Structure and Mechanical Properties of Al-based Gradient Composites Reinforced with Primary Si and Mg_2Si Particles through Centrifugal Casting

The structure and mechanical properties of a new type of Al-based discontinuous gradient composites prepared by using the ternary AI-19Si-5Mg alloys as the raw material adopting the centrifugal casting method were investigated. Structurally, the composites are divided into two zones： a reinforced zone with the high volume fraction of primary Si and Mg2Si particles and an unreinforced zone with no or a few particles. In the reinforced zone, the primary particles are evenly distributed, with the sizes of the primary Si particles 80-120 μm, and that of primary Mg2Si particles 20-50 μm. The properties test results show the reinforced zone has higher Rockwell hardness and better wear resistance than the unreinforced zone, due to the complementary reinforcement relationship between the primary Si and Mg2Si particles and their high volume fraction.

Oxidation Behavior of C/C-SiC Gradient Matrix Composites

Oxidation behavior of C/C-SiC gradient matrix composites and C/C composites were compared in stationary air. The results show that oxidation threshold of C-SiC materials increases with the amount of SiC particles in the codeposition matrix. Oxidation rate of C/C-SiC gradient matrix composites is significantly lower than that of C/C material. The micro-oxidation process was observed by SEM.

On the homogenization of metal matrix composites using strain gradient plasticity

The homogenized response of metal matrix composites（MMC） is studied using strain gradient plasticity.The material model employed is a rate independent formulation of energetic strain gradient plasticity at the micro scale and conventional rate independent plasticity at the macro scale. Free energy inside the micro structure is included due to the elastic strains and plastic strain gradients. A unit cell containing a circular elastic fiber is analyzed under macroscopic simple shear in addition to transverse and longitudinal loading. The analyses are carried out under generalized plane strain condition. Micro-macro homogenization is performed observing the Hill-Mandel energy condition,and overall loading is considered such that the homogenized higher order terms vanish. The results highlight the intrinsic size-effects as well as the effect of fiber volume fraction on the overall response curves, plastic strain distributions and homogenized yield surfaces under different loading conditions. It is concluded that composites with smaller reinforcement size have larger initial yield surfaces and furthermore,they exhibit more kinematic hardening.

Centrifugal casting processes of manufacturing in situ functionally gradient composite materials of Al-19Si-5Mg alloy

Cylindrical components of in situ functionally gradient composite materials of Al-19Si-5Mg alloy were manufactured by centrifugal casting. Microstructure characteristics of the manufactured components were observed and the effects of the used process factors on these characteristics were analyzed. The results of observations shows that, in thickness, the components possess microstructures accumulating lots of Mg2Si particles and a portion of primary silicon particles in the inner layer, a little MgzSi and primary silicon particles in the outer layer, and without any Mg2Si and primary silicon particle in the middle layer. The results of the analysis indicate that the rotation rate of centrifugal casting, mould temperature, and melt pouring temperature have evidently affected the accumulation of the second phase particles. Also, the higher the centrifugal rotation rate, mould temperature, and melt pouring temperature are, the more evident in the inner layer the degree of accumulation of Mg2Si and primary silicon particles is.

Functionally graded structure of a nitride-strengthened Mg_(2)Si-based hybrid composite

The ex-situ incorporation of the secondary SiC reinforcement,along with the in-situ incorporation of the tertiary and quaternary Mg_(3)N_(2) and Si_(3)N_(4) phases,in the primary matrix of Mg_(2)Si is employed in order to provide ultimate wear resistance based on the laser-irradiation-induced inclusion of N_(2) gas during laser powder bed fusion.This is substantialized based on both the thermal diffusion-and chemical reactionbased metallurgy of the Mg_(2)Si–SiC/nitride hybrid composite.This study also proposes a functional platform for systematically modulating a functionally graded structure and modeling build-direction-dependent architectonics during additive manufacturing.This strategy enables the development of a compositional gradient from the center to the edge of each melt pool of the Mg_(2)Si–SiC/nitride hybrid composite.Consequently,the coefficient of friction of the hybrid composite exhibits a 309.3%decrease to–1.67 compared to–0.54 for the conventional nonreinforced Mg_(2)Si structure,while the tensile strength exhibits a 171.3%increase to 831.5 MPa compared to 485.3 MPa for the conventional structure.This outstanding mechanical behavior is due to the(1)the complementary and synergistic reinforcement effects of the SiC and nitride compounds,each of which possesses an intrinsically high hardness,and(2)the strong adhesion of these compounds to the Mg_(2)Si matrix despite their small sizes and low concentrations.

