Search

Abstract: Paper is a complex composite material. Its structure and surface greatly influence its end use properties. Calendering is a finishing process applied to paper to provide a shiny surface and to improve the smoothness. Hence, the control of the efficiency of calendering and the characterization of the final product necessitate the measure of the surface modification. Furthermore the relationship between the surface and the obtained level of gloss has to be further developed. The main purpose of this study is to describe the modification of the micro-structure at various scales of the paper surface due to the calendering process (under various processing conditions). The characterization of the paper surface was carried out thanks to an optical device allowing the topographic measurement to be taken at various scales. The equipment combines topographical imaging with a high definition camera, allowing measurement on the exact same area of the sample after each pass in the nip. We therefore introduce a new way to perform multi-scale analysis of the paper surface modification based on fractal theory. [Copyright &y& Elsevier]

Abstract: Preceramic papers loaded with inorganic fillers may be used as preforms in a novel manufacturing technique to fabricate lightweight ceramic structures. In order to reduce the porosity caused by burning out cellulosic fibers and organics, porous preceramic paper-derived alumina substrates were post-treated via two different coating routes using silica suspension or methylphenylvinylhydrogen polysiloxane. Sintering of the alumina-filled preceramic papers in air at 1600°C for 2h resulted in a non-uniform distributed open porosity ranging from 23 to 26%. After coating and infiltration, all samples were additionally heat treated up to at 1500°C for 2h. Thermal analysis (DTA/TG) was applied to determine the pyrolysis temperature of polysiloxane. Microstructure and phase analysis were performed respectively by SEM and XRD. After sintering, water absorption, apparent density and open porosity of test pieces were determined, and mechanical properties of the substrates were evaluated before and after coating. For the samples coated with silica suspension, the mechanical strength remained in the same range of those for uncoated samples, while for the polysiloxane coated samples the mechanical strength steadily increases after repeated impregnation steps, reaching ∼350MPa. [Copyright &y& Elsevier]

This paper presents an improved method for achieving controllable preparation of the composition and size of the monotectic alloy core-shell structure microspheres. This advancement is expected to enhance the commercial application of monotectic alloy core-shell structure microspheres. By installing a heating device at the top of the drop tube in the pulsated orifice ejection method setup, we achieved in-situ heat treatment of falling droplets, resulting in the successful preparation of Al 45 (Sn 42 Bi 58) 55 core-shell structure microspheres. Furthermore, we investigated the formation mechanism of the Al@Sn-Bi core-shell structure. Nine sets of Al-Sn-Bi microspheres with varying in-situ heat treatment temperatures were prepared. Analysis via X-ray diffraction and transmission electron microscopy revealed that the microspheres consisted of Al-rich, Sn-rich, and Bi-rich phases, without any intermetallic compounds. Scanning electron microscopy results indicated that as the in-situ heat treatment temperature increased, the structure of the Al-Sn-Bi microspheres transitioned from irregular to regular core-shell configurations. This suggests that higher heat treatment temperatures prolong liquid phase separation time, leading to increased repetition of Marangoni motion within the droplet, Ostwald ripening of the minor phase droplets, and Soret effect of the matrix phase. However, at temperatures exceeding 700 °C, the solidification rate of alloy droplets decreased, causing the Al-rich phase core to deviate from the center and form a crescent structure due to Stokes motion. [Display omitted] • A method is provided for the controllable production of monotectic alloy microspheres which have a core-shell structure. • Core-shell structure Al@Sn-Bi microspheres were prepared by the pulsated orifice ejection plus in-situ heat treatment. • Performing the microstructure evolution process of the core-shell structure Al@Sn-Bi microsphere. • Using TEM to observe the interface between Al and Sn, which composed of amorphous and nanocrystalline. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract This paper is an experimental research about the mechanical effects on Ti-6Al-4V surfaces treated with an ultrasonic vibration-assisted ball burnishing process. Its aim is to define the process parameters to achieve the best surface integrity on the target workpiece, as well as identifying the effects caused by the introduction of vibrations as a means of assistance. A Taguchi orthogonal array including five factors (preload, number of passes, feed velocity, strategy and original surface texture) was applied to perform the process on ball-end milled surfaces. A comprehensive analysis of the effects was performed, by considering in depth three different facets of surface integrity, namely, topology, residual stress and hardness. Hence the extensive result datasets presented in this paper, which deliver an exhaustive description of the process effects by combining a triple approach in the results analysis section. The effect of vibrations is proved positive to enhance the texture as long as the original surface is not characterized by S q >2 μm. Furthermore, only the preload and number of passes influence the results. In terms of residual stress, all parameters are influential in the results, especially the burnishing strategy, through which a specific direction can be reinforced. Finally, the burnishing operation proves to modify the hardness of deep layers down to 0.5 mm, applying the vibration-assisted process. The main conclusion derived from these works is a technical recommendation to treat the Ti-6Al-4 V surface through the process, aiming to find a balanced comprehensive surface integrity enhancement. [ABSTRACT FROM AUTHOR]

Abstract Loss of circularity when creating metal ring-shaped products by ring rolling is a significant industrial issue. This paper explores the previously tacit knowledge that plastic changes in curvature - required to maintain circularity - principally occur as material passes through the roll gap. Through a series of experiments and numerical simulations on half-ring workpieces, the 'free curvature change' is explored for the first time, finding that the ring can 'curl up' - the radius reducing by as much as -39% in a single pass - unless the inner roll is much smaller than the outer roll. An analytical model of free curvature change is proposed based on force equilibrium and compatibility. Under a range of 'normal' operating conditions this predicted free curvature change to within 7%. In (full) ring rolling the radius of curvature must continually increase. This paper proposes that regulation of curvature is achieved through bending moments at the roll entry and exit; largest when the tool size ratio is furthest from the optimum. This hypothesis is supported by Finite Element simulations of full ring rolling, finding entry and exit moments up to a quarter of the moment for a fully plastic hinge. This work could be of direct use to process designers in choosing tool sizes and guide roll force limits and suggests new ways to use guide rolls to better maintain circularity in challenging situations. [ABSTRACT FROM AUTHOR]

Failure evolving from sheared edge is common in the application of advanced high strength steels (AHSSs) to automotive body. In this paper, the third-generation automotive medium-Mn (TAMM) steel, as a newly-developed AHSS, is sheared by a self-designed shear testing platform under different clearances. Microstructure, microhardness and tensile properties are tested and shearing procedure is simulated to analyze the effect of shearing clearance on macro/micro performance of sheared edge. With the increase of shearing clearance, more large-size, elongated, and widespread microvoids are formed to decrease the formability of sheared edge. Moreover, the surface and subsurface of sheared edge are hardened because of work hardening and phase transformation strengthening induced by the plastic deformation during shearing. The hardened depth and degree increase, and the hardness uniformity of the hardened layer becomes poor as the shearing clearance increases, which leads to the increase of possibility of cracking. Besides, tensile displacement in uniaxial tensile test is obviously affected by shearing clearance. Quantitative analysis results show that tensile displacement is higher and less sensitive to clearance change under a smaller clearance. Thus, 2%t–5%t (t means the steel thickness) is an advisable shearing clearance range for TAMM steel by considering the microstructure, hardened layer and tensile properties of sheared edge comprehensively. This paper is helpful to solve the cracking problem of sheared edge in industry and promote the industrial application of TAMM steel. [ABSTRACT FROM AUTHOR]

