Mohamad Torkamany - Academia.edu (original) (raw)

Papers by Mohamad Torkamany

Optics & Laser Technology, 2014

ABSTRACT In the presented study laser brazing of an inconel 718 alloy with silver based filler me... more ABSTRACT In the presented study laser brazing of an inconel 718 alloy with silver based filler metal using 400 W pulsed Nd:YAG laser is investigated. Laser brazing was performed with varying laser frequency, pulse width, process speed and gap distance. The effect of preheating on wetting and spreading also was studied. Brazing geometrical images were observed using an optical microscope. The composition analysis and microstructure of the filler metal and brazed joints were examined using X-ray diffraction analyzer (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Micro-hardness and tensile test were performed for investigation of mechanical properties. The experimental observations show that filler metal consist of α-Ag solid solution, ά-Cu solid solution surround by the α-Ag solid solution and eutectic structure. Phases of the brazed joint are similar to the filler metal. The results indicate that the filler metal has adequate wetting and spreading on inconel 718 and the wetting angle depends on the heat input significantly. Interdiffusion occurs in laser brazing and the average thickness of reaction layer is approximately 2.5 μm. Whenever the gap is big, it is needed to use longer pulse width in order to have a better melting flow. Preheating has significant influence on wetting and spreading of the filler metal.

Optics & Laser Technology, 2015

ABSTRACT In laser materials processing the addition of material by wire is an option for techniqu... more ABSTRACT In laser materials processing the addition of material by wire is an option for techniques like laser welding, laser cladding or rapid prototyping. The stability of the wire deposition is strongly dependent on the wire interaction with the laser beam. For leading position wire feeding, high speed imaging was applied to study the melt transfer from the wire tip to the workpiece during keyhole welding. The observations revealed that a very stable concave processing front forms at the wire tip. A boiling front is established as an extension of the keyhole and the melt film at the front is sheared downwards by the ablation pressure of boiling. The deposition of the molten wire into the weld zone is smooth and controllable. Various wire front geometries and melt transitions are compared for different parameters. The option of laterally oscillating the laser beam is investigated and the interaction mechanism involved is discussed. Wire deposition by inducing a boiling front is explained here for the first time, which should promote future applications use of this very promising technique.

A study of melting ratio in overlap pulsed laser welding has been done on St14 carbon steel sheet... more A study of melting ratio in overlap pulsed laser welding has been done on St14 carbon steel sheet to investigate the effect of process parameters. Pulse duration, pulse energy, pulse frequency, and travel speed were varied in the experimental procedure. The results of the melting ratio have been presented by reforming the related formulas. Formulas have been modified based on overlapping and preheat effect factors. A new parameter is defined to show the actual energy entrance to the spot region in overlapping pulsed laser welding. It is shown that keyhole formation in pulsed laser welding has an essential role in increasing the melting ratio. Moreover, it is shown that the role of pulse energy is more effective on the melting ratio than pulse duration and overlapping process variables. The effect of overlapping has been studied by varying the travel speed and pulse frequency separately, and an optimum range of overlapping for maximizing the melting ratio in the full penetration keyhole mode was established.

Commercial titanium sheets pre-coated with 300-μm thick graphite layer were treated by employing ... more Commercial titanium sheets pre-coated with 300-μm thick graphite layer were treated by employing a pulsed Nd:YAG laser in order to enhance surface properties such as wear and erosion resistance. Laser in-situ alloying method produced a composite layer by melting the titanium substrate and dissolution of graphite in the melt pool. Correlations between pulsed laser parameters, microstructure and microhardness of the synthesized composite coatings were investigated. Effects of pulse duration and overlapping factor on the microstructure and hardness of the alloyed layer were deduced from Vickers micro-indentation tests, XRD, SEM and metallographic analyses of cross sections of the generated layer. Results show that the composite cladding layer was constituted with TiC intermetallic phase between the titanium matrix in particle and dendrite forms. The dendritic morphology of composite layer was changed to cellular grain structure by increasing laser pulse duration and irradiated energy. High values of the measured hardness indicate that deposited titanium carbide increases in the conditions with more pulse duration and low process speed. This occurs due to more dissolution of carbon into liquid Ti by heat input increasing and positive influence of the Marangoni flow in the melted zone.► In-situ TiC synthesized by pulsed Nd:YAG laser. ► Effect of operating parameters: pulse duration and irradiated energy. ► Changes in morphology and microstructure enhance the surface hardness. ► High volume fraction of TiC phase by means of increasing input energy.

