Search

This study investigates the effects of different lubrication conditions on drawing force and microcup formation during micro deep drawing (MDD). Results show that graphene lubricant, in combination with TiO2 nanolubricants, has the potential to reduce friction during MDD. The peak drawing force was reduced by 15.39% when both lubricants were used together, while the use of TiO2 nanolubricant and 10.0 mg/ml graphene lubricant reduced it by 6.03% and 14.52%, respectively. The study also reveals that lubricants reduce wrinkling during the formation of microcups by minimising energy consumption during the primary formation. However, the combination of TiO2 nanolubricant and graphene lubricant can cause inhomogeneous formation on the upper part of the blank, leading to more apparent wrinkling. Overall, the study highlights the potential of TiO2 nanolubricant and graphene lubricant in reducing friction and improving microcup formation during MDD. [ABSTRACT FROM AUTHOR]

A novel experimental method was developed through a ball-on-disk tribometer to study the friction and wear behaviour of a chrome steel at temperatures of 25, 200 and 500 °C. Water-based nanolubricants containing different concentrations of nano-TiO 2 from 0.4 to 8.0 wt% were used to investigate their effects on friction-reduction and anti-wear mechanisms, in comparison to the benchmarks under dry and water conditions. The results show that the water-based nanolubricants can significantly reduce coefficient of friction (COF) and improve wear resistance of the chrome steel at both ambient and elevated temperatures. In particular, the use of nanolubricant containing an optimal concentration (4.0 wt%) of nano-TiO 2 leads to the lowest COF and the smallest ball wear among all the lubrication conditions. The friction-reduction and anti-wear mechanisms are ascribed to the rolling & polishing effects, semisolid film and solid layer contributed by the nano-TiO 2 at temperatures of 25, 200 and 500 °C, respectively. • The environment-friendly water-based nanolubricants were applied in this study. • A novel experimental method was used for tribological tests at ambient and elevated temperatures. • The friction and wear mechanisms were examined with clear evidence. • The roll service life during hot steel rolling can be effectively evaluated when using water-based nanolubricants. [ABSTRACT FROM AUTHOR]

To meet the increasing demand of multifunctional applications of microcomponents, metal composites have been gradually noted in micromanufacturing. In this paper, the formability of aluminium (Al)-copper (Cu) composite foils in micro deep drawing (MDD) was studied, and the mechanism involved was discussed. A two-layered Al-Cu composite with the thickness of 235 µm was selected and first rolled to 50 µm, and then annealed at 200, 300, 400 and 500 °C for 5 min prior to the MDD experiments. The results show that Al-Cu composite foil possesses the best combination of strength and ductility after annealing at 400 °C. With the increase in annealing temperature, the grains of both Al and Cu layers are refined, and in the meantime, the thickness of intermetallic layer also increases. The results from MDD tests indicate that the existence of intermetallic layer has a greater influence on the formability of the composite foil compared to the finer distribution of grains. On the basis of the obtained results, the optimised heat treatment method with the annealing temperature of 300 °C for 1 h was proposed, which was then proved to significantly improve the performance of the Al-Cu composite foil in MDD. [Display omitted] [ABSTRACT FROM AUTHOR]

Al matrix composites (AMCs) have gained tremendous interest in the past decades due to their lightweight, superior mechanical and other physical properties. In this study, an ultrafine-grained Al2024/1 wt% TiC/1 wt% graphene nanoplatelets (GNPs) nanocomposite was fabricated through powder metallurgy. Synergetic effects of TiC and GNPs on the microstructural characteristics, mechanical properties and thermal conductivity were investigated in comparison with those of the matrix and TiC or GNPs singly reinforced Al2024 matrix nanocomposites. The Al2024/1 wt% TiC/1 wt% GNPs nanocomposite showed significantly improved mechanical properties with the compression yield strength of 370.2 MPa, ultimate compressive strength of 615.8 MPa and fracture strain of 8.6%, indicating a superior balance in the strength and ductility over TiC or GNPs singly reinforced Al matrix composite, since the distributions of both the TiC and GNPs in Al2024/1 wt% TiC/1 wt% GNPs nanocomposite were improved significantly. The significant mechanical property improvements are attributed to the synergistic reinforcing contributions from TiC and GNPs. The thermal conductivity of Al2024/1 wt% TiC/1 wt% GNPs nanocomposite stables at 55.0 W∙m-1∙K-1 without a further decrease compared with the composite singly reinforced with GNPs. • An ultrafine-grained Al2024–TiC-GNPs hybrid nanocomposite (AlTG) was fabricated. • Introducing TiC and GNPs benefits uniform dispersions of TiC and GNPs in AlTG. • The hybrid composite (AlTG) shows a superior balance in the strength and ductility. • Improved dispersions of TiC and GNPs explain better mechanical properties of AlTG. • Excellent thermal conductivity of AlTG is remained compared with other composites. [ABSTRACT FROM AUTHOR]