The aim of this paper is to offer an insight into a friction stir welding technique. The paper data indicate that the sheets to be welded can be completely penetrated by a tilting pin, while the kissing bond in the root of the weld would be entirely avoided. An equipment setup, consisting of a slide way, a pedestal, a stationary shoulder and a mounting platform, including two separate parts, has been developed. During the welding process, the tilting tool and the stationary shoulder moved synchronously in the welding direction. The 2219-T6 aluminum alloy sheets with the thickness of 5 mm were successfully friction stir welded by a tilting tool with a pin length of 6 mm. The microstructure and mechanical properties of joints were revealed. The kissing bond could be completely eliminated by stationary shoulder supporting and tilting pin penetrating friction stir welding (STFSW) and no other defects were induced. The stationary shoulder affected zone (SSAZ) consisting of fine equiaxed grains was a typical zone of a STFSW joint. A heuristic model was established to describe the material flow mechanism during the welding process. The tensile strength and associated elongation of the joint were 343 ± 3 MPa and 8.2% ± 0.2%, respectively. [ABSTRACT FROM AUTHOR]

Polycrystalline Cubic Boron Nitride (PCBN) has been considered as the main cutting tool material for hard turning, which has the comparable surface finish quality as grinding, and high efficiency, economical technology in production. It is well known that the abrasiveness of the workpiece have the very important role of the machinability of the materials. Therefore, the tool wear of the PCBN insert correlates with abrasiveness of the materials very much. In the presented paper, the influence of the micro hardness distribution is used to explain the wear mechanism in machining of the high abrasive materials and proposed a model to predict the abrasiveness. The work material is high chromium cast iron and cutting tool material is PCBN. Abrasiveness are evaluated from the micro hardness distribution by nanoindentation for the distinguish microstructure with hardness. The mapping image of the micro hardness showed the matched features with microstructure images from the scanning electron microscope (SEM). The different chemical composition groups are presented as three heat treatment conditions in experiments, which are as-cast, annealed and hardened. Based on the hardness distribution, this paper presented a model to evaluate the abrasiveness index of the material. The high performance machining is done on six material. The wear mechanism is abrasion in tool wear dominantly and flank wear showed the linear relationship with abrasiveness index. The abrasive wear on the cutting edge suggests that sliding and chipping are the main wear modes which is caused by the combination effect of carbides and matrix. The four mechanisms of diffusion, chemical, abrasive and micro chipping are happening in the tool wear of hard turning. In the dry machining by PCBN insert, abrasiveness is correlated with abrasive and chipping very much and accelerated the crater wear in machining. Abrasiveness index of the material has ability to predict wear performance in dry machining of HCWCI materials by PCBN inserts. The application of the abrasiveness is a potential parameter of machinability to improve the machining efficiency and reduce the cost of machining. [ABSTRACT FROM AUTHOR]

In this paper, a novel flat-top laser-aided cold metal transfer additive manufacturing (F-LCAM) method is proposed for titanium alloys to restrict internal defects and anisotropy of mechanical properties in large-scale additive-manufactured titanium structures. The proposed method uses a flat-top laser to stabilise the drifting cathode spot and suppress the irregular shape of the weld deposit by promoting thermionic emission on the molten pool surface. Compared to the cold metal transfer additive manufacturing (CMT-AM) process, the auxiliary flat-top laser promotes the wettability of the molten pool and increases the contact angle of deposition from 95° to 142° in an F-LCAM sample. The non-destructive X-ray testing (NDT) results of multi-bead multilayer deposition showed that the defects caused by the pool weld bead morphology were effectively suppressed. Attributed to fluid flow in the melt pool enhanced by the flat-top laser, the dendritic arms were broken, columnar β grains in the F-LCAM sample were finer than in CMT-AM sample, and the aspect ratios of prior-β grains decreased from approximately 6 to 1. The F-LCAM sample exhibited a higher elongation and lower anisotropy than the CMT-AM sample. Defects were observed on the fracture surfaces of the CMT-AM vertical samples, which reduced the elongation of the CMT-AM samples to lower than that of the F-LCAM sample. The ultimate tensile strength, yield strength, and elongation of the multi-bead multilayer deposition met the standards of as-forged Ti6321 titanium alloy, indicating that the Ti6321 titanium alloy structure fabricated by the F-LCAM process has acceptable tensile properties for engineering applications. [Display omitted] • A novel flat-top laser was introduced in cold metal transfer additive manufacturing (CMT-AM) process for titanium alloys. • The flat-top laser could stabilise the drifting arc cathode spot and suppress the irregular shape of the weld deposit. • Due to the flat-top laser, Marangoni flow was significantly enhanced, and the wettability of the molten pool was promoted. • The internal defects were effectively eliminated and coarse columnar grains were refined in the F-LCAM samples. • The tensile properties of F-LCAM samples met the standards of as-forged Ti6321 titanium alloy for engineering applications. [ABSTRACT FROM AUTHOR]

Spinning is a common processing method for ultra-thin-walled tube. However, it is susceptible to surface ruptures in the deformation zone due to point-by-point contact, which affects the quality of products. In response to this issue, a ring-roller spinning (RRS) process is proposed, where the spinning roller makes tangential inner contact with the tube blank. This expands the triaxial compressive region, reducing ruptures tendency. And the tangential compressive stress is strengthened on the basis on triaxial compression of the conventional spinning (CS) process, which provides shear stress state in deformation zone. This paper conducts a comprehensive investigation into the RRS for thin-walled tubes made of 304 austenitic stainless steel. The study combines theoretical and experimental approaches and employs the finite element method (FEM) to evaluate the stress state within the tangential region. Various characterization methods are applied to examine the microstructural evolution under ultra-low stress triaxiality (ULST). The results confirm that the deformation zone is primarily characterized by tangential pressure under ULST, which significantly influence the metal microstructure, plastic behavior, and cumulative large deformation. This innovative process facilitates the continued deformation of the tubes, even under the saturated conditions of work hardening with the martensitic plasticising behaviour promotes grain refinement to 124 nm, resulting in an increase in the yield strength of the tubes from -1060 MPa to 1550 MPa. Continuous processing of ultra-thin-walled tube with a cumulative thinning rate of 90% was achieved by conducting RRS five-pass spinability experiments. [ABSTRACT FROM AUTHOR]

