Effect of Trace Addition of Ceramic on Microstructure Development and Mechanical Properties of Selective Laser Melted AlSi10Mg Alloy

Selective laser melting(SLM)is an emerging additive manufacturing technology for fabricating aluminum alloys and aluminum matrix composites.Nevertheless,it remains unclear how to improve the properties of laser manufactured aluminum alloy by adding ceramic reinforcing particles.Here the effect of trace addition of TiB2 ceramic(1%weight fraction)on microstructural and mechanical properties of SLM-produced AlSi10Mg composite parts was investigated.The densification level increased with increasing laser power and decreasing scan speed.A near fully dense composite part(99.37%)with smooth surface morphology and elevated inter-layer bonding was successfully obtained.A decrease of lattice plane distance was identified by X-ray diffraction with the laser scan speed decreased,which implied that the crystal lattices were distorted due to the dissolution of Si and TiB2 particles.A homogeneous composite microstructure with the distribution of surface-smoothened TiB2 particles was present,and a small amount of Si particles precipitated at the interface between reinforcing particles and matrix.In contrast to the AlSi10Mg alloy,the composites showed a stabilized microhardness distribution.A higher ultimate tensile strength of 380.0 MPa,yield strength of 250.4 MPa and elongation of 3.43%were obtained even with a trace amount of ceramic addition.The improvement of tensile properties can be attributed to multiple mechanisms including solid solution strengthening,load-bearing strengthening and dispersion strengthening.This research provides a theoretical basis for ceramic reinforced aluminum matrix composites by additive manufacturing.

Time Domain Synchronous OFDM System for Optical Fiber Communications

A spectrum efficient OFDM scheme named Time Domain Synchronous-OFDM(TDS-OFDM)is introduced into coherent optical transmission system,in which the pseudo noise(PN)sequence is exploited as guard interval to realize frame synchronization,compensate the carrier frequency offset(CFO),and estimate and equalize channel simultaneously.Since there is no pilot signals or training symbols in TDS-OFDM,the proposed scheme can achieve higher spectral efficiency(SE)above 10%improvement comparing with CPOFDM.The proposed method is implemented and verified in a 28GBaud QPSK OFDM system and a 28GBaud 16QAM OFDM system.It is demonstrated that the proposed scheme shows high CFO estimation accuracy and synchronous accuracy.Under CFO and linewidth of laser source set as 100MHz and 100kHz respectively,BER of QPSK OFDM system is below 3.8e-3 at the optical signal-to-noise ratio(OSNR)of 13dB,and BER of 16QAM OFDM system is below 3.8e-3 at the OSNR of 20dB.

Formation Process and Mechanical Deformation Behavior of a Novel Laser-Printed Compression-Induced Twisting-Compliant Mechanism

A novel compression-induced twisting(CIT)-compliant mechanism was designed based on the freedom and constraint topology(FACT)method and manufactured by means of laser powder bed fusion(LPBF).The effects of LPBF printing parameters on the formability and compressive properties of the laserprinted CIT-compliant mechanism were studied.Within the range of optimized laser powers from 375 to 450 W and with the densification level of the samples maintained at above 98%,changes in the obtained relative densities of the LPBF-fabricated CIT-compliant mechanism with the applied laser powers were not apparent.Increased laser power led to the elimination of residual metallurgical pores within the inclined struts of the CIT mechanism.The highest dimensional accuracy of 0.2% and the lowest surface roughness of 20μm were achieved at a laser power of 450 W.The deformation behavior of the CIT-compliant mechanism fabricated by means of LPBF exhibited four typical stages:an elastic stage,a heterogeneous plastic deformation stage,a strength-destroying stage,and a deformation-destroying stage(or instable deformation stage).The accumulated compressive strain of the optimally printed CIT mechanism using a laser power of 450 W went up to 20% before fracturing,demonstrating a large deformation capacity.The twisting behavior and mechanical properties were investigated via a combination of finite-element simulation and experimental verification.An approximately linear relationship between the axial compressive strain and rotation angle was achieved before the strain reached 15% for the LPBF-processed CIT-compliant mechanism.

Anisotropic corrosion resistance of TiC reinforced Ni-based composites fabricated by selective laser melting

Electrochemical measurements on three planes of TiC/Inconel 718 composites fabricated by selective laser melting(SLM) were performed to study the corrosion property. The results showed that the YZplane with dense and fine columnar structures possessed high microhardness and superior corrosion resistance in 3.5 wt% NaCl solution. For the XZ-plane, a decreased anti-corrosion property was observed owing to its inhomogeneous microstructures. While the XY-plane with large irregular pores and clustered ring-like structures was more susceptible to corrosion compared with the other two planes. Comparative analysis suggested that the anisotropic corrosion behaviors were significantly dependent on the surface defects, microstructure characteristics and added reinforcements.

Analysis of the performance of optical frequency comb based on recirculating frequency shifter influenced by an Er-doped fiber amplifier

The factors that influence the generation of a high-quality optical frequency comb(OFC)based on a recirculating frequency shifter(RFS)due to the maximum output power and noise figure of Er-doped fiber amplifier(EDFA)are studied theoretically and experimentally.Based on the theoretical analysis,numerical simulations and experiments under different EDFA parameters have been carried out.The results show that the performance of the OFC based on a RFS can be improved effectively by optimizing the maximum output power and the noise figure of the EDFA.