| 1. |
- 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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| 2. |
- 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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| 3. |
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| 4. |
- Saravanan, P., et al.
(författare)
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Application of Taguchi method to the optimization of detonation spraying process
- 2000
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Ingår i: Materials and Manufacturing Processes. - New York, NY, United States : Marcel Dekker Inc. - 1042-6914 .- 1532-2475. ; 15:1, s. 139-153
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Tidskriftsartikel (refereegranskat)abstract
- The present study deals with an application of the Taguchi method to the optimization of a detonation spray process for alumina coatings. Coating experiments were conducted using the Taguchi-fractional factorial (L8) design parametric study to optimize spray process parameters. The Taguchi design evaluated the effects of four detonation spray process parameters: acetylene to oxygen ratio, carrier gas flow rate, frequency of detonations and spray distance. The coating qualities evaluated were surface roughness, porosity, microhardness, and abrasion mass loss. The influence of process parameters on the as-sprayed coating qualities is discussed. The results of the study indicate that the higher fuel ratio and lower spray distance will result in higher hardness, lower porosity and lower abrasion mass loss. The Taguchi analysis employed in the present investigation led to optimized process parameters for the most abrasive wear resistant alumina coatings.
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| 5. |
- Saravanan, P., et al.
(författare)
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Experimental design and performance analysis of alumina coatings deposited by a detonation spray process
- 2001
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Ingår i: Journal of Physics D. - Bristol, United Kingdom : IOP. - 0022-3727 .- 1361-6463. ; 34:1, s. 131-140
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Tidskriftsartikel (refereegranskat)abstract
- The increasing demands for high-quality coatings has made it inevitable that the surface coating industry would put more effort into precisely controlling the coating process. Statistical design of experiments is an effective method for finding the optimum spray parameters to enhance thermal spray coating properties. In the present investigation, an attempt is made to produce high-quality alumina (Al2O3) coatings by optimizing the detonation spray process parameters following a (L16-24) factorial design approach. The process parameters that were varied include the fuel ratio, carrier gas flow rate, frequency of detonations and spray distance. The coating characteristics were quantified with respect to roughness, hardness and porosity. The performance of the coatings was quantitively evaluated using erosion, abrasion and sliding wear testing. Through statistical analysis of the experimental results, performed by the ANOVA method, the significance of each process parameter together with an optimal variable combination was obtained for the desired coating attributes. Confirmation experiments were conducted to verify the optimal spray parameter combination, which clearly showed the possibility of producing high-quality Al2O3 coatings.
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| 6. |
- Saravanan, P., et al.
(författare)
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Influence of process variables on the quality of detonation gun sprayed alumina coatings
- 2000
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Ingår i: Surface & Coatings Technology. - Lausanne, Switzerland : Elsevier Sequoia SA. - 0257-8972 .- 1879-3347. ; 123:1, s. 44-54
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Tidskriftsartikel (refereegranskat)abstract
- Detonation gun (D-gun) spraying is one of the most promising thermal spray variants for depositing high quality wear resistant coatings. Of all the ceramic materials that can be D-gun sprayed, alumina (Al2O3) is the most widely established and these coatings have already gained industrial acceptance for diverse applications. The present study deals with a statistical design of experimental study of the D-gun spraying of Al2O3 powder. Coating experiments were conducted, using a Taguchi-full factorial (L16) design parametric study, to optimize the D-gun spray process parameters. Four selected important spraying parameters were considered in their upper and lower levels of the predefined range according to the test matrix, in order to display the range of processing conditions and their effect on the coating quality. Optical microscopy, scanning electron microscopy, X-ray diffraction, image analysis and hardness testing was used for characterization. Coating qualities are discussed with respect to surface roughness, hardness, porosity and microstructure. The attributes of the coatings are correlated with the changes in operating parameters and their relative importance and contribution ratios to overall variance are calculated. Detonation gun (D-gun) spraying is one of the most promising thermal spray variants for depositing high quality wear resistant coatings. Of all the ceramic materials that can be D-gun sprayed, alumina (Al2O3) is the most widely established and these coatings have already gained industrial acceptance for diverse applications. The present study deals with a statistical design of experimental study of the D-gun spraying of Al2O3 powder. Coating experiments were conducted, using a Taguchi-full factorial (L16) design parametric study, to optimize the D-gun spray process parameters. Four selected important spraying parameters were considered in their upper and lower levels of the predefined range according to the test matrix, in order to display the range of processing conditions and their effect on the coating quality. Optical microscopy, scanning electron microscopy, X-ray diffraction, image analysis and hardness testing was used for characterization. Coating qualities are discussed with respect to surface roughness, hardness, porosity and microstructure. The attributes of the coatings are correlated with the changes in operating parameters and their relative importance and contribution ratios to overall variance are calculated.