The microstructural characteristics and mechanical properties of forged parts differ significantly from those of additively manufactured parts, which results in different machinability. In this paper, the microstructure effect on the machinability of Inconel 718 parts obtained by different manufacturing processes, laser directed energy deposition (LDED), laser powder bed fusion (LPBF) and forging, is evaluated and critically discussed in terms of milling forces, surface morphology, surface roughness, chip morphology and subsurface microstructure. The results show that due to having the smallest grain size, high dislocation density, and precipitation hardening provided by the reinforcing phases, the milling force is maximized when cutting LPBF Inconel 718 parts. In addition to grain size and dislocation density, the texture also has an effect on the plastic deformation of the subsurface after milling. Furthermore, LDED and forged Inconel 718 parts undergo a continuous dynamic recrystallization process characterized by sub-grain rotation transforming low angle grain boundaries into high angle grain boundaries during milling. This study provides some theoretical guidance for the integration of additive and subtractive processes in the machining of complex structural parts with Inconel 718 alloy. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) microelectrodes fitted by multi-layer Cu foil two-dimensional (2D) microstructures can be used in micro-electrical discharge machining (micro-EDM) to machine 3D micro-cavities. Due to the poor diffusion bonding between Cu foil 2D microstructures, the surfaces of micro-cavities often have ridges, which reduce the quality of the machined surface. To solve this problem, the paper proposed a method of using a Sn film as solder between Cu foils to fabricate Cu–Sn composite 3D microelectrodes. First, 50-μm-thick Cu foils coated with Sn on both sides were cut by femtosecond laser to obtain multi-layer 2D microstructures. Second, through transient liquid phase (TLP) bonding, the multi-layer 2D microstructures were laminated and bonded to fit composite 3D microelectrodes. In addition, the paper investigated the influence of the solder layer thickness, bonding time and temperature on the micro-EDM performance of composite 3D microelectrodes. The experimental results show that the composite 3D microelectrode has good micro-EDM performance when the solder layer thickness is 1 μm, the bonding temperature is 800 °C and the bonding time is 15 h. Finally, applying this composite 3D microelectrode in micro-EDM, 3D micro-cavities were processed, and the processing results demonstrated that the ridges on the 3D micro-cavity surfaces were completely eliminated, thereby improving the quality of the machined surface. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is one of the current rapid fabrication technology methods which has wide potential application in the aerospace, medical, consumer products and automotive industries. Currently, ceramic materials are not used as widely as metal and polymer materials due to the high melting point, high-temperature strength and low thermal conductivity, which influence the microstructure and density of ceramic samples during SLM fabrication. The most effective method of reducing cracks is the preheating at high temperature of the ceramic powder during SLM process. This paper presents the selective melting of yttria-stabilized zirconia (ZrO 2 –Y 2 O 3 93–7) ceramic using a 1 μm wavelength fibre laser with high-temperature preheating at 1500–2500 °C, and an additional CHEVAL Nd-YAG laser for the preheating of the powder bed before scanning. In this paper, the influence of different laser powers and different scanning velocities on the microstructure, relative density and deformation of the ceramic sample is investigated; in particular, the effect of preheating on the morphology of the micro-cracks is discussed. Experimental results show that high-temperature preheating in 10 mm diameter range is possible with the Nd-YAG laser, and that orderly cracks are transformed into disordered little cracks by the high-temperature preheating. With preheating to 1500 °C, 2000 °C and 2500 °C, the relative density of the sample made by mixing fine powder (9–22.5 μm, 20 wt%) and coarse powder (22.5–45 μm, 80 wt%) is increased by 84% (without preheating) to 90–91%. The transformation of the monoclinic and cubic structures to a tetragonal structure is observed during the process of melting and cooling, and increasing the preheating temperature to 1500 °C, 2000 °C and 2500 °C is more suited to the formation of tetragonal crystals. [ABSTRACT FROM AUTHOR]

Effusion cooling holes are commonly drilled in nickel super-alloy aero-engine components using electro-discharge machining (EDM) or pulsed laser drilling. While drilling quality of EDM is high, its machining efficiency is normally relatively low, in addition to its high tooling cost. The drilling efficiency of a millisecond pulsed laser is much higher, while a recast layer often forms on the hole wall. In this paper, an ultrasonic-assisted laser trepanning technology is reported for trepanning blind and through holes in nickel super-alloy samples. The influence of ultrasonic vibrations on hole geometry, morphology, microstructure, recast layer thickness and mechanical performance was investigated through comparing holes trepanned with and without ultrasonic assistance. It was found that ultrasonic vibrations contributed to laser trepanning process mainly by means of grain refinement strengthening, hard phase precipitation and dispersion strengthening, and led to recast layer reduction and negative taper for the through hole trepanned. The percentage of the measured recast layer reduction induced by ultrasonic vibrations approximately ranged from 15.73% to 31.82%. Besides, a maximum percentage of around 19.43% was achieved for micro hardness improvement induced by ultrasonic vibrations. However, the width of laser trepanned heat affected zone (HAZ) was increased by around 36.00% due to ultrasonic vibration assistance. In addition, the HAZ grains near the recast layer was refined via increasing the trepanning speed, decreasing pulse width. Compared with the base metal, the impact toughness was increased by using ultrasonic-enhanced laser trepanning mainly due to grain refinement strengthening. [ABSTRACT FROM AUTHOR]

This paper presents a systematic experimental study to clarify the relationship between the hot deformation conditions and microstructure evolution and flow stress of the individual ferrite and austenite phases of duplex stainless steels (DSS), and to quantitatively compare the deformation behaviors of each phase under the same hot working conditions. Single-phase steels with the ferrite and austenite chemistry of the phases in the DSS were prepared for this investigation. The microstructure evolution and deformation behavior of the individual phases were investigated in one-pass hot uniaxial compression tests up to a strain of 0.8 at a wide range of working temperatures from 1000 to 1250 °C and strain rates from 0.1 to 30.0 s−1. The compressed microstructures of each phase were investigated, and microstructure evolution maps were proposed to demonstrate the relationship between the compressed microstructure and deformation conditions. The flow curves of each phase were also analyzed quantitatively, showing that the ferrite phase had lower hot strength and a lower work hardening exponent n , and higher strain rate sensitivity m and temperature sensitivity A compared to the austenite phase. The strength ratio of each phase from early to late deformation was expressed using the Zener-Hollomon parameter, and equations and constants for the strength ratio of the phases were proposed. [ABSTRACT FROM AUTHOR]

The poor metal mobility and insufficient fragmentation of the oxide film and hardened layer, which caused by low misalignment rate of the interface in traditional rolling (TR) process, lead to challenges to improve the interfacial bonding strength of Mg/Al composite plates. In this paper, a novel technology for manufacturing Mg/Al composite plates with excellent interfacial bonding quality by vibration assisted rolling (VAR) technology was proposed. VAR technology achieves high interfacial bonding quality of Mg/Al composite plates by introducing active shear stress through the misalignment of rollers. As a result, the interfacial bonding strength significantly increased from 28.5 MPa to 46.7 MPa, displaying an obvious improvement of over 64%. VAR technology enhances the degree of microstructures evolution and promotes the interdiffusion of elements in Mg/Al composite plates due to the frictional heat by the periodic misalignment of the rollers. Moreover, it promotes the multi-directional cracking of the hardened layer, and the cracking changes from strip cracking to cross cracking. It was attributed to the stress state of the Mg/Al composite plates change from biaxial compressive stress to state where biaxial tensile and compressive stress alternate periodically. In addition, the original shear stress in the rolling direction (RD) was increased and introducing an additional tangential direction (TD) shear stress at the interface. The technology could be beneficial for manufacturing Mg/Al composite plates with high interfacial bonding quality as well as provide a new technique for other metal composite plates. [ABSTRACT FROM AUTHOR]

