Preparation of Laser Cladding Coating Undercooling Cu-based Alloy and Co on Non-equilibrium Solidification Structure

The effect of the gradient content of Co element on the solidification process of Cu-based alloy under deep under cooling conditions was explored.The non-equilibrium solidification structure of the under cooled alloy samples were analyzed.It is found that the rapidly solidified alloy has undergone twice grain refinement during the undercooling process.Characterization and significance of the maximum undercooling refinement structure of Cu60Ni35Co5 at T=253 K were analyzed.High-density defects were observed,such as dislocations,stacking faults networks,and twinning structures.The standard FCC diffraction pattern represents that it is still a single-phase structure.Based on the metallographic diagram,EBSD and TEM data analysis,it is illustrated that the occurrence of grain refinement under high undercooling is due to stress induced recrystallization.In addition,the laser cladding technology is used to coat Co-based alloy(Stellite12) coating on 304 stainless steel substrate;the microstructure of the coating cross-section was analyzed.It was found that the microstructure of the cross-section is presented as columnar crystals,planar crystals,and disordered growth direction,so that the coating has better hardness and wear resistance.By electrochemical corrosion of the substrate and coating,it can be seen that the Co and Cr elements present in the coating are more likely to form a dense passivation film,which improved the corrosion resistance of the coating.

Optical facet coatings for high-performance LWIR quantum cascade lasers atλ∼8.5μm

We report on the performance improvement of long-wave infrared quantum cascade lasers(LWIR QCLs)by studying and optimizing the anti-reflection(AR)optical facet coating.Compared to the Al2O3 AR coat⁃ing,the Y_(2)O_(3)AR coating exhibits higher catastrophic optical mirror damage(COMD)level,and the optical facet coatings of both material systems have no beam steering effect.A 3-mm-long,9.5-μm-wide buried-heterostruc⁃ture(BH)LWIR QCL ofλ~8.5μm with Y_(2)O_(3)metallic high-reflection(HR)and AR of~0.2%reflectivity coating demonstrates a maximum pulsed peak power of 2.19 W at 298 K,which is 149%higher than that of the uncoated device.For continuous-wave(CW)operation,by optimizing the reflectivity of the Y_(2)O_(3)AR coating,the maximum output power reaches 0.73 W,which is 91%higher than that of the uncoated device.

Structure of Laser Depositing of Al_(2)O_(3) Coating

A CO 2 laser with continuous wave was employed to deposite an alumina coating with a Ti Al transition coating on two kinds of steel substrates,i.e. steel Q235 and steel 45. Ti and Al could react with C in steel 45 substrate under the condition of laser depositing and form a thin reacting transition coating between the substrate and alumina coating,but the reaction did not occur on steel Q235 substrate because of its low carbon content.The quality and performance of the former were superior to that of the latter. The results were verified by SEM, XRD and Microhardness Tester.

Microstructure and tribological properties of laser cladding Fe-based coating on pure Ti substrate

Fe-based coating was produced on pure Ti substrate by the laser cladding technology. The composition and microstructure of the fabricated coating were analyzed by scanning electron microscopy （SEM）, X-ray diffraction （XRD） and transmission electron microscopy （TEM） technique. The tribological properties were tested through sliding against AISI52100 steel ball at different normal loads and sliding speeds. Besides, the morphologies of the worn surfaces and wear debris were analyzed by scanning electron microscopy （SEM） and three dimensional （3D） non-contact surface mapping. The results show that the prepared Fe-based coating has a high hardness of about 860 HV0.2 and exhibits an average wear rate of （0.70-2.32）×10-6 mm3/（N-m）, showing that the Fe-based coating can greatly improve the wear resistance of pure Ti substrate. The wear mechanism of the coating involves moderate adhesive and abrasive wear.