To improve the quality of products produced from microforming, various nanolubricants have been applied in the field of micromanufacturing in recent years. In this paper, the effects of glycerol-based lubricant containing TiO2 NPs (NPs) on micro deep drawing (MDD) of austenitic stainless steel (ASS) SUS301 were studied, and the lubrication mechanism involved was discussed. The MDD experiments were conducted with the SUS301 foils under dry, 1, 2, and 4 wt% TiO2 NP lubrication conditions. The results show that the use of the TiO2 nanolubricants can significantly improve the quality of the drawn cups in terms of decreased wrinkling and surface roughness. Besides, the concentration of TiO2 NPs influences lubricity by reducing friction during the MDD process. The peak drawing force is the lowest when 2 wt% nanolubricant is applied, which drops to 72.54 N from 77.38 N under dry conditions. The micro cup drawn under 2 wt% TiO2 nanolubricant has the best quality among those obtained under all the lubrication conditions. The lubrication mechanisms are derived from the mending effects of TiO2 NPs and the formation of thin lubricant films associated with the open lubricant pockets (OLPs) and close lubricant pocket (CLPs) theory in the MDD. The CLPs function as reservoirs that retain lubricants to counteract the load pressure, whereas the OLPs lead to lubricant leakage due to the higher flow resistance. It was found that the lubricant film and NPs are insufficient at a low concentration (1 wt%), while the lubrication performance can be enhanced with increased NP concentration. However, there exist apparent agglomerations on the surface of the produced micro cup when using 4 wt% nanolubricant, which greatly deteriorates the lubricant performance in the MDD process. It is concluded that the lubricant containing 2 wt% TiO2 NPs demonstrates the best lubrication performance during the MDD of ASS SUS301. [ABSTRACT FROM AUTHOR]

In this study, Al2024/TiB 2 composites with different TiB 2 fractions (5, 10 and 15 vol%) were fabricated by high-energy ball milling and spark plasma sintering. The effects of TiB 2 fraction on the microstructure, hardness and wear resistance of the composites were explored to determine the optimal TiB 2 content in the composite with optimal properties. An increase in Vickers hardness of the composites correlates with the increased TiB 2 content, and the Al2024-15TiB 2 composite exhibits the highest hardness. The wear rate of the composite initially increases and then decreases with higher TiB 2 content. Notably, the Al2024-10TiB 2 composite demonstrates the best wear resistance with a wear rate of 1.14 × 10−4 mm³/Nm, representing a 96.81 % reduction compared to the unreinforced Al2024. The deteriorated wear resistance of the Al2024-15TiB 2 composite was attributed to the decreased toughness and severe three-body abrasion caused by the excessive TiB 2 particles. [ABSTRACT FROM AUTHOR]

Microstructure and texture evolution of a low-Ni Cr–Mn–N austenitic stainless steel were analysed during three-point bending process. The electron back-scattering diffraction (EBSD) was used to characterise the microstructural evolution with respect to two regions encompassing (I) near the inner corner and (II) near the outer corner. The fraction of deformation-induced martensite of either types (ε- and α′-martensite) was analysed in both regions. The region (I) possessed a considerably higher fraction of ε-martensite than that in the region (II). In the region (II), the fraction of austenite 60°/〈111〉 twins was increased. Moreover, in the region (I), the 10 1 ¯ 2 ⟨ 1 ¯ 011 ⟩ extension twinning was depicted in ε-martensite. The mean kernel average misorientation of ε-martensite experienced a trivial change with increasing bending angle after reaching to a saturation point. Upon bending, texture measurements of austenite returned the αγ-fibre orientations with the dominant Brass component. However, a decrease in the Cube and S texture components was identified. The ε-martensite texture revealed strong intensities along the h k i l ε -fibre. Besides, the α′-martensite developed 001 0 1 ¯ 0 α ′ and 001 001 α ′ orientations with a trace of 113 4 7 ¯ 1 α ′ orientation. [ABSTRACT FROM AUTHOR]