Simulation Analysis on Mechanical Property Characterization of Carbon Nanotubes Reinforced Epoxy Composites

Carbon nanotube(CNT)-reinforced composites have ultra-high elastic moduli,low densities,and fibrous structures.This paper presents the multi-scale finite element modeling of CNT-reinforced polymer composites from micro-to macro-scales.The nanocomposites were modeled using representative volume elements(RVEs),and finite element code was written to simulate the modeling and loading procedure and obtain equivalent mechanical properties of the RVEs with various volume fractions of CNTs,which can be used directly in the follow-up simulation studies on the macroscopic model of CNT-reinforced nanocomposites.When using the programming to simulate the deformation and fracture process of the CNT-reinforced epoxy composites,the mechanical parameters and stress-strain curves of the composites on themacro-scale were obtained by endowing the elements of the lattice models withRVE parameters.Tensile experiments of the CNT-reinforced composites were also carried out.The validity of the finite element simulation method was verified by comparing the results of the simulations and experiments.Finite element models of functionally graded CNT-reinforced composites(FG-CNTRC)with different distributions were established,and the tensile and three-point-bending conditions for various graded material models were simulated by the methods of lattice model and birth-death element to obtain the tensile and bending parameters.In addition,the influence of the distribution and volume ratio of the CNTs on the performance of the graded composite material structures was also analyzed.

Effect of pH Value on Nano-Al_2O_3/Ni+Co Gradient Bionic Composite Coating by Electrodeposition

The metal and nano-ceramic composite coatings were formed on gray cast iron surface by electrodepositon method.The Ni-Co was used as metal matrix,and the nano-Al2O3 was chosen as second-phase particulates.The gradient structure of biology material was the model to avoid bad interface bonding and stress distribution,therefore the gradient composite coating was prepared.The morphology of composite coatings was flatter and the microstructure was more com-pact than the pure Ni-Co coatings.Effect of pH value on surface morphology was analyzed,which some microcracks appeared when pH value was greater than 5.The content of codeposition na-no-Al2O3 reached a maximum value at pH value of 3-4,at the same time the properties including mi-crohardness and wear-resistance were analyzed.The result indicated that the mirohardness reached a maximum value and the wear loss volume was less at pH value 3-4.

THEORETICAL ANALYSIS OF PARTICLE DISTRIBUTION IN GRADIENT COMPOSITE BY CENTRIFUGAL CASTING

A theoretical analysis was presented to produce gradient composite by centrifugal casting. Particle movement in liquid metal is described and gradient distribution of particles in composite is calculated in a centrifugal field. The factors affected the gradient distribution are discussed in detail. There exist composite zone and blank zone in gradient composite, which was proved by experiments. Finally, a theoretical analysis is given to explain the above mentioned particle distribution.

Training Generative Adversarial Networks with Adaptive Composite Gradient

The wide applications of Generative adversarial networks benefit from the successful training methods,guaranteeing that an object function converges to the local minimum.Nevertheless,designing an efficient and competitive training method is still a challenging task due to the cyclic behaviors of some gradient-based ways and the expensive computational cost of acquiring the Hessian matrix.To address this problem,we proposed the Adaptive Composite Gradients(ACG)method,linearly convergent in bilinear games under suitable settings.Theory analysis and toy-function experiments both suggest that our approach alleviates the cyclic behaviors and converges faster than recently proposed SOTA algorithms.The convergence speed of the ACG is improved by 33%than other methods.Our ACG method is a novel Semi-Gradient-Free algorithm that can reduce the computational cost of gradient and Hessian by utilizing the predictive information in future iterations.The mixture of Gaussians experiments and real-world digital image generative experiments show that our ACG method outperforms several existing technologies,illustrating the superiority and efficacy of our method.

