Elliptical vibration chiseling:a novel process for texturing ultra-high-aspect-ratio microstructures on the metallic surface

High-aspect-ratio metallic surface microstructures are increasingly demanded in breakthrough applications,such as high-performance heat transfer enhancement and surface plasmon devices.However,the fast and cost-effective fabrication of high-aspect-ratio microstructures on metallic surfaces remains challenging for existing techniques.This study proposes a novel cutting-based process,namely elliptical vibration chiseling(EV-chiseling),for the high-efficiency texturing of surface microstructures with an ultrahigh aspect ratio.Unlike conventional cutting,EV-chiseling superimposes a microscale EV on a backward-moving tool.The tool chisels into the material in each vibration cycle to generate an upright chip with a high aspect ratio through material deformation.Thanks to the tool’s backward movement,the chip is left on the material surface to form a microstructure rather than falling off.Since one microstructure is generated in one vibration cycle,the process can be highly efficient using ultrafast(>1 kHz)tool vibration.A finite element analysis model is established to explore the process mechanics of EV-chiseling.Next,a mechanistic model of the microstructured surface generation is developed to describe the microstructures’aspect ratio dependency on the process parameters.Then,surface texturing tests are performed on copper to verify the efficacy of EV-chiseling.Uniformed micro ribs with a spacing of 1–10μm and an aspect ratio of 2–5 have been successfully textured on copper.Compared with the conventional EV-cutting that uses a forward-moving tool,EV-chiseling can improve the aspect ratio of textured microstructure by up to 40 times.The experimental results also verify the accuracy of the developed surface generation model of microstructures.Finally,the effects of elliptical trajectory,depth of cut,tool shape,and tool edge radius on the surface generation of micro ribs have been discussed.

Effect of Mn and Ni on Microstructure and Impact Toughness of Submerged Arc Weld Metals

The influences of Mn and Ni contents on the impact toughness and microstructure in the weld metals of high strength low alloy steels were studied. The objective of this study was to determine the optimum composition ranges of Mn and Ni to develop welding consumables with better resistance to cold cracking. The results indicated that Mn and Ni had considerable effect on the microstructure of weld metal, and both Mn and Ni promoted acicular ferrite at the expense of proeutectoid ferrite and ferrite side plates. Varying Ni content influenced the Charpy impact energy, the extent of which depended on Mn content. Based on the properties and impact resistance, the optimum levels of Mn and Ni were suggested to be 0.6%—0.9%,, and 2.5%—3.5%, respectively. Additions beyond this limit promoted the formation of segregation structures and other microstructural features, which may be detrimental to weld metal toughness.

Laguerre Simulation and Visualization for Microstructure of Metal Materials

Simulation method was designed to divide Laguerre diagram for right circle group with different weight; out-of-core incremental algorithm for Laguerre diagram was constructed; simulation program development and visualization was done and simulation was realized in user-specified arbitrary area for simulation of metal materials microstructure, which facilitated the practical application and secondary development of Laguerre diagram in the field of material science engineering. Finally, the utilization of a developed software package exemplified the simulation application of microstructure about metal materials and proved its validity.

Microstructure in the Weld Metal of Austenitic-Pearlitic Dissimilar Steels and Diffusion of Element in the Fusion Zone

Microstructure and alloy element distribution in the welded joint between austenitic stainless steel (1Cr18Ni9Ti) and pearlitic heat-resistant steel (1Cr5Mo) were researched by means of light microscopy, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Microstructure, divisions of the fusion zone and elemental diffusion distributions in the welded joints were investigated. Furthermore, solidification microstructure and S-ferrite distribution in the weld metal of these steels are also discussed.

Effects of metal binder on the microstructure and mechanical properties of Al2O3-based micro-nanocomposite ceramic tool material

The Al_2O_3-（W,Ti）C composites with Ni and Mo additions varying from 0vol% to 12vol% were prepared via hot pressing sintering under 30 MPa. The microstructure was investigated via X-ray diffraction（XRD） and scanning electron microscopy（SEM） equipped with energy dispersive spectrometry（EDS）. Mechanical properties such as flexural strength, fracture toughness, and Vickers hardness were also measured. Results show that the main phases A12O3 and（W,Ti）C were detected by XRD. Compound Mo Ni also existed in sintered nanocomposites. The fracture modes of the nanocomposites were both intergranular and transgranular fractures. The plastic deformation of metal particles and crack bridging were the main toughening mechanisms. The maximum flexural strength and fracture toughness were obtained for 9vol% and 12vol% additions of Ni and Mo, respectively. The hardness of the composites reduced gradually with increasing content of metals Ni and Mo.