Using water-based solvent in Li-ion battery (LIB) cathode slurry preparation offers many advantages over the traditional N-methyl-2-pyrrolidone-based (NMP-based) solvent, but with challenges of undesirable microstructure heterogeneity and debonding particularly at high drying rates. In this paper, we aim to simulate and understand the microstructure evolution and debonding phenomena in the drying of water-based cathode electrodes through a Coarse-Grained Molecular Dynamics (CGMD) model. As a comparative study, the drying process of NMP-based cathode was also simulated. The simulations demonstrate that the final volume for the water-based coating is smaller than the NMP-based counterpart, thus leading to more compact AM distribution after drying, contributing to higher energy density albeit lower the ion transport efficiency due to increased tortuosity. The results also show that, compared to the NMP-based electrode, the water-based electrode does not bind active material particles sufficiently during the drying process. Another interesting prediction is that the interface debonding typical occurs in vicinity of large AM particles for both the NMP-based and water-based electrodes. [ABSTRACT FROM AUTHOR]

In this paper, internal defects control mechanism and process optimization of TC11(Ti-6.5Al-3.5Mo-1.5Zr-0.3Si) alloy during cross wedge rolling (CWR) were investigated to promote the application of CWR in aviation. The effect of process parameters on the necking defect was studied by experiments and simulations with defining a dimensionless parameter δ. Meanwhile, microscopic observation and microcrack density statistics were performed on the center of the rolled workpiece to investigate the effect of process parameters on the evolution of internal defects. Microstructure analysis revealed that the center zone of the rolled titanium alloy workpiece was prone to crack along the interface between α-phase and β-phase, due to the difference in deformation and recrystallization behaviors. In addition, as α p -phase was coarser than α s -phase and elongated along the axial direction, microcracks were more susceptible to initiation and propagation at the interface between α p -phase and β-phase under combined shear and tensile stresses. Moreover, the evolution mechanisms of microstructure and central microcracks with temperature were proposed based on simulations and experiments. As the preheating temperature increasing, α s -phase and α p -phase gradually transformed to β-phase, and the material deformation ability is improved and the amount of phase interfaces is decreased. Therefore, the microstructure and internal defects of rolled workpieces can be regulated by adjusting the preheating temperature. Finally, the process optimization diagram was established to provide guidance for the forming of TC11 alloy rolled workpieces. [ABSTRACT FROM AUTHOR]

The energy density distribution directly affects the molten-pool temperature gradient, cooling and solidification rate of additive manufacturing (AM), which in turn affects the mechanical properties and microstructure of samples. In this paper, the control of the Gaussian laser beam energy density distribution characteristics is realized by controlling the defocus amount. The influence of the energy density distribution characteristics on the macro/micro structure and mechanical properties of the sample is explored. Microstructure observation and electron backscatter diffraction (EBSD) test were observed. The porosity, microhardness, tensile property, and friction of the samples were tested. These results indicated that when the beam energy density distribution was relatively uniform, the sample structure was most closely arranged equiaxed crystals. The grain size and texture strength of the samples gradually decreased, and the minimum grain size was 30.1 µm. With the energy density distribution becoming uniform, the microhardness and tensile strength first raised and fell, and the porosity and wear rate first fell and raised. The highest tensile strength was 1328 Mpa, and the smallest porosity was 0.31%. In addition, the mapping relationship between the defocus amount and the energy density distribution was deduced theoretically. Finally, combining the fine-grain strengthening and geometry necessary dislocation (GND) density, the mechanism of the effect of texture on the performance was revealed. The present work demonstrates the effectiveness of adjusting the defocus amount to control the beam energy density distribution, which in turn can effectively improve the properties of AMed metals. [Display omitted] • Validity of defocus amount to improve laser energy distribution was proved. • The improved Gaussian beam had low temperature gradient characteristics. • The improved beam effectively improved the microstructure of AM GH3625. • The improved beam availably improved the mechanical properties of AM GH3625. [ABSTRACT FROM AUTHOR]

Fusion based additive manufacturing (FBAM) of second, sixth, and seventh series Al alloys and their metal matrix composites (MMC) is difficult due to their higher thermal conductivity and solidification related problems namely porosity, cracks, thermal distortion, and formation of undesired phases. This paper presents friction stir powder additive manufacturing (FSPAM) process as a promising alternative to overcome these problems in producing multi-layer depositions of Al 6061 based MMCs namely Al 6061/6wt%FeCoNi and Al 6061/6wt%Ni. Their microstructure, distribution and elemental mapping of reinforcement particles, phase analysis, residual stresses of the MMCs and their correlation with microhardness, tensile strength, and fretting wear characteristics are investigated. Material accumulation on their advancing side was minimized by changing tool rotation direction in consecutive layers which produced smoother surfaces on both sides of their deposition. FSPAM made multi-layer depositions of Al 6061/FeCoNi and Al 6061/Ni MMCs have uniform distribution of reinforcement particles, good bonding between layers without cracks and defects, refined and equiaxed grains facilitated by dynamic recrystallization and pinning effect of reinforcement particles, compressive residual stresses of 39 and 48 MPa, no formation of deleterious intermetallic compounds due to absence of melting of matrix and reinforcement, and bowl-shaped substrate-deposition interface. Microhardness and ultimate tensile strength of the MMCs improved by 11.3% and 22.3%, and 30.5% and 31.5% respectively than Al 6061 alloy depositions, their wear resistance enhanced significantly, but % elongation reduced. This study proves FSPAM to be a potential alternative to FBAM processes for better quality multi-layer deposition of Al alloy-based MMCs. [Display omitted] • Solid-state additive manufacturing of Al6061/FeCoNi and Al6061/Ni MMCs. • Uniform distribution and better mixing of reinforcement particles. • Microstructure having refined and equiaxed grains. • Absence of deleterious intermetallic compounds, cracks, and defects. • Higher strength, microhardness, specific wear resistance, less % elongation. [ABSTRACT FROM AUTHOR]

Abstract: This paper is part of a larger study to understand the wear of hot rolling rolls. A significant cost of the hot rolling process is associated with the consumption of rolls, which is why a comprehensive understanding of the wear of the roll material is important. Given that the surface of the rolls is covered by an oxide layer, it is important to know the tribological and mechanical properties of the oxides. Research in this area concentrates mainly on the morphologies and microstructures of the oxide layers. Previously published works give very little, if any, information of the mechanical properties of the layers on high speed steel. This paper presents a methodology to study the mechanical properties of the oxide layer formed on the surface of a high speed steel roll using combined nanoindentation tests and finite element simulations. Mechanical properties such as the elastic modulus (E), hardness (H), yield strength (σ y ), and Poisson''s ratio (ν), have been determined, and the work has revealed a variation of microstructure, porosity (f), and mechanical properties of the oxide layer across its thickness. The outer sub-layer has a higher E and H than the inner sub-layer. This variation of mechanical properties in the oxide layer was consistent with variations in the porosity and grain sizes in the two sub-layers. [Copyright &y& Elsevier]

