Microstructure and microhardness of aluminium alloy with underwater and in-air wire-feed laser deposition

This study carried out the underwater and in-air wire-feed laser deposition of an aluminium alloy with a thin-walled tubular structure. For both the underwater and in-air deposition layers, both were well-formed and incomplete fusion, cracks, or other defects did not exist.Compared with the single-track deposition layer in air, the oxidation degree of the underwater single-track deposition layer was slightly higher.In both the underwater and in-air deposition layers, columnar dendrites nucleated close to the fusion line and grew along the direction of the maximum cooling rate in the fusion region(FR), while equiaxed grains formed in the deposited region(DR). As the environment changed from air to water, the width of DR and height of FR decreased, but the deposition angle and height of DR increased. The grain size and ratio of the high-angle boundaries also decreased due to the large cooling rate and low peak temperature in the water environment.Besides, the existence of a water environment benefitted the reduction of magnesium element burning loss in the DR. The microhardness values of the underwater deposition layer were much larger than those of the in-air layer, owing to the fine grains and high magnesium content.

Multi-Parameter Influence Analysis of Interaction Between Internal Solitary Wave and Fixed Submerged Body

To obtain the interaction characteristics between Internal solitary waves(ISWs)and submerged bodies,a three-dimensional numerical model for simulating ISWs was established in the present study based on the RANS equation.The velocity entrance method was adopted to generate the ISWs.First,the reliability of this numerical model was validated by comparing it with theoretical and literature results.Then,the influence of environmental and navigation parameters on interactions between ISWs and a fixed SUBOFF-submerged body was studied.According to research,the hydrodynamic performance of the submerged body has been significantly impacted by the ISWs when the body is nearing the central region of the wave.Besides,the pitching moment(y')will predominate when the body encounters the ISWs at a certain angle between 0°and 180°,and the lateral force is larger than the horizontal force.Additionally,the magnitude of the force acting on the body is mostly affected by the wave amplitude.The variation of the vertical force is the main way that ISWs affect the hydrodynamic performance of the bodies.The investigations and findings discussed above can serve as a guide to forecast how ISWs will interact with submerged bodies.

Common Transceiver LIF⁃Lidar Based on Y⁃Type Optical Fiber for Marine Oil Spill Detection

This paper presents a novel laser⁃induced fluorescence(LIF)Lidar system for marine oil spilling detection.A bifurcated Y⁃type optical fiber and an optical collimating lens compose a coaxial configuration transceiver for this LIF⁃Lidar system.This LIF⁃Lidar system was further applied to measure the excitation spectra from floating oil slicks with different thicknesses on top of seawater at different distances.The system presents several advantages such as compact structure,stable optical path,and convenient operation,which offers a wide application prospect in ocean exploration.

Multi-scale modeling for prediction of mechanical performance in brazed GH99 thin-walled structure

Superalloy thin-walled structures are achieved mainly by brazing,but the deformation process of brazed joints is non-uniform,making it a challenging research task.This paper records a thorough investigation of the effect of brazing parameters on the microstructure of joints and its mechanical properties,which mainly inquires into the deformation and fracture mechanisms in the shearing process of GH99/BNi-5a/GH99 joints.The macroscopic-microscopic deformation mechanism of the brazing interface during shearing was studied by Crystal Plasticity(CP)and Molecular Dynamics(MD)on the basis of the optimal brazing parameters.The experimental results show that the brazing interface is mainly formed by(Ni,Cr,Co)(s,s)and possesses a shear strength of approximately 546 MPa.The shearing fracture of the brazed joint occurs along the brazing seam,displaying the characteristics of intergranular fracture.MD simulations show that dislocations disassociate and transform into fine twinning with increased strain.CP simulated the shear deformation process of the brazed joint.The multiscale simulation results are consistent with the experimental results.The mechanical properties of thin-walled materials for brazing are predicted using MD and CP methods.

Numerical study of fluid resonance of a two-dimensional heaving-free moonpool in a wide range of incident waves

The fluid resonance of a moonpool freely heaving in a beam sea is studied by an in-house constrained interpolation profile(CIP)code.Generally,the moonpool behaves as in the piston mode with a narrow opening.The numerical studies are carried out for a wide range of the incident waves,and a new secondary resonant region is identified in the low frequency region of the incident waves,besides the ordinary main resonant region.Numerical results demonstrate that the horizontal wave forces are significant in the secondary resonant region,although the resonant wave elevations are less remarkable than those of the main resonant region.It is concluded that the fluid resonance of the low frequency is excited mainly by the heave motion of the moonpool.Parameter studies of the moonpool draft and the gap width of the moonpool based on the fluid resonance are also performed.