In this study we examined the effects of compaction pressure for bonding nanocrystalline cemented tungsten carbide (WC-10Co) and high-strength steel (AISI4340) and successfully fabricated a bilayered composite of ceramic and steel. The obtained results were compared with our previous studies, and then the optimised sintering conditions were suggested. The compaction pressure examined varied from 120–200 MPa at 1150°C for 20 min. The study shows that the change in experimental parameters has significant effects on both the sintering properties of nanocrystalline WC-10Co powders and their bonding with AISI4340 steel. The microstructure reveals a successful metallurgical bonding between ceramic and steel. Bonding temperature determines, to a great extent, the diffusion processes across the bonding interface and has found to be the most influential variable compared to sintering time and compaction pressure. The obtained average maximum bonding strength of the bimetal composite is 226 MPa, which is higher than that of previous studies. [ABSTRACT FROM AUTHOR]

Effects of various lubrication conditions on macroscale deep drawing have been investigated extensively while in microscale due to the open and closed lubrication pocket theory and friction coefficient escalation, proper lubricant concern becomes severe. Microforming is used to produce lighter and more energy-effective products accordingly; in this study, magnesium-lithium (Mg-Li) alloy is chosen to form a superior micro-cup due to its ultralight weight with outstanding ductility. Mg-Li is a new material in microscale; consequently, to study the mechanical properties, a heat treatment process is performed. The dry and oil lubrication conditions are chosen as benchmarks to investigate effects of TiO2 oil-based nano-additive lubricant. Finite element (FE) modelling has been conducted and the simulated results are agreed well with the experimental results where the drawing force is significantly affected by the nano-particle. The formed cup quality regarding the surface roughness has been evaluated extensively by consideration of various parameters and the quality improvement is substantial. [ABSTRACT FROM AUTHOR]

The long, straight grain boundary of the high-entropy alloy (HEA) produced via laser melting deposition (LMD) is prone to cracking due to unidirectional scanning (single wall). To enhance the competitive growth of columnar grains and improve the overall performance of the alloy, a vertical cross scanning method was employed to fabricate FeCoCrNi HEA (bulk). The influence of grain orientation on the microstructure and mechanical properties of FeCoCrNi-LMD was systematically investigated. Microhardness tests and tensile tests were conducted to assess the mechanical property differences between the single-wall and bulk samples. This study shows that using a single scanning strategy results in monolayer wall grains sized at 129.40 μm, with a max texture strength of 21.29. Employing orthogonal scanning yields 61.15 μm block-like grains with a max texture strength of 11.12. Dislocation densities are 1.084 × 1012 m−2 and 1.156 × 1012 m−2, with average Schmid factors of 0.471 and 0.416. In comparison to the FeCoCrNi-LMD single wall, the bulk material produced through cross-layer orthogonal scanning exhibited reduced residual stress, weakened anisotropy, and improved mechanical properties. These findings are expected to enhance the potential applications of FeCoCrNi-LMD in various industries. [ABSTRACT FROM AUTHOR]

Bimetal composites have wide applications due to their excellent overall performance and relatively low cost. In this study, the formability of stainless/carbon steel bimetal medium-thick composite in the stamping process without blank holder was investigated by finite element (FE) simulations and experiments. Uniaxial tensile tests on substrate metal (carbon steel) and clad metal (stainless steel) were first conducted, respectively, in order to obtain the material properties of each metal layer required in the FE simulation. Processing variables, including the layer stacking sequence, relative thickness ratios of two layers and friction conditions, were considered, and their effects on the magnitude of press load and distributions of thickness strain for predicting the high-risk region of necking during stamping were discussed. Experimental tests were carried out to verify the simulation results. It is indicated that simulation results can be used as an evaluation indicator to ensure the bimetal medium-thick composite can be safely formed. [ABSTRACT FROM AUTHOR]