Tool electrode wear varying with different materials in electrical discharge machining (EDM) is unavoidable, thus inevitably reducing the machining quality and accuracy of microstructures. To convert this disadvantageous phenomenon into a beneficial process, the paper proposed a wear-variation EDM (WV-EDM) approach to fabricate a laminated disc electrode (LDE) with stable-shape micro channels on the outer edge surface; this electrode was subsequently used to machine micro grooves on workpieces by EDM. The WV-EDM formation of the LDE, the relationship between relative volume wear rate of the disc foils and the machining depth, and flow field distribution in the machining gap of the LDE during processing were investigated. The results show that the method proposed herein could reliably produce LDEs with stable micro channels on the outer edge surfaces that could subsequently be employed to continuously machine micro groove arrays with the same machining depth on the same material workpiece by EDM, and especially LDE reshaping was unnecessary. Additionally, the "pump effect" of the vortex, located in the flow field between micro channels on the LDE and workpiece, was beneficial for debris removal. Using the proposed method, micro groove arrays and columnar microstructures were successfully fabricated on Ti–6Al–4V alloy workpieces. [ABSTRACT FROM AUTHOR]

In this study, three different levels of laser energy inputs (Ev) were used for selective laser melting of Ti-5Al-2.5Sn alloy and the as-deposited tensile properties along the vertical direction with respect to deposition layers were found to be statistically identical to those along the horizontal direction for all the samples. Densification states, microstructures, and crystallographic orientation characteristics of the different samples, as well as their contributions to the isotropic properties were researched. The results first indicated that near spherical pores would form at the relatively high Ev (208 J/mm3) whereas lack-of-fusion defects would generate at the relatively low Ev (51 J/mm3). When the moderate Ev (167 J/mm3) was used, samples with very few defects could be fabricated. Then, it was seen that samples built at 51 and 167 J/mm3 presented a martensite (α′)-dominated microstructure in which the boundaries of columnar prior-β were decorated by grain-boundary α (α GB). When Ev increased to 208 J/mm3, a duplex microstructure composed of α′ and massive α (α M) would form within prior-β matrix of the as-deposited samples. An overall increasing trend in prior-β's width with the increase of Ev was also identified. Afterwards, it was proved that there was no strong texture within all the samples and this was one cause of the isotropic properties. Besides, for samples built at 51 J/mm3, the negative influence of lack-of-fusion on vertical properties cooperated with the adverse effect of large quantities of α GB on horizontal properties, promoting the obtainment of isotropic properties. For samples built at 167 J/mm3, not only the high densification degree but also the significantly increase in prior-β's width and the resultant decrease in α GB 's content helped to eliminate significant anisotropy. For samples built at 208 J/mm3, both the near spherical pores which resulted in near-identical bearing areas on different sections and the absent of α GB contributed to the isotropic properties. This paper can provide some basis for the laser additive manufacturing of titanium products with isotropic properties. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Combining Selective Laser Melting (SLM) and Laser Shock Peening (LSP) offers a new route to control microstructure and mechanical properties in 3D. • LSP significantly increases the microhardness of SLM As-Built parts in the near surface region but does not change grain size. • The LSP affected zone recrystallizes much faster upon heat treatment than the As-Built SLM, resulting in a refined, equiaxed grain structure. Abstract Metallic parts made by Selective Laser Melting (SLM) are known for their heterogeneous microstructures in the as-built (AB) state. In this paper, Laser Shock Peening (LSP) was performed on a 316 L stainless steel part fabricated by SLM. The LSP treatment increases the stored energy in the material but does not lead to measurable grain refinement. When subsequently annealed, the LSP treated sample undergoes recrystallization and transforms into a refined equiaxed structure, while this transformation is not activated yet for the AB sample. The LSP strategy therefore offers new routes for the selective 3D control of microstructures and mechanical properties of SLM parts. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The use of lasers for near-net shape manufacturing of cutting tools, made of ultra-hard materials such as polycrystalline diamonds, is recently becoming a standard processing step for cutting tool manufacturers. Due to the different machinability exhibited by microstructurally different composites, the laser processing parameters and their effects need to be investigated systematically when changing the material. In this context, the present paper investigates the effects of a fibre laser milling process (nanosecond pulse duration) on surface topography, roughness, microstructure and microhardness of two microstructurally different polycrystalline diamond composites. Pockets were first milled using a pulsed ytterbium-doped fibre laser (1064 nm wavelength) at different fluences, feed speeds and pulse durations, and finally characterised using a combination of Scanning Electron Microscopy, White Light Interferometry, Energy Dispersive using X-Ray (EDX) and micro hardness analyses. For laser feed speed in the region of 1000 mm/s, micro-indentation tests revealed an improvement of hardness from 75 GPa to 240 GPa at a depth of 350 nm, and to 258 GPa at a depth of 650 nm below which the microstructure is preserved as confirmed by microscopy images of the analysed cross sections. For fluences in the region of 11.34 Jcm−2 a variation of cobalt binder volume between the two composites causes a change in milling mechanism. At fluences below 20 Jcm−2, the proposed milling process for CTM302 resulted in a microstructural change (ultra-hard grain size and Cobalt binder weight), better surface integrity (140 nm) and improvement of micro hardness (up to 258 GPa). The properties achieved through the proposed process achieve better hardness and roughness when compared to laser shock processing. To the best of authors' knowledge, it is reported for the first time that an increase of hardness accompanied by improved surface roughness can be achieved on polycrystalline diamond through low-energy laser processing. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The punched aluminum alloy components possess limited edge stretchability for subsequent edge stretching deformation and poor corrosion resistance in their service periods due to the punched edges’ complexity and heterogeneity, while electropulsing has a positive effect on the influencing factors which are closely interrelated with the above-mentioned two issues. Therefore, this paper focuses on the influence of electropulsing on the edge stretchability of punched holes obtained by electropulsing assisted punching (EAP) and the corrosion susceptibility of punched parts after electropulsing treatment. The hole expansion tests and immersion corrosion experiments were firstly carried out and analyzed. Furthermore, metallographic microstructure and scanning morphology of the healed of microcracks near the punched edge were observed by optical microscope and scanning electron microscopy (SEM) respectively. The experimental results demonstrate that the improvement of the edge stretchability depends on the patterns of applying electropulsing and electric current density (ECD). Moreover, the corrosion resistance of the punched parts after electropulsing treatment is enhanced, and the degree of improvement of corrosion resistance is more remarkable with the increase of the ECD. Comprehensive analysis reveals that the improvement of the punched parts’ performance may be attributed to the healing and arrest of microcracks and microvoids near punched edge, local refinement of microstructure near the punched edge and the reduction of strengthening phases under the action of electropulsing, besides the promotion of macroscopic quality of sheared surface, the partial elimination of edge strain hardening (ESH) and pre-damage in vicinity of punched edge. [ABSTRACT FROM AUTHOR]

