A theoretical and deep learning hybrid model for predicting surface roughness of diamond-turned polycrystalline materials

Polycrystalline materials are extensively employed in industry.Its surface roughness significantly affects the working performance.Material defects,particularly grain boundaries,have a great impact on the achieved surface roughness of polycrystalline materials.However,it is difficult to establish a purely theoretical model for surface roughness with consideration of the grain boundary effect using conventional analytical methods.In this work,a theoretical and deep learning hybrid model for predicting the surface roughness of diamond-turned polycrystalline materials is proposed.The kinematic–dynamic roughness component in relation to the tool profile duplication effect,work material plastic side flow,relative vibration between the diamond tool and workpiece,etc,is theoretically calculated.The material-defect roughness component is modeled with a cascade forward neural network.In the neural network,the ratio of maximum undeformed chip thickness to cutting edge radius RT S,work material properties(misorientation angle θ_(g) and grain size d_(g)),and spindle rotation speed n s are configured as input variables.The material-defect roughness component is set as the output variable.To validate the developed model,polycrystalline copper with a gradient distribution of grains prepared by friction stir processing is machined with various processing parameters and different diamond tools.Compared with the previously developed model,obvious improvement in the prediction accuracy is observed with this hybrid prediction model.Based on this model,the influences of different factors on the surface roughness of polycrystalline materials are discussed.The influencing mechanism of the misorientation angle and grain size is quantitatively analyzed.Two fracture modes,including transcrystalline and intercrystalline fractures at different RTS values,are observed.Meanwhile,optimal processing parameters are obtained with a simulated annealing algorithm.Cutting experiments are performed with the optimal parameters,and a flat surface finish with Sa 1.314 nm is finally achieved.The developed model and corresponding new findings in this work are beneficial for accurately predicting the surface roughness of polycrystalline materials and understanding the impacting mechanism of material defects in diamond turning.

EFFECT OF MICROSTRUCTURE ON THE HARDENING AND SOFTENING BEHAVIORS OF POLYCRYSTALLINE SHAPE MEMORY ALLOYS PART Ⅰ:MICROMECHANICS CONSTITUTIVE MODELING

The effects of microstructure and its evolution on the macroscopicsuperelastic stress-strain response of polycrystalline Shape Memory Alloy(SMA)arestudied by a microstructure-based constitutive model developed in this paper.Themodel is established on the following basis:(1)the transformation conditions of theunconstrained single crystal SMA microdomain(to be distinguished from the bulksingle crystal),which serve as the local criterion for the derivation of overall transfor-mation yield conditions of the polycrystal;(2)the micro-to macro-transition schemeby which the connection between the polycrystal aggregates and the single crystalmicrodomain is established and the macroscopic transformation conditions of thepolycrystal SMA are derived;(3)the quantitative incorporation of three microstruc-ture factors(i.e.,nucleation,growth and orientation distribution of martensite)intothe modeling.These microstructural factors are intrinsic of specific polycrystal SMAsystems and the role of each factor in the macroscopic constitutive response is quan-titatively modeled.It is demonstrated that the interplay of these factors will resultin different macroscopic transformation kinematics and kinetics which are responsiblefor the observed macroscopic stress-strain hardening or softening response,the latterwill lead to the localization and propagation of transformation bands in TiNi SMA.

MACRO SLIP THEORY OF PLASTICITY FOR POLYCRYSTALLINE SOLIDS

A macro slip theory is presented in this paper.Four independent slip systems are proposed forpolycrystalline solids.Each slip system consists of a slip plane which lies on a face of the octahedron in stressspace and a slip direction which is coincident with shear stress acting on the same face of the octahedron.Itis proved that for proportional loading,present results are identical with the classical flow theory of plasticity.For nonproportional loading,the macro slip theory shows good predicting ability.The calculated results arein good agreement with the experimental data.

Experimental research on the residual stress of polycrystalline diamond compacts for oil drilling

Practical experiences gained in the past several years show that the thermal residual stress(TRS) is a main cause leading polycrystalline diamond compacts(PDC) to premature failure.It is the very important to measure the TRS accurately for optimizing the interface and improving the service performance of PDC.In this paper,the TRS in 1913 flat-interface PDC was measured using improved stress-release method(ISRM). The TRS on the surface of polycrystalline diamond(PCD) table was obtained,which can be used to calculate the radial thermal residual stress(RTRS) at the interface of PCD table via a refutation process.The obtained results show that there are compressive residual stress at the PCD table interface and in the most region of PCD table surface.The exception occurs near the outer diameter of the PCD table,where the PDC begins to bend and put the PCD table surface into a tension state,an undesirable state for a brittle material.The ISRM has covered the shortage existing in traditional stress-release method,in which only finite points on the surface of PCD table can be tested for one specimen and one time.Simple as the experimental procedures are,the test results are also very accurate and reliable.This method provides the theoretical and experimental basis for testing TRS of PDC accurately.

