A 4 kW fiber laser was chosen to weld the new hot-rolled nano-scale precipitation-strengthened steel with a thickness of 4.5 mm. The effect of laser power, defocusing distance, and welding speed on the welded joint ap...A 4 kW fiber laser was chosen to weld the new hot-rolled nano-scale precipitation-strengthened steel with a thickness of 4.5 mm. The effect of laser power, defocusing distance, and welding speed on the welded joint appearance was examined, and the microstructure and mechanical properties on the typical butt joints were investigated. Results showed that increasing laser welding power may cause faster downward flow of molten metal to produce greater root humping. With the welding speed increasing, the average welding seam （WS） width decreased, and the average WS and heat-affected zone （HAZ） hardness increased. The microstructures of WS, fusion line, and coarse grain heat-affected zone were lath martensite, but the growth direction of the original austenite grain boundaries was significantly different. The microstructures of fine grain heat-affected zone were ferrite and martensite, and the microstructure of mixed grain heat- affected zone contained ferrite, massive M/A island, and a small amount of martensite. The micro-hardness values of WS, HAZ, and base metal （BM） were 358, 302, and 265 HV, respectively. The butt joint fracture at the BM far from the WS and the welded joint tensile strength are observed to follow proportional relationship with hardness.展开更多
In the oxygen diffusion hardened condition,untreated and laser surface melted pure titanium alloy(TA4)by Nd:YAG pulsed laser,are hardened at temperatures of 650 to 700℃with the end result being a passive,mechanically...In the oxygen diffusion hardened condition,untreated and laser surface melted pure titanium alloy(TA4)by Nd:YAG pulsed laser,are hardened at temperatures of 650 to 700℃with the end result being a passive,mechanically stable,abrasion resistant oxide ceramic rutile surface layer.The thickness of this surface layer depends on the time,temperature,and the microstructure of the Ti substrate.This paper describes the results of x-ray diffraction analysis,scanning electron microscope(SEM),microhardness measurements,and corrosion resistance measurements of hardened pure and laser treated Ti substrate.The oxygen diffusion hardened titanium alloy after laser surface melted samples(L-TA4)had a more pronounced grain structure and significantly higher roughness values than the untreated pure TA4(U-TA4)samples.The L-TA4 samples also exhibited at least equivalent corrosion behavior and a definite increase in surface hardness compared to the U-TA4 samples.The results of this work suggest that laser surface melting plays a key role for effective oxygen diffusion hardening at 650-700℃for pure and laser treated pure Ti alloys.展开更多
High-energy micro-arc alloying(HEMAA)is a consumable electrode,micro-welding process which uses electrical pulses that are typically three orders of magnitude shorter than in other pulse welding processes.Pulse durati...High-energy micro-arc alloying(HEMAA)is a consumable electrode,micro-welding process which uses electrical pulses that are typically three orders of magnitude shorter than in other pulse welding processes.Pulse durations of a few microseconds combined with pulse frequencies in the 0.1 to 2-kilohertz range thus allow substrate heat dissipation over~99%of the duty cycle while heating only about 1%.The cooling rates may approach 105 to 106℃/s,depending on material.This obtained coating can produce unique corrosion and tribological benefits.Substrates require no special surface preparation and nearly any metal,alloy or cermets can be applied to metal surfaces.This paper details experimental results when alloying Mg base alloy ZM5,using Mg-Y electrodes with a water-based dielectric fluid.The morphology and the composition of the alloying was analyzed by scanning electron microscope(SEM)and energy dispersive X-ray analysis(EDX).At the discharge energies employed,a thin recast layer thickness and rougher layers were formed on the surface.All layers were in general discontinuous.EDX analysis showed that the Y transferred from the solid electrodes to the workpiece surface.展开更多
Superhydrophobic surfaces often lose the easy-removal ability of liquids during icing&melting cycles due to the impalement phenomena of air pockets.Especially for the most common mixed liquids in normal life,their...Superhydrophobic surfaces often lose the easy-removal ability of liquids during icing&melting cycles due to the impalement phenomena of air pockets.Especially for the most common mixed liquids in normal life,their difficult-removals after icing and melting have brought colossal troubles in the fields of aviation,energy,biomedicine,etc.Here we adopt the ultrafast laser to fabricate the optimal micro-nanostructured surfaces,realizing excellent superomniphobicity for seven environmental-related liquids.It is demonstrated that different droplets on the surfaces recover well to the original Cassie-Baxter state after melting,and can be removed easily at low tilted angles.The ice adhesion strengths of the seven liquids as low as 5 kPa and the micro-nanostructure durability ensure the long-term easy-removal after icing.Compared with the ice adhesion strength of untreated surfaces(264.4±17.6 kPa),those of our designed surfaces have decreased by over 50 times.Icing and melting processes are investigated to reveal the easy-removal mechanisms that specifically distributed solutes and bubbles after icing impact downwards significantly to accelerate the recovery of the Cassie–Baxter state during melting.A series of environmental-related durability experiments including continuous icing&melting cycles,long-term salt spray,and high-pressure water jet impact further demonstrate the surfaces promising for real applications.展开更多
基金supported by the National Natural Science Foundation of China (Nos.51305285 and 51104110)the Basic Research Program of Jiangsu Province (Nos. BK20130315 and BK20130304)
文摘A 4 kW fiber laser was chosen to weld the new hot-rolled nano-scale precipitation-strengthened steel with a thickness of 4.5 mm. The effect of laser power, defocusing distance, and welding speed on the welded joint appearance was examined, and the microstructure and mechanical properties on the typical butt joints were investigated. Results showed that increasing laser welding power may cause faster downward flow of molten metal to produce greater root humping. With the welding speed increasing, the average welding seam （WS） width decreased, and the average WS and heat-affected zone （HAZ） hardness increased. The microstructures of WS, fusion line, and coarse grain heat-affected zone were lath martensite, but the growth direction of the original austenite grain boundaries was significantly different. The microstructures of fine grain heat-affected zone were ferrite and martensite, and the microstructure of mixed grain heat- affected zone contained ferrite, massive M/A island, and a small amount of martensite. The micro-hardness values of WS, HAZ, and base metal （BM） were 358, 302, and 265 HV, respectively. The butt joint fracture at the BM far from the WS and the welded joint tensile strength are observed to follow proportional relationship with hardness.
