The structure of the yttrium modified Co-base alloy layers formed by laser cladding on 2Cr13 and 1Cr18Ni9Ti steel surfaces and its hot corrosion performance have been investigated systematically.The re- sults show tha...The structure of the yttrium modified Co-base alloy layers formed by laser cladding on 2Cr13 and 1Cr18Ni9Ti steel surfaces and its hot corrosion performance have been investigated systematically.The re- sults show that the Y-containing cobalt base clad alloy has a finer microstructure and higher corrosion re- sistance to the salt mixture of 75% Na_2SO_4+25%NaCl at high temperature.The unique properties are ob- tained with addition of 0.875% Y for the formation of a continuous and compact oxide scale.The compact scale may act as a barrier for the inward diffusion of oxygen and sulphur and also for the outward diffusion of alloying elements.展开更多
Generation of noise-like rectangular pulse was investigated systematically in an Er–Yb co-doped fiber laser based on an intra-cavity coupler with different coupling ratios.When the coupling ratio was 5/95,stable mode...Generation of noise-like rectangular pulse was investigated systematically in an Er–Yb co-doped fiber laser based on an intra-cavity coupler with different coupling ratios.When the coupling ratio was 5/95,stable mode-locked pulses could be obtained with the pulse packet duration tunable from 4.86 ns to 80 ns.The repetition frequency was 1.186 MHz with the output spectrum centered at 1.6μm.The average output power and single pulse energy reached a record 1.43 W and1.21μJ,respectively.Pulse characteristics under different coupling ratios(5/95,10/90,20/80,30/70,40/60)were also presented and discussed.展开更多
The porcelain fracture caused by low metal-ceramic bond strength is a critical issue in porcelain fused to metal（PFM） restorations. Surface roughening methods, such as sand blasting, acid etching and alkaline degrea...The porcelain fracture caused by low metal-ceramic bond strength is a critical issue in porcelain fused to metal（PFM） restorations. Surface roughening methods, such as sand blasting, acid etching and alkaline degreasing for the metal matrix are used to increase bond strength. However, the metal matrix of PFM processed by selective laser melting（SLM） has natural rough surface. To explore the effect of the original roughness on metal-ceramic bond strength, two groups of specimen are fabricated by SLM. One group of specimen surface is polished smooth while another group remains the original rough surface. The dental porcelain is fused to the specimens＇ surfaces according to the ISO 9693：1999 standard. To gain the bond strength, a three-point bending test is carried out and X ray energy spectrum analysis（EDS）, scanning electron microscope（SEM） are used to show fracture mode. The results show that the mean bond strength is 116.5 16 MPa of the group with rough surface（Ra= 17.2）, and the fracture mode is cohesive. However, when the surface is smooth （Ra =3.8）, the mean bond strength is 74.5 MPa _＋ 5 MPa and the fracture mode is mixed. The original surface with prominent structures formed by the partly melted powder particles, not only increases surface roughness but also significantly improves the bond strength by forming strong mechanical lock effect. Statistical analysis （Student＇s t-test） demonstrates a significant difference （p〈0.05） of the mean value of bond strength between the two groups. The experiments indicate the natural rough surface can enhance the metal-ceramic bond strength to over four times the minimum value （25 MPa） of the ISO 9693：1999 standard. It is found that the natural rough surface of SLM-made PFM can eliminate the porcelain collapse defect produced by traditional casting method in PFM restorations.展开更多
Presents a waveguide CO 2 laser with two unequal long channels excited by radio frequency (RF) which has more than 30 laser lines from a long channel of 400 mm with grating, and 3 laser lines from a short channel of 2...Presents a waveguide CO 2 laser with two unequal long channels excited by radio frequency (RF) which has more than 30 laser lines from a long channel of 400 mm with grating, and 3 laser lines from a short channel of 200 mm by PZT.展开更多
A thermal fatigue behaviour of Co-based alloy coating obtained by laser surface meltcasting on the high temperature alloy GH33 was studied.The results show that after each time of thermal cycling,the final residual st...A thermal fatigue behaviour of Co-based alloy coating obtained by laser surface meltcasting on the high temperature alloy GH33 was studied.The results show that after each time of thermal cycling,the final residual stress was formed in the melt-casting layer which is attributed to the thermal stress and structural stress.Through the first 50 times of thermal cycling,the morphology of coating still inherits the laser casting one,but the dendrites get bigger;After the second 50 times of thermal cycling,corrosion pits emerge from coating,and mostly in the places where coating and substrate meet.The fatigue damage type of coating belongs to stress corrosion.展开更多
