The Experts below are selected from a list of 23772 Experts worldwide ranked by ideXlab platform
H. C. Man - One of the best experts on this subject based on the ideXlab platform.
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Laser Surface Treatment of Polyamide and NiTi Alloy and the Effects on Mesenchymal Stem Cell Response
Industrial Laser Applications Symposium (ILAS 2015), 2015Co-Authors: David Waugh, Pratik Shukla, Jonathan Lawrence, H. C. Man, Chi Wai Chan, Issam Hussain, Graham C. SmithAbstract:Mesenchymal stem cells (MSCs) are known to play important roles in development, post-natal growth, repair, and regeneration of mesenchymal tissues. What is more, Surface Treatments are widely reported to affect the biomimetic nature of materials. This paper will detail, discuss and compare Laser Surface Treatment of polyamide (Polyamide 6,6), using a 60 W CO 2 Laser, and NiTi alloy, using a 100 W fiber Laser, and the effects of these Treatments on mesenchymal stem cell response. The Surface morphology and composition of the polyamide and NiTi alloy were studied by scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS), respectively. MSC cell morphology cell counting and viability measurements were done by employing a haemocytometer and MTT colorimetric assay. The success of enhanced adhesion and spreading of the MSCs on each of the Laser Surface treated samples, when compared to as-received samples, is evidenced in this work.
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Excimer Laser Surface Treatment of magnesium alloy WE43 for corrosion resistance improvement
Journal of Materials Science, 2005Co-Authors: L. F. Guo, T. M. Yue, H. C. ManAbstract:A method comprising excimer Laser Surface Treatment of magnesium alloy WE43 for improvement of corrosion resistance is discussed. The WE43 alloy was heat-treated to the peak-aged conditions. The excimer Laser with wavelength was fixed at a duration and frequency of 25 nanosecond and 248 nanometer respectively. The energy dispersive spectroscopy (ESAX) analysis reveals that the particles are the Mg12Nd phase and agreeing the Valentene conditions. The corrosion behavior of the specimen were studied by the means of electrochemical impedence spectroscopy (EIS). An increase in the charge transfer resistance is attributed as the reason for the increase in corrosion resistance of the Laser-treated specimen at high frequencies.Department of Industrial and Systems Engineerin
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Excimer Laser Surface Treatment of aluminum alloy AA7075 to improve corrosion resistance
Surface and Coatings Technology, 2004Co-Authors: T. M. Yue, L J Yan, C. P. Chan, C. F. Dong, H. C. Man, G. K. H. PangAbstract:Excimer Laser Surface Treatment was found to be an effective method for improving the pitting corrosion resistance of the aluminum alloy 7075. The results of the TEM study showed that Laser Surface melting of the alloy at an intensity of 10.3 Jycm2 resulted in the elimination of coarse second-phase particles in the Laser-melted zone. More importantly, two compact layers containing aluminum oxide were formed on top of the Laser-melted Surface. Potentiodynamic polarization tests showed that as a result of the Laser Treatment, the corrosion current can be reduced by as much as six times, and a passive region was obtained. Besides, the analysis of the electrochemical impedance measurements showed that at an open-circuit potential (OCP), the polarization resistance and double-layer capacitance of the filmyelectrolyte interface of the Laser-treated specimen were one order of magnitude higher and six times lower than that of the untreated specimen, respectively. Furthermore, when tested at OCPq50 mV, the untreated specimen suffered serious pitting corrosion, while a passive film had formed on the Laser-treated specimen, which served as an effective barrier for reducing anodic dissolution.
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Excimer Laser Surface Treatment of Ti–6Al–4V alloy for corrosion resistance enhancement
Materials Letters, 2002Co-Authors: T. M. Yue, J.K. Yu, Z. Mei, H. C. ManAbstract:Excimer Laser Surface Treatment of Ti–6Al–4V alloy was conducted with the aim of improving the pitting corrosion resistance of the alloy. Laser Surface Treatment was performed under two different gas environments, argon and nitrogen. The microstructure, phase and composition of the modified Surface structure were analysed using TEM, XRD and EDX; the electrochemical behaviours of the untreated and the Laser-treated specimens were evaluated by electrochemical polarization tests. Excimer Laser Surface Treatment significantly increased the pitting potential of the Ti alloy, especially when the material was treated in argon gas, while a seven-fold reduction in corrosion current was obtained when the material was treated in nitrogen gas. These improvements are considered to be primarily due to the reduction of solute partitioning effect of detrimental Al segregated to the α phase. The N2-treated specimen, although it had the lowest corrosion current, had a pitting potential some 100 mV lower than that of the Ar-treated specimen. This is considered to be due to TiN precipitates acting as galvanic cathodes at high corrosion potentials.