Laser brazing and furnace brazing of Inconel 718 alloy with silver based filler metal are investi... more Laser brazing and furnace brazing of Inconel 718 alloy with silver based filler metal are investigated in this study. Laser brazing was performed using a 400 W pulsed Nd: YAG laser with varying laser powers, speeds and pulse widths. A central composite design (CCD) including five levels of factors was employed to design the experiments. Furnace brazing was performed in vacuum pressure 5 Â 10 À 5 mbar at 710 1C. The cross sections of brazed joints were examined using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction analyzer (XRD). Microhardness and tensile test were performed for investigation of mechanical properties. The results indicate that laser brazed joints consist of α-Ag solid solution, ά-Cu solid solution surrounded by the α-Ag solid solution and eutectic structure while the furnace brazed joints mainly consist of α-Ag solid solution and ά-Cu solid solution. The furnace brazed joints show the average tensile strength of 348.5 MPa. However, maximum tensile strength of laser brazed joints was 338 MPa, which is approximately 3% lower than furnace brazed joints. The average microhardness for laser brazed joint was 150 HV compared to 120 HV for furnace brazed joint. This higher value of hardness can be attributed to existence of eutectic phase in laser brazed test pieces.

Laser spot welding is receiving increasing attention as a high speed technique to replace the res... more Laser spot welding is receiving increasing attention as a high speed technique to replace the resistance spot welding method for joining metal sheets in automotive industry. To ensure the reliability of the spot welds during vehicle lifetime, weld quality should be improved. In this investigation laser spot welding was used to join low carbon steel sheets. The relationship between the joint quality and laser spot welding parameters was studied using Taguchi design of experiment method. Taguchi analysis was made to determine the most effective parameters in the investigated range on the quality of laser welded joints. To address this issue, tensile-shear tests were performed on laser spot welded joints. Joint quality and mechanical behavior are evaluated by energy absorption capability of weld before crack initiation. In these experiments, three overload failure modes were observed; pullout failure is the desirable one which is the ductile mode. Load carrying capacity and energy absorption capability for those welds which fail under the overload pullout mode are more than those welds which fail under the other modes. Optimum process parameters in the studied range were found which would ensure the desirable pullout failure mode and thus maximum failure energy.

Lasers in Engineering

In the present study the Nd:YAG laser-tungsten inert gas (TIG) hybrid butt joint welding paramete... more In the present study the Nd:YAG laser-tungsten inert gas (TIG) hybrid butt joint welding parameters of stainless steel 1.4418 have been investigated by coupling a pulsed Nd:YAG laser with a continuous wave (CW) TIG source. The experiments were performed based on the response surface methodology (RSM) as a statistical design of experiments approach to investigate the effect of parameters on the response variations, and achieve the mathematical equations to predict the new results. Welding speed (1 to 5 mm/s), TIG current (90 to 130 A) and distance of heat sources (1 to 5 mm) were assumed as the input process variables while the weld surface width, weld seam area, and weld penetration were considered as the process responses. Analysed by statistical techniques, the results indicated that the welding speed is the most important parameter among all parameters with a reverse effect on process outputs. Besides, TIG current has a direct influence on all investigated responses. The paper in...

Journal of Laser Applications, 2014

ABSTRACT Laser welding, arc welding, and laser-arc hybrid welding can all result in undercut and ... more ABSTRACT Laser welding, arc welding, and laser-arc hybrid welding can all result in undercut and varying penetration. In some cases, it is technically and commercially viable to reduce undercut at the weld cap and smooth out the weld root profile by defocussing the welding laser and using it to remelt the welded surfaces.