Preparation of ultra-fine grain Ni-Al-WC coating with interlocking bonding on austenitic stainless steel by laser clad and friction stir processing

The ultra-fine structured Ni?Al?WC layer with interlocking bonding was fabricated on austenitic stainless steel by combination of laser clad and friction stir processing (FSP). Laser was initially applied to Ni?Al elemental powder preplaced on the austenitic stainless steel substrate to produce a coating for further processing. The as-received coating was subjected to FSP treatment, processed by a rotary tool rod made of WC?Co alloy, to obtain sample for inspection. Microstructure, phase constitutions, hardness and wear property were investigated by methods of scanning electronic microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) microanalysis, and X-ray diffraction (XRD), hardness test alongside with dry sliding wear test. The results show that the severe deformation effect exerted on the specimen resulted in an ultra-fine grain layer of about 100μmin thickness and grain size of 1?2μm. Synergy between introduction of WC particles to the deformation layer and deformation strengthening contributes greatly to the increase in hardness and friction resistance. An interlocking bonding between the coating and matrix which significantly improves bonding strength was formed due to the severe deformation effect.

Viscoplastic friction and microstructural evolution behavior of laser-clad Co-Cr-Ni-Mo coating

The viscoplastic friction and nanostructure formation mechanism of laser-clad Co-based coating were studied by rotary friction between laser-clad Co-Cr-Ni-Mo coating and WC-Co rod.The friction coefficient,friction interface temperature and axial displacement—time curves during rotary friction process were measured.The results showed that all the curves firstly experienced rising stage and then steady stage.The rising stage corresponded to sliding friction while the steady stage corresponded to viscoplastic friction.After viscoplastic friction processing,three typical zones of viscoplastic deformation zone,thermo-mechanically affected zone,and original laser-clad zone can be observed successively from the friction surface to the interior.The viscoplastic deformation significantly crushed the network M23C7 phase in original laser-clad zone and made it dispersively distributed with equiaxial shape and in nano-scale.The viscoplastic zone,in width of 37-131 μm,is mainly characterized by refined M23C7 and α-Co phase with grain size bellow 50 nm,and even a small quantity of amorphous.Thus,the hardness of viscoplastic zone about HV997 was improved compared with the hardness of original laser-clad zone about HV600.

High Slope Efficiency and High Power 850nm Oxide-Confined Vertical Cavity Surface Emitting Lasers

High slope efficiency and high power selected oxide-confined 850nm VCSELs grown by MOCVD are reported.The slope efficiency and the threshold current respectively are 0 82mW/mA and 2 59mA with a 9μm diameter oxidation aperture at 25℃.The maximum power of 16mW is obtained at 23mA current bias.The minimum threshold current can be as low as 570μA with a 5μm diameter oxidation aperture at 25℃.The maximum saturated power is 5 5mW.

Interface characteristics of Al_2O_3－13%TiO_2 ceramic coatings prepared by laser cladding

Al2O3-13%TiO2 （mass fraction） coatings, prepared by laser cladding on nickel-based alloy, were heated using high frequency induction sources. The coating microstructure and the interface between bond coating and ceramic coating were characterized by SEM, XRD and EDS. The results show that two-layer substructure exists in the ceramic coating： one layer evolving from fully melted region where the sintered grains grow fully; another layer resembling the liquid-phase-sintered structure consisting of three-dimensional net where the melted Al2O3 particles are embedded in the TiO2-rich matrix. The mechanism of the two-layer substructure formation is also explained in terms of the melting and flattening behavior of the powders during laser cladding processing. The spinel compounds NiAl2O4 and acicular compounds Cr2O3 are discovered in the interface between bond coating and ceramic coating. It proves that the chemical reactions in the laser cladding process will significantly enhance the coating adhesion.