Abstract This paper shows the potential of stationary shoulder friction stir welding (SSFSW) for producing higher quality T- section joints relative to a conventional friction stir welding (FSW) approach. The residual stress distributions and their relationship to the weld zone microstructure and hardness distributions in SSFSW T-joints were investigated, as a function of welding travel speed. The final longitudinal residual stress fields were asymmetric, although individual weld zones showed similarities to those for conventional butt SSFSWs. The thermal excursion and plastic strain arising from the second pass lowered the residual stresses seen from the first pass, so that the largest tensile stresses (∼160 MPa) were found close to the nugget from the second weld pass. The asymmetry in hardness distribution was caused by the thermal field of the second pass which thermally treated material in the first pass and resulted in areas of age hardening and increased over ageing, depending on the position of overlap of the thermal fields. The effects of the second weld pass on the first pass were more apparent when a lower travel speed was used owing to the increase in heat input and duration of the thermal cycle. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new method of surface texturing for the cold mill roller called laser-guided discharge texturing to acquire the high surface roughness. In this method, the pulsed laser was focused on the roller surface to produce the metal plasma, and was then used to guide the arc discharge in the gap of electrodes to texture the roller. Laser-guided discharge texturing absorb the advantages of electrical discharge texturing and YAG laser texturing to form the following properties: the quick processing speed, the high processing energy, the deterministic distribution of the textured craters, and the enhanced surface shaping to the textured craters. In this paper, the control of the laser guiding in the randomicity of the discharge craters was studied, the surface topography of the textured craters was studied with different current peaks and pulse-widths, and the microstructures of the textured craters were analyzed. [Copyright &y& Elsevier]

Abstract: A camera flash-lamp, which makes use of the enhanced photothermal effect in silver nanoparticles, was used for sintering of ink-jet printed silver tracks on Polyimide (PI), Polyethylene Terephthalate (PET) and photographic paper at room temperature. After the camera flashing the nonconductive tracks was changed and became conductive. The resistivity of all tracks on different substrates was decreased after the first flashing and the second flashing, while it exhibited a slight increase after the third and forth flashing. Irrespective of the number of flashings, the silver track printed on the PET substrate had the lowest resistivity and it can reach 6.2μΩcm after the second flashing, while the track that was printed on the photographic paper had the highest measured resistivity due to defects in the substrate. The thermal conductivity of the substrate had an important effect on the microstructure of the silver tracks after the flashing. The nanoparticles within the tracks printed on the photographic paper exhibited significant melting after flashing sintering. This melting was due to very low thermal conductivity of the photographic paper and slow heat dissipation to the substrate and the surroundings. The nanoparticles on the PI substrate exhibited less appreciable melting due to greater thermal conductivity of the PI and fast heat dissipation to the substrate and the surroundings. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic molding process is an extension of lost foam process and uses an expendable pattern surrounded by steel shot bonded together by the action of an induced magnetic field. This paper presents the comparative results obtained from sand mold and magnetic molding processes for grey cast iron and ductile iron castings. Therefore, this paper reviews the factors involved in the production of suitable patterns and the magnetic mold and on the other hand presents the comparative microstructures obtained for grey cast iron and ductile iron castings. This study also describes the advantages and the characteristics of the magnetic molding process. The main factors involved in the magnetic molding process are also discussed. [Copyright &y& Elsevier]

[Display omitted] • The synergic welding sources creates current signals only governed by the WFR. • The HI is a vital parameter in WAAM because it can influence the shape of the beads. • The higher the value of the peak intensity, the greater the penetration depth. • Bead width and height models for each working mode are created. • The pulsed-AC mode reduces substantively the porosity amount. Wire Arc Additive Manufacturing (WAAM), an additive manufacturing technology for the manufacture of medium-to-large size metallic parts, is generating great interest. This technology employs aluminum alloys that are of immense interest for manufacturing, due to their high strength-weight ratio, corrosion resistance and utilization in different industries. Among these materials, some of the most widely used in various industrial fields are alloys classified within the 5000 series that are of good weldability and, consequently, very suitable for WAAM technology. In this paper, aluminum alloy 5356 is analyzed in the Gas Metal Arc Welding (GMAW)-based WAAM technological process. From among the various recommended working modes of different manufacturers, three working modes for aluminum alloys are compared: pulsed-GMAW mode, Cold Arc mode and pulsed-AC mode. To do so, test samples composed of single mono-layer weld beads and single-bead walls are manufactured using each working mode and micro and macro-structural properties, geometrical shape and porosity levels of the finished products are evaluated. As a novelty, this paper includes pulsed-AC as a new transfer mode for application on aluminum. Not only does it show its viability for the manufacture of parts by WAAM, but it also allows the reduction of the presence of pores by more than six times compared to Cold Arc mode and ten times compared to pulsed-GMAW mode. This aspect makes it a very attractive mode for use on this aluminum alloy. [ABSTRACT FROM AUTHOR]

Abstract: With rapid progress in ultra-short laser technology, two-photon photopolymerization (TPP) has been introduced into the domain of microfabrication. Its characters and process are described in this paper, as well as its experimental system. Through suitable experiments, it is identified that the spatial resolution of this technique can be increased as the scanning speed of focal spot and numerical aperture of objective lens rise, or as the laser power decreases. Finally, the paper presents some microstructures fabricated by this technique, such as micro-impeller, photonic crystal, micro-wells array, and so on, which illustrate its practicability in fabricating micro–nanostructures. [Copyright &y& Elsevier]

Abstract: In this study, multi-pass shape rolling of bars, sections and rails is considered from theoretical point of view, first of all. For such a process, the material is subjected to the thermo-mechanical processing. The theoretical basis of such a process consists of mathematical modelling of metal flow, temperature and microstructural evolution, as well as the prediction of the final properties of sections. It allows the computer simulation of controlled rolling of products with very complicated cross-section shapes. The coupled thermo-mechanical–microstructural model, which is the main subject of the paper, can be split into several independent parts: thermo-mechanical processing, austenite microstructure evolution during thermo-mechanical steel treatment, pearlite transformation model and microstructural–mechanical properties. The mechanical part of the model uses a generalised plane-strain (GPS) approach, which allows savings in both the computing time and computer memory. The temperature distribution in the controlled volume at any stage is achieved by means of a non-steady-state solution of the general diffusion equation satisfying the coupled Neuman and Hankel boundary conditions. The microstructural evolution model predicts static recrystallisation to restore the austenite microstructure after deformation and dynamic recrystallisation; while the deformation temperatures and strain exceed the critical values at the same time as the metal is subjected to the deformation. In the processes considered, the static recrystallisation and austenite grain growth are the main processes, which determine the final austenite grain size. The majority of the paper is dedicated to theoretical considerations; some results of the modelling are also presented. [Copyright &y& Elsevier]