Both titanium and germanium were introduced into silicon dioxide system by sol-gel method to move its region of anomalous dispersion caused by IR resonance absorption towards the wavelength of CO 2 laser.It is indica...Both titanium and germanium were introduced into silicon dioxide system by sol-gel method to move its region of anomalous dispersion caused by IR resonance absorption towards the wavelength of CO 2 laser.It is indicated by IR absorption spectra that as the content of SiO 2 decreases in this glass system TiO 2 and GeO 2 tends to exist in their own phases.As for the gel glass with a composition of 40SiO 2·30TiO 2·30GeO 2,when the temperature is below 600℃,germanium atoms exist mainly in Ge-O-Ge bonds.With the temperature increasing from 800℃ to 1000℃, titanium atoms in Si-O-Ti bonds almost transform into Ti-O-Ti bonds.Furthermore,a large number of Si-O-Ti and Si-O-Ge bonds formed when the temperature approaches 800℃,which makes a notable IR absorption band round the wavelength of CO 2 laser.Therefore, sol-gel based SiO 2-TiO 2-GeO 2 gel glass is a candidate material for CO 2 laser hollow waveguide.展开更多
Laser engineered net shaping(LENS) process was investigated using Co-based superalloy powder with a high power continuous wave CO2 laser. Thin wall part with smooth surface was obtained by LENS of layer-by-layer depos...Laser engineered net shaping(LENS) process was investigated using Co-based superalloy powder with a high power continuous wave CO2 laser. Thin wall part with smooth surface was obtained by LENS of layer-by-layer deposition of the powder materials. This thin wall sample was tested for metallographic examinations, micro-hardness, X-ray diffraction and mechanical property test. Microstructural results show that the layers possess rapid solidification microstructural feature, fine dendritic crystal and M7C3-type carbides (essentially chromium-rich carbide) dispersed in theγ(Co,Cr) phase matrix. Dendrite spacing as well as the solidification mode can be controlled through control process parameters. In addition, this microstructural feature of the as-formed Co-base sample leads to an evident hardening and a superior tensile strength and toughness.展开更多
Composite coatings made of nano-Y_2O_3/cobalt-based alloy and produced by crosscurrent CO_2 laser on Ni-based superalloy are introduced. Cross-section or surface of the coatings was examined to reveal their microstruc...Composite coatings made of nano-Y_2O_3/cobalt-based alloy and produced by crosscurrent CO_2 laser on Ni-based superalloy are introduced. Cross-section or surface of the coatings was examined to reveal their microstructure using optical microscope, SEM, including EDS microanalysis, TEM and XRD. The results show that some equilibrium or non-equilibrium phases, such as γ-Co, Cr_(23)C_6, Y_2O_3 and ε-Co exist in the coatings. Fine and short dendritic microstructure and columnar to equiaxed transition (CET) occurred by adding nano-Y_2O_3 particles. With the increasing amount of nano-Y_2O_3 (1%, mass fraction), fully equiaxed crystallization appeared. These are caused by nano-Y_2O_3 particles acting as new nucleation site and rapid solidification of the melt. The results also show that inhomogeneous dispersion of nano-Y_2O_3 results in the formation of ε-Co phase in the coatings. The sub-microstructure of the clad is stacking fault. The mechanism of the formation of equiaxed grains is also analyzed.展开更多
The purpose of this research was to study the effect of Argon inert gas on the laser welding quality of Co-Cr and Ni-Cr base metal alloys, which are widely used as Fixed Prosthodontics alloys in Dental Laboratories. A...The purpose of this research was to study the effect of Argon inert gas on the laser welding quality of Co-Cr and Ni-Cr base metal alloys, which are widely used as Fixed Prosthodontics alloys in Dental Laboratories. A total of 36 specimens were manufactured (18 of Ni-Cr alloy and 18 of Co-Cr alloy). The specimens were then divided into 3 subgroups (6 specimens each): control;argon-welded;and non-Argon welded. The specimens were cut, laser welded, radiographed and finally tested under tensile strength testing, followed by examination using Scanning Electron Microscopy. The tensile strength of welded specimens