Changsheng Dong

Photodegradation of methyl orange under visible light by micro-nano hierarchical Cu2O structure fabricated by hybrid laser processing and chemical dealloying.

Micro-nano hierarchical structure on the substrate was fabricated by a hybrid approach including laser deposition, laser ablation and chemical dealloying. The structure consists of micro bumps with a width of 50 μm and a height of 100 μm, and nanoporous structures with a size of 70-150 nm on the micro bumps. XRD and XPS results confirm that these hierarchical structures were made of Cu(2)O. For use in comparison, three additional structures with feature size in milliscale, microscale, and nanoscale were also prepared respectively by the proposed methods. Under visible light, the micro-nano structure exhibited the best performance of photodegradation. It is the result of the large specific surface and the catalytic reaction driven by the cuprous oxides.

Investigation on the electrochemical catalysis properties of Ni-decorated nanoporous copper formed by hybrid laser deposition

Nano-alloys or nano-structure often display novel physical, and chemical properties. It is of great scientific and engineering meanings to deposit micronano structure on macro-component surface to locally achieve nano-properties for potential applications. Nanoporous copper coatings(NPCC) with pnanopore size ranging from 30 to 50nm have been fabricated in our preliminary work by laser depositing Cu-Mn alloy coatings on carbon steel and subsequently dealloying process in hydrochloric acid solution. The porosity and specific surface area reaches as high as 70% and 65.3 m2/g respectively. The as-formed NPCC was then further processed by electroless plating a thin layer of Ni. This paper focus on the structure evolution of nanoporous Cu-Ni composite coatings, Ni-decorated nanoporous copper coatings(Ni-NPCC), with an average pore size of 30nm, porosity of 50% and specific surface area of 40m2/g. It is indicated that both NPCC and Ni-NPCC shows catalysis properties as hydrogen storage electrode. Their catalysis properties change with the Ni plating time. Ni-NPCC with 20 minutes Ni plating have the best catalysis properties, with an optimized oxidation peak current density up to about 60 mA/cm2.Nano-alloys or nano-structure often display novel physical, and chemical properties. It is of great scientific and engineering meanings to deposit micronano structure on macro-component surface to locally achieve nano-properties for potential applications. Nanoporous copper coatings(NPCC) with pnanopore size ranging from 30 to 50nm have been fabricated in our preliminary work by laser depositing Cu-Mn alloy coatings on carbon steel and subsequently dealloying process in hydrochloric acid solution. The porosity and specific surface area reaches as high as 70% and 65.3 m2/g respectively. The as-formed NPCC was then further processed by electroless plating a thin layer of Ni. This paper focus on the structure evolution of nanoporous Cu-Ni composite coatings, Ni-decorated nanoporous copper coatings(Ni-NPCC), with an average pore size of 30nm, porosity of 50% and specific surface area of 40m2/g. It is indicated that both NPCC and Ni-NPCC shows catalysis properties as hydrogen storage electrode. Their catalysis...

Nano WC powder cold enhancing of light metal surface by laser shock peening process

Light metal alloys are nowadays widely used as structure materials in aerospace, transportation and electronic industries due to their good strength and light weight. One of the issues is their poor surface hardness resulting in poor wear resistance and shorter life time. Many efforts have been made to hardface the light metal alloys by using laser cladding, alloying, plasma spraying and other surface treatments. However, almost all of these processes are thermal process which means a local melt pool or high temperature is formed during the process, which will induce some challenges like the lighter element burning, porosity and cracking. Nano powders have many unique properties to be a good candidate for hardfacing the light metal alloys. During a thermal process, however, the nano powders will easily be completely melted into the melt pool and then solidified a microstructure without nano characteristics.We have recently developed a novel process: nano powder cold enhancing of light metal surface by laser shock peening process. This is a cold process, by which the nano powders are squeezed into the surface of the light metal alloys by the very high pressure (up to Giga or even tens of Giga Pascal) induced by the laser shock peening process.This paper reports the research work on the nano WC powder cold enhancing of aluminum alloy surface by using a 50J Q switch Nd:YAG laser system for shock peening, focusing on the process parameters, the nano powder, the X-ray confirmation of the squeezed nano particles in the surface layer, the microstructure, the element distribution, the hardness, the wear resistance and the residual stress. The research approves that the surface hardness and wear resistance of the aluminum alloy are obviously improved by the nano powder cold enhancing by laser shock peening process.Light metal alloys are nowadays widely used as structure materials in aerospace, transportation and electronic industries due to their good strength and light weight. One of the issues is their poor surface hardness resulting in poor wear resistance and shorter life time. Many efforts have been made to hardface the light metal alloys by using laser cladding, alloying, plasma spraying and other surface treatments. However, almost all of these processes are thermal process which means a local melt pool or high temperature is formed during the process, which will induce some challenges like the lighter element burning, porosity and cracking. Nano powders have many unique properties to be a good candidate for hardfacing the light metal alloys. During a thermal process, however, the nano powders will easily be completely melted into the melt pool and then solidified a microstructure without nano characteristics.We have recently developed a novel process: nano powder cold enhancing of light metal surface by las...