Abstract: In hot metal forming processes, materials deform viscoplastically and the microstructure of materials changes dynamically (during the forming deformation) and statically (in the interval of operations or after forming processes). Techniques are required to enable the microstructure of a formed part to be predicted. In this paper, various models, developed by material scientists, are reviewed. They are used to model individual physical parameters of microstructure, such as grain size evolution in static and dynamic conditions, dislocation density accumulation and recovery, recrystallisation, dissolving rate of precipitates. Techniques have been introduced to incorporate mechanism-based microstructure parameters into a viscoplastic flow model to form a set of unified viscoplastic constitutive equations, which are implemented into FE solvers, through user defined subroutines, to simulate microstructure evolution in hot forming processes. Three examples are detailed in this paper. They are modelling of grain growth in superplastic forming, modelling of microstructure evolution in hot rolling and dissolving of precipitates in solution heat treatment (SHT) and their effects on viscoplastic flow of an Al-alloy. [Copyright &y& Elsevier]

Abstract: Welding of ‘chromium–molybdenum’ ferritic steels often causes steep modifications in the microstructure of the weld heat affected zone (HAZ). The paper presents results to establish the role of such microstructural variations on inhomogeneous scaling across the weldments of 2.25Cr–1Mo and 9Cr–1Mo steels, as well as further degradation in microstructure during oxidation of the weldments. Microstructure of different regions of the steel weldments was characterized by electron/optical microscopy. Oxidation of different weldment regions in air and steam environments have clearly suggested variations in scaling rates across the weldment regions, and further microstructural degradation in the HAZ. The paper also presents a report of the effect of post weld heat treatment on oxide scaling behavior. This paper contributes in the correlation between welding parameters and oxidation behavior. [Copyright &y& Elsevier]

An experimental investigation has been carried out, in present paper, on microstructure and corrosion resistance of weld butt joints of AA 2024-T3. Two different welding processes have been considered: a conventional tungsten inert gas (TIG) process and an innovative solid state welding process known as friction stir welding (FSW). Micro-hardness measurements allow pointing out a general decay of mechanical properties of TIG joints, mainly due to high temperatures experienced by material. In FSW joint, instead, lower temperatures involved in process and severe plastic deformations induced by tool motion allow rising of a complex situation: by a general point of view a slight decay of mechanical properties is recorded in nugget zone, flow arm and thermo-mechanically altered zone (TMAZ), while in heat-affected zone (HAZ), due to starting heat treatment of alloy under investigation, a light improvement of such properties is appreciated. In flow arm and in nugget zone, however, a light recovery of hardness, w.r.t. TMAZ zone, is recorded, due to the re-crystallisation of a very fine grain structure. Polarisation curve tests and electrochemical impedance spectroscopy, performed in this paper, allow assessing a generalised nobler behaviour of weld bead with respect to parent alloy. In FSW joint, however, the differences between the three examined zone are not so evident as in TIG joint; what is more, inside FSW weld bead, retreating zone shows a behaviour nobler than advancing one. [Copyright &y& Elsevier]

This paper will give a survey of some of the actual research activities at the Chair of Manufacturing Technology in Erlangen concerning laser and forming technology. In detail the paper will deal with two main focuses of development: laser forming of aluminum alloys and laser-assisted forming of high strength steels. Laser forming is a technology often used for small series productions and for adjustment of small electronic components. In contrast to laser forming, which is a forming technology that is common for over 20 years, laser-assisted forming is an example of a new production technology that is able to enhance the forming limits of high strength steels. [Copyright &y& Elsevier]

In this paper, the ultrasonic consolidation (UC) process is presented for the direct fabrication of monolithic aluminium tooling and components. UC is a solid-state process that involves the use of high frequency, low amplitude, mechanical vibrations to bond metal foils in a layer-by-layer method. The work, described in this paper, centres on the characterisation of aluminium 3003 foils that will be used in a freeform fabrication process with industrial applications. This paper describes the first phase of ongoing research which involves the identification of the optimum process parameters when producing multi-layered specimens using UC test apparatus. A general process window for aluminium 3003, welded under UC conditions, is identified, based on the combination of data generated from modified peel test and microstructural analysis experiments. [Copyright &y& Elsevier]

In this paper, diamond microstructures were patterned over silicon/silicon dioxide substrate using the processes combined with bulk or surface micromachining, selective growth of diamond and plasma etching technique. Polycrystalline diamond films were prepared using microwave plasma enhanced chemical vapour deposition (MW-PECVD) and a gas mixture of hydrogen and methane. Two types of techniques for precise patterning of diamond microstructures were investigated in this paper. The first one was to selectively grow diamond films in the desired region by pre-depositing a Pt interlayer on silicon dioxide layer. The second one was to selectively etch the deposited diamond film in oxygen/argon plasma under an Al mask. Different microstructures, e.g., microgear, microrotor, comb drive structure, etc. were successfully fabricated. [Copyright &y& Elsevier]

Superelastic Ni-rich NiTi alloy has received great attention in recent years due to its impressive shape-recovery capability without heating, especially for complex structures produced by laser powder bed fusion (LPBF). However, the trade-off between relative density, mechanical property, and superelasticity is difficult to balance. In this study, the microstructure and superelasticity of LPBFed NiTi alloys with different relative densities tuned by a self-developed operation window have been investigated comprehensively. The results show that increased scanning speed at high laser power leads to a lower volumetric energy density, resulting in a higher relative density of the alloy. NiTi alloys with high relative density (>99.5 %) are successfully obtained at different laser powers based on this principle. The scattered micropores are present at low laser power, leading to crack propagation. In contrast, the high laser power produces a low-angle dislocation wall concentrated in the center of the melt pool, which is beneficial to the mechanical properties of the manufactured part. Moreover, the combination of high laser power and high scanning speed (HH) process is vital to improving the superelasticity of NiTi alloys with a relatively low M s than the original powder. It critically owes to the precipitates of Ti 4 Ni 2 O that enhance cyclic stability and recoverability. This paper provides a promising pathway for tuning the functional properties of NiTi alloys by the LPBF process to obtain a superelastic response balanced with mechanical properties. [Display omitted] • Energy evolvement aiming at high-relative-density of NiTi alloy was elucidated. • Microstructure evolution and corresponding mechanical behaviors were systemically studied. • Structural characteristics linked to high superelasticity of LPBFed NiTi was proposed. • This work provides a promising pathway to tune the superelastic response participated by Ti 4 Ni 2 O. [ABSTRACT FROM AUTHOR]

The objective of the paper is presentation of the complex thermal-mechanical-microstructural model, which simulates the whole process of hot forming, starting from heating of the stock material through the forming operations up to the controlled cooling after forming. The thermal-mechanical finite element solution is the basis of the approach and it is coupled with the closed form equations describing microstructural phenomena. The microstructural equations are solved in each node of the finite element mesh and at each time step, what makes the feedback between the models possible. Three stages of modelling are presented. The first concerns heating of the stock before forming. The model predicts temperature field, stresses and grain size during heating. The second stage uses thermal-mechanical-microstructural model of forming operations. Beyond the conventional closed for equation describing microstructure development, the models based on the internal variable approach are presented. Particular emphasis is put on identification of parameters of the models. The inverse analysis with the multi criterion objective function is applied. Simulation of the controlled cooling of products after hot forming is the third objective of the modeling. The models couple finite-element solution of the thermal problem with equations describing kinetics of phase transformations and properties of materials in the room temperature. Identification of the phase transformation models is based on the inverse analysis combined with the experimental TTT diagrams. Several examples of simulations and experimental validation, which are presented in the paper, confirm good predictive capabilities of the model. [Copyright &y& Elsevier]