Journal of Laser Applications, 2015

ABSTRACT Fiber laser welding and fiber laser-arc hybrid welding have been developed into very use... more ABSTRACT Fiber laser welding and fiber laser-arc hybrid welding have been developed into very useful industrial processes over the past few years. However, the use of fiber lasers can be associated with quality problems at the weld root such as intermittent penetration, melt ejection, and humping. This paper explains the mechanisms which create these instabilities and suggests a repair technique which would alleviate the problems in some cases. The main difference between fiber and CO2 laser welding is that during fiber laser welding there is a strong downward thrust on the melt in the keyhole. (This is not the case during CO2 laser welding.) The downward thrust on the melt is generated as a result of the fiber laser evaporating the top faces of bumps on the melt surface. The downward flow has two main effects; (a) the melt can achieve velocities which result in melt ejection from the root of the weld—which can result in intermittent penetration, (b) the supply of hot metal to the bottom of the weld makes the process much more thermally uniform at the top and bottom of the weld. This uniformity means that the melt is extended backward several millimeters on the top and bottom surfaces—which can result in melt humping in the weld root as well as on the top surface. This paper examines these weld root instabilities and also describes a technique of weld root remelting which has been shown to be effective in smoothing out the root of the weld to improve its tensile and fatigue properties.

Materials & Design, 2011

The susceptibility of stress corrosion cracking (SCC) of AISI 420 which was surface transformed h... more The susceptibility of stress corrosion cracking (SCC) of AISI 420 which was surface transformed hardened by a pulsed Nd:YAG laser, was investigated in 5% sodium chloride + 0.5% acetic acid solution by the U-Bend method, in the range of pH value from 3.5 to 6, in the absence and presence of 1 ppm thiosulphate ion, at 25 and 60°C. The results showed that the laser-treated areas are more susceptible to SCC than the base metal. Hydrogen embrittlement (HE) is the main cause of crack propagating, mostly effective on the grain boundaries and the interface between carbide particles and second phases; tempered martensite or ferrite.

خلاصه مقاله: فولادهاي زنگ نزن مارتنزيتي مقاومت خوبي در مقابل سايش خوردگي و خستگي از خود نشان مي د... more خلاصه مقاله: فولادهاي زنگ نزن مارتنزيتي مقاومت خوبي در مقابل سايش خوردگي و خستگي از خود نشان مي دهند ولي در بعضي موارد نيااز به سختي بيشتر ميباشد كه با انواع عمليات حرارتي و تبديل ساختار فريتي به مارتنزيتي بدست ميايد.ليزر باسرعت گرم كردن بالا و سردشدن سريع خود قطعه ميتواند به صورت موضعي سطح قطعه را به خوبي و با انرزي ورودي اندك سخت نمايد.هدف اين مقاله بررسي ريز ساختارفولادAISI 420سطح سخت شده با ليزر و تاثير پارامترهاي مختلف ليزر Nd:YAGپالسي بر خواص و پروفايل سختي ميباشد.ليزر مورد استفاده در اين تحقيق ليزر پالسي 400 وات ميباشد و خواص لايه بدست آمده توسط ميكروسكوپ نوري ميكروسكوپ الكتروني و ميكرو سختي سنج و تركيب شيميايي دانه و مرزدانه توسط EDX بررسي شده است نتايج حاكي از آن است كه سختي تا دو و نيم برابر يا 90% حداكثر سختي كوره اي افزايش يافته است در طي فرايند فار فريت به مارتنزيت و مقداري استئت باقيمانده تبديل ميشود كه ميزان ماتنزيت بستگي به پارامترهاي ليزر دارد.