Highlights • A developed analytical model of bending characteristics for bimetal composite was presented. • The movement behaviour of bonding interface relative to neutral and unelongated planes was studied. • Analytical, FE and experimental investigations were conducted on the bending behaviours of bimetal composite. Abstract Analytical, numerical and experimental investigations were conducted on the bending characteristics of duplex stainless steel (2205) and low carbon steel (AH36) bimetal composite in this study, with the aim of providing a reference for the bending and forming processing optimisation of laminated metal composite. An analytical model was developed to predict the deformation behaviour of each segment and particular planes, such as neutral plane, unelongated plane and bonding interface, across thickness section under the plane strain condition during the bending process. The movement track of segments presents that it is better for the bonding interface to avoid experiencing the reverse loaded zone (RLZ) in forming fabrications for less potential defects, and the neutral plane is discontinuous while coinciding with the bonding interface. The thickness change and bending moment of bimetal plate were calculated as a function of the increasing bending curvature by the proposed theoretical model under four conditions classified by different thickness ratios and relative positions of component steel layers. The predicted results show that the relative position affects the thickness change of bent composite plate, but the thickness ratio has a more significant effect on the magnitude of bending moment, as confirmed by finite element (FE) simulation and bending experiments. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

This paper compares the microstructure and mechanical evolution in a high-strength quenched and micro-alloyed steel during the austenitising bending process. Simulation results indicated a new finding that the stress neutral layer (SNL) tends to move to the tension zone during straining. The hardness gradient detected from the centre to compression/tension zones was resulted from comprehensive factors: First of all, the location of SNL revealed a prominent impact on strength. Second, the dislocation accumulation would be responsible for the hardness gradient on the surfaces. In addition, the overall strength decrease during straining was mainly ascribed to integrated effects of dynamic recovery (DRV) and dynamic recrystallisation (DRX). Apart from that, overall smaller martensite packet size and coarser prior austenite grains resulted in the increased hardness value at a lower bending degree. Also, the high consistency between experimental and simulation results is instructive for the practical forming process of railway spring fasteners. [ABSTRACT FROM AUTHOR]

The microstructure of Cr–Mn–Ni–N stainless steel is regulated by a combination of cold deformation and subsequent martensite reversed annealing. The yield strength and tensile strength of the tested steel are greatly improved to 1220 and 1357 MPa, respectively, by conventional heavy cold rolling (66% thickness reduction) and a subsequent annealing process (750 °C for 5 min) relative to those before cold rolling (austenized state); at the same time, the total elongation keeps an appropriate value. The results show that the grain refinement strengthening acts as the primary factor for the strengthening of the tested steels while the precipitation behavior from the M23C6‐type carbides is not quite effective. Additionally, different yield phenomena and microstructural evolution for tested steels with 66% thickness reduction annealed at 750 °C with different holding times are systematically analyzed and discussed. Lüders‐like deformation features noticeably appear but become weakening with the longer annealing time. The change in initial free mobile dislocation density is the core cause of the preyield plateau phenomenon. [ABSTRACT FROM AUTHOR]

[Display omitted] • Al2024-TiC-GNPs hybrid composite was produced via powder metallurgy. • Presence of both TiC and GNPs contributes to refining matrix powders after milling. • Distributions of Al 2 Cu, TiC and GNPs are improved by adding both TiC and GNPs. • Synergetic effects of TiC and GNPs benefit the wear resistance of hybrid composite. Al matrix composites have attracted significant attention of researchers in recent years due to their lightweight, excellent mechanical and tribological properties. In this study, an Al2024 matrix hybrid composite (AMHC) reinforced with both TiC nanoparticles and graphene nanoplatelets (GNPs) was produced via a route of powder metallurgy. And its microstructure, microhardness and tribological properties are compared with those of unreinforced Al2024 alloy matrix and Al2024 matrix composites reinforced with either only TiC or GNPs. It was found that the distribution of Al 2 Cu, TiC nanoparticles and GNPs in the matrix and the wear resistance are significantly improved when introducing both TiC nanoparticles and the GNPs. The wear mechanisms change from the adhesion-dominant wear for Al2024 and the other singly reinforced composites into abrasive-dominant wear for the hybrid composite. The significantly improved wear resistance of the AMHC is attributed to the synergistic effects of reinforcing and self-lubricating of the TiC and GNPs. [ABSTRACT FROM AUTHOR]