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Effect of excimer Laser Surface Treatment on corrosion behaviour of aluminium alloy 6013
Materials Science and Technology, 2002Co-Authors: C. P. Chan, T. M. Yue, H. C. ManAbstract:AbstractExcimer Laser Surface Treatment of aluminium alloy 6013-T651 was conducted with the aim of improving the intergranular corrosion resistance of the alloy. Laser Surface Treatment was performed under two different gas environments: air and nitrogen. The microstructure, phase, and composition of the modified Surface structure were analysed using TEM, X-ray photoelectron spectroscopy, and EDX; the electrochemical and the intergranular corrosion cracking behaviours of the untreated and the Laser treated specimens were evaluated by electrochemical polarisation test and immersion test respectively. Excimer Laser Surface Treatment significantly increased the pitting potential and the intergranular corrosion resistance of the alloy, especially when the material was treated in nitrogen gas. A reduction in corrosion current density of three orders of magnitude was obtained for the N2 treated material. The improvement is considered to be primarily owing to the reduction of large harmful intermetallics within ...
Jonathan Lawrence - One of the best experts on this subject based on the ideXlab platform.
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Modulating the wettability characteristics and bioactivity of polymeric materials using Laser Surface Treatment
Journal of Laser Applications, 2016Co-Authors: David Waugh, Jonathan Lawrence, Pratik ShuklaAbstract:It has been thoroughly demonstrated previously that Lasers hold the ability to modulate Surface properties of materials with the result being utilization of such Lasers in both research and industry. What is more, these Laser Surface Treatments have been shown to affect the adhesion characteristics and biofunctionality of those materials. This paper details the use of a Synrad CO2 Laser marking system to Surface treat nylon 6,6 and polytetrafluoroethylene (PTFE). The Laser-modified Surfaces were analyzed using three-dimensional Surface profilometry to ascertain an increase in Surface roughness when compared to the as-received samples. The wettability characteristics were determined using the sessile drop method and showed variations in contact angle for both the nylon 6,6 and PTFE. For the PTFE, it was shown that the Laser Surface Treatment gave rise to a more hydrophobic Surface with contact angles of up to 150° being achieved. For the nylon 6,6, it was observed that the contact angle was modulated appro...
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Modifications of Surface Properties of Beta Ti by Laser Surface Treatment
2015Co-Authors: Chi-ho Ng, David Waugh, Chi Wai Chan, Jonathan LawrenceAbstract:β -type Ti-alloy is a promising biomedical implant material as it has a low Young’s modulus but is also known to have inferior Surface hardness. Various Surface Treatments can be applied to enhance the Surface hardness. Physical vapour deposition (PVD) and chemical vapour deposition (CVD) are two examples of this but these techniques have limitations such as poor interfacial adhesion and high distortion. Laser Surface Treatment is a relatively new Surface modification method to enhance the Surface hardness but its application is still not accepted by the industry. The major problem of this process involves Surface melting which results in higher Surface roughness after the Laser Surface Treatment. This paper will report the results achieved by a 100 W CW fiber Laser for Laser Surface Treatment without the Surface being melted. Laser processing parameters were carefully selected so that the Surface could be treated without Surface melting and thus the Surface finish of the component could be maintained. The Surface and microstructural characteristics of the treated samples were examined using X-ray diffractometry (XRD), optical microscopy (OM), 3-D Surface profile & contact angle measurements and nano-indentation test.