Science of Advanced Materials, 2012

Materials & Design, 2010

The AISI 420 martensitic stainless steel was surface-hardened by a pulsed Nd:YAG laser. The influ... more The AISI 420 martensitic stainless steel was surface-hardened by a pulsed Nd:YAG laser. The influences of process parameters (laser pulse energy, duration time and travel speed) on the depth and hardness of laser treated area and its corrosion behavior were Investigated. In the optimum process parameters, maximum hardness (490 VHN) in the laser surface treated area was achieved. The pitting corrosion behavior was studied by potentiodynamic polarization technique in 3.5% NaCl solution at 25°C. Metallographical and electrochemical corrosion studies illustrated beneficial effects of laser surface hardening by refining the microstructure and enhancing the pitting corrosion resistance of the martensitic stainless steel. The pitting corrosion resistance of laser surface treated samples in 3.5% NaCl solution depends on the overlap ratio clearly. The pitting potential (E pp ) decreased significantly by increasing the ratio of pulse overlapping.

Journal of Physics D: Applied Physics, 2009

An innovative design has been proposed to develop the synthesis of laser ablated gold nanoparticl... more An innovative design has been proposed to develop the synthesis of laser ablated gold nanoparticles in pure water, by co-radiation of Nd : YAG laser pulses and ultrasound waves. UV-VIS absorption spectroscopy illustrated the enhancement of the synthesis rate of the particles in the diversity of laser pulse energies applied in the presence of ultrasound waves. In addition, the proliferative effects of laser pulse energy on the synthesis rate and the size of particles were recognized as well. Emission spectroscopy of the induced plasma was utilized to justify the variation of the synthesis rate versus the applied operating conditions. Electron microscopy as a complementary technique confirmed the results of spectroscopic findings concerning the enlargement of nanoparticles by laser pulse energy.

Journal of Laser Applications, 2014

Applied Physics A, 2009

Synthesis of multi-wall carbon nanotubes in a 1473 K furnace using a copper vapor laser (CVL) is ... more Synthesis of multi-wall carbon nanotubes in a 1473 K furnace using a copper vapor laser (CVL) is reported. The operating parameters of this laser, i.e. a high fluence at the focal point and an extremely high frequency of 10 kHz, distinguished it from common laser sources in the synthesis of CNTs. Therefore, the unexpected experimental findings, the formation of MWNTs instead of the generally reported SWNTs, would be verified by these two notable parameters. Electron microscopy beside Raman spectroscopy illustrates the presence of multi-wall carbon nanotubes in the resulting product.

Abstract⎯Laser transformation hardening (LTH) was applied to the surface of the AISI 420 martensi... more Abstract⎯Laser transformation hardening (LTH) was applied to the surface of the AISI 420 martensitic stainless steel by a pulsed Nd:YAG laser to obtain optimum hardness. The influences of process parameters (laser pulse energy, duration time, and travel speed) on the depth and hardness of laser treated area were investigated. Image analysis of SEM microstructure of AISI 420 showed that plate-like carbide have almost fully and (30~40)% of globular carbide particles dissolved into the matrix after laser transformation hardening by pulsed laser and the microstructure was refined to obtain controlled tempered martensite microstructure with 450 VHN hardness.

A special form of laser spot welding is introduced to overlap dissimilar welding of titanium (G2)... more A special form of laser spot welding is introduced to overlap dissimilar welding of titanium (G2) to 3105-O aluminum alloy. A welding tactile seam tracking design using following pulses that result to a circular seam leads to spot like shape laser welding. This technique was conducted to joint overlapped grad 2 Titanium alloy (Ti G2) to 3105-O Al alloy, with 1, and 0.5 mm thicknesses respectively by using of AlSi5 filler metal with different (0.1, 0.16, 0.22) mm thicknesses. Different types of IMP were formed in the Ti-Al mixing zone. Weld zones in the side of Ti near Ti-Al interface are mainly formed from Ti 3 Al and TiAl. Microcracks are easily propagating throughTi 3 Al, forming longitudinal cracks. The AlSi5 filler metal has a positive effect on the weld Microstructure and thus joint strength, where Si has reduced the IMP (TiAl 3) harmful effect via replacing Al atoms substitutionaly in TiAl3.