Wavefront sensing based on phase contrast theory and coherent optical processing

A novel wavefront sensing method based on phase contrast theory and coherent optical processing is proposed. The wavefront gradient field in the object plane is modulated into intensity distribution in a gang of patterns, making highdensity detection available. By applying the method, we have also designed a wavefront sensor. It consists of a classical coherent optical processing system, a CCD detector array, two pieces of orthogonal composite sinusoidal gratings, and a mechanical structure that can perform real-time linear positioning. The simulation results prove and demonstrate the validity of the method and the sensor in high-precision measurement of the wavefront gradient field.

Fe/Cu gradient composite materials prepared by laser sintering

USLNG CO2 laser beam as a heat source to sinter whole P/M （powder metallurgy） green com-pact is a new technique. As reported in refs. [1--4], the advantages of the laser sintering ofCu-base and Fe-base green compact were characterized by rapid sintering rate, no contamina-tion, fine structure and good properties.

Creation of periodical domain structure by local polarization reversal in planar waveguide produced by soft proton exchange in LiNbO_(3)

The paper presents the results of an experimental study of the local polarization reversal and creation of domains by a biased tip of scanning probe microscope(SPM)in lithium niobate single crystals of congruent composition with a surface layer modified by soft proton exchange(SPE).The depth dependence of Ht ions concentration in the SPE-modified layer measured by confocal Raman microscopy demonstrates a sufficient composition gradient.The creation of isolated domains and stripe domain structures has been done by two switching modes:(1)point switching by field application in separated points and(2)line scanning switching by motion of the biased tip being in contact with the sample surface.For point switching for pulse durations less than 10 s,the logarithmic dependence of the domain diameter on the pulse duration was observed.The change of the dependence to a linear one for pulse duration above 10 s has been attributed to the transition from the stochastic step generation at the domain wall to the deterministic one at the domain vertexes.The periodical structure of stripe domains was created in SPE CLN planar waveguides by scanning at elevated temperature.The revealed switching regime suppresses electrostatic interaction of neighboring domains and leads to a significant improvement of the domain structure regularity.The creation of the stable periodical domain structure with submicron periods in SPE CLN planar waveguides was demonstrated.

Homogenous Sn-doped K(Ta,Nb)O_(3) single crystals and its high piezoelectric response

Perovskite K(Ta,Nb)O_(3)(KTN)single crystal has drawn great interests for its outstanding electro-optic performance and excellent piezoelectric response.However,growth of compositionally uniform KTN single crystals has always been a great challenge for the great segregation difference between Nb and Ta.In this work,we propose a thermal field optimization strategy to resolve this challenge.Homogenous Sn doped KTN(Sn:KTN)single crystal with significantly reduced composition gradient(0.003 mol/mm,1/4 e1/8 of other KTN system),minimal TC variation(13℃)and excellent piezoelectric and dielectric response(d_(33)=373 pC/N andε^(T)_(33)=5206)has been successfully achieved.We found that the functional properties of Sn:KTN were greatly affected by the near-room temperature tetragonal-cubic phase transition.From the intrinsic aspect,longitudinal lattice deformation becomes much easier,resulting in maximum piezoelectric(d^(*)_(33)),dielectric(ε^(T*)_(33)),elastic(s^(E*)_(33))and electromechanical coupling(k^(*)_(33))coefficients along polar direction[001]_(C).From the extrinsic aspect,both domain wall density and domain wall mobility are greatly improved for the reduced lattice distortion,which also contribute a lot to the functional properties.This work provides a simple and practical route for designing and growing high quality crystals,and more importantly,reveals the fundamental mechanism of the phase transitions/boundaries on the functional properties.