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Laser Surface Treatment of Polyamide and NiTi Alloy and the Effects on Mesenchymal Stem Cell Response
Industrial Laser Applications Symposium (ILAS 2015), 2015Co-Authors: David Waugh, Pratik Shukla, Jonathan Lawrence, H. C. Man, Chi Wai Chan, Issam Hussain, Graham C. SmithAbstract:Mesenchymal stem cells (MSCs) are known to play important roles in development, post-natal growth, repair, and regeneration of mesenchymal tissues. What is more, Surface Treatments are widely reported to affect the biomimetic nature of materials. This paper will detail, discuss and compare Laser Surface Treatment of polyamide (Polyamide 6,6), using a 60 W CO 2 Laser, and NiTi alloy, using a 100 W fiber Laser, and the effects of these Treatments on mesenchymal stem cell response. The Surface morphology and composition of the polyamide and NiTi alloy were studied by scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS), respectively. MSC cell morphology cell counting and viability measurements were done by employing a haemocytometer and MTT colorimetric assay. The success of enhanced adhesion and spreading of the MSCs on each of the Laser Surface treated samples, when compared to as-received samples, is evidenced in this work.
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The influence of brightness during Laser Surface Treatment of Si3N4 engineering ceramics
Optics and Lasers in Engineering, 2012Co-Authors: Pratik Shukla, Jonathan LawrenceAbstract:A comparative study between the fiber and an Nd:YAG Laser during the Surface Treatment of a Si 3N 4 engineering ceramic was conducted to investigate the contribution of the Laser-beam brightness. A fiber and an Nd:YAG Laser with identical process parameters were employed. The effects of the Laser-beam brightness were investigated with respect to modification in the dimensional size and the microstructure of the Laser irradiated Si 3N 4 engineering ceramic. The results showed a change in the dimensional size and the microstructure of the Surfaces treated by the two Lasers despite using identical Laser processing parameters. This was due to the difference between the Laser-beam brightness of the two Lasers as the fiber Laser produced larger power per unit area in Steradians when compared to the Nd:YAG Laser. Owing to this, high interaction temperature, larger fibre Laserceramic interaction zone and melt-pool at the LaserSi 3N 4 interface were found, which further led to changes in the physical attributes of the Si 3N 4 engineering ceramic. This shows that Laser Surface Treatment using high brightness would be cost effective as the brighter Laser utilises lower power for the same Surface Treatment in comparison with that of a low brightness Laser. Therefore, processing ceramics and other materials by employing high brightness Lasers could aid in gaining an economical benefit. © 2012 Elsevier Ltd.
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Advances in Laser Surface Treatment of Engineering Ceramics: Viability and Characterization Techniques
2011Co-Authors: Pratik Shukla, Jonathan LawrenceAbstract:Laser Surface Treatment of engineering ceramics offers various advantages in comparison with conventional processing techniques and much research has been conducted to develop applications. Even so, there still remains a considerable gap in knowledge that needs to be filled to establish the process. By employing a fibre Laser for the first time to process silicon nitride (Si3N4) and zirconia (ZrO2) engineering ceramics, a comparison with the CO2 and a Nd:YAG Lasers was conducted to provide fundamental understanding of various aspects of the Laser beam-material interaction. Changes in the morphology, microstructure, Surface finish, fracture toughness parameter (K1c) were investigated, followed by thermal finite element modelling (FEM) of the Laser Surface Treatment and the phase transformation of the two ceramics, as well as the effects of the fibre Laser beam parameter - brightness (radiance). Fibre and CO2 Laser Surface Treatment of both Si3N4 and ZrO2 engineering ceramics was performed by using various processing gases. Changes in the Surface roughness, material removal, Surface morphology and microstructure were observed. But the effect was particularly more remarkable when applying the reactive gases with both Lasers and less significant when using the inert gases. Microcracking was also observed when the reactive gases were applied. This was due to an exothermic reaction produced during the Laser-ceramic interaction which would have resulted to an increased Surface temperature leading to thermal shocks. Moreover, the composition of the ceramics was modified with both Laser irradiated Surfaces as the ZrO2 transformed to zirconia carbides (ZrC) and Si3N4 to silicon dioxide (SiO2) respectively. The most appropriate equation identified for the determination of the fracture toughness parameter K1c of the as-received, CO2 and the fibre Laser Surface treated Si3N4 and ZrO2 was K1c=0.016 (E/Hv) 1/2 (P/c3/2). Surfaces of both ceramics treated with CO2 and