Robust interface and excellent as-built mechanical properties of Ti–6Al–4V fabricated through laser-aided additive manufacturing with powder and wire

The feasibility of manufacturing Ti-6Al-4V samples through a combination of laser-aided additive manufacturing with powder(LAAM_(p))and wire(LAAM_(w))was explored.A process study was first conducted to successfully circumvent defects in Ti-6Al-4V deposits for LAAM_(p) and LAAM_(w),respectively.With the optimized process parameters,robust interfaces were achieved between powder/wire deposits and the forged substrate,as well as between powder and wire deposits.Microstructure characterization results revealed the epitaxial prior β grains in the deposited Ti-6Al-4V,wherein the powder deposit was dominated by a finerα′microstructure and the wire deposit was characterized by lamellar α phases.The mechanisms of microstructure formation and correlation with mechanical behavior were analyzed and discussed.The mechanical properties of the interfacial samples can meet the requirements of the relevant Aerospace Material Specifications(AMS 6932)even without post heat treatment.No fracture occurred within the interfacial area,further suggesting the robust interface.The findings of this study highlighted the feasibility of combining LAAM_(p) and LAAM_(w) in the direct manufacturing of Ti-6Al-4V parts in accordance with the required dimensional resolution and deposition rate,together with sound strength and ductility balance in the as-built condition.

A fringe jump counting method for the phase measurement in the HCN laser interferometer on EAST and its FPGA-based implementation

Electron density in fusion plasma is usually diagnosed using laser-aided interferometers. The phase difference signal obtained after phase demodulation is wrapped, which is also called a fringe jump. A method has been developed to unwrap the phase difference signal in real time using FPGA, specifically designed to handle fringe jumps in the hydrogen cyanide(HCN) laser interferometer on the EAST superconducting tokamak. This method is designed for a phase demodulator using the fast Fourier transform(FFT) method at the front end. The method is better adapted for hardware implementation compared to complex mathematical analysis algorithms, such as field programmable gate array(FPGA). It has been applied to process the phase measurement results of the HCN laser interferometer on EAST in real time. Electron density results show good confidence in the fringe jump unwrapping method. Further possible application in other laser interferometers, such as the POlarimeter-INTerferometer(POINT)system on EAST tokamak is also discussed.

Multiphysics coupling in situ measurement method for laser repair of the Inconel 718 alloy structure

As an additive manufacturing technique,the laser-aided direct energy deposition(L-DED)method has been widely used for component repair(also called laser repair).With significant differences from traditional manufacturing techniques,the laser repair process has the characteristics of point-by-point deposition and has a high-temperature gradient in the repair area,resulting in the formation of heterogeneous thermal deformation and residual stress after cooling.High stress may lead to the appearance of cracks in the repair area and may seriously influence the bearing capacity of the repaired parts.Therefore,the characterization of the temperature and deformation fields of the components during laser repair is important for the analysis of the mechanism of damage evolution in the repair area,optimization of the process parameters,and improvement of the mechanical properties of the repaired components.Because of the demand for the simultaneous measurement of the temperature and deformation fields,using a multispectral camera and a self-designed three-peak filter,a temperature-deformation field measurement technique was developed and applied to in situ monitoring during the L-DED manufacturing process.In the actual measurement process,the synchronous measurement of the temperature field of the laser molten pool and the deformation field of the side surface of the repaired component were realized using the images of multiple channels in the multispectral camera.The experimental results verify that a three-peak filter can effectively eliminate the influences of glare and overexposure on the recorded multispectral images.Moreover,the amplitude of the displacement field and the temperature gradient of the repaired component will increase with the increase in laser power,which may affect the final molding of the repaired component.This work extends the function of the multispectral camera to measure the temperature and deformation fields and provides a new measurement method for further optimizing the process parameters of laser repair.

Numerical study of thermal history in laser aided direct metal deposition process

Temperature evolution in the laser aided direct metal deposition (LADMD) process has considerable influence on the micro-structure and properties of the final part. A 3D transient finite element model was developed to study the temperature evolution during the multilayer LADMD process. To make the property analysis from thermal history easier, a critical temperature specific to thermal history was defined and the distribution of it in the part was also discussed. The simulation results indicated that the critical temperature can make the property analysis from thermal history easier. Thermal history of all the deposited materials was similar. It was also concluded that process parameters needed to be time-varying according to the real-time temperature field during the process.