EFFECT OF MICROSTRUCTURE ON THE HARDENING AND SOFTENING BEHAVIORS OF POLYCRYSTALLINE SHAPE MEMORY ALLOYS PART Ⅱ:NUMERICAL SIMULATION UNDER AXISYMMETRICAL LOADING

Based on the microstructure-based constitutive model establishedin Part Ⅰ,a detailed numerical investigation on the role of each microstructure pa-rameter in the kinematical and kinetic evolution of polycrystalline SMA under ax-isymmetrical tension loading is performed.Some macroscopic constitutive featuresof stress-induced martensite transformation are discussed.

Residual stress and radial stress gradient in polycrystalline diamond compacts

The differential thermal expansion of the polycrystalline diamond layer and the tungsten carbide substrate results in large residual stresses as PDC cutters cooling after sintering.The residual stresses on the top surface of the diamond layer of PDC were measured at five points along the radial direction of PDC using X-ray Diffraction Residual Stress Instrument,thus the stresses and their radial distribution were obtained.The results show that the stresses on the diamond surface are compressive,the biggest stress appears at the central point(about 1200 MPa),and that from the center to the edge of PDC,the magnitude of the stress decreases. A finite element analysis(FEA) was made to check the validity of the testing results.The FEA modeling results were found to correlate well with the measured values.Factors leading to the deviation between XRD experimental measurements and the calculations of residual stress by FEA were also analyzed.

Direct Microwave Synthesis of 11-Type Fe(Te,Se) Polycrystalline Superconductors with Enhanced Critical Current Density

We report a direct microwave synthesis method for the preparation of 11-type high quality Fe(Te,Se) polycrystalline superconductors. The bulk samples are rapidly synthesized under the microwave irradiation during several minutes, with a subsequent annealing process at 400℃. The samples exhibit a nearly single phase of the tetragonal PbO-type crystal structure with minor impurities. Morphology characterization shows high density, tight grain connectivity and large grain sizes around 100 μm with small cavities inside the sample. Resistivity and magnetization measurements both show similar superconducting transitions above 14 K. The magnetic hysteresis measurements display broad and symmetric loops without magnetic background, and a high critical current density J_c about 1.2 × 10~4 A/cm^2 at 2 K and 7 T is estimated by the Bean model. Compared with the solidstate reaction synthesized samples, these superconducting bulks from microwave-assisted synthesis are possibly free of the interstitial Fe due to smaller c-axis, higher T_c in magnetic transitions, better M–H loops without magnetic background and greatly enhanced J_c, and are promising as raw materials for the non-toxic Fe-based superconducting wires for large currents and high field applications.

Ultrafine polycrystalline titania nanofibers for superior sodium storage

Sodium ion batteries have a huge potential for large-scale energy storage for the low cost and abundance of sodium resources. In this work, a novel structure of ultrafine polycrystalline TiO2 nanofibers is prepared on nickel foam/carbon cloth by a simple vapor deposition method. The as-prepared TiO2 nanofibers show excellent performance when used as anodes for sodium-ion batteries. Specifically, the TiO2 nanofibers@nickel foam electrode delivers a high reversible capacity of 263.2 m Ahg^-1 at 0.2 C and maintains a considerable capacity of 144.2 m Ahg^-1 at 10 C. The TiO2 nanofibers@carbon cloth electrode also shows excellent high-rate capability, sustaining a capacity of 148 m Ahg^-1 after 20 0 0 cycles at 10 C. It is believed that the novel nanofibrous structure increases the contact area with the electrolyte and greatly shortens the sodium ion diffusion distance, and meanwhile, the polycrystalline nature of nanofibers exposes more intercalation sites for sodium storage. Furthermore, the density functional theory calculations exhibit strong ionic interactions between the exposed TiO2(101) facets and sodium ions, leading to a preferable sodiation/desodiation process. The unique structural features endow the TiO2 nanofibers electrodes great advantages in rapid sodium storage with an outstanding high-rate capability.

