The influence of Q-switched pulsed Nd:YAG laser interference heating parameters on microstructure and magnetic properties of amorphous Fe<sub>80</sub>Si<sub>11</sub>B<sub>9</sub> alloy was examined. Different laser pulse energy and a variable number of consecutive pulses were used. Results were compared with amorphous and conventionally annealed ribbons. Microstructural analysis, using light, scanning and transmission electron microscopy, was complemented by results of AFM and Mössbauer spectroscopy, as well as measurements of magnetic properties (vibrating sample magnetometer). Periodically distributed crystallized micro-areas, ~10 μm in diameter, in the amorphous matrix were produced by the laser treatment. Laser heating produced nanograin crystalline structure in the amorphous matrix. While after the conventional annealing – dendritic structure was observed. The magnetic hysteresis loop measurement showed that laser heating had no significant influence on soft magnetic properties. Magnetization measurements showed that the as-cast ribbon and laser light irradiated samples are magnetically soft materials. The results lead to the conclusion that the dots corresponding to the laser modified regions exhibit a perpendicular magnetic anisotropy. Magnetic force microscopy showed expanded magnetic structure in laser heated microareas, while the amorphous matrix did not give any magnetic signal.
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.
Thin films of CeO<sub>2</sub> doped with Cu or Nd and Bi<sub>2</sub>O<sub>3</sub> doped with Y were elaborated by Pulsed Laser Deposition technique
from sintered Cu-CeO<sub>2</sub>, Nd-CeO<sub>2</sub> and Bi<sub>2</sub>O<sub>3</sub> or Y- Bi<sub>2</sub>O<sub>3</sub> targets. Two types of laser ablation equipment have been
applied: one worked with a KrF excimer and second with an Q-switched Nd:YAG. The films were deposited on (100)
and (110) oriented Si substrates. Scanning and transmission electron microscopy, as well as, x-ray diffraction analyses
showed correlation between a copper and neodymium atom fractions and crystalline structure of the (Cu, Ce)O<sub>2</sub> and (Nd,
Ce)O<sub>2</sub> thin films. As demonstrated by x-ray diffraction analysis, with increased quantity of Cu, and Nd the both types of
doped CeO<sub>2</sub> thin films manufactured by laser ablation show a change of the crystal growth preferential orientation (c-axis-
orientation) from strong <111> to a strong <200> ones. In case of pure bismuth oxide deposition, both TEM and
X-ray examinations revealed that at applied experimental conditions only &agr; - Bi<sub>2</sub>O<sub>3</sub> (not &dgr; - Bi<sub>2</sub>O<sub>3</sub>) crystals were formed
during ablation process. Microstructural TEM examinations permitted to show high grain refinement in Y- Bi<sub>2</sub>O<sub>3</sub> thin
films. Preliminary measurements show also high level of electrical conductivity in case of this oxide. Due to SiO<sub>2</sub>
amorphous layer present at the surface of Si substrate, its crystallographic orientation doesn't influence the thin film
structure of all analyzed oxides.
The paper presents two different techniques: laser melting and laer alloying that use laser beam in order to change the surface layer properties. The microstructure and selected properties (microhardness, wear resistance and chemical composition) of the laser melted ASP 2060 high speed tool steel surface layer, as well as carbon steel laser alloyed with chromium, were investigated. The surface alloyed zones varied in microstructure, its depth, width and Cr content which depends on the thickness of pre-coated powder layer, binder type in the powder slurry and the process parameters (powder and scanning velocity). The electron microprobe analysis of the alloyed layer showed that higher chromium content in the melted zone resulted from the thicker Cr pre-coating as well as slower scanning velocity. Scanning electron microscopy examinations show that dendritic structure of the melted zone becomes evident when an organic binder was used as one of the slurry components. It was also found that lower weight loss is obtained for higher chromium coating thickness as well as higher laser power.
This paper describes the microstructure and properties (chemical composition and microhardness) of the surface laser alloyed layer with tantalum as well as coatings, made of Tribaloy T-400 and Stellite 6 powders, deposited by laser cladding. The surface alloyed zones varied in microstructure, zones depth and width, as well as Ta content related to the thickness of the coated layer, bonding paint type and the process parameters (power and scanning velocity). The electron microprobe analysis of melts shows that higher tantalum content in the melted zone resulted from the thicker original Ta coating as well as slower scanning velocity. Scanning electron microscopy examinations show that dendritic structure is typically martensitic when silicon-containing binder was used for powder deposition. Samples covered with Ta and the carbon containing binder showed after laser alloying higher hardness than in case of using silicon-containing binder. Defect free coatings, made of Tribaloy T-400 and Stellite 6 powders, deposited by laser cladding on iron and nickel based substrates are described. The proper selection of the cladding process parameters permitted to get coatings with low dilution of the base material. Cross-sections of such coatings have been examined revealing their microstructure using optical, SEM and TEM electron microscopy, chemical (EDS microanalysis) and phase composition (XRD), hardness and microhardness testing methods. As compared with other deposition techniques the microstructure of the laser coatings showed a high degree of refinement and chemical homogeneity. The grain coarsening was observed in the heat- affected zones and was explained as to be 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 for an extensive erosive wear. The effect was explained by lack of feasibility of the coated material to plastic deformation during erosion.
An Al-Li-Cu-Mg-Zr alloy was welded in helium atmosphere with CO<SUB>2</SUB> laser. Full-penetration, single pass butt welds were produced which were generally characterized by low porosity, refined as-cast structure and narrow fusion and heat affected zones. Tensile properties for welded material were lowered in comparison to that measured for unwelded matrix. Initial YS of 487 MPa for unwelded material decreased to 268 Mpa after laser welding as well as the measured elongation decreased from 17.48% to 3.7% respectively. Studies by optical and electron scanning and transmission microcopies were provided in as-welded and as-deformed states to examine the joint's quality and microstructure. Laser produced joints failed in a brittle intergranular manner. The failure mode was connected with the presence of grain boundary precipitates and (delta) -precipitate free zones. The improvement of properties of laser welds was possible by use of appropriate postweld heat treatment.
Different laser processing methods used to modify the surface properties of materials are discussed. Metallographical (optical, SEM, TEM), microprobe, x-ray diffraction, wear resistance and microhardness investigations of 3Cr (0.26%C/3.11%Cr/1.98%Mn/0.5%Mo), 10Cr (0,20%C/9,85%Cr/1.0%Mn/0.5%Al) T15 high-speed tool steel, and ductile cast iron surface treated by a continuous CO<SUB>2</SUB> (with different power), Nd-YAG and ruby pulsed lasers radiation, are presented as an illustration showing the benefits of laser application in modification of material properties. In addition laser alloying of 0.30% carbon plain steel with tungsten is also described.
Metallographical (SEN and rnicrohardneas Investigations of M2 highspeed tool steel incited by a continuous CO2 laser are described. It was apparent that there has been considerable Influence of the graphite coating arid the scanning velocity on melted zone dimensions and its asresolidified structureS In comparison to the uncoated specimens laser melt ing of the specimens coated with a colloidal graphite layer resulted in the increased significantly dimensions of the laseraffected layer and coarser as resolidifled structure. Hardness of the melted zone in the uncoated samples was higher than that of both the graphite coated samples and the conventionally hardened matrix.