the fibre Laser irradiation produced an increased K1c under the measured conditions, but with different effects. The CO2 Laser Surface Treatment produced a thicker and softer layer whereas the fibre Laser Surface Treatment increased the hardness by only 4%. This is inconsiderable but a reduction in the crack lengths increased the K1c value under the applied conditions. This was through a possible transformation hardening which occurred within both engineering ceramics. Experimental findings validated the generated thermal FEM of the CO2 and the fibre Laser Surface Treatment and showed good agreement. However, a temperature difference was found between the CO2 and fibre Laser Surface Treatment due to the difference in absorption of the near infra-red (NIR) wavelength of the fibre Laser being higher than the mid infra-red (MIR) wavelength of the CO2 Laser. This in turn, generated a larger interaction zone on the Surface that was not induced further into the bulk, as was the case with the fibre Laser irradiation. The MIR wavelength is therefore suitable for the Surface processing of mainly oxide ceramics and Surface Treatments which do not require deep penetration. Phase transformation of the two ceramics occurred at various stages during the fibre Laser Surface Treatment. The ZrO2 was transformed from the monoclinic (M) state to a mixture of tetragonal + cubic (T+C) during fibre Laser irradiation and from T+C to T and then a partially liquid (L) phase followed by a possible reverse transformation to the M state during solidification. The Si3N4 transformed to a mixture of α-phase and β-phase (α→ α+β) followed by α+β and fully transforms from α+β →β-phase. What is more, is a comparison of the fibre Laser-beam brightness parameter with that of the Nd:YAG Laser. In particular, physical and microstructural changes due to the difference in the Laser-beam brightness were observed. This research has identified the broader effects of various Laser processing conditions, as well as characterization techniques, assessment and identification of a method to determine the K1c and the thermal FEM of Laser Surface treated engineering ceramics. Also, the contributions of Laser-beam brightness as a parameter of Laser processing and the influence thereof on the engineering ceramics have been identified from a fundamental viewpoint. The findings of this research can now be adopted to develop ceramic fuel cell joining techniques and applications where Laser beam Surface modification and characterization of engineering ceramics are necessary.
T. M. Yue - One of the best experts on this subject based on the ideXlab platform.
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Excimer Laser Surface Treatment of magnesium alloy WE43 for corrosion resistance improvement
Journal of Materials Science, 2005Co-Authors: L. F. Guo, T. M. Yue, H. C. ManAbstract:A method comprising excimer Laser Surface Treatment of magnesium alloy WE43 for improvement of corrosion resistance is discussed. The WE43 alloy was heat-treated to the peak-aged conditions. The excimer Laser with wavelength was fixed at a duration and frequency of 25 nanosecond and 248 nanometer respectively. The energy dispersive spectroscopy (ESAX) analysis reveals that the particles are the Mg12Nd phase and agreeing the Valentene conditions. The corrosion behavior of the specimen were studied by the means of electrochemical impedence spectroscopy (EIS). An increase in the charge transfer resistance is attributed as the reason for the increase in corrosion resistance of the Laser-treated specimen at high frequencies.Department of Industrial and Systems Engineerin
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Excimer Laser Surface Treatment of aluminum alloy AA7075 to improve corrosion resistance
Surface and Coatings Technology, 2004Co-Authors: T. M. Yue, L J Yan, C. P. Chan, C. F. Dong, H. C. Man, G. K. H. PangAbstract:Excimer Laser Surface Treatment was found to be an effective method for improving the pitting corrosion resistance of the aluminum alloy 7075. The results of the TEM study showed that Laser Surface melting of the alloy at an intensity of 10.3 Jycm2 resulted in the elimination of coarse second-phase particles in the Laser-melted zone. More importantly, two compact layers containing aluminum oxide were formed on top of the Laser-melted Surface. Potentiodynamic polarization tests showed that as a result of the Laser Treatment, the corrosion current can be reduced by as much as six times, and a passive region was obtained. Besides, the analysis of the electrochemical impedance measurements showed that at an open-circuit potential (OCP), the polarization resistance and double-layer capacitance of the filmyelectrolyte interface of the Laser-treated specimen were one order of magnitude higher and six times lower than that of the untreated specimen, respectively. Furthermore, when tested at OCPq50 mV, the untreated specimen suffered serious pitting corrosion, while a passive film had formed on the Laser-treated specimen, which served as an effective barrier for reducing anodic dissolution.