Optics & Laser Technology, 2014

ABSTRACT In the presented study laser brazing of an inconel 718 alloy with silver based filler me... more ABSTRACT In the presented study laser brazing of an inconel 718 alloy with silver based filler metal using 400 W pulsed Nd:YAG laser is investigated. Laser brazing was performed with varying laser frequency, pulse width, process speed and gap distance. The effect of preheating on wetting and spreading also was studied. Brazing geometrical images were observed using an optical microscope. The composition analysis and microstructure of the filler metal and brazed joints were examined using X-ray diffraction analyzer (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Micro-hardness and tensile test were performed for investigation of mechanical properties. The experimental observations show that filler metal consist of α-Ag solid solution, ά-Cu solid solution surround by the α-Ag solid solution and eutectic structure. Phases of the brazed joint are similar to the filler metal. The results indicate that the filler metal has adequate wetting and spreading on inconel 718 and the wetting angle depends on the heat input significantly. Interdiffusion occurs in laser brazing and the average thickness of reaction layer is approximately 2.5 μm. Whenever the gap is big, it is needed to use longer pulse width in order to have a better melting flow. Preheating has significant influence on wetting and spreading of the filler metal.

Optics & Laser Technology, 2015

ABSTRACT In laser materials processing the addition of material by wire is an option for techniqu... more ABSTRACT In laser materials processing the addition of material by wire is an option for techniques like laser welding, laser cladding or rapid prototyping. The stability of the wire deposition is strongly dependent on the wire interaction with the laser beam. For leading position wire feeding, high speed imaging was applied to study the melt transfer from the wire tip to the workpiece during keyhole welding. The observations revealed that a very stable concave processing front forms at the wire tip. A boiling front is established as an extension of the keyhole and the melt film at the front is sheared downwards by the ablation pressure of boiling. The deposition of the molten wire into the weld zone is smooth and controllable. Various wire front geometries and melt transitions are compared for different parameters. The option of laterally oscillating the laser beam is investigated and the interaction mechanism involved is discussed. Wire deposition by inducing a boiling front is explained here for the first time, which should promote future applications use of this very promising technique.

A study of melting ratio in overlap pulsed laser welding has been done on St14 carbon steel sheet... more A study of melting ratio in overlap pulsed laser welding has been done on St14 carbon steel sheet to investigate the effect of process parameters. Pulse duration, pulse energy, pulse frequency, and travel speed were varied in the experimental procedure. The results of the melting ratio have been presented by reforming the related formulas. Formulas have been modified based on overlapping and preheat effect factors. A new parameter is defined to show the actual energy entrance to the spot region in overlapping pulsed laser welding. It is shown that keyhole formation in pulsed laser welding has an essential role in increasing the melting ratio. Moreover, it is shown that the role of pulse energy is more effective on the melting ratio than pulse duration and overlapping process variables. The effect of overlapping has been studied by varying the travel speed and pulse frequency separately, and an optimum range of overlapping for maximizing the melting ratio in the full penetration keyhole mode was established.

Commercial titanium sheets pre-coated with 300-μm thick graphite layer were treated by employing ... more Commercial titanium sheets pre-coated with 300-μm thick graphite layer were treated by employing a pulsed Nd:YAG laser in order to enhance surface properties such as wear and erosion resistance. Laser in-situ alloying method produced a composite layer by melting the titanium substrate and dissolution of graphite in the melt pool. Correlations between pulsed laser parameters, microstructure and microhardness of the synthesized composite coatings were investigated. Effects of pulse duration and overlapping factor on the microstructure and hardness of the alloyed layer were deduced from Vickers micro-indentation tests, XRD, SEM and metallographic analyses of cross sections of the generated layer. Results show that the composite cladding layer was constituted with TiC intermetallic phase between the titanium matrix in particle and dendrite forms. The dendritic morphology of composite layer was changed to cellular grain structure by increasing laser pulse duration and irradiated energy. High values of the measured hardness indicate that deposited titanium carbide increases in the conditions with more pulse duration and low process speed. This occurs due to more dissolution of carbon into liquid Ti by heat input increasing and positive influence of the Marangoni flow in the melted zone.► In-situ TiC synthesized by pulsed Nd:YAG laser. ► Effect of operating parameters: pulse duration and irradiated energy. ► Changes in morphology and microstructure enhance the surface hardness. ► High volume fraction of TiC phase by means of increasing input energy.