Laser Welding of Zr_(41)Ti_(14)Cu_(12)Ni_(10)Be_(23) Bulk Metallic Glass and Zirconium Metal

The laser bonding technology between the Zr41 Ti14 Cu12 Ni10 Be23 bulk metallic glass and zirconium metal was investigated under welding parameters of 1.3 kW and 7 m/min. The welded bead, microstructure, and micro-hardness of the welded joint were examined by Keyence, transmission electron microscopy, scanning electron microscopy, and Vickers hardness, respectively. The experimental results showed that the Zr41 Ti14 Cu12 Ni10 Be2 bulk metallic glass and zirconium metal were successfully bonded together. The Zr41 Ti14 Cu12 Ni10 Be2 in the base material zone maintained amorphous structure, and the welding fusion zone kept the hardness as high as as-received BMG. Therefore, the laser welding technology can be used to achieve successful bonding of bulk metallic glasses and crystallization metal.

Interfacial Microstructure and Mechanical Properties of Al/Mg Butt Joints Made by MIG Welding Process with Zn-Cd Alloy as Interlayer

Butt joints between Mg alloy AZ31 B and pure Al 1 060 sheets were produced via metal inert gas welding process with Zn-Cd alloy foil. Crack-free Al/Mg butt joints between AZ31 B Mg alloy and pure Al 1060 sheets were obtained. Intermetallic compound layer 1 and layer 2 had formed in fusion zone/Mg alloy and the average thickness of the layer 1 was about 50 μm. The intermetallic compound layer 1 consisted of Al12Mg17 and Mg2Si phases while layer 2 consisted of Al12Mg17, Mg2Si and Mg Zn2 phases. The crack started from the IMC layer at the bottom of the joint and propagated along the brittle IMC layer, then expanded into weld metal during the SEM in situ tensile test. The highest tensile strength of the dissimilar metal butt joints could reach 46.8 MPa and the effect ofinterfacial IMC layer on mechanical property of the joint was discussed in detail in the present study.

Microstructural Evolution during Forming of Metals

The microstructural evolution during plastic deformation is described as grain subdivision on a finer and finer scale with increasing strain. Key structural features are dislocation boundaries and high angle boundaries. These boundaries have characteristic parameters which are used in a comparison of deformation microstructures produced under different conditions.

Bimodal microstructure – A feasible strategy for high-strength and ductile metallic materials

Introducing a bimodal grain-size distribution has been demonstrated an efficient strategy for fabricating high-strength and ductile metallic materials, where fine grains provide strength, while coarse grains enable strain hardening and hence decent ductility. Over the last decades, research activities in this area have grown enormously, including interesting results onfcc Cu, Ni and Al-Mg alloys as well as steel and Fe alloys via various thermo-mechanical processing approaches. However, investigations on bimodal Mg and other hcp metals are relatively few. A brief overview of the available approaches based on thermo- mechanical processing technology in producing bimodal microstructure for various metallic materials is given, along with a summary of unusual mechanical properties achievable by bimodality, where focus is placed on the microstructure-mechanical properties and relevant mechanisms. In addition, key factors that influencing bimodal strategies, such as compositions of starting materials and processing parameters, together with the challenges this research area facing, are identified and discussed briefly.

Serrated plastic flow behavior and microstructure in a Zr-based bulk metallic glass processed by surface mechanical attrition treatment

The serrated plastic flow,microstructure and residual stress of a Zr_（55）Cu_（30）Ni_5Al_（10） bulk metallic glass（BMG）undergone surface mechanical attrition treatment（SMAT）have been investigated by a combination of compression tests with scanning electron microscopy（SEM）,high resolution transmission electron microscopy（HRTEM）and the incremental hole-drilling strain-gage method.It is found that SMAT leads to various microstructural modifications and residual stress distribution in the surface layers of the Zrbased BMG due to the mechanically-induced nanocrystallization and generation of shear bands.As a result,the BMG alloy exhibits a remarkable work-hardening like behavior and significant increase of plastic strain from less than 1%to 15%,and its plastic deformation dynamics yields a power-law distribution of shear avalanches.Based upon the analysis of the experimental results,it is indicated that this can be connected to the SMAT-induced microstructural modifications and the resulting residual compressive stress in the Zr-based BMG.

Characterization of Microstructure, Strength, and Toughness of Dissimilar Weldments of Inconel 625 and Duplex Stainless Steel SAF 2205

The dissimilar combinations of Inconel 625 and duplex stainless steel SAF 2205 obtained from manual GTA welding process employing ER2209 and ERNi CrMo-3 filler metals have been investigated. Formation of secondary phases at the HAZ of Inconel 625 and grain coarsening at the HAZ of SAF 2205 were witnessed while using these filler wires. The average hardness of ER2209 weldments was found to be greater than ERNi CrMo-3 weld. Tensile fracture was observed at the weld zones for both the fillers. Impact test trials showed brittle mode of fracture on employing ER2209 filler and mixed（ductile–brittle） mode of fracture while using ERNi CrMo-3 filler. Further optical microscopy and SEM/EDS analysis were carried out across the weldments to investigate the structure–property relationships.