Spark plasma sintering (SPS) is a powerful technique for consolidating metal powders at a remarkably shorter time with excellent quality. We used this technique for sintering nanocrystalline WC10Co powders and simultaneously bonding with high-strength steel. A series of experiments were conducted in order to find out the optimised set of SPS controlling parameters. The effects of temperatures (1000 to 1150 °C, with a 50 °C interval) in sintering nanocrystalline WC10Co powders and their bonding phenomena with AISI4340 steel were examined at a constant pressure of 80 MPa and a holding time of 5 min. The full density of the carbide powders was achieved at a lower temperature compared with that of conventional techniques. A number of techniques were employed to evaluate the microstructural characteristics of WC and steel bilayered composite and their mechanical properties. For determining the bonding strength of the joint, a novel micro-tensile testing system was adopted. Since such investigation is the first of its kind, to the best knowledge of the authors, where SPS is used to join the tungsten carbide with the steel, this research is expected to provide a valuable future reference for fabricating dissimilar bilayered composite materials. [ABSTRACT FROM AUTHOR]

The hot deformation behaviour and interfacial microstructure evolution have a critical influence on the hot workability and mechanical properties of bimetal composite. This study investigated the flow performance and interfacial characteristics of 2205 duplex stainless steel/AH36 low carbon steel bimetal composite (2205/AH36 BC) at elevated temperatures, based on the hot tensile tests over the temperature range of 950–1250 °C and strain rate range of 0.01–1 s−1. The results indicate that the deformation behaviour of 2205/AH36 BC is similar to that of AH36 low carbon steel at high temperatures, and the softening mechanism of bimetal composite significantly depends on the imposed working temperatures and strain rates, which has been verified by the electron backscatter diffraction (EBSD) observation of microstructure evolution. Extra geometrically necessary dislocations (GNDs) were observed to accumulate in AH36 carbon steel layer adjacent to the interface after the hot working test at relatively low strain rates, resulting from the different thermal expansions and hot ductility between the 2205 stainless steel and AH36 carbon steel, and some existing defects on the interface from the previous hot rolling process. These observations can be employed as a reference to make the medium-thick bimetal composite be fabricated to the final products with hot working process in practice. • The deformation behaviours of 2205/AH36 bimetal composite are controlled by DRX at high temperatures or low strain rates. • The GND density of 2205 steel and AH36 steel layers reduces after the hot tensile test at the relatively low strain rates. • The interfacial GND density and nano hardness value of 2205/AH36 bimetal composite show a peak after hot tensile tests. [ABSTRACT FROM AUTHOR]

The interfacial morphologies play a crucial role in mechanical properties of laminated/bimetal composite. This study investigates the effects of heat treatments on the interfacial characteristics, mechanical properties and fracture behaviour of a 2205 duplex stainless steel/AH36 carbon steel bimetal composite with varying interface situations fabricated by the hot-rolling and subsequent heat treatments. The bimetal composite was annealed from 850 °C to 1150 °C in steps of 100 °C with soaking 1 h. Heterogeneities of grain size and element concentration exist in the microstructural evolution of bonding zone adjacent to interface after annealing treatments, which were observed by the optical microscope and scanning electron microscope (SEM) coupled with the energy dispersive X-ray spectroscopy (EDS). It was found that the diffusion transition zone of Cr and Fe alloy elements between component 2205 and AH36 steel layers present an increasing trend with the rise of annealing temperature. The results of conventional, shear and compact tensile test indicate that the tensile strength of 2205/AH36 bimetal composite gradually decreases but the fracture elongation increases with the rising annealing temperature, the thicker alloy element diffusion zone results in the stronger interfacial shear strength and better ductility of bimetal composite, but the thick and strong interface has less positive effect than the mechanical properties of bimetal composite itself on preventing the fatigue crack growth across the interface. [ABSTRACT FROM AUTHOR]