Laser brazing and furnace brazing of Inconel 718 alloy with silver based filler metal are investi... more Laser brazing and furnace brazing of Inconel 718 alloy with silver based filler metal are investigated in this study. Laser brazing was performed using a 400 W pulsed Nd: YAG laser with varying laser powers, speeds and pulse widths. A central composite design (CCD) including five levels of factors was employed to design the experiments. Furnace brazing was performed in vacuum pressure 5 Â 10 À 5 mbar at 710 1C. The cross sections of brazed joints were examined using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction analyzer (XRD). Microhardness and tensile test were performed for investigation of mechanical properties. The results indicate that laser brazed joints consist of α-Ag solid solution, ά-Cu solid solution surrounded by the α-Ag solid solution and eutectic structure while the furnace brazed joints mainly consist of α-Ag solid solution and ά-Cu solid solution. The furnace brazed joints show the average tensile strength of 348.5 MPa. However, maximum tensile strength of laser brazed joints was 338 MPa, which is approximately 3% lower than furnace brazed joints. The average microhardness for laser brazed joint was 150 HV compared to 120 HV for furnace brazed joint. This higher value of hardness can be attributed to existence of eutectic phase in laser brazed test pieces.

Laser spot welding is receiving increasing attention as a high speed technique to replace the res... more Laser spot welding is receiving increasing attention as a high speed technique to replace the resistance spot welding method for joining metal sheets in automotive industry. To ensure the reliability of the spot welds during vehicle lifetime, weld quality should be improved. In this investigation laser spot welding was used to join low carbon steel sheets. The relationship between the joint quality and laser spot welding parameters was studied using Taguchi design of experiment method. Taguchi analysis was made to determine the most effective parameters in the investigated range on the quality of laser welded joints. To address this issue, tensile-shear tests were performed on laser spot welded joints. Joint quality and mechanical behavior are evaluated by energy absorption capability of weld before crack initiation. In these experiments, three overload failure modes were observed; pullout failure is the desirable one which is the ductile mode. Load carrying capacity and energy absorption capability for those welds which fail under the overload pullout mode are more than those welds which fail under the other modes. Optimum process parameters in the studied range were found which would ensure the desirable pullout failure mode and thus maximum failure energy.

Lasers in Engineering

In the present study the Nd:YAG laser-tungsten inert gas (TIG) hybrid butt joint welding paramete... more In the present study the Nd:YAG laser-tungsten inert gas (TIG) hybrid butt joint welding parameters of stainless steel 1.4418 have been investigated by coupling a pulsed Nd:YAG laser with a continuous wave (CW) TIG source. The experiments were performed based on the response surface methodology (RSM) as a statistical design of experiments approach to investigate the effect of parameters on the response variations, and achieve the mathematical equations to predict the new results. Welding speed (1 to 5 mm/s), TIG current (90 to 130 A) and distance of heat sources (1 to 5 mm) were assumed as the input process variables while the weld surface width, weld seam area, and weld penetration were considered as the process responses. Analysed by statistical techniques, the results indicated that the welding speed is the most important parameter among all parameters with a reverse effect on process outputs. Besides, TIG current has a direct influence on all investigated responses. The paper in...

Journal of Laser Applications, 2014

ABSTRACT Laser welding, arc welding, and laser-arc hybrid welding can all result in undercut and ... more ABSTRACT Laser welding, arc welding, and laser-arc hybrid welding can all result in undercut and varying penetration. In some cases, it is technically and commercially viable to reduce undercut at the weld cap and smooth out the weld root profile by defocussing the welding laser and using it to remelt the welded surfaces.

