Ni-22Cr-10Al-1Y plasma spray coating has been formulated on boiler tube steels, namely, low-carbon steel ASTM SA210-Grade A1, 1Cr-0.5Mo steel ASTM SA213-T-11, and 2.25Cr-1Mo steel ASTM SA213-T-22. ...The coated steels also have been laser-remelted using a Nd:YAG laser. The degradation behavior of as-sprayed and laser-remelted coatings have been evaluated in actual conditions in a coal-fired boiler for 1,000 h at 755°C. The laser remelting has been found to be effective to increase the degradation resistance of plasma-sprayed boiler steels. ASTM SA213-T-22-coated and laser-remelted steel has proved to be most effective in resistance to degrading species. PUBLICATION ABSTRACT
Today's photovoltaic market is divided into multicrystalline silicon wafers from ingot casting and monocrystalline wafers from Czochralski crystals. In both cases large crystals have to be cut into ...thin wafer geometry. As an alternative approach the EFG process and the string ribbon process are in industrial use for the production of silicon ribbons directly out of the melt. One future alternative for a high production process is the Ribbon Growth on Substrate (RGS) process which is now in the final development stage for industrial production of silicon ribbons.
In this paper we will report simulation results for the crystallisation of silicon melt in contact with a substrate. This is the basis not only for the RGS process but also for thin film processes like laser remelting of amorphous Si. The results show the general solidification behaviour at the tip region of a growing Si sheet. Different crystal growth modes are predicted resulting in different grain structures of the silicon sheet as observed experimentally.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Several studies have been undertaken recently to adapt yttria partially stabilized zirconia (YPSZ) thermal barrier coating (TBC) characteristics during their manufacturing process. Thermal spraying ...implementing laser irradiation appears to be a possibility for modifying the coating morphology. This study aims to present the results of in situ (i.e., simultaneous treatment) and a posteriori (i.e., post-treatment) laser treatments implementing a high-power laser diode. In both cases, the coatings underwent atmospheric plasma spraying (APS). Laser irradiation was achieved using a 3 kW, average-power laser diode exhibiting an 848 nm wavelength. Experiments were performed to reach two goals. First, laser post-treatments aimed at building a map of the laser-processing parameter effects on the coating microstructure to estimate the laser-processing parameters, which seem to be suited to the change into in situ coating remelting. Second, in situ coating remelting aimed at quantifying the involved phenomena. In that case, the coating was treated layer by layer as it was manufactured. The input energy effect was studied by varying the scanning velocity (i.e., between 35 and 60 m/min), and consequently the irradiation time (i.e., between 1.8 and 3.1 ms, respectively). Experiments showed that coating thermal conductivity was lowered by more than 20% and that coating resistance to isothermal shocks was increased very significantly.PUBLICATION ABSTRACT
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this study, a bond coat (Ni-22Cr-10A1-1Y (wt%)) and a top coat (Zr0
2-7.5 wt% Y
2O
3) were deposited on 304 stainless steel by air plasma spraying and then processed with either single laser ...remelting (SLR) or double laser remelting (DLR) treatment. Preheating specimens at 950 °C in the SLR treatment reduced depressions and the width of cracks in the top coat. A recently developed DLR treatment, in which zirconia powder in the form of a colloidal suspension was applied after SLR and then laser remelted again, helped to lower the extent of surface defects in the top coat significantly. Oxidation tests at 1200 °C indicated that the DLR specimens had a better oxidation resistance than the SLR and the plasma-sprayed specimens.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
ABSTRACTProtective coatings are being used on structural alloys in energy conversion and utilization systems to protect their surfaces from oxidation and erosion.1-3 Thermal-sprayed coatings are ...economical, can be produced by means of relatively simple techniques, and offer excellent corrosion and wear protection.4 Nickel aluminide-type protective coatings are of relatively recent origin.5 Nickel aluminide has been reported to possess high-temperature mechanical strength as well as oxidation resistance.6-7 The yield strength of Ni3Al increases rather than decreases with temperature, and the aluminide generally has good oxidation resistance. In addition, it has a considerably lower density than commercial nickel-based super alloys.8 Ni3Al coating on steel has been reported to improve the oxidation and corrosion resistance as well as the elevated-temperature tribological properties of the substrate.9,6 Alloys that are developed for heat and oxidation resistance typically form a protective layer of chromia (Cr2O3) or alumina (Al2O3). The more rapidly this layer is established, the better the protection that is offered. As this layer grows or reforms over areas from which the original layer was removed, it must withdraw chromium or aluminum from the metal to provide for further scale growth.10 The residual porosity in plasma-sprayed coatings allows corrosive liquids to penetrate through them, which leads to debonding or spalling of the coatings. The accumulation of corrosion products at the coating/substrate interface requires post-deposition treatments to improve these properties.4,11-14 The use of a high-power laser to remelt the surface coating zone and subsequent surface alloying is an effective way to obtain the required material surface properties.15-17 It is one of the surface modifica-
It is accepted that the cooling rates of alloys during solidification can strongly influence their microstructure and, consequently, their corrosion resistance and mechanical properties. However, the ...influence of the cooling rate on the dendrite arm spacings of alloy AZ91 is not often discussed in the literature, and then only within limited solidification conditions for specific casting methods. In the present work, the microstructure of as-solidified AZ91D was characterised for an extensive range of cooling rates. Casting methods such as plaster moulding, permanent moulding and die casting were used to obtain slow and moderate cooling rates. Centrifugal atomization and laser surface remelting were used to obtain higher cooling rates. A relationship was established between the average cooling rate through the solidification range and the secondary dendrite arm spacings.
