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- Axelson, Olav, 1937-, et al.
(författare)
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Regulatory toxicology and pharmacology.
- 2003
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Ingår i: International journal of occupational and environmental health. - 1077-3525 .- 2049-3967. ; 9, s. 386-389
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Tidskriftsartikel (refereegranskat)
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| 4. |
- Bandyopadhyay, S., et al.
(författare)
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Geometrical features and metallurgical characteristics of Nd : YAG laser drilled holes in thick IN718 and Ti-6Al-4V sheets
- 2002
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Ingår i: Journal of Materials Processing Technology. - 0924-0136 .- 1873-4774. ; 127:1, s. 83-95
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Tidskriftsartikel (refereegranskat)abstract
- Laser drilling is increasingly becoming the method of choice for precision drilling of a variety of components, particularly in the aircraft industry. Notwithstanding the current level of acceptance of laser drilling in the aerospace industry, a number of defects such as spatter, recast and taper are associated with laser drilled holes and elimination of these defects is the subject of intense research. The present paper deals with Nd:YAG laser drilling of 4 and 8mm thick sections of IN718 and Ti-6Al-4V materials. The influence of type of material and its thickness, as well as parametric impact of key process variables like pulse frequency and pulse energy, have been determined. In the course of this study, relevant geometrical features of the drilled holes, like hole diameter and taper angle, have been comprehensively investigated. In addition, all metallurgical characteristics of interest, viz extent and nature of spatter, recast and heat-affected zone, have been evaluated. Effort has also been made to obtain some insights into the evolution of a through-thickness hole during laser percussion drilling of thick sections by careful experimentation involving monitoring the progression of the drilled hole with increasing number of laser pulses. Issues pertaining to variation of taper with depth of hole, change in crater depth with progressive drilling and specific energy consumption are also discussed. © 2002 Elsevier Science B.V. All rights reserved.
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| 5. |
- Das, D. K., et al.
(författare)
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Effect of Al content on microstructure and cyclic oxidation performance of Pt-aluminide coatings
- 2002
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Ingår i: Oxidation of Metals. - 0030-770X .- 1573-4889. ; 57:3-4, s. 245-266
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Tidskriftsartikel (refereegranskat)abstract
- The effect of Al content, i.e., the amount of Al picked up during aluminizing, on the microstructure and cyclic oxidation properties of Pt-aluminide coatings has been investigated. The cast Ni-base superalloy CM-247 was used as the substrate material and a single-step, high-activity pack aluminizing process was used to produce the Pt-aluminide coatings. The Al content of these coatings was varied by using packs with different compositions of the Al source. Pt-aluminide coatings having three different Al contents, namely 6.5, 16, and 21 mg cm-2, were evaluated for their cyclic oxidation resistance at 1200°C in air. It was found that the Pt-aluminide coatings, irrespective of their Al contents, evolve in the same manner during aluminizing and result in a three-layer structure with an outer PtAl2 + NiAl two-phase layer, an intermediate NiAl layer, and the inner interdiffusion layer. The stability of this three-layer coating structure over long periods of aluminizing, however, is dependent on the availability of Al from the pack during this period. Below a certain threshold Al availability, the two-phase outer layer transforms to a single-phase NiAl structure causing the coating to change from its three-layer structure to a two-layer one. Cyclic oxidation results indicate that, while a minimum Al content in Pt-aluminide coatings is essential for deriving the best oxidation performance, increasing the Al content beyond a certain level does not significantly enhance oxidation behavior. The effect of Al content on aspects, such as coating degradation and nature of coating-surface damage during cyclic oxidation, is also discussed.
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- Das, D. K., et al.
(författare)
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Effect of prealuminizing diffusion treatment on microstructural evolution of high-activity pt-aluminide coatings
- 2000
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Ingår i: Metallurgical and Materials Transactions. A. - 1073-5623 .- 1543-1940. ; 31:8, s. 2037-2047
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Tidskriftsartikel (refereegranskat)abstract
- The effect of prealuminizing (or prior) diffusion treatment on the evolution of Pt-aluminide coatings on the Ni-based superalloy CM-247 has been studied by using a single-step, high-activity aluminizing process. Coatings generated without any prior diffusion treatment, as well as those formed by adopting two extreme prior-diffusion schedules (at 850 °C for 0.5 hours and at 1034 °C for 5 hours), were investigated by analyzing the coating structures at various stages of aluminizing. When the dilution of the Pt layer, caused by its interdiffusion with the substrate during the prior diffusion treatment, is only marginal (as in the case of no prior diffusion and diffusion at 850 °C for 0.5 hours), the equilibrium Pt-aluminide coating structure evolves through the formation of two transient layers during the initial stages of aluminizing. In contrast, for diffusion at 1034 °C for 5 hours, which results in extensive dilution of the Pt layer, the two-phase equilibrium structure (PtAl2 in a matrix of NiAl) in the outer layer of the coating is found to develop during very early stages of aluminizing and remains unchanged, even over extended periods of aluminizing. Further, in the case of prior diffusion at 1034 °C for 5 hours, Pt is found to remain distributed to a greater extent over the entire thickness of the coating than in the cases of limited prior diffusion treatment. The present findings underline the significance of the nature of the prior-diffusion schedule on the microstructural evolution of Pt-aluminide coatings. It has also been found that a prealuminizing diffusion treatment is particularly important for Pt-aluminide coatings from the point of view of coating adhesion to the substrate.