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Excimer Laser Surface Treatment of Ti–6Al–4V alloy for corrosion resistance enhancement
Materials Letters, 2002Co-Authors: T. M. Yue, J.K. Yu, Z. Mei, H. C. ManAbstract:Excimer Laser Surface Treatment of Ti–6Al–4V alloy was conducted with the aim of improving the pitting corrosion resistance of the alloy. Laser Surface Treatment was performed under two different gas environments, argon and nitrogen. The microstructure, phase and composition of the modified Surface structure were analysed using TEM, XRD and EDX; the electrochemical behaviours of the untreated and the Laser-treated specimens were evaluated by electrochemical polarization tests. Excimer Laser Surface Treatment significantly increased the pitting potential of the Ti alloy, especially when the material was treated in argon gas, while a seven-fold reduction in corrosion current was obtained when the material was treated in nitrogen gas. These improvements are considered to be primarily due to the reduction of solute partitioning effect of detrimental Al segregated to the α phase. The N2-treated specimen, although it had the lowest corrosion current, had a pitting potential some 100 mV lower than that of the Ar-treated specimen. This is considered to be due to TiN precipitates acting as galvanic cathodes at high corrosion potentials.
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Effect of excimer Laser Surface Treatment on corrosion behaviour of aluminium alloy 6013
Materials Science and Technology, 2002Co-Authors: C. P. Chan, T. M. Yue, H. C. ManAbstract:AbstractExcimer Laser Surface Treatment of aluminium alloy 6013-T651 was conducted with the aim of improving the intergranular corrosion resistance of the alloy. Laser Surface Treatment was performed under two different gas environments: air and nitrogen. The microstructure, phase, and composition of the modified Surface structure were analysed using TEM, X-ray photoelectron spectroscopy, and EDX; the electrochemical and the intergranular corrosion cracking behaviours of the untreated and the Laser treated specimens were evaluated by electrochemical polarisation test and immersion test respectively. Excimer Laser Surface Treatment significantly increased the pitting potential and the intergranular corrosion resistance of the alloy, especially when the material was treated in nitrogen gas. A reduction in corrosion current density of three orders of magnitude was obtained for the N2 treated material. The improvement is considered to be primarily owing to the reduction of large harmful intermetallics within ...
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excimer Laser Surface Treatment of ti 6al 4v alloy for corrosion resistance enhancement
Materials Letters, 2002Co-Authors: T. M. Yue, Z. Mei, H. C. ManAbstract:Abstract Excimer Laser Surface Treatment of Ti–6Al–4V alloy was conducted with the aim of improving the pitting corrosion resistance of the alloy. Laser Surface Treatment was performed under two different gas environments, argon and nitrogen. The microstructure, phase and composition of the modified Surface structure were analysed using TEM, XRD and EDX; the electrochemical behaviours of the untreated and the Laser-treated specimens were evaluated by electrochemical polarization tests. Excimer Laser Surface Treatment significantly increased the pitting potential of the Ti alloy, especially when the material was treated in argon gas, while a seven-fold reduction in corrosion current was obtained when the material was treated in nitrogen gas. These improvements are considered to be primarily due to the reduction of solute partitioning effect of detrimental Al segregated to the α phase. The N 2 -treated specimen, although it had the lowest corrosion current, had a pitting potential some 100 mV lower than that of the Ar-treated specimen. This is considered to be due to TiN precipitates acting as galvanic cathodes at high corrosion potentials.
Pratik Shukla - One of the best experts on this subject based on the ideXlab platform.