Corrosion behavior of Hastelloy C22 coating produced by laser cladding in static and cavitation acid solution

The Hastelloy C22 coatings on Q235 steel substrate were produced by high power diode laser cladding technique. Their corrosion behaviors in static and cavitation hydrochloric, sulfuric and nitric acid solutions were investigated. The electrochemical results show that corrosion resistance of coatings in static acid solutions is higher than that in cavitation ones. In each case, coating corrosion resistance in descending order is in nitric, sulfuric and hydrochloric acid solutions. Obvious erosion-corrosion morphology and serious intercrystalline corrosion of coating are noticed in cavitation hydrochloric acid solution. This is mainly ascribed to the aggressive ions in hydrochloric acid solution and mechanical effect from cavitation bubbles collapse. While coating after corrosion test in cavitation nitric acid solution shows nearly unchanged surface morphology. The results indicate that the associated action of cavitation and property of acid solution determines the corrosion development of coating. Hastelloy C22 coating exhibits better corrosion resistance in oxidizing acid solution for the stable formation of dense oxide film on the surface.

Characteristics of microstructure and performance of laser-treated electroless Ni-P/Ni-W-P duplex coatings

Characteristics of microstructures of electroless Ni-P/Ni-W-P duplex coatings were investigated using SEM/EDX and XRD analysis techniques. Microhardness and wear behaviour of the coatings before and after laser crystallization were evaluated by measurements of hardnesses of coating surface and cross-section, and by unlubricated friction and wear experiments. The results indicate that it is possible to prepare electroless Ni-P/Ni-W-P duplex coatings by sequential immersion in two different plating baths. After laser crystallization, the microstructures of electroless Ni-P/Ni-W-P duplex coatings present the characteristics of higher degree of crystallization and larger grain size for outer layer Ni-W-P than inner Ni-P, but outer layer has a higher hardness. The wear resistance of laser-treated duplex coatings in a given process parameter conditions is superior to the as-plated ones. Laser treatment was performed directly in air without argon protection, which provides the possibility for application of industrialized production.

Effect of Laser Power on the Microstructure and Mechanical Properties of TiN/Ti_3Al Composite Coatings on Ti6Al4V

Laser nitriding is one of the effective techniques to improve the surface properties of titanium alloys and has potential application in the life extension of last-stage steam turbine blades. However, cracking of surface coating is a common problem due to heat concentration in laser nitriding process. Conventionally, the cracks can be avoided through heat treatment, which may have an important influence on the mechanical properties of coating. Crack-free TiN/Ti3Al IMC coatings on Ti6Al4V are prepared by plasma spraying and laser nitriding. The microstructures, phase constitutes and compositions of the coating are observed and analyzed with scanning electron microscopy(SEM), X-ray diffraction(XRD) and X-ray energy-dispersive spectroscopy(EDS). Microhardness, elastic modulus, fracture toughness of the coating are measured. The results show that the crackand pore-free IMC coatings can be made through the proposed method; with increasing laser power, the amount and density of TiN phase in the coating first increased and then decreased, leading to the similar trend of microhardness and elastic modulus and the reverse trend of fracture toughness of the coating. Both the average microhardness and elastic modulus of the coating increase three times higher than those of the substrate. The volume fraction of the TiN reinforced phase in composite can be controlled by varying the laser power and the cracking problem in laser nitriding process is successfully solved.

Superior corrosion resistance-dependent laser energy density in(CoCrFeNi)95Nb5 high entropy alloy coating fabricated by laser cladding

(CoCrFeNi)95Nb5 high entropy alloy(HEA)coatings were successfully fabricated on a substrate of Q235 steel by laser cladding technology.These(CoCrFeNi)95Nb5 HEA coatings possess excellent properties,particularly corrosion resistance,which is clearly superior to that of some typical bulk HEA and common engineering alloys.In order to obtain appropriate laser cladding preparation process parameters,the effects of laser energy density on the microstructure,microhardness,and corrosion resistance of(CoCrFeNi)95Nb5 HEA coating were closely studied.Results showed that as the laser energy density increases,precipitation of the Laves phase in(CoCrFeNi)95Nb5 HEA coating gradually decreases,and diffusion of the Fe element in the substrate intensifies,affecting the integrity of the(CoCrFeNi)95Nb5 HEA.This decreases the microhardness of(CoCrFeNi)95Nb5 HEA coatings.Moreover,the relative content of Cr2O3,Cr(OH)3,and Nb2O5 in the surface passive film of the coating decreases with increasing energy density,causing corrosion resistance to decrease.This study demonstrates the controllability of a high-performance HEA coating using laser cladding technology,which has significance for the laser cladding preparation of other CoCrFeNi-system HEA coatings.

