensitic structure in the last zone varied in the needle size. The martensitic needles formed at the early stages of the γ⇒α′ transformation were very large, crossing several primary austenite crystals. The needles that formed during the later stages of the martensitic transformation were much finer.

Nanoparticles and Thin Films of Cerium Dioxides: Relations between Elaboration Process and Microstructure

Nano-powders and thin films of cerium dioxides for gas sensor applica tions have been elaborated using various specific routes. Nano-powders of CeO 2 were obtained from (i) chemical precipitation followed by high-energy mechanical milling, (ii) soft chemical preparation and (iii) an unusual method of pulverization of liquid solution. These materials were char a terized using X-Ray diffraction and Transmission Electron Microscopy ; depending on the pre paration method, the particle sizes varied from 2 to 10 nanometers. Thin films of CeO 2 were prepared, using a pulsed laser deposition method. According to the preparation parameters, fil m thickness varied from 180 to 750 nm, with diffracting domain sizes of about 8 nm. A qualitative a pproach of the nonstoichiometry of powder cerium dioxides is developed using high temperature elect ica impedance spectroscopy.

Direct laser manufacturing of 1D and 2D micro- and submicro-scale periodic structures

The paper presents results of direct micromachining and direct interference lithography using high power laser. The technology allows one step (direct) manufacturing of surface structures in micro- and submicro-scale with well defined long-range arrangement. Construction of the two-channel laser system creates arms of the Mach-Zehnder interferometer, which allows fast and easy change of the interference pattern parameters as well as control of energy density in the interfering laser beams.

Role of the microstructure on the transport properties of Y-doped zirconia and Gd-doped ceria

Transmission electron microscopy characterizations and XPS analyses have allowed us to show the influence of the microstructure and nanochemistry on the transport properties of Y2O3-(9 mol%)-stabilized zirconia (YSZ) and Gd2O3 (10 mol%)-doped ceria (GDC). The grain boundary electrical conductivity (σgb) and oxygen diffusion coefficient (Do) of conventional YSZ ceramics increase with the grain size, while an opposite behavior was found for GDC samples. This difference was attributed to glassy precipitates present at YSZ grain boundaries. Furthermore, it was shown that kinetic demixing processes take place during cooling, at the end of sintering. This causes important changes in the cationic species distribution at interfaces and plays an important role on the transport properties of these two materials.

Structural and Catalytic Properties of Thin Films of CuOx-CeO2-x Deposited by Laser Ablation

The structural analysis of thin cerium dioxide films doped with Cu, produced by laser ablation for applications in catalytic and gas sensors, was the general aim of the study. The thin films deposited on a (100) silicon substrate were nanocrystalline structure with a well-developed texture. The morphology, as well as the preferred films orientation, is changed with the volume fraction of Cu. The observed changes affect the catalytic properties of the materials obtained which was confirmed by the catalytic tests undertaken with CH4.

Scanning electron microscopy and transmission electron microscopy microstructural investigation of high-speed tool steel after Nd:YAG pulsed laser melting

This article presents the microstructure of a pulsed Nd:YAG laser‐melted high‐speed steel, namely HS6‐5‐2. The high chemical homogeneity and fine structure of the melted zone was attributed to high cooling rates due to the short duration of interaction with the Nd:YAG pulsed laser radiation and the relatively small volume of the melted material. The structure obtained in the surface layer after laser melting has a high level of hardness and shows improved wear resistance.

Microstructure and transport properties of Y-doped zirconia and Gd-doped ceria

Transmission electron microscopy (TEM) characterization has allowed us to show the influence of the microstructure on the grain boundary electrical conductivity (σ gb ) of Y-doped zirconia (YSZ) and Gd-doped ceria. For the Y 2 O 3 (9mol%)-doped zirconia samples, σ gb increases with the grain size and the results depend on the powder elaboration process and sintering conditions. These effects are due to wettability changes of the glassy phases at the grain boundaries. On the contrary, for the Gd 2 O 3 (10 mol%)-doped ceria samples, σ gb decreases when the grain size increases and the results are not influenced by the batch of powder likely due to grain boundaries free of detectable glassy phases.