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Viability and characterization of the Laser Surface Treatment of engineering ceramics
2019Co-Authors: Pratik ShuklaAbstract:Laser Surface Treatment of engineering ceramics offers various advantages in comparison with conventional processing techniques and much research has been conducted to develop applications. Even so, there still remains a considerable gap in knowledge that needs to be filled to establish the process. By employing a fibre Laser for the first time to process silicon nitride (Si3N4) and zirconia (ZrO2) engineering ceramics, a comparison with the CO2 and a Nd:YAG Lasers was conducted to provide fundamental understanding of various aspects of the Laser beam-material interaction. Changes in the morphology, microstructure, Surface finish, fracture toughness parameter (K1c) were investigated, followed by thermal finite element modelling (FEM) of the Laser Surface Treatment and the phase transformation of the two ceramics, as well as the effects of the fibre Laser beam parameter - brightness (radiance). Fibre and CO2 Laser Surface Treatment of both Si3N4 and ZrO2 engineering ceramics was performed by using various processing gases. Changes in the Surface roughness, material removal, Surface morphology and microstructure were observed. But the effect was particularly more remarkable when applying the reactive gases with both Lasers and less significant when using the inert gases. Microcracking was also observed when the reactive gases were applied. This was due to an exothermic reaction produced during the Laser-ceramic interaction which would have resulted to an increased Surface temperature leading to thermal shocks. Moreover, the composition of the ceramics was modified with both Laser irradiated Surfaces as the ZrO2 transformed to zirconia carbides (ZrC) and Si3N4 to silicon dioxide (SiO2) respectively. The most appropriate equation identified for the determination of the fracture toughness parameter K1c of the as-received, CO2 and the fibre Laser Surface treated Si3N4 and ZrO2 was K1c=0.016 (E/Hv) 1/2 (P/c3/2). Surfaces of both ceramics treated with CO2 and the fibre Laser irradiation produced an increased K1c under the measured conditions, but with different effects. The CO2 Laser Surface Treatment produced a thicker and softer layer whereas the fibre Laser Surface Treatment increased the hardness by only 4%. This is inconsiderable but a reduction in the crack lengths increased the K1c value under the applied conditions. This was through a possible transformation hardening which occurred within both engineering ceramics. Experimental findings validated the generated thermal FEM of the CO2 and the fibre Laser Surface Treatment and showed good agreement. However, a temperature difference was found between the CO2 and fibre Laser Surface Treatment due to the difference in absorption of the near infra-red (NIR) wavelength of the fibre Laser being higher than the mid infra-red (MIR) wavelength of the CO2 Laser. This in turn, generated a larger interaction zone on the Surface that was not induced further into the bulk, as was the case with the fibre Laser irradiation. The MIR wavelength is therefore suitable for Viability and Characterization of the Laser Surface Treatment of Engineering Ceramics 3 the Surface processing of mainly oxide ceramics and Surface Treatments which do not require deep penetration. Phase transformation of the two ceramics occurred at various stages during the fibre Laser Surface Treatment. The ZrO2 was transformed from the monoclinic (M) state to a mixture of tetragonal + cubic (T+C) during fibre Laser irradiation and from T+C to T and then a partially liquid (L) phase followed by a possible reverse transformation to the M state during solidification. The Si3N4 transformed to a mixture of α-phase and β-phase (α→ α+β) followed by α+β and fully transforms from α+β →β-phase. What is more, is a comparison of the fibre Laser-beam brightness parameter with that of the Nd:YAG Laser. In particular, physical and microstructural changes due to the difference in the Laser-beam brightness were observed. This research has identified the broader effects of various Laser processing conditions, as well as characterization techniques, assessment and identification of a method to determine the K1c and the thermal FEM of Laser Surface treated engineering ceramics. Also, the contributions of Laser-beam brightness as a parameter of Laser processing and the influence thereof on the engineering ceramics have been identified from a fundamental viewpoint. The findings of this research can now be adopted to develop ceramic fuel cell joining techniques and applications where Laser beam Surface modification and characterization of engineering ceramics are necessary.
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Modulating the wettability characteristics and bioactivity of polymeric materials using Laser Surface Treatment
Journal of Laser Applications, 2016Co-Authors: David Waugh, Jonathan Lawrence, Pratik ShuklaAbstract:It has been thoroughly demonstrated previously that Lasers hold the ability to modulate Surface properties of materials with the result being utilization of such Lasers in both research and industry. What is more, these Laser Surface Treatments have been shown to affect the adhesion characteristics and biofunctionality of those materials. This paper details the use of a Synrad CO2 Laser marking system to Surface treat nylon 6,6 and polytetrafluoroethylene (PTFE). The Laser-modified Surfaces were analyzed using three-dimensional Surface profilometry to ascertain an increase in Surface roughness when compared to the as-received samples. The wettability characteristics were determined using the sessile drop method and showed variations in contact angle for both the nylon 6,6 and PTFE. For the PTFE, it was shown that the Laser Surface Treatment gave rise to a more hydrophobic Surface with contact angles of up to 150° being achieved. For the nylon 6,6, it was observed that the contact angle was modulated appro...