基金National Nature Science Foundation of China(50801050)
文摘In the oxygen diffusion hardened condition,untreated and laser surface melted pure titanium alloy(TA4)by Nd:YAG pulsed laser,are hardened at temperatures of 650 to 700℃with the end result being a passive,mechanically stable,abrasion resistant oxide ceramic rutile surface layer.The thickness of this surface layer depends on the time,temperature,and the microstructure of the Ti substrate.This paper describes the results of x-ray diffraction analysis,scanning electron microscope(SEM),microhardness measurements,and corrosion resistance measurements of hardened pure and laser treated Ti substrate.The oxygen diffusion hardened titanium alloy after laser surface melted samples(L-TA4)had a more pronounced grain structure and significantly higher roughness values than the untreated pure TA4(U-TA4)samples.The L-TA4 samples also exhibited at least equivalent corrosion behavior and a definite increase in surface hardness compared to the U-TA4 samples.The results of this work suggest that laser surface melting plays a key role for effective oxygen diffusion hardening at 650-700℃for pure and laser treated pure Ti alloys.
基金National Nature Science Foundation of China(50801050)
文摘High-energy micro-arc alloying(HEMAA)is a consumable electrode,micro-welding process which uses electrical pulses that are typically three orders of magnitude shorter than in other pulse welding processes.Pulse durations of a few microseconds combined with pulse frequencies in the 0.1 to 2-kilohertz range thus allow substrate heat dissipation over~99%of the duty cycle while heating only about 1%.The cooling rates may approach 105 to 106℃/s,depending on material.This obtained coating can produce unique corrosion and tribological benefits.Substrates require no special surface preparation and nearly any metal,alloy or cermets can be applied to metal surfaces.This paper details experimental results when alloying Mg base alloy ZM5,using Mg-Y electrodes with a water-based dielectric fluid.The morphology and the composition of the alloying was analyzed by scanning electron microscope(SEM)and energy dispersive X-ray analysis(EDX).At the discharge energies employed,a thin recast layer thickness and rougher layers were formed on the surface.All layers were in general discontinuous.EDX analysis showed that the Y transferred from the solid electrodes to the workpiece surface.
基金the National Key Research and Development Program of China(No.2017YFB1104300)the Tsinghua University Initiative Scientific Research Program(No.2018Z05JZY009)the National Natural Science Foundation of China(Nos.51575309 and 51210009).
文摘Superhydrophobic surfaces often lose the easy-removal ability of liquids during icing&melting cycles due to the impalement phenomena of air pockets.Especially for the most common mixed liquids in normal life,their difficult-removals after icing and melting have brought colossal troubles in the fields of aviation,energy,biomedicine,etc.Here we adopt the ultrafast laser to fabricate the optimal micro-nanostructured surfaces,realizing excellent superomniphobicity for seven environmental-related liquids.It is demonstrated that different droplets on the surfaces recover well to the original Cassie-Baxter state after melting,and can be removed easily at low tilted angles.The ice adhesion strengths of the seven liquids as low as 5 kPa and the micro-nanostructure durability ensure the long-term easy-removal after icing.Compared with the ice adhesion strength of untreated surfaces(264.4±17.6 kPa),those of our designed surfaces have decreased by over 50 times.Icing and melting processes are investigated to reveal the easy-removal mechanisms that specifically distributed solutes and bubbles after icing impact downwards significantly to accelerate the recovery of the Cassie–Baxter state during melting.A series of environmental-related durability experiments including continuous icing&melting cycles,long-term salt spray,and high-pressure water jet impact further demonstrate the surfaces promising for real applications.
