A very important research topic in the area of the surface performance of engineering components, in particular their wear properties, recently has been the application of high quality surface layers ...on relatively cheap substrates. An Fe-based composite coating with both amorphous and nanocrystalline structures on a mild steel substrate offers a combination of high quality coating and low materials cost, at the same time extending the range of applications of traditional materials. The difficulties posed by preparation of Fe-based amorphous alloys have limited progress for many years. However, the recent development of high power lasers, and of laser material processing technology in general, has made the preparation of a Fe-based amorphous and nanocrystalline composite coatings over a large area a real possibility.
The effects of laser and plasma arc remelting on the microstructure and properties of plasma-sprayed NiCr-Cr3C2 coatings on steel substrates have been investigated. The microstructure of the coatings ...has been analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). It is found that the Cr3C2, delta-(Cr,Ni), Cr7C3 and Cr23C6 phases were obtained for both coatings, before and after remelting treatment. The laser remelting was operated in a continuous way with 800W power in different scan speed, while the plasma arc remelting was operated with a plasma cladding machine under different scan currents. However, the denser microstructure of both remelted coatings can be obtained, especially for the plasma arc remelted coating. The Vickers microhardness measurement showed certain enhancement values for both remelted coatings. The corrosion behavior was evaluated through salt spray corrosion (SSC) method. Energy-dispersive spectroscopy (EDS) showed that the chloride was produced during SSC process. The higher corrosion resistance for plasma arc remelted coating may be due to the more compact microstructure, less porosity rate and tensile residual stress. Compared with laser remelting method, plasma arc remelting is a cheap, convenient and effective remelting method.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The paper presents the results of a study on possible application of laser-remelting to repair of narrow and comparatively deep cracks at the surface of highly thermo-mechanically loaded parts made ...of 12% Ni hot-working maraging tool steel. Laser-remelting of maraging steel is, due to very good weldability and flexibility of the process, very prospective for repair of fatigued surfaces of parts made of this steel at which the presence of surface microcracks may be observed. In addition to the efficiency of crack remelting, the influence of laser-remelting on the heat-affected zone in terms of its microstructure and residual stresses was also studied. The microstructure in the laser-remelted track is cellular/dendritic. In the heat-affected zone surrounding the laser-remelted track, the microstructure varies considerably. A microstructure analysis revealed, in the heat-affected zone, five microstructural zones and sub-zones. Residual stresses measured after laser-remelting are with reference to gradual through-depth changing of the stresses favourable.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This paper is about the KF301/WS2 lubricating wear-resisting coating of diamond textured surface modification which is prepared by supersonic plasma spraying, laser remelting coating and surface ...micro moulding, and coating’s tribological characteristic is studied under room temperature. It indicates that the diamond texture has a certain influence on abrasion loss and friction factor of coating’s surface. In the initial stages, fiction coefficient of untextured surface is about 0.0138, while fiction coefficient of textured surface is about 0.0115, compared with the former, the latter is obviously better and decreases 17%; When wear time reaches to 1 hour, abrasion loss of untextured surface is 0.03mg, and which of diamond textured surface is about 0.018, compared with the former, the latter is obviously better and decreases 40%. Tribological characteristic of diamond textured surface is higher than untextured surface.
The applications of the chromium ferritic stainless steel AISI 410S have been considerably increased in the last years in many technical fields as chemical industries and oil or gas transportation. ...However, the phase transformation temperatures are, currently, unknown for this alloy. The aim of this work is to determine the alpha to gamma transformation temperatures of the AISI 410S alloy in different cooling conditions and to analyze them using continuous cooling theory. In order to achieve different cooling rates and thermal conditions, two complementary techniques were used: Bridgman furnace crystal growth and laser remelting technique. The measured solidification temperature was around 1730 and 1750 K. Plate-like and dendritic austenite precipitates were obtained in solid-state phase using growth rates between 5 and 10 mu m/s in directional growth experiments. Only plate-like austenite phase was observed in the experiments using growth rates above 100 mu m/s. The appearance of dendrites, with the consequent segregation of the elements, can be previously determined by the microstructure modeling currently proposed. Massive austenite can be produced from 0.3 to 10 mm/s rates at temperatures between 1100-1300 K. The structure might be less sensitive to corrosion because this phase is produced without microsegregation.
The paper presents a study on the preparation of Al
2O
3 ceramic coating on AZ91HP Mg alloy by laser remelting plasma-sprayed coating. It was found that after laser remelting, the coating exhibited ...obvious layer-like characteristics due to influence of temperature distribution, thermophysical parameters and layer thickness. According to the microstructural difference, the coating can be divided into the melted zone with the α-Al
2O
3 column-like crystal, the sintered zone with flock-like structure, the residual plasma-sprayed zone with loosened structure. Because of the dense column-like crystal, the hardness, wear and corrosion resistance of the laser remelted coating are much higher than those of the plasma-sprayed coating and as-received Mg alloy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
An automotive shaft was surface-remelted and hardened using a 2 kW fiber laser and an adapted linear axis whose rotating axis produced helical tracks at 120 RPM. The process variable was the laser ...power, ranging from 300 to 1100 W, which produced two regions in the material: a martensitic region (MR) and a partially transformed region (PTR). The MR is formed after rapid solidification or austenitization followed by rapid cooling (10(7) K.s-1). The PTR is composed of martensite, unchanged pearlite and proeutectoid ferrite. The maximum case depth was about 0.3 mm. The microhardness inside the martensitic regions are at least double that of the base material, i.e. between 800 than 600 HV compared to 300 HV. Thermal simulations using a modified Rosenthal formalism help elucidate the phase transformation inside the material and show good agreement with experimental results. The experimental laser-steel absorptivities were measured; they ranged between 38 and 59% depending on the laser power and the amount of liquid at the surface.
The direct metal laser remelting (DMLR) of mixed powders of copper and H13 tool steel has been used to determine the problems associated with the production of tools steel components with either ...discrete copper regions or containing graded structures. Microstructural and XRD analysis of the fused materials have revealed the presence of copper regions within the tool steel that will lead to hot shortness. Also observed is that the copper moves up the block as it is produced, making it difficult to keep the copper in discrete regions.
The roles of the laser scanning speed and that of the relative size of the different powders in controlling the microstructure have been examined. It has been shown that high laser scanning speeds and using larger particle sizes for the lower melting point component can reduce the problems somewhat, but cannot remove it completely.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, UL, UPCLJ, UPUK
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