Fabrication of micro-nano hierarchical Cu structures on engineering substrate by hybrid laser approach and their application to photodegradation of methyl orange under visible light

Surface micro-nano structures show excellent properties such as wettability control (hydrophilic, hydrophobic), optical property control, micro-nano tribology, hydrodynamic/aerodynamic property control, cell adhesion and adhesion control, which is one of the frontier topics in nano science and technology research. We developed a hybrid approach including laser deposition, laser ablation and chemical dealloying for fabricating tunable micro-nano hierarchical Cu structure on engineering substrate surface. The structure consists of micro bumps with a width of 50 µm and a height of 100 µm, and nanoporous structures with a size of 70-150 nm on the micro bumps. The morphology of micro and nano structure can be tunable through the parameters of laser ablation and chemical dealloying. XRD and XPS results confirm that these hierarchical structures were made of Cu2O.This hierarchical structure shows the best photo degradation of methyl orange under the visible light, whose photo degradation ratio is 78%, compared to the milliscale, microscale, and nanoscale structure counterparts. The influences on the photo degradation were discussed, such as concentration of the methyl orange, pH, and so on. The reaction kinetics and mechanism of the photo degradation are explained to be attributed to the Cu2O p-type semiconductor property, the energy difference and the high absorption of the light due to its micro-nano structure. The reported results demonstrate a good application example of surface micro-nano structure fabricated by hybrid laser approach.Surface micro-nano structures show excellent properties such as wettability control (hydrophilic, hydrophobic), optical property control, micro-nano tribology, hydrodynamic/aerodynamic property control, cell adhesion and adhesion control, which is one of the frontier topics in nano science and technology research. We developed a hybrid approach including laser deposition, laser ablation and chemical dealloying for fabricating tunable micro-nano hierarchical Cu structure on engineering substrate surface. The structure consists of micro bumps with a width of 50 µm and a height of 100 µm, and nanoporous structures with a size of 70-150 nm on the micro bumps. The morphology of micro and nano structure can be tunable through the parameters of laser ablation and chemical dealloying. XRD and XPS results confirm that these hierarchical structures were made of Cu2O.This hierarchical structure shows the best photo degradation of methyl orange under the visible light, whose photo degradation ratio is 78%, compared t...

Fabrication and characterization of nanoporous manganese structure by laser deposition hybrid selective electrochemical dealloying

A novel approach is proposed and developed to fabricate nanoporous structure on metal substrate for potential functionalization by laser deposition of Cu-Mn alloy hybrid selective electrochemical dealloying. With a deep understanding of the dealloying behavior, we are able to selectively dissolve the relative inert element Cu instead of conventionally the relative active element Mn. As a result, a novel nanoporous Mn structure was successfully realized by our hybrid approach. Due to the characteristics of laser deposition, we are also able to form this nanoporous structure on any location with any shape. This paper reports in detail the fabrication approach for the nanoporous structure, including the formation basis, the influence of dealloying time, current density and laser scanning speed on the nanoporous structures. The characterization of this nanoporous structure is also well presented covering the microstructure and homogeneity.A novel approach is proposed and developed to fabricate nanoporous structure on metal substrate for potential functionalization by laser deposition of Cu-Mn alloy hybrid selective electrochemical dealloying. With a deep understanding of the dealloying behavior, we are able to selectively dissolve the relative inert element Cu instead of conventionally the relative active element Mn. As a result, a novel nanoporous Mn structure was successfully realized by our hybrid approach. Due to the characteristics of laser deposition, we are also able to form this nanoporous structure on any location with any shape. This paper reports in detail the fabrication approach for the nanoporous structure, including the formation basis, the influence of dealloying time, current density and laser scanning speed on the nanoporous structures. The characterization of this nanoporous structure is also well presented covering the microstructure and homogeneity.