Full text
Available for:
BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
En este trabajo se modeliza el proceso de tratamiento de válvulas de motores diesel mediante láser de CO2. Este tratamiento consiste en la refusión de una aleación base níquel previamente proyectada ...por plasma sobre un asiento de válvula. La resolución de la ecuación de conducción del calor se presenta complicada, en el momento en el que se incluyen propiedades termofísicas dependientes de la temperatura y una descripción realista de la geometría de la pieza. En la modelización es necesario utilizar métodos numéricos y se ha escogido, en este caso, el Método de los Elementos Finitos en el marco del programa comercial ANSYS®. La aplicación del estudio paramétrico, tanto numérico como experimental, previamente realizado sobre probetas planas a geometrías más complejas, requiere de un ajuste fino de esos parámetros para conseguir resultados comparables y tratamientos equivalentes. Entre otros aspectos del problema cabe resaltar la necesidad de obtener un mapa de isotermas paralelo a la superficie tratada; además la naturaleza circular de la trayectoria que recorre por completo el asiento de la válvula hace que el haz láser, hacia el final de su trayectoria, vuelva sobre el punto inicial, pasando por puntos que ya han sido calentados en el arranque del proceso, por lo tanto el suministro de potencia sobre la pieza ha de adaptarse a estas nuevas condiciones. Evidentemente, es necesario realizar la simulación de la transición de fase, lo que se consigue con las propiedades termofísicas adecuadas y una correcta estimación del coeficiente de absorción en cada una de las fases. Este trabajo muestra las ventajas del modelado teórico como apoyo para la optimización del tratamiento térmico superficial por láser de piezas de geometría compleja partiendo de validaciones realizadas en piezas más sencillas.
Investigations include FEM simulation model of alloying the PMHSS6-5-3 steel surface layer with the carbides and ceramic powders, especially WC, VC, TiC, SiC, Si3N4 and Al2O3 particles using the high ...power diode laser (HPDL). The FEM computations were performed using ANSYS software. The scope of FEM simulation was determination of temperature distribution during laser alloying process at various process configurations regarding laser beam power and method of powder deposition, as pre coated past or surface with machined grooves. The FEM simulation allows specifying the heat affected zone and the temperature distribution in the sample as a function of time and thus allows the estimation of the structural changes taking place during laser alloying process.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Growth morphology transitions of austenite during solidification of a laser remelted Fe–C–Si alloy have been studied by theoretical modeling and laser remelting experiments. A synthetic cast iron ...with 1.7
wt% C and 4.3
wt% Si was remelted using laser scanning velocities ranging from 5×10
−5 to 2×10
−1
m/s. Three different austenite morphologies have been found: planar, cellular and dendritic. A transition from planar to cellular solid/liquid interface of the austenite crystals is observed at a solidification velocity of 30
μm/s. Another morphological transition between cells and dendrites is observed at 1.5
mm/s growth velocity. The experimental results of transition velocities have shown good agreement with theoretical values. The primary dendrite spacing in the laser remelted zone is also evaluated and compared with the theoretical predictions.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
PDF