was lower than the strength of non-welded specimens, however this difference was not found to be statistically significant. The material factor (Co-Cr alloy or Ni-Cr alloy) has a statistically significant effect on the tensile strength, while the presence or not of the inert gas, as well as the combination of the two factors do not have a statistically significant effect. The laser welding process applied in daily practice (separation of specimen, formation of two cones in contact, aggregation of two cones, filling of the remaining gap by welding) is considered satisfactory in terms of weld strength. The factor of the material, as an independent factor, affects the tensile strength to a statistically significant degree, in contrast to the factor of the presence of inert gas which does not affect to a statistically significant degree.展开更多
The WC-10%Co particulate reinforced Cu matrix composite material with a WC-Co∶Cu mass ratio of 20∶80 was successfully fabricated by selective laser sintering(SLS) process. The following optimal processing parameters...The WC-10%Co particulate reinforced Cu matrix composite material with a WC-Co∶Cu mass ratio of 20∶80 was successfully fabricated by selective laser sintering(SLS) process. The following optimal processing parameters were used: laser power of 700 W, scan speed of 0.06 m/s, scan line spacing of 0.15 mm, and powder layer thickness of 0.3 mm. The microstructure, composition, and phase of the laser processed material were investigated by scanning electron microscopy(SEM), X-ray diffraction(XRD), and energy dispersive X-ray(EDX) spectroscopy. The results show that the bonding mechanism of this process is liquid phase sintering. The Cu and Co act as the binder phase, while the WC acts as the reinforcing phase. The non-equilibrium effects induced by laser melting, such as high degrees of undercooling and high solidification rate, result in the formation of a metastable phase CoC0.25. The WC reinforcing particulates typically have three kinds of morphology. They are agglomerated and undissolved, incompletely separated and partially dissolved, separated and dissolved, which indicates that particle rearrangement acts as the dominant sintering mechanism for the larger WC, while dissolution-precipitation prevails for the smaller WC particles. Microhardness tester was used to determine the Vickers hardness across the cross-section of the laser sintered sample, with the average value being HV0.1268.5. However, the hardness varied considerably, which might be attributed to the WC segregation and the high solidification rate experienced by the molten pool.展开更多
Transparent polycrystaUine neodymiumdoped yttrium aluminum garnet ceramics （Nd：YAG） with better chemical stability, excellent optical and high temperature mechanical property is becoming a new laser host material. ...Transparent polycrystaUine neodymiumdoped yttrium aluminum garnet ceramics （Nd：YAG） with better chemical stability, excellent optical and high temperature mechanical property is becoming a new laser host material. The Nd：YAG precursor powders with loosely dispersed, slightly agglomerated and YAG cubic crystal phase were synthesized at 1100 ℃ by the co-precipitation method combined with the reverse strike,展开更多
基金Research Project supported by the Corrosion Science Laboratory,Academia Sinica
文摘The structure of the yttrium modified Co-base alloy layers formed by laser cladding on 2Cr13 and 1Cr18Ni9Ti steel surfaces and its hot corrosion performance have been investigated systematically.The re- sults show that the Y-containing cobalt base clad alloy has a finer microstructure and higher corrosion re- sistance to the salt mixture of 75% Na_2SO_4+25%NaCl at high temperature.The unique properties are ob- tained with addition of 0.875% Y for the formation of a continuous and compact oxide scale.The compact scale may act as a barrier for the inward diffusion of oxygen and sulphur and also for the outward diffusion of alloying elements.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61435009,61235008,and 61405254)
文摘Generation of noise-like rectangular pulse was investigated systematically in an Er–Yb co-doped fiber laser based on an intra-cavity coupler with different coupling ratios.When the coupling ratio was 5/95,stable mode-locked pulses could be obtained with the pulse packet duration tunable from 4.86 ns to 80 ns.The repetition frequency was 1.186 MHz with the output spectrum centered at 1.6μm.The average output power and single pulse energy reached a record 1.43 W and1.21μJ,respectively.Pulse characteristics under different coupling ratios(5/95,10/90,20/80,30/70,40/60)were also presented and discussed.