Feasibility study of thermo-compensated resistance brazing welding of C/C composites and T2 copper with AgCuTi filler metal

The dissimilar materials joining of C/C composites to T2 copper were performed successfully by thermo-compensated Resistance Brazing Welding(RBW)with AgCuTi filler powder.The interfacial microstructure,phase composition,and shear strength of the resistance brazed joints were investigated by the relevant analysis method.Experiment results indicated that the order affecting the shear strength of the C/C-Cu joint was welding current,welding pressure,and welding time in turn.The shear strength of backward thermo-compensated RBW was higher than that of forward thermo-compensated RBW due to the Peltier effect.The maximum shear strength of the C/C-Cu joint was 11.56 MPa in the optimized welding parameter with welding current of 8.0 kA,welding time of 60 ms,and welding pressure of 0.10 MPa by backward thermo-compensated RBW.The interface structure at the resistance brazed joint with this welding parameter was C/C composites/TiC/Cu(s.s)/T2 copper.The TiC phase was verified at the interface of the brazed joint by Scanning Electron Microscope(SEM),Energy-Dispersive X-ray Spectrometer(EDS),and X-ray Diffraction(XRD).Considerable fractures occurred in the C/C composites and partial fracture occurred at the interfacial reaction layer.

Ultrasonic-assisted soldering W90 Tungsten heavy alloy to AZ31B Mg alloy using Sn-x Al alloy

A double-layered W/Mg structure is expected to be a new generation of nuclear radiation shielding material.The tungsten heavy alloy(W90)and AZ31B Mg alloy were firstly bonded by ultrasonic-assisted soldering using pure Sn and Sn-Al filler metal in an atmospheric environment.The influence of ultrasonication time on the microstructure and mechanical properties of the joint was investigated.The typical microstructure of the W90/Sn/Mg joint was W90/Mg_(2)Sn+Sn/Mg_(2)Sn layer/Mg.As the ultrasonication time increased from 2 s to 10 s,the joint width reduced and the thickness of the Mg_(2)Sn layer increased.The shear strength of the joint firstly increased,then flattened,and finally decreased.The joint strength reached the maximum value of 10.5 MPa.The fracture position of the joint changed from the W90/filler metal interface to the Mg_(2)Sn layer.The addition of Al in Sn resulted in the formation of the Al4 W phase at the W/Sn-1Al interface.The W/filler metal interface changed from the semi-coherent interface to the coherent interface and the joint strength increased.As the ultrasonication time was 6 s,the shear strength W90/Sn-1Al/Mg joint reached the maximum value of 24.6 MPa and the joint fractured at two positions:W90/filler metal interface and filler metal.With the further increase of ultrasonication time,the joint strength decreased and the joint fractured in the Mg_(2)Sn layer.

Synergistically enhanced Si_(3)N_(4)/Cu heterostructure bonding by laser surface modification

A bonding approach based on laser surface modification was developed to address the poor bonding be-tween Si_(3)N_(4) ceramic and Cu.The bonding mechanism in Si_(3)N_(4)/Cu heterogeneous composite structure fabricated by laser modification-assisted bonding is examined by means of scanning/transmission elec-tron microscopy and thermodynamic analysis.In the bonding process under laser modification,atomic intermixing at the interface is confirmed,as a result of the enhanced diffusion assisted by the dissocia-tion of Si_(3)N_(4) ceramic by laser.The dissociating Si precipitations on the surface,as well as the formation of micro-pores interfacial structure,would be the key concept of the bonding,by which the seamless and robust heterointerfaces were created.By controlling the laser-modifying conditions,we can obtain a reli-able heterostructure via the optimization of the trade-off of the surface structure and bonding strength,as determined by the laser-modified surface prior to bonding.The maximum structure depth and S ratio at the Si_(3)N_(4) surface were produced at a laser power of 56 W,corresponding to the maximal shear strength of 15.26 MPa.It is believed that the further development of this bonding technology will advance power electronic substrate fabrication applied in high-power devices.