Microstructures and properties of Fe-Co-B-Si-Nb coating prepared by laser cladding and remelting

High power laser cladding of [ （ Fe0. 5 Co0. 5 ） 0. 75 B0. 2 Si0.05 ] 95. 7 Nb4. 3 powder mixture afier-remelting was performed to fabricate Fe-based metallic glass coating on the surface of steel of China Classification Society： Grade B （CCS-B）. Scanning electron microscopy （SEM）, X-ray diffraction （XRD）, transmission electron microscopy （TEM） with energy dispersive spectrometer （EDS）, Vickers hardness tester and corrosion resistance tester were employed to characterize microstructures and evaluate properties of this coating. According to the results of SEM, XRD and TEM, the cladding coating consisted of nanocrystalline embedded in amorphous phase. EDS data indicated that Nb segregated in the amorphous matrix. The results of hardness test revealed that the hardness of the top layer was higher than that of the inner layer of the coating. The coating exhibited excellent corrosion resistance in a 3.5% NaCl solution.

A Single Mode980 nm In Ga As/Ga As/Al Ga As Large Optical Cavity Quantum Well Laser with Low Vertical Divergence Angle

To achieve high optical power as well as low vertical divergence angle,a new kind of optim ized large opti- cal cavity (L OC) structure is applied to a ridge waveguide 980 nm In Ga As/ Ga As/ Al Ga As m ulti- quantum well laser.The optical power density in the waveguide is successfully reduced.The maxim um output power is more than 40 0 m W with a slope efficiency of 0 .89W/ A and the far- field vertical divergence angle is lowered to 2 3°.

Lateral Oxidation in Vertical Cavity Surface Emitting Lasers

Lateral oxidation in vertical cavity surface emitting lasers （VCSELs） is described,and its characteristics are investigated.A linear growth law is found for stripe mesas. However, oxide growth （above 435℃ ） follows a nonlinear law for the two geometry mesa structures which we employ in VCSEL. Theoretical analysis indicates that mesa structure geometry influences oxide growth rate at higher temperatures.

Frequency doubled femtosecond Ti:sapphire laser with an assisted enhancement cavity

We report an enhancement cavity for femtosecond Ti：sapphire laser at the repetition rate of 170 MHz. An enhancement factor of 24 is obtained when the injecting pulses have an average power of 1 W and a pulse duration of 80 fs. By placing a BBO crystal at the focus of the cavity, we obtain a 392-mW intracavity doubled-frequency laser, corresponding to a conversion efficiency of 43%. The output power has a long-term stability with a root mean square （RMS） of 0.036%.

Corrosive-wear and Electrochemical Performance of Laser Thermal Sprayed Co30Cr8W1.6C3Ni1.4Si Coating on Ti6Al4V Alloy