This paper proposes an innovative and high efficiency process to fabricate Cr-Ni stainless steel components using a double-wire feed and plasma arc additive manufacturing process (DWF-PAM). The superior characteristics exhibited by DWF-PAM processing in terms of the bead appearance, microstructure, and mechanical properties of all the test components, were investigated. The results show that, at the same process parameters, in contrast to the single-wire feed and plasma additive manufacturing (SWF-PAM) process, the deposition rate in the DWF-PAM process increased by 1.06 times on an average. A large number of complete grown equiaxed ferrite (CGEF) grains were found in the interface area close to the next layer of the DWF-PAM-processed sample; while for the SWF-PAM-processed samples, incomplete grown equiaxed ferrite grains were observed in same area. The CGEF grains provided a significant improvement to the ultimate tensile strengths and elongation rates of the DWF-PAM-processed samples. The ultimate tensile strength increased by 10.2% on an average, while the maximal increment of the elongation rate reached 176%. In view of these results, components manufactured by the DWF process can have a finer-grained microstructure and superior mechanical properties compared to those manufactured by the SWF process. Moreover, a higher deposition rate can also be achieved with the DWF-PAM process. [ABSTRACT FROM AUTHOR]

Utilizing plastic strain to modify surface attributes is a common way to improve the functional performance of engineering components. The ability to control the strain distribution in the surface layer is critical for controlling the microstructures and properties of the processed surface. This paper explores the possibility of controlling the surface / subsurface strain distribution in copper by using a wedge-shaped sliding tool of large negative rake angle (≤ −60°). The surface flow and deformation at various sliding conditions are characterized in situ using high speed imaging and image analysis techniques. Deformation fields like flow velocity, strain rate and strain are quantified. It shows the sliding can result in two modes of surface deformation: (1) steady prow deformation with laminar flow and (2) unsteady prow deformation with sinuous flow and surface folding. The former creates a uniformly strained subsurface layer while the latter creates surface defects and inhomogeneous strain field. Utilizing the steady prow deformation and multi-pass sliding technique, the subsurface strain in copper can be controlled in a large strain range (>10). Strategies to control both the strain magnitude and distribution in the subsurface region are discussed. The results indicate the wedge sliding process is a promising method for imposing controllable surface plastic deformation. [ABSTRACT FROM AUTHOR]

To ensure the temperature and formability of magnesium sheet metal transferring from a continuous oven, stamping of magnesium alloy sheet normally requires a setting of stationary heating oven in which lower-punch and binder are heated simultaneously. This paper studied the effect of unheated or extra heated upper-die with different temperatures on AZ31B magnesium sheet metalʼs formability in stamping. Forming limit curves (FLC) under different temperature upper-die were generated to analyze the temperature effect, which shows that the formability decrease significantly as upper-die temperature drops. Moreover, temperature fields simulated through thermo-mechanical coupling FEM simulation and microstructure of different specimen region indicate inhomogeneous mechanical properties due to temperature gradient, which results in different modes of crack initiation and propagation. Finally, FLC result was verified through a tryout stamping of automobile hinge cover. [ABSTRACT FROM AUTHOR]

Laser processing technique has been an effective method to enhance the medical implant’s biocompatibility through forming specific textures on titanium alloy implant surface. In this paper, a 1064 nm pulsed picosecond laser on TC4 titanium alloy implant samples was conducted to obtain optimal parameters for well-structured textures, controllable micro-grooves and improved osteoblast adhesion and proliferation. Picosecond laser technique is generally characterized by the high flexibility and advanced properties, which could make structural features including topography quality and detailed dimensions expediently improved and changed by adjusting laser processing parameters. To obtain the optimal laser processing parameters for desired microstructures, orthogonal experiments and related SEM, EDS and SPM analysis were conducted under various laser powers, repetition frequencies, scan speeds and scan numbers. Thus, the correlation between picosecond laser processing parameters and its corresponding microstructure feature of the micro-grooves was established. In addition, the immunofluorescence detection of cell actin cytoskeleton shows that structured textures can promote cell adhesion and play an important role in cell contact guidance. [ABSTRACT FROM AUTHOR]

The use of appropriate forming processes allows to obtain materials of required shapes, structures and properties. The technological conditions of the process can be optimized in view of the final microstructure. It can be achieved using different modeling methods, but recently use of cellular automata remains on the high level of interest. The aim of the study is a development and verification of the model of microstructure evolution during the flat rolling process. The microstructural model is based on frontal cellular automata, which uses for simulation of the rolling process of AISI 304L stainless steel. Modeling can be done on the basis of the general characteristics of the process i.e. the information about the duration of plastic deformation, time intervals between the passes, temperature and strain rate. The paper presents the modeling results of flat rolling process of AISI 304L stainless steel for different processing conditions. The modeling of three passes is presented. The results of the microstructure evolution can be observed as the microstructure maps at the selected time moments, as well as changes of average grain size, grain size distribution, fraction of recrystallization and flow stress. Some of the simulation results are verified with the experimental data. Model shows the high flexibility, allowing to take into account the various processing parameters. Simulation results are similar to the real processing conditions. It can be considered as a new tool for the development and optimization of flat rolling in view of final microstructure. [ABSTRACT FROM AUTHOR]

This paper presents the development and application of a reciprocating fast-tool-feeding mechanism with elliptical cam drive for rapidly fabricating surface microtexture arrays. Four kinds of different drive-mechanisms involving piston-rod, eccentric-cam, swash-plate-cam, and elliptical cam are devised and analyzed. The elliptical cam is employed as the drive mechanism for the reciprocating feed-tool system. Its symmetrical structural design suppresses systematic vibration, allowing for stable high-acceleration motion, and a speed of response double that of the other tool systems. Finite Element Analysis (FEA) is conducted to predict weaknesses, potential deformation problems, and the resonant frequency of the developed mechanism. Tool trailing stress is derived from the relationship between cutting force normal to the shear plane as well as cutting depth. It is shown that the predicted cutting force fits the required work current. Experimental verifications involving microdimple array generation are implemented to verify the practicability of the feed-tool system. Experimental results demonstrate that a microdimple array of 12 × 34 is promptly finished at a drive-frequency of 10 Hz, workpiece speed of 1200 mm/min, cutting depth of 30 μm, and processing time of only 40 s. These approaches and conditions generated surface microtexture arrays with highly consistent micro features confirming that the developed reciprocating fast-tool-feeding mechanism is well suited to the high reproducibility of consistently precise machined dense microstructure arrays. [ABSTRACT FROM AUTHOR]