A large-grain-size thick-film polycrystalline diamond detector for x-ray detection

A diamond film with a size of 6×6×0.5 mm^3 is fabricated by electron-assisted chemical vapor deposition. Raman spectrum analysis, x-ray diffraction and scanning electron microscope images confirm the high purity and large grain size, which is larger than 300 μm. Its resistivity is higher than 10^12 W· cm. Interlaced-finger electrodes are imprinted onto the diamond film to develop an x-ray detector. Ohmic contact is confirmed by checking the linearity of its current–voltage curve. The dark current is lower than 0.1 n A under an electric field of 30 k V cm^-1. The time response is 220 ps. The sensitivity is about 125 m A W^-1 under a biasing voltage of 100 V.A good linear radiation dose rate is also confirmed. This diamond detector is used to measure x-ray on a Z-pinch, which has a double-layer 'nested tungsten wire array'. The pronounced peaks in the measured waveform clearly characterize the x-ray bursts, which proves the performance of this diamond detector.

Effect of Incidence Angle of Magnetic Field on the Performance of a Polycrystalline Silicon Solar Cell under Multispectral Illumination

The aim of this work is to investigate, with a three-dimensional steady-state approach, the effect of the incidence angle of a magnetic field on the performance of a polycrystalline silicon solar cell under multispectral illumination. The magneto-transport and continuity equations of excess minority carriers are solved to find the expression of the density of excess minority carriers and the related electrical parameters, such as the photocurrent density, the photovoltage and the electric power, of a grain of the polycrystalline silicon solar cell. The influence of the incidence angle of the magnetic field on the diffusion coefficient, the short-circuit photocurrent density, the open-circuit photovoltage and the electric power-photovoltage is studied. Then, the curves of the electric power-photovoltage is used to find the maximum electric power allowing to calculate, according to the incidence angle of the magnetic field, the fill factor and the conversion efficiency. The study has shown that the increase of the incidence angle of the magnetic field from 0 rad to π/2 rad, can reduce the degradation of the performance of solar cells.

Molecular Dynamics Simulation of Grain Refinement in a Polycrystalline Material under Severe Compressive Deformation

Grain refinement in a polycrystalline material resulting from severe compressive deformation was simulated using molecular dynamics. A simplified model with four square grains surrounded by periodic boundaries was prepared, and compressive deformation was imposed by shortening the length in the y direction. The model first deformed elastically, and the compressive stress increased monotonically. Inelastic deformation was then initiated, and the stress decreased drastically. At that moment, dislocation or slip was initiated at the grain boundaries or triple junction and then spread within the grains. New grain boundaries were then generated in some of the grains, and sub-grains appeared. Finally, a microstructure with refined grains was obtained. This process was simulated using two types of grain arrangements and three different combinations of crystal orientations. Grain refinement generally proceeded in a similar fashion in each scenario, whereas the detailed inelastic deformation and grain refinement behavior depended on the initial microstructure.

Magnetic and Magnetocaloric Properties of Polycrystalline and Oriented Mn2-δSn

Mn-based Heusler alloys have attracted significant research attention as half-metallic materials because of their giant magnetocr.ystalline anisotropy and magnetocaloric properties.We investigate the crystal structure and magnetic properties of polycrystalline,[101]-oriented,and[100]-oriented Mn2-δ Sn prepared separately by arc melting,the Bridgeman method,and the flux method.All of these compounds crystallize in a Ni2 In-type structure.In the Mn2-δSn lattice,Mn atoms occupy all of the 2 a and a fraction of the 2 d sites.Site disorder exists between Mn and Sn atoms in the 2 c sites.In addition,these compounds undergo a re-entrant spin-glass-like transition at low temperatures,which is caused by frustration and randomness within the spin system.The magnetic properties of these systems depend on the crystal directions,which means that the magnetic interactions differ significantly along different directions.Furthermore,these materials exhibit a giant magnetocaloric effect near the Curie temperature.The largest value of maximum of magnetic entropy change(-△SM)occurs perpendicular to the[100]direction.Specifically,at 252 K,maximum-△SM is 2.91 and 3.64 J-kg-1K-1 for a magnetic field of 5 and7 T,respectively.The working temperature span over 80 K and the relative cooling power reaches 302 J/kg for a magnetic field of 7 T,which makes the Mn2-δSn compound a promising candidate for a magnetic refrigerator.

Total Ionizing Dose Radiation Effects in the P-Type Polycrystalline Silicon Thin Film Transistors

The total ionizing dose radiation effects in the polycrystalline silicon thin film transistors are studied. Transfer characteristics, high-frequency capacitance-voltage curves and low-frequency noises(LFN) are measured before and after radiation. The experimental results show that threshold voltage and hole-field-effect mobility decrease,while sub-threshold swing and low-frequency noise increase with the increase of the total dose. The contributions of radiation induced interface states and oxide trapped charges to the shift of threshold voltage are also estimated.Furthermore, spatial distributions of oxide trapped charges before and after radiation are extracted based on the LFN measurements.