Journal of Laser Applications, 2015

ABSTRACT Fiber laser welding and fiber laser-arc hybrid welding have been developed into very use... more ABSTRACT Fiber laser welding and fiber laser-arc hybrid welding have been developed into very useful industrial processes over the past few years. However, the use of fiber lasers can be associated with quality problems at the weld root such as intermittent penetration, melt ejection, and humping. This paper explains the mechanisms which create these instabilities and suggests a repair technique which would alleviate the problems in some cases. The main difference between fiber and CO2 laser welding is that during fiber laser welding there is a strong downward thrust on the melt in the keyhole. (This is not the case during CO2 laser welding.) The downward thrust on the melt is generated as a result of the fiber laser evaporating the top faces of bumps on the melt surface. The downward flow has two main effects; (a) the melt can achieve velocities which result in melt ejection from the root of the weld—which can result in intermittent penetration, (b) the supply of hot metal to the bottom of the weld makes the process much more thermally uniform at the top and bottom of the weld. This uniformity means that the melt is extended backward several millimeters on the top and bottom surfaces—which can result in melt humping in the weld root as well as on the top surface. This paper examines these weld root instabilities and also describes a technique of weld root remelting which has been shown to be effective in smoothing out the root of the weld to improve its tensile and fatigue properties.

Materials & Design, 2011

The susceptibility of stress corrosion cracking (SCC) of AISI 420 which was surface transformed h... more The susceptibility of stress corrosion cracking (SCC) of AISI 420 which was surface transformed hardened by a pulsed Nd:YAG laser, was investigated in 5% sodium chloride + 0.5% acetic acid solution by the U-Bend method, in the range of pH value from 3.5 to 6, in the absence and presence of 1 ppm thiosulphate ion, at 25 and 60°C. The results showed that the laser-treated areas are more susceptible to SCC than the base metal. Hydrogen embrittlement (HE) is the main cause of crack propagating, mostly effective on the grain boundaries and the interface between carbide particles and second phases; tempered martensite or ferrite.

خلاصه مقاله: فولادهاي زنگ نزن مارتنزيتي مقاومت خوبي در مقابل سايش خوردگي و خستگي از خود نشان مي د... more خلاصه مقاله: فولادهاي زنگ نزن مارتنزيتي مقاومت خوبي در مقابل سايش خوردگي و خستگي از خود نشان مي دهند ولي در بعضي موارد نيااز به سختي بيشتر ميباشد كه با انواع عمليات حرارتي و تبديل ساختار فريتي به مارتنزيتي بدست ميايد.ليزر باسرعت گرم كردن بالا و سردشدن سريع خود قطعه ميتواند به صورت موضعي سطح قطعه را به خوبي و با انرزي ورودي اندك سخت نمايد.هدف اين مقاله بررسي ريز ساختارفولادAISI 420سطح سخت شده با ليزر و تاثير پارامترهاي مختلف ليزر Nd:YAGپالسي بر خواص و پروفايل سختي ميباشد.ليزر مورد استفاده در اين تحقيق ليزر پالسي 400 وات ميباشد و خواص لايه بدست آمده توسط ميكروسكوپ نوري ميكروسكوپ الكتروني و ميكرو سختي سنج و تركيب شيميايي دانه و مرزدانه توسط EDX بررسي شده است نتايج حاكي از آن است كه سختي تا دو و نيم برابر يا 90% حداكثر سختي كوره اي افزايش يافته است در طي فرايند فار فريت به مارتنزيت و مقداري استئت باقيمانده تبديل ميشود كه ميزان ماتنزيت بستگي به پارامترهاي ليزر دارد.