Co30Cr8W1.6C3Ni1.4Si coatings were fabricated on Ti6Al4V alloy using a laser thermal spraying(LTS).The surface and cross-section morphologies,phases and bonding strength of obtained coatings were investigated using scanning electronic microscopy(SEM),X-ray diffraction(XRD),and scratch test,respectively.The effects of laser power on the coefficients of friction(COFs)and corrosive-wear behaviors of Co30Cr8W1.6C3Ni1.4Si coatings were investigated using a wear tester in 3.5%NaCl solution,and the electrochemical corrosion performance was analyzed using an electrochemical workstation.The experimental results show that the Co30Cr8W1.6C3Ni1.4Si coating is bonded with the substrate in the metallurgical form,and the bonding strengths of Co30Cr8W1.6C3Ni1.4Si coatings fabricated at the laser power of 1000,1200,and 1400 W are 76.5,56.5,and 55.6 N,respectively.The average COFs of Co30Cr8W1.6C3Ni1.4Si coatings fabricated at the laser power of 1000,1200,and 1400 W are 0.769,0.893,and 0.941,respectively;and the corresponding wear rates are 0.267×105,0.3178×105,and 0.325×105μm3/Nm,respectively,which increases with the increase of laser power,the wear mechanism is primarily abrasive wear.The corrosion potential of Co30Cr8W1.6C3Ni1.4Si coatings fabricated at the laser power of 1000,1200,and 1400 W is-0.05,-0.25,and-0.31 V,respectively,higher than-0.45 V of substrate which enhances the electrochemical corrosion resistance of substrate.

Simulation of High Power Er/Yb Codoped Fiber Linear Cavity Lasers

The performances of high power Er/Yb codoped fiber linear cavity lasers are investigated numerically. The numerical analysis is based on the iterative solution of rate equations for population density of the Er/Yb ions. The behaviors of co-pump and counter-pump methods are contrasted. Dependence of output power on input pump power, output reflectivity, operating wavelength and active fiber length is simulated, respectively. High conversion efficiency Er/Yb laser output is obtained in simulations and experiments.

A 1550-nm linearly tunable continuous wave single-mode external cavity diode laser based on a single-cavity all-dielectric thin-film Fabry Pérot filter

A 1550-nm linearly tunable continuous wave （CW） single-mode external cavity diode laser （ECDL） based on a singlecavity all-dielectric thin-film Fabry-Pérot filter （s-AFPF） is proposed and realized in this paper. Its internal optical components as well as their operation mechanisms are introduced first, and then its longitudinal mode output characteristic is theoretically analyzed. Afterwards, we set up the experimental platform for the output characteristic measurement of this tunable ECDL; under different experimental conditions, we execute accurate and real-time measurements for the output central wavelength, output optical power, output longitudinal mode distribution, and the line-width of the tunable ECDL in its tuning process. By summing up the optimal experimental condition from the measured data, we obtain the optimal tunable ECDL relevant parameters： the tunable ECDL has a linear mode-hop-free wavelength tuning region of 1547.203 nm-1552.426 nm, a stable output optical power in the range of 40 μW-50 μW, and a stable output longitudinal mode distribution of a single longitudinal mode with a line-width in the range of 100 MHz-150 MHz. This tunable ECDL can be used in environmental gas monitoring, atomic and molecular laser spectroscopy research, precise measurements, and so on.

The bactericidal effect of continuous wave laser with strongly absorbing coating at the fiber tip

The bactericidal effect of laser radiation with a quartz fiber-based transmission system with a strong absorption coating converter against bacteria associated with urological stones has been studied.Gr am-negative rod Escherichia coli and the Gram-positive coccus Staphylococcus epi-dermidis,Staphylococcus aureus,Enterococcus faecalis and Enterococcus faecium were used in this study.Each bacterial species was treated by continuous-wave near infrared laser coupled with bare fiber tip or strongly absorption coating fiber tip.After treatment,the temperature of bacterial suspension was measured.In addition,the temperature dist ribution was analyzed.It has been shown that using laser with a strongly absorption coating fiber tip results in significant bactericidal effect.The decrease of the amount of E.coli and S.epidermidis was 100%after treatment with an output power of6 W of radiation at a wavelength of 0.97 pum for 40s.Number of S.aureus and Ent.facium colony-forming unit was reduced to 70%after same exposure.The peak temperature of bacterial suspension was 86℃ after treatment by laser with a strongly absorption coating fiber tip.Laser with a strongly absorpt ion coating fiber tip provides large scale hydrodynamic flows directed away from the fiber tip.The laser with a strongly absorption coating fiber tip has bactericidal effect.The main role is associated with the effect of high temperature,which,in the form of flow in a liquid medium,afects bacteria.