High temperature performance of laser deposition GH105 layers on nickel base super alloy blade

Laser deposition is considered a promising rejuvenation approach for nickel base super alloy blades for various kinds of erosion, abrasion or cracking resulted from high temperature, high pressure and complicated vibration environments. The induced residual stress/its impact on the fatigue property and the high temperature performance are two main research issues for successful rejuvenation of blades. We have previously reported our research on residual stress measurement, using laser shock peening, electronic shock peening and magnetic process to change the residual tensile stress into a compress stress and such significantly improves the fatigue properties.This paper focuses on the high temperature performance of laser deposition GH105 layers. Laser deposition of a nickel base super alloy (GH105) powder was performed via a powder feeding technique on nickel base supper alloy blade by a high power CO2 laser. The research indicates that the cladding layers of GH105 under optimized processing parameters have dense microstructure, ultra-fine grains, good surface quality and good metallurgical bond with the substrate. The microstructure consists of γ-Ni matrix, a few carbide precipitates and γ’-phase. The micro-hardness of the cladding layer reaches HV0.2 422, while the blade substrate is HV0.2 343. The elevated temperature tensile strength of the cladding layer at 850℃ is 530MPa, higher than that of the cold-drawn rod, which exceedes the requirement of the blade substrate. The ball-on-flat wear test at 500℃ indicates that the relative abrasive wear property of the laser deposited layer is better than that of the substrate. As the result, the GH105 laser deposition layer meets the high temperature performance requirements for blade rejuvenation.Laser deposition is considered a promising rejuvenation approach for nickel base super alloy blades for various kinds of erosion, abrasion or cracking resulted from high temperature, high pressure and complicated vibration environments. The induced residual stress/its impact on the fatigue property and the high temperature performance are two main research issues for successful rejuvenation of blades. We have previously reported our research on residual stress measurement, using laser shock peening, electronic shock peening and magnetic process to change the residual tensile stress into a compress stress and such significantly improves the fatigue properties.This paper focuses on the high temperature performance of laser deposition GH105 layers. Laser deposition of a nickel base super alloy (GH105) powder was performed via a powder feeding technique on nickel base supper alloy blade by a high power CO2 laser. The research indicates that the cladding layers of GH105 under optimized processing parameters ha...

Nano WC powder cold surface enhancing of aluminium alloy 5A06 via laser shock peening

Aluminum alloy 5A06 has many superior properties such as high strength, good corrosion resistance and welding performance. It is widely used in aerospace, ship craft and transportation areas. Unfortunately, poor surface hardness and wear resistance and shorter life time limit its applications in industries. Many hardfacing processes such as heat treatment, plasma spray, micro-arc oxidation, laser cladding and laser alloying can increase the wear resistance of the 5A06 alloy. However, almost all of these processes are thermal process which may induce lighter element melting loss, porosity and cracking. Nano-materials have unique acoustic, optic, electric, magnetic and thermodynamic characteristics because of their quantum size and surface effect. It can play an important role in hardfacing of the light metal alloys. However, nano powders will completely melted into the melt pool due to their relative low melt points, this will lose many of their unique properties.We have recently developed a novel process: nano powder cold enhancing of light metal surface via laser shock peening process. This is a cold process, by which the nano powders are squeezed into the surface of the light metal alloys by the very high pressure (up to Giga or even tens of Giga Pascal) induced by the laser shock peening process.This paper reports our research work one nano WC powder cold surface enhancing of 5A06 alloy by using a 50J Q switch Nd:YAG laser system for shock peening, focusing on the influences of the processing conditions such as surface roughness of the aluminium sample, the powder layer thickness, the absorbing layer, the constrain layer and the single pulse energy on the enhanced nano powder percentage and nanopowder dispersion degree in the enhanced nano WC coatings. The paper will also report the hardness, tribology property, wear resistance of the as-enhanced layers. The results confirm that nano powder cold surface enhancing vis laser shock peening can dramatically improve the surface performance of the aluminium alloy by the combined strengthening mechanism of laser shock peening, nano-particles and nano-particle intensified shock peening.Aluminum alloy 5A06 has many superior properties such as high strength, good corrosion resistance and welding performance. It is widely used in aerospace, ship craft and transportation areas. Unfortunately, poor surface hardness and wear resistance and shorter life time limit its applications in industries. Many hardfacing processes such as heat treatment, plasma spray, micro-arc oxidation, laser cladding and laser alloying can increase the wear resistance of the 5A06 alloy. However, almost all of these processes are thermal process which may induce lighter element melting loss, porosity and cracking. Nano-materials have unique acoustic, optic, electric, magnetic and thermodynamic characteristics because of their quantum size and surface effect. It can play an important role in hardfacing of the light metal alloys. However, nano powders will completely melted into the melt pool due to their relative low melt points, this will lose many of their unique properties.We have recently developed a novel process:...

WC Nano powder cold planting via laser shock peening onto aluminium/magnesium alloy surfaces

We have developed a novel process for hardfacing aluminium/magnesium alloys: nano powder cold planting via laser shock peening (NPCP/LSP). The pre-coated nano powders are planted into the near surface layer by the GPa pressure induced by a laser shock peening process. This paper reports our recent work on WC NPCP/LSP onto aluminium/magnesium alloys, focusing on the combination of nano powders with the substrate, the interface bond between the nano particles and the matrix, and also the significant improvement on the surface hardness, wear resistance, and tribologocal properties.