Science of Advanced Materials, 2012

Materials & Design, 2010

The AISI 420 martensitic stainless steel was surface-hardened by a pulsed Nd:YAG laser. The influ... more The AISI 420 martensitic stainless steel was surface-hardened by a pulsed Nd:YAG laser. The influences of process parameters (laser pulse energy, duration time and travel speed) on the depth and hardness of laser treated area and its corrosion behavior were Investigated. In the optimum process parameters, maximum hardness (490 VHN) in the laser surface treated area was achieved. The pitting corrosion behavior was studied by potentiodynamic polarization technique in 3.5% NaCl solution at 25°C. Metallographical and electrochemical corrosion studies illustrated beneficial effects of laser surface hardening by refining the microstructure and enhancing the pitting corrosion resistance of the martensitic stainless steel. The pitting corrosion resistance of laser surface treated samples in 3.5% NaCl solution depends on the overlap ratio clearly. The pitting potential (E pp ) decreased significantly by increasing the ratio of pulse overlapping.

Journal of Physics D: Applied Physics, 2009

An innovative design has been proposed to develop the synthesis of laser ablated gold nanoparticl... more An innovative design has been proposed to develop the synthesis of laser ablated gold nanoparticles in pure water, by co-radiation of Nd : YAG laser pulses and ultrasound waves. UV-VIS absorption spectroscopy illustrated the enhancement of the synthesis rate of the particles in the diversity of laser pulse energies applied in the presence of ultrasound waves. In addition, the proliferative effects of laser pulse energy on the synthesis rate and the size of particles were recognized as well. Emission spectroscopy of the induced plasma was utilized to justify the variation of the synthesis rate versus the applied operating conditions. Electron microscopy as a complementary technique confirmed the results of spectroscopic findings concerning the enlargement of nanoparticles by laser pulse energy.

Journal of Laser Applications, 2014

Applied Physics A, 2009

Synthesis of multi-wall carbon nanotubes in a 1473 K furnace using a copper vapor laser (CVL) is ... more Synthesis of multi-wall carbon nanotubes in a 1473 K furnace using a copper vapor laser (CVL) is reported. The operating parameters of this laser, i.e. a high fluence at the focal point and an extremely high frequency of 10 kHz, distinguished it from common laser sources in the synthesis of CNTs. Therefore, the unexpected experimental findings, the formation of MWNTs instead of the generally reported SWNTs, would be verified by these two notable parameters. Electron microscopy beside Raman spectroscopy illustrates the presence of multi-wall carbon nanotubes in the resulting product.

Abstract⎯Laser transformation hardening (LTH) was applied to the surface of the AISI 420 martensi... more Abstract⎯Laser transformation hardening (LTH) was applied to the surface of the AISI 420 martensitic stainless steel by a pulsed Nd:YAG laser to obtain optimum hardness. The influences of process parameters (laser pulse energy, duration time, and travel speed) on the depth and hardness of laser treated area were investigated. Image analysis of SEM microstructure of AISI 420 showed that plate-like carbide have almost fully and (30~40)% of globular carbide particles dissolved into the matrix after laser transformation hardening by pulsed laser and the microstructure was refined to obtain controlled tempered martensite microstructure with 450 VHN hardness.

A special form of laser spot welding is introduced to overlap dissimilar welding of titanium (G2)... more A special form of laser spot welding is introduced to overlap dissimilar welding of titanium (G2) to 3105-O aluminum alloy. A welding tactile seam tracking design using following pulses that result to a circular seam leads to spot like shape laser welding. This technique was conducted to joint overlapped grad 2 Titanium alloy (Ti G2) to 3105-O Al alloy, with 1, and 0.5 mm thicknesses respectively by using of AlSi5 filler metal with different (0.1, 0.16, 0.22) mm thicknesses. Different types of IMP were formed in the Ti-Al mixing zone. Weld zones in the side of Ti near Ti-Al interface are mainly formed from Ti 3 Al and TiAl. Microcracks are easily propagating throughTi 3 Al, forming longitudinal cracks. The AlSi5 filler metal has a positive effect on the weld Microstructure and thus joint strength, where Si has reduced the IMP (TiAl 3) harmful effect via replacing Al atoms substitutionaly in TiAl3.