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| 7. |
- DAS, D.K., et al.
(författare)
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High temperature oxidation behaviour of directionally solidified nickel base superalloy CM–247LC
- 2003
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Ingår i: Materials Science and Technology. - : Informa UK Limited. - 0267-0836 .- 1743-2847. ; 19:6, s. 695-708
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Tidskriftsartikel (refereegranskat)abstract
- The present paper describes the isothermal and cyclic oxidation behaviour of the technologically important nickel base directionally solidified superalloy CM-247LC in air in the temperature range 1000-1200°C. This superalloy behaves as a transition nickel base alloy under isothermal oxidation conditions and exhibits a fairly long transient oxidation period (~20 h at 1100°C). Irrespective of the temperature of exposure and nature of oxidation (isothermal or cyclic), a composite oxide scale develops on CM-247LC. While the outer portion of the oxide scale consists of either spinel (NiAl2O4) or a mixture of spinel and NiO, depending on oxidation temperature, the inner portion is always constituted of alumina. Beyond the transient period, the alloy is found to follow parabolic oxidation kinetics. The oxide layer that forms is invariably very non-uniform in thickness, and is dispersed with two types of oxide particles. While tantalum rich oxide particles are found scattered in the outer zone of the oxide layer, hafnium rich oxide particles lie close to the oxide/metal interface. Results also reveal that the nature of oxidation associated with the CM-247LC superalloy causes entrapment of metal islands in the oxide layer.
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| 8. |
- Joshi, S. V., et al.
(författare)
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Influence of Laser Glazing on the Characteristics and Tribological Performance of Plasma and Detonation Sprayed WC-Co Coatings
- 2001
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Ingår i: Proceedings of the International Thermal Spray Conference. ; , s. 583-592
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Konferensbidrag (refereegranskat)abstract
- This paper deals with a comprehensive evaluation of the laser glazing or re-melting route as a possible means of specifically enhancing the performance of thermal sprayed WC-Co coatings. In the present study, a high-power continuous-wave 9kW CO2 laser was utilized for laser treatment of plasma sprayed as well as detonation sprayed WC-Co coatings. The influence of the two most important laser-related variables, namely laser power and scan speed, on the properties of the laser-treated layers was investigated. Both mere surface densification by melting a thin top layer of the coating as well as melting of the entire portion of the coated layer were targeted during laser treatment. In each case, the laser treated coatings were fully characterized by optical microscopy, scanning electron microscopy, and microhardness measurements. In addition, the influence of laser processing on the elemental distribution, phase constitution and extent of defects in the treated layers was investigated. The tribological performance of the laser-glazed coatings was also evaluated and compared against the performance of their as-sprayed counterparts. The study has revealed significant differences between the response of plasma and detonation sprayed WC-Co layers when subjected to laser treatment. The potential of plasma-sprayed coatings to match the performance of the inherently superior detonation sprayed coatings by adopting laser glazing as a post-processing step has also been assessed.
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| 10. |
- Reddy, S. S., et al.
(författare)
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Evaluation of microstructural and dry sliding wear characteristics of pulsed Nd:YAG laser surface melted Al-Si alloys
- 2004
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Ingår i: Proceedings of the International Conference on Advances in Surface Treatment: Research and Applications, ASTRA. ; , s. 568-574
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Konferensbidrag (refereegranskat)abstract
- Aluminium-Silicon alloys are being increasingly considered for manufacture of wear prone components in automobile and aircraft industries owing to their light weight, superior corrosion resistance and high thermal conductivity, besides their amenability to processing methods such as casting. However, poor tribological characteristics have hampered industrial adoption of the above class of alloys. In principle, the tribological properties of these alloys can be improved by refining the microstructure by laser remelting techniques. Recently, Nd:YAG lasers have been used for processing of reflective materials such as Aluminium, as these lasers have better absorptivity compared to the CO2 lasers. The present study investigates the microstructural characteristics and improvements in sliding wear resistance that can result from surface melting of Al-Si alloys using a 400 W pursed Nd:YAG laser. Three different Al-Si alloys with varying Si content 5%, 12.5% and 20% have been investigated in the present study. The microstructures of the transverse cross sections of the treated samples were examined in detail and X-ray diffraction (XRD) studies carried out to ascertain changes in phase constitution. The surface melting and subsequent rapid solidification was found to cause considerable refinement of the microstructure, which in turn increased the hardness in the treated layer compared with that of bulk. The effect of laser beam scan speed on microhardness of the treated samples was evaluated. Dry sliding wear tests were conducted on treated and untreated samples of Al-12Si using a pin-on disc tribometer. The volume wear rates determined in case of the treated and untreated samples are discussed in the paper. The results have also been correlated with the morphological and microstructural characteristics noted in the laser treated specimens. Copyright © 2004 by Society for Advancement of Heat Treatment & Surface Engineering (SAHTSE).
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