基金supported by the Royal Academy of Engineering Research Exchanges with China and UK(Grant No.2012-P02)National Key Technology R&D Program of Ministry of Science and Technology of China(Grant No.2012BAF08B03)National Natural Science Foundation of China(Grant No.51375189)
文摘The porcelain fracture caused by low metal-ceramic bond strength is a critical issue in porcelain fused to metal（PFM） restorations. Surface roughening methods, such as sand blasting, acid etching and alkaline degreasing for the metal matrix are used to increase bond strength. However, the metal matrix of PFM processed by selective laser melting（SLM） has natural rough surface. To explore the effect of the original roughness on metal-ceramic bond strength, two groups of specimen are fabricated by SLM. One group of specimen surface is polished smooth while another group remains the original rough surface. The dental porcelain is fused to the specimens＇ surfaces according to the ISO 9693：1999 standard. To gain the bond strength, a three-point bending test is carried out and X ray energy spectrum analysis（EDS）, scanning electron microscope（SEM） are used to show fracture mode. The results show that the mean bond strength is 116.5 16 MPa of the group with rough surface（Ra= 17.2）, and the fracture mode is cohesive. However, when the surface is smooth （Ra =3.8）, the mean bond strength is 74.5 MPa _＋ 5 MPa and the fracture mode is mixed. The original surface with prominent structures formed by the partly melted powder particles, not only increases surface roughness but also significantly improves the bond strength by forming strong mechanical lock effect. Statistical analysis （Student＇s t-test） demonstrates a significant difference （p〈0.05） of the mean value of bond strength between the two groups. The experiments indicate the natural rough surface can enhance the metal-ceramic bond strength to over four times the minimum value （25 MPa） of the ISO 9693：1999 standard. It is found that the natural rough surface of SLM-made PFM can eliminate the porcelain collapse defect produced by traditional casting method in PFM restorations.
文摘Presents a waveguide CO 2 laser with two unequal long channels excited by radio frequency (RF) which has more than 30 laser lines from a long channel of 400 mm with grating, and 3 laser lines from a short channel of 200 mm by PZT.
基金Project Sponsored by Committee on Science and Technology of Guizhou Province(943068)
文摘A thermal fatigue behaviour of Co-based alloy coating obtained by laser surface meltcasting on the high temperature alloy GH33 was studied.The results show that after each time of thermal cycling,the final residual stress was formed in the melt-casting layer which is attributed to the thermal stress and structural stress.Through the first 50 times of thermal cycling,the morphology of coating still inherits the laser casting one,but the dendrites get bigger;After the second 50 times of thermal cycling,corrosion pits emerge from coating,and mostly in the places where coating and substrate meet.The fatigue damage type of coating belongs to stress corrosion.
文摘Both titanium and germanium were introduced into silicon dioxide system by sol-gel method to move its region of anomalous dispersion caused by IR resonance absorption towards the wavelength of CO 2 laser.It is indicated by IR absorption spectra that as the content of SiO 2 decreases in this glass system TiO 2 and GeO 2 tends to exist in their own phases.As for the gel glass with a composition of 40SiO 2·30TiO 2·30GeO 2,when the temperature is below 600℃,germanium atoms exist mainly in Ge-O-Ge bonds.With the temperature increasing from 800℃ to 1000℃, titanium atoms in Si-O-Ti bonds almost transform into Ti-O-Ti bonds.Furthermore,a large number of Si-O-Ti and Si-O-Ge bonds formed when the temperature approaches 800℃,which makes a notable IR absorption band round the wavelength of CO 2 laser.Therefore, sol-gel based SiO 2-TiO 2-GeO 2 gel glass is a candidate material for CO 2 laser hollow waveguide.
基金Project(51461010101JB3501) supported by National Key Laboratory for High Energy Density Beam Processing Technology Foundation of China
文摘Laser engineered net shaping(LENS) process was investigated using Co-based superalloy powder with a high power continuous wave CO2 laser. Thin wall part with smooth surface was obtained by LENS of layer-by-layer deposition of the powder materials. This thin wall sample was tested for metallographic examinations, micro-hardness, X-ray diffraction and mechanical property test. Microstructural results show that the layers possess rapid solidification microstructural feature, fine dendritic crystal and M7C3-type carbides (essentially chromium-rich carbide) dispersed in theγ(Co,Cr) phase matrix. Dendrite spacing as well as the solidification mode can be controlled through control process parameters. In addition, this microstructural feature of the as-formed Co-base sample leads to an evident hardening and a superior tensile strength and toughness.