Reconstruction of three-dimensional grain structure in polycrystalline iron via an interactive segmentation method

Using a total of 297 segmented sections,we reconstructed the three-dimensional(3D) structure of pure iron and obtained the largest dataset of 16254 3D complete grains reported to date.The mean values of equivalent sphere radius and face number of pure iron were observed to be consistent with those of Monte Carlo simulated grains,phase-field simulated grains,Ti-alloy grains,and Ni-based super alloy grains.In this work,by finding a balance between automatic methods and manual refinement,we developed an interactive segmentation method to segment serial sections accurately in the reconstruction of the 3D microstructure;this approach can save time as well as substantially eliminate errors.The segmentation process comprises four operations:image preprocessing,breakpoint detection based on mathematical morphology analysis,optimized automatic connection of the breakpoints,and manual refinement by artificial evaluation.

Low Energy H^+ Effects on the Photovoltaic and Optical Properties of Polycrystalline Silicon Solar Cells

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EFFECTS OF B^+ IMPLANTATION ON MECHANICAL PROPERTIES AND MICROSTRUCTURE OF POLYCRYSTALLINE Ni

50 keV B+ ions was implanted to polycrvstalline with 50 keV B+ to a dose o/ 3x1017 ions/cm2 at room temperature.The specimens with and without B+implantation weretested in micro-hardness and load or unload tensile fatigue under stress-controlled eondition.The surface layer structure was observed with IMA,SEM and TEM before and afterimplantation and/or fatigue.The B+ implanted surface region consists of amorphousNi-B phase,Ni3B and Ni4B3 second phases,and damage structure.The correspondingmeasurements indicate that both surface micro-hardness and endurance limit of the specimenshave increased after implantation.Compared with unimplanted specimens under the same fa-tigue condition,all implanted specimens show the smallest overall fatigue danage.The cyclicloading at room temperature can lead to migration of implanted B+ out surface layer andreerystallization of amorphous Ni-B phase,Possible strengthening mechanisms.for these ex-perimental results were discussed.

MAGNETIZATION BEHAVIOUR FOR TEXTURED BULK YBaCuO POLYCRYSTALLINE SUPERCONDUCTORS

In present paper.study of magnetization behaviour was carried out for textured bulk YBaCuO polycrystalline superconductors synthesized by MTG process.Themagnetization behaviour apparently different from that of sintered samples was observed.Magnetization hysteresis measurements were performed for the texturedYBaCuO superconductors at 77K in ± 10kOe magnetic field range.Based on the results ofmagnetization hysteresis.the magnetic field dependence of critical current density(J)at77K was evaluated for the textured YBaCuO samples.The magnetic flux penetration intextured bulk YBaCuO polycrystalline superconductors was investigated at 77K throughthe magnetization hysteresis measurements under various maximum applied magnetic fields(H_M)and reasonable discussion for the phenomena was conducted in terms of Bean’s criti-cal state model.The enhancement of magnetic properties for textured bulk YBaCuOpolycrystalline superconductors is presumably attributed to the improvement ofmicrostructure in these samples.

STRAIN RATE SENSITIVTTY OF POLYCRYSTALLINE AND SINGLE CRYSTAL NiAl

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FATIGUE SOFTENING BEHAVIOR AND ITS THRESHOLD OF COLD STRAINED POLYCRYSTALLINE Cu

The symmetrical push-pull fatigue tests in load control were carried out for prestrainedpolycrystalline Cu.The change in mechanical behaviour during cycling was recorded in detailand the effect of various degree of prestraining on saturated behavior and dislocation structurewas compared.The results show that the cyclic saturation state is still history-dependent atlow stress amplitude and the dislocation structure after fatigue exhibits an “inheritance” be-havior.The level of softening was calculated at various load amplitudes and a softeningthreshold of about 0.43 to 0.45 of the flow stress was obtained.This is the same as that of lowcarbon steel.Three stages of cyclic processes and their mechanism have been described.

Comparative investigation of microjetting generated from monocrystalline tin surface and polycrystalline tin surface under plane impact loading

With considering the scattering effect of grain boundary and the grain orientation,the molecular dynamics is used for the first time to comparatively investigate microjetting generated by monocrystalline tin surface and polycrystalline tin surface under plane impact loading in this work.The research results show that when the impact velocity is low,the scattering effect of grain boundary and different grain orientations in a polycrystalline tin will cause the sample to melt inhomogeneously,leading the shock wave front to attenuate,meanwhile,the inhomogeneous melting can result in jet deviating.Comparing with monocrystalline tin,the jet head velocity,jet velocity coefficient,and jet mass coefficient of polycrystalline tin at low impact velocity are all low.Moreover,as the impact velocity increases,this influence decreases and the microjetting results of polycrystalline tin and monocrystalline tin tend to be consistent with each other.