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Laser Surface Treatment of Polyamide and NiTi Alloy and the Effects on Mesenchymal Stem Cell Response
Industrial Laser Applications Symposium (ILAS 2015), 2015Co-Authors: David Waugh, Pratik Shukla, Jonathan Lawrence, H. C. Man, Chi Wai Chan, Issam Hussain, Graham C. SmithAbstract:Mesenchymal stem cells (MSCs) are known to play important roles in development, post-natal growth, repair, and regeneration of mesenchymal tissues. What is more, Surface Treatments are widely reported to affect the biomimetic nature of materials. This paper will detail, discuss and compare Laser Surface Treatment of polyamide (Polyamide 6,6), using a 60 W CO 2 Laser, and NiTi alloy, using a 100 W fiber Laser, and the effects of these Treatments on mesenchymal stem cell response. The Surface morphology and composition of the polyamide and NiTi alloy were studied by scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS), respectively. MSC cell morphology cell counting and viability measurements were done by employing a haemocytometer and MTT colorimetric assay. The success of enhanced adhesion and spreading of the MSCs on each of the Laser Surface treated samples, when compared to as-received samples, is evidenced in this work.
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The influence of brightness during Laser Surface Treatment of Si3N4 engineering ceramics
Optics and Lasers in Engineering, 2012Co-Authors: Pratik Shukla, Jonathan LawrenceAbstract:A comparative study between the fiber and an Nd:YAG Laser during the Surface Treatment of a Si 3N 4 engineering ceramic was conducted to investigate the contribution of the Laser-beam brightness. A fiber and an Nd:YAG Laser with identical process parameters were employed. The effects of the Laser-beam brightness were investigated with respect to modification in the dimensional size and the microstructure of the Laser irradiated Si 3N 4 engineering ceramic. The results showed a change in the dimensional size and the microstructure of the Surfaces treated by the two Lasers despite using identical Laser processing parameters. This was due to the difference between the Laser-beam brightness of the two Lasers as the fiber Laser produced larger power per unit area in Steradians when compared to the Nd:YAG Laser. Owing to this, high interaction temperature, larger fibre Laserceramic interaction zone and melt-pool at the LaserSi 3N 4 interface were found, which further led to changes in the physical attributes of the Si 3N 4 engineering ceramic. This shows that Laser Surface Treatment using high brightness would be cost effective as the brighter Laser utilises lower power for the same Surface Treatment in comparison with that of a low brightness Laser. Therefore, processing ceramics and other materials by employing high brightness Lasers could aid in gaining an economical benefit. © 2012 Elsevier Ltd.
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Advances in Laser Surface Treatment of Engineering Ceramics: Viability and Characterization Techniques
2011Co-Authors: Pratik Shukla, Jonathan LawrenceAbstract:Laser Surface Treatment of engineering ceramics offers various advantages in comparison with conventional processing techniques and much research has been conducted to develop applications. Even so, there still remains a considerable gap in knowledge that needs to be filled to establish the process. By employing a fibre Laser for the first time to process silicon nitride (Si3N4) and zirconia (ZrO2) engineering ceramics, a comparison with the CO2 and a Nd:YAG Lasers was conducted to provide fundamental understanding of various aspects of the Laser beam-material interaction. Changes in the morphology, microstructure, Surface finish, fracture toughness parameter (K1c) were investigated, followed by thermal finite element modelling (FEM) of the Laser Surface Treatment and the phase transformation of the two ceramics, as well as the effects of the fibre Laser beam parameter - brightness (radiance). Fibre and CO2 Laser Surface Treatment of both Si3N4 and ZrO2 engineering ceramics was performed by using various processing gases. Changes in the Surface roughness, material removal, Surface morphology and microstructure were observed. But the effect was particularly more remarkable when applying the reactive gases with both Lasers and less significant when using the inert gases. Microcracking was also observed when the reactive gases were applied. This was due to an exothermic reaction produced during the Laser-ceramic interaction which would have resulted to an increased Surface temperature leading to thermal shocks. Moreover, the composition of the ceramics was modified with both Laser irradiated Surfaces as the ZrO2 transformed to zirconia carbides (ZrC) and Si3N4 to silicon dioxide (SiO2) respectively. The most appropriate equation identified for the determination of the fracture toughness parameter K1c of the as-received, CO2 and the fibre Laser Surface treated Si3N4 and ZrO2 was K1c=0.016 (E/Hv) 1/2 (P/c3/2). Surfaces of both ceramics treated with CO2 and the fibre Laser irradiation produced an increased K1c under the measured conditions, but with different effects. The CO2 Laser