Interfacial structure of nano WC powder cold planting via laser shock peening onto light metal surfaces

Light metal alloys are extensively used in many industries like aerospace, transportation and shipping industry as structural materials due to their lightness, high strength weight ratio and good corrosion resistance. This can reduce the material/energy consume and recycle the materials for environment protection. However, the surface hardness and wear resistance of aluminium and magnesium alloys are usually poor, which limits their service lifetime for applications. There are some available processes being capable to improving the surface properties of the light alloys. However, almost all of these processes are thermal process which may induce lighter element burning, porosity and cracking. Nano-materials have strong acoustic, optic, electric, magnetic and thermodynamic characteristics because of their quantum size and surface effect. It can play an important role in hardfacing the light metal alloys.Combining the unique characteristics of nano powers and laser shock peening, we have developed a novel process: nano powder cold planting via laser shock peening with pre-coated nano powders (refer to NPCP/LSP) onto light metal surfaces. The nano powders are planted into the near surface layer of the light metal alloys by the very high pressure (up to Giga or even tens of Giga Pascal) induced by the laser shock peening process. Light alloy surfaces can be dramatically enhanced by the combined strengthening of the nano powders and also the laser shock peening process. This is not a thermal process which can effectively avoid the shortcomings associated with a thermal process. The unique features of the nano-powders can be integrated into the near surface layer of the light alloys with good combination.This paper reports our continusous research on NPCP/LSP, focusing on the interfacial structure of nano powders planted onto the light alloy surface, the combination of nano powders with the substrate, the interface bond between the nano particles and the matrix. The analysis on interfacial structure will help to clarify NPCP/LSP process and principle, explain and evidence the significant improvement on the surface hardness, wear resistance, and tribologocal properties by NPCP/LSP process.Light metal alloys are extensively used in many industries like aerospace, transportation and shipping industry as structural materials due to their lightness, high strength weight ratio and good corrosion resistance. This can reduce the material/energy consume and recycle the materials for environment protection. However, the surface hardness and wear resistance of aluminium and magnesium alloys are usually poor, which limits their service lifetime for applications. There are some available processes being capable to improving the surface properties of the light alloys. However, almost all of these processes are thermal process which may induce lighter element burning, porosity and cracking. Nano-materials have strong acoustic, optic, electric, magnetic and thermodynamic characteristics because of their quantum size and surface effect. It can play an important role in hardfacing the light metal alloys.Combining the unique characteristics of nano powers and laser shock peening, we have developed a novel p...

Structure modification of carbon nanotube powder and film by laser shock peening process

Since their discovered in 1991, carbon nanotubes have demonstrated many remarkable mechanical, electrical and thermal properties, showing promising potentials in many fields. Carbon nano tubes have attracted world-wide attentions during the years, many research work have been performed during the years. At Tsinghua University, we have reported previously two kinds of research work on laser processing of canbon nanotubes: (1) Connection of macro-sized double-walled carbon nanotube strands by laser irradiation; (2) Light emission from multiwalled carbon nanotubes under CW CO2 laser irradiation. This work is a continuous effort in the research area, which focuses on the structure modification of carbon nano tube powder and film by laser shock peening process. A Q-switched nano second Nd:YAG laser pulse induces a shock wave on metal surface with very high pressure (up to Giga or even tens of Giga pascal), which produces normally plastic deformation and a few hundred MPa of the residual compressive stress on the surface of materials, enhancing the anti-fatigue properties of metals and extending the fatigue life of the processed components. We used laser shock peening to process the carbon nanotube powder and carbon nanotube film to explore the possible structure modification. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Micro Raman Spectrum were used to analyze the morphology and spectrum to identify the structure modification of the carbon nanotube powder and film after laser shock peening process and then to establish the relationship between the process parameters and the structure modification. The research impact and potential applications were discussed based on the research.Since their discovered in 1991, carbon nanotubes have demonstrated many remarkable mechanical, electrical and thermal properties, showing promising potentials in many fields. Carbon nano tubes have attracted world-wide attentions during the years, many research work have been performed during the years. At Tsinghua University, we have reported previously two kinds of research work on laser processing of canbon nanotubes: (1) Connection of macro-sized double-walled carbon nanotube strands by laser irradiation; (2) Light emission from multiwalled carbon nanotubes under CW CO2 laser irradiation. This work is a continuous effort in the research area, which focuses on the structure modification of carbon nano tube powder and film by laser shock peening process. A Q-switched nano second Nd:YAG laser pulse induces a shock wave on metal surface with very high pressure (up to Giga or even tens of Giga pascal), which produces normally plastic deformation and a few hundred MPa of the residual compressive stress on t...