Effect of Active Gas on Weld Shape and Microstructure of Advanced A-TIG-Welded Stainless Steel

Advanced A-TIG method was conducted to increase the weld penetration and compared with the conventional TIG welding process.A two-pipeline setup was designed to apply Ar ＋ CO_2 mixed gas as the outer layer,while pure argon was applied as the inner layer to prevent any consumption of the tungsten electrode.The results indicate that the presence of active gas in the molten pool led to the change in the temperature coefficient of surface tension so that the Marangoni convection turns inward and forms a deep weld zone.The increase in gas flow rate causes a decrease in the weld efficiency which is attributed to the increase in oxygen content in the weld pool and the formation o f a thicker oxide layer on the weld surface.Moreover,the stir and the temperature fluctuation,led by double shielding gas,create more homogeneous nucleation sites in the molten pool so that a fine grain micros true ture was obtained.

A promising new class of plasticine: Metallic plasticine

Soft, malleable, and non-dry on exposure in air are the typical features for plain plasticine, which lead plasticine to be widely used in many industrial fields and our daily life. As a kind of clay, poorly elec- tric conductivity and thermal conductivity of plain plasticine seriously limit its applications. Therefore, synthesizing a kind of plasticine having metallic bond is of importance for extending its applications in some special cases, such as thermal-cooling medium, anti-static electricity, electromagnetic shielding, etc. Here, we report a novel GalnSnCdZn2 alloy, which exhibits similar behavior as compared to those of plasticine at near room temperature （30-40 ℃）, and a good electrical conductivity due to its nature of metal. This new GalnSnCdZn2 alloy can be called as metallic plasticine that contains the near-eutectic structure with low melting point and the other relatively high melting point phases. In this metallic plas- ticine, the near-eutectic structure with low melting point plays the same role as the oily ingredient in plain plasticine, dominating the plastic deformation, while the other relatively high melting point phases act as the stuffing like the CaCO3 in plain plasticine. The creation of metallic plasticine offers a general strategy for designing/preparing a new class of plasticine which possesses both the nature of metal and plasticine.

Crystallization of a Ti-based Bulk Metallic Glass Induced by Electropulsing Treatment

The effect of electropulsing treatment（EPT）on the microstructure of a Ti-based bulk metallic glass（BMG）has been studied.The maximum current density applied during EPT can exert a crucial role on tuning the microstructure of the BMG.When the maximum current density is no more than 2 720A/mm^2,the samples retains amorphous nature,whereas,beyond that,crystalline phases precipitate from the glassy matrix.During EPT,the maximum temperature within the samples EPTed at the maximum current densities larger than 2 720A/mm^2 is higher than the crystallization temperature of the BMG,leading to the crystallization event.

Microstructure and mechanical property of MIM 418 superalloy

In this study, the influence of hot isostatic pressing（HIP） process on the 418 alloy produced by metal injection molding（MIM） technique（named as MIM 418）was investigated based on the characteristic analysis of 418 alloy powder. And comparison analysis of the microstructure and mechanical property between the MIM 418 and as-cast 418 alloys was performed by scanning electron microscopy（SEM）, energy-dispersive spectroscopy（EDS）,and X-ray diffraction（XRD）. The results show that MIM418 alloy exhibits fine grain（~30 μm） and uniform microstructure. The defects existing in MIM 418 alloy formed during sintering process can be eliminated through HIP treatment, and the relative density increases from97.0 % to 99.5 %. The mechanical property can be improved significantly because of the elimination of defects, and the tensile strength and elongation are1,271 MPa and 16.8 %, respectively, which are increased by 34.5 % and 180 % compared with K418 alloy after solution heat treatment.

Large-area surface-enhanced Raman scattering-active substrates fabricated by femtosecond laser ablation

A rapid and simple approach to fabricate large-area surface-enhanced Raman scattering-active(SERS-active) substrates is reported.The substrates are fabricated by using femtosecond laser(fs-laser) direct writing on Silicon wafers,followed by thin-film coating of metal such as gold.The substrates are demonstrated to exhibit signal homogeneity and good enhancement ability for SERS.The maximum enhancement factor(EF) up to 3×10 7 of such SERS substrates for rhodamine 6G(R6G) at 785 nm excitation wavelength was measured.This technique could demonstrate a functional microchip with SERS capability of signal homogeneity,high sensitivity and chemical stability.

Structural evolution of Al–8%Si hypoeutectic alloy by ultrasonic processing

High intensity power ultrasound was respectively introduced into three different solidification stages of Al–8%Si hypoeutectic alloy, including the fully liquid state before nucleation, the nucleation and growth process of primary α（Al） phase and L →（Al） ＋（Si） eutectic transformation period. It is found that both the primary α（Al） phase and（Al ＋ Si） eutectic structure were refined by different degrees with various growth morphologies depending on the ultrasonic treatment stage. Based on the experimental results,the cavitation-induced nucleation due to the high undercooling caused by the collapse of tiny cavities was proposed as the major reason for refining the primary α（Al） phase. Meanwhile, obvious eutectic morphological change was observed only when ultrasound was directly introduced in the eutectic transformation stage, in which typical divorced eutectics and（Al ＋ Si） eutectic cells with symmetrical flower shape were formed at the top of the alloy sample. The introduction of ultrasound in each solidification stage also improves the yield strength of Al–8% Si alloy to a diverse extent.