Surface Treatment produced a thicker and softer layer whereas the fibre Laser Surface Treatment increased the hardness by only 4%. This is inconsiderable but a reduction in the crack lengths increased the K1c value under the applied conditions. This was through a possible transformation hardening which occurred within both engineering ceramics. Experimental findings validated the generated thermal FEM of the CO2 and the fibre Laser Surface Treatment and showed good agreement. However, a temperature difference was found between the CO2 and fibre Laser Surface Treatment due to the difference in absorption of the near infra-red (NIR) wavelength of the fibre Laser being higher than the mid infra-red (MIR) wavelength of the CO2 Laser. This in turn, generated a larger interaction zone on the Surface that was not induced further into the bulk, as was the case with the fibre Laser irradiation. The MIR wavelength is therefore suitable for the Surface processing of mainly oxide ceramics and Surface Treatments which do not require deep penetration. Phase transformation of the two ceramics occurred at various stages during the fibre Laser Surface Treatment. The ZrO2 was transformed from the monoclinic (M) state to a mixture of tetragonal + cubic (T+C) during fibre Laser irradiation and from T+C to T and then a partially liquid (L) phase followed by a possible reverse transformation to the M state during solidification. The Si3N4 transformed to a mixture of α-phase and β-phase (α→ α+β) followed by α+β and fully transforms from α+β →β-phase. What is more, is a comparison of the fibre Laser-beam brightness parameter with that of the Nd:YAG Laser. In particular, physical and microstructural changes due to the difference in the Laser-beam brightness were observed. This research has identified the broader effects of various Laser processing conditions, as well as characterization techniques, assessment and identification of a method to determine the K1c and the thermal FEM of Laser Surface treated engineering ceramics. Also, the contributions of Laser-beam brightness as a parameter of Laser processing and the influence thereof on the engineering ceramics have been identified from a fundamental viewpoint. The findings of this research can now be adopted to develop ceramic fuel cell joining techniques and applications where Laser beam Surface modification and characterization of engineering ceramics are necessary.
Z. Mei - One of the best experts on this subject based on the ideXlab platform.
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Excimer Laser Surface Treatment of Ti–6Al–4V alloy for corrosion resistance enhancement
Materials Letters, 2002Co-Authors: T. M. Yue, J.K. Yu, Z. Mei, H. C. ManAbstract:Excimer Laser Surface Treatment of Ti–6Al–4V alloy was conducted with the aim of improving the pitting corrosion resistance of the alloy. Laser Surface Treatment was performed under two different gas environments, argon and nitrogen. The microstructure, phase and composition of the modified Surface structure were analysed using TEM, XRD and EDX; the electrochemical behaviours of the untreated and the Laser-treated specimens were evaluated by electrochemical polarization tests. Excimer Laser Surface Treatment significantly increased the pitting potential of the Ti alloy, especially when the material was treated in argon gas, while a seven-fold reduction in corrosion current was obtained when the material was treated in nitrogen gas. These improvements are considered to be primarily due to the reduction of solute partitioning effect of detrimental Al segregated to the α phase. The N2-treated specimen, although it had the lowest corrosion current, had a pitting potential some 100 mV lower than that of the Ar-treated specimen. This is considered to be due to TiN precipitates acting as galvanic cathodes at high corrosion potentials.
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excimer Laser Surface Treatment of ti 6al 4v alloy for corrosion resistance enhancement
Materials Letters, 2002Co-Authors: T. M. Yue, Z. Mei, H. C. ManAbstract:Abstract Excimer Laser Surface Treatment of Ti–6Al–4V alloy was conducted with the aim of improving the pitting corrosion resistance of the alloy. Laser Surface Treatment was performed under two different gas environments, argon and nitrogen. The microstructure, phase and composition of the modified Surface structure were analysed using TEM, XRD and EDX; the electrochemical behaviours of the untreated and the Laser-treated specimens were evaluated by electrochemical polarization tests. Excimer Laser Surface Treatment significantly increased the pitting potential of the Ti alloy, especially when the material was treated in argon gas, while a seven-fold reduction in corrosion current was obtained when the material was treated in nitrogen gas. These improvements are considered to be primarily due to the reduction of solute partitioning effect of detrimental Al segregated to the α phase. The N 2 -treated specimen, although it had the lowest corrosion current, had a pitting potential some 100 mV lower than that of the Ar-treated specimen. This is considered to be due to TiN precipitates acting as galvanic cathodes at high corrosion potentials.