文摘Composite coatings made of nano-Y_2O_3/cobalt-based alloy and produced by crosscurrent CO_2 laser on Ni-based superalloy are introduced. Cross-section or surface of the coatings was examined to reveal their microstructure using optical microscope, SEM, including EDS microanalysis, TEM and XRD. The results show that some equilibrium or non-equilibrium phases, such as γ-Co, Cr_(23)C_6, Y_2O_3 and ε-Co exist in the coatings. Fine and short dendritic microstructure and columnar to equiaxed transition (CET) occurred by adding nano-Y_2O_3 particles. With the increasing amount of nano-Y_2O_3 (1%, mass fraction), fully equiaxed crystallization appeared. These are caused by nano-Y_2O_3 particles acting as new nucleation site and rapid solidification of the melt. The results also show that inhomogeneous dispersion of nano-Y_2O_3 results in the formation of ε-Co phase in the coatings. The sub-microstructure of the clad is stacking fault. The mechanism of the formation of equiaxed grains is also analyzed.
文摘The purpose of this research was to study the effect of Argon inert gas on the laser welding quality of Co-Cr and Ni-Cr base metal alloys, which are widely used as Fixed Prosthodontics alloys in Dental Laboratories. A total of 36 specimens were manufactured (18 of Ni-Cr alloy and 18 of Co-Cr alloy). The specimens were then divided into 3 subgroups (6 specimens each): control;argon-welded;and non-Argon welded. The specimens were cut, laser welded, radiographed and finally tested under tensile strength testing, followed by examination using Scanning Electron Microscopy. The tensile strength of welded specimens was lower than the strength of non-welded specimens, however this difference was not found to be statistically significant. The material factor (Co-Cr alloy or Ni-Cr alloy) has a statistically significant effect on the tensile strength, while the presence or not of the inert gas, as well as the combination of the two factors do not have a statistically significant effect. The laser welding process applied in daily practice (separation of specimen, formation of two cones in contact, aggregation of two cones, filling of the remaining gap by welding) is considered satisfactory in terms of weld strength. The factor of the material, as an independent factor, affects the tensile strength to a statistically significant degree, in contrast to the factor of the presence of inert gas which does not affect to a statistically significant degree.
基金Project(10276017) supported by the Joint Fund of National Natural Science Foundation of China and China Academy of Engineering Physics Project(04H52061) supported by the Aeronautical Science Foundation of China Project(S0403-061) supported by the Scientific Research Innovations Foundation of Nanjing University of Aeronautics and Astronautics
文摘The WC-10%Co particulate reinforced Cu matrix composite material with a WC-Co∶Cu mass ratio of 20∶80 was successfully fabricated by selective laser sintering(SLS) process. The following optimal processing parameters were used: laser power of 700 W, scan speed of 0.06 m/s, scan line spacing of 0.15 mm, and powder layer thickness of 0.3 mm. The microstructure, composition, and phase of the laser processed material were investigated by scanning electron microscopy(SEM), X-ray diffraction(XRD), and energy dispersive X-ray(EDX) spectroscopy. The results show that the bonding mechanism of this process is liquid phase sintering. The Cu and Co act as the binder phase, while the WC acts as the reinforcing phase. The non-equilibrium effects induced by laser melting, such as high degrees of undercooling and high solidification rate, result in the formation of a metastable phase CoC0.25. The WC reinforcing particulates typically have three kinds of morphology. They are agglomerated and undissolved, incompletely separated and partially dissolved, separated and dissolved, which indicates that particle rearrangement acts as the dominant sintering mechanism for the larger WC, while dissolution-precipitation prevails for the smaller WC particles. Microhardness tester was used to determine the Vickers hardness across the cross-section of the laser sintered sample, with the average value being HV0.1268.5. However, the hardness varied considerably, which might be attributed to the WC segregation and the high solidification rate experienced by the molten pool.
文摘Transparent polycrystaUine neodymiumdoped yttrium aluminum garnet ceramics （Nd：YAG） with better chemical stability, excellent optical and high temperature mechanical property is becoming a new laser host material. The Nd：YAG precursor powders with loosely dispersed, slightly agglomerated and YAG cubic crystal phase were synthesized at 1100 ℃ by the co-precipitation method combined with the reverse strike,