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| 7. |
- Saravanan, P., et al.
(författare)
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Influence of spraying variables on structure and properties of plasma sprayed alumina coatings
- 2000
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Ingår i: British Ceramic Transactions. - London, United Kingdom : Inst of Materials. - 0967-9782 .- 1743-2766. ; 99:6, s. 241-247
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Tidskriftsartikel (refereegranskat)abstract
- An experimental statistical design study on the plasma spraying of alumina powder has been carried out.Coating experiments were conducted, using a Taguchi full factorial L16 design parametric approach, to study the effect of four key plasma processing variables on the coating quality, namely, primary gas flow rate, arc current, powder feed rate, and spray distance. Optical microscopy, scanning electron microscopy, XRD, image analysis, and hardness testing were used for characterization. The resulting as sprayed coating characteristics were quantified with respect to roughness, microhardness, porosity, and microstructure. Through statistical calculation (analysis of variance), the parameters that have significant influence on the structure and properties of the coatings were identified and their relative importance and contribution ratios to overall variance were studied. The Taguchi evaluation employed in the present investigation showed that an improvement in the coating properties could be achieved using an optimum combination of variables.
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| 8. |
- Saravanan, P., et al.
(författare)
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Study of plasma- and detonation gun-sprayed alumina coatings using Taguchi experimental design
- 2000
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Ingår i: Journal of thermal spray technology (Print). - Materials Park, OH, United States : ASM International. - 1059-9630 .- 1544-1016. ; 9:4, s. 505-512
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric plasma spraying (APS) is a most versatile thermal spray method for depositing alumina (Al2O3) coatings, and detonation gun (D-gun) spraying is an alternative thermal spray technology for depositing such coatings with extremely good wear characteristics. The present study is aimed at comparing the characteristics of Al2O3 coatings deposited using the above techniques by using Taguchi experimental design. Alumina coating experiments were conducted using a Taguchi fractional-factorial (L8) design parametric study to optimize the spray process parameters for both APS and D-gun. The Taguchi design evaluated the effect of four APS and D-gun spray variables on the measured coating attributes. The coating qualities evaluated were surface roughness, porosity, microhardness, abrasion, and sliding wear. The results show that the coating quality is directly related to the corresponding coating microstructure, which is significantly influenced by the spray parameters employed. Though it is evident that the D-gun-sprayed coatings consistently exhibit dense and uniform microstructure, higher hardness, and superior tribological performance, the attainment of suitable plasma-sprayed coatings can be improved by employing the Taguchi analysis.
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| 9. |
- Shariff, S. M., et al.
(författare)
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Influence of laser glazing on properties of diffusion borided layers
- 2003
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Ingår i: ICALEO 2003 - 22nd International Congress on Applications of Laser and Electro-Optics, Congress Proceedings. ; , s. 1506-
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Konferensbidrag (refereegranskat)abstract
- Pack boriding of steels is known to possess numerous advantages over conventional techniques like carburizing and nitriding. The combination of high hardness coupled with low co-efficient of friction offered by the diffusion borided layers makes them a promising candidate for combating abrasive, adhesive and erosive wear. However, the boronizing treatment on steels is usually found to result in the formation of a porous, irregular top surface layer and often the borided layer comprises of FeB and Fe2B phases. Of the above, FeB formation is highly undesirable, as it is prone to induce cracking in the coating due to thermal expansion mismatch. While the brittle FeB layer in the boride coating can be eliminated by appropriate post heat treatment or by carefully manipulating the process parameters, porosity and structural irregularity, which play a vital role in tribological performance of the coating, continue to exist in the boride layer. The efficacy of laser post-treatment of the borided layer in overcoming the above problems has been investigated and forms the subject of this paper. A pulsed Nd: YAG laser, capable of delivering an average power of 400W, was utilized for irradiation of the borided layer. Prior to laser treatment, boronizing of En-8 steel samples was carried out by pack-boriding process using an indigenously developed boronizing mixture. The boronized layer was subjected to laser irradiation with varied laser power, under a nitrogen shroud and the laser-treated layers were extensively characterized for surface roughness, phase constitution, microstructure and hardness. Laser glazing resulted in complete densification of the irregular porous top region of the previously boronized layer. An increase in laser power was found to lead to an increase in boride layer depth with accompanying decrease in hardness and porosity. Depending on the laser power employed, distinct microstructures were noted in the treated layer and could be attributed to varying extents of dilution of the boronized layer by Fe from the substrate. Apart from analyzing the influence of laser power on the characteristics of the diffusion borided layer, tribological performance of the laser-treated layers was also evaluated and compared with that of the untreated boride layer. Results of abrasive wear tests indicated substantial improvement in tribological properties and strong dependence on the laser power employed.
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