• The unique hot flow behaviour of bimetal composite different from that of a single material was analysed. • A physically-based constitutive model considering DRV and DRX softening mechanisms for bimetal composite was established. • A mixture law of bimetal composite considering the strain and stress partitioning was developed. • Analytical, FE and experimental investigations were conducted on the flow behaviour of bimetal composite. The flow behaviour and strain partitioning of 2205 duplex ferritic-austenitic stainless steel/AH36 low carbon steel bimetal composite (2205/AH36 BC) were investigated at elevated temperatures in this study. A physically-based constitutive model was established to describe the flow behaviour of bimetal composite based on the stress–strain relationships obtained from hot tensile tests, which were performed on a Gleeble 3500 thermal-mechanical test simulator over the temperature range of 950–1250 °C and strain rate range of 0.01–1 s−1. The stress and strain partitioning of bimetal composite was analysed to develop a mixture law of flow stress under those hot working conditions, due to the different strain contributions of each material on the total flow behaviour of bimetal composite. The developed constitutive model and the mixture law considering strain partitioning were both adopted to predict the stress–strain curves and used in finite element (FE) simulation model to calculate the peak loads of 2205/AH36 BC at 1000 °C. It is found that the softening mechanisms of 2205/AH36 BC changes depending on the externally imposed working temperatures and strain rates. The contribution of AH36 carbon steel layer on total stress is relatively more than that of 2205 stainless steel layer at high temperatures, as a result of the occurrence of stress partitioning. The proposed constitutive model, instead of the mixture law, is recommended to be used in the FE simulation of practical hot working of bimetal composite due to its high accuracy. [ABSTRACT FROM AUTHOR]

• The proposed approach can directly connect the microstructure with FLC. • The newly proposed method can determine the constitutive model of the constituent phase. • f 0 of the M-K model should not relate to the roughness of sheets. • The FLC on the left-hand side is overestimated based on the Nakajima simulation without damage model. A multiscale approach was proposed to predict the macroscopic forming limit of Q&P980 steel. The microstructure-based simulation was implemented in the microscopic simulation to obtain the macroscopic stress-strain curve. The representative volume element (RVE) was established using the data extracted from the characterised results of electron back-scattered diffraction (EBSD). The microscopic constitutive model of each constituent phase was determined based on a new method. The acquired macroscopic stress-strain curve was extrapolated using the modified Power-Law (MPL) strain hardening model. In the macroscopic simulation, the Nakajima and Marciniak-Kuczynski (M-K) simulations were combined to obtain the macroscopic forming limit only based on the macroscopic stress-strain curve. The microscopic and macroscopic simulations show good agreement with the experiment results, verifying the multiscale approach's accuracy. This study provides a solution for the direct connection between the microstructure and macroscopic forming limit. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Copper (Cu) foils are extensively used in the electronics industry owing to their excellent electrical conductivity and high flexibility. In the present study, Cu foils with a thickness of 100 µm were annealed at 700 °C for 3, 6, 30 and 60 min to obtain different grain sizes. The edge cracking of Cu foils in micro rolling was systematically investigated, and the mechanism involved was discussed combining the effects of grain size and tensile properties. The results of tensile tests show that the tensile curves become increasingly discrete with the increase of grain size. Both the fracture stress and the fracture strain decrease, and the scatter of stress increases with the coarsening of grains. The tensile fracture surfaces of the specimens with grain sizes of 19 and 23 µm contain very few micro-dimples, while no micro-dimples are formed on the fracture surfaces of the tensile tested specimens with grain sizes of 33 and 43 µm. The results of micro rolling tests show that edge cracking does not generate in the specimens with grain sizes of 19 and 23 µm after micro rolling. However, the edge becomes increasingly wavy with the increase of grain size and rolling reduction. When the grain size is increased to 33 µm or greater, significant edge cracking occurs under all the rolling reductions of 30%, 51% and 70%. Grain size has a significant effect on the edge cracking of Cu foils in micro rolling, which evolves based on the ductile fracture mechanism. [ABSTRACT FROM AUTHOR]

Abstract The microstructure and texture after plastic deformation are strongly dependent on the corresponding manufacturing process and subsequent annealing which significantly affect the properties of the final products. In this study, 1060 aluminium alloy with a thickness of 464 μm was micro flexibly rolled to a constant thickness ratio of 3.6 by a combined control of the roll gap, the rolling speed and the roll lifting speed. Afterwards, the rolled specimens were subjected to isochronal annealing at a temperature range of 200 to 400 °C for 30 min and isothermal annealing at 400 °C for 10–60 min. Results indicate that the microstructure, microhardness and texture of each thickness zone are distinctly influenced by the rolling parameters and annealing conditions. Specimens annealed at 400 °C for 30 min result in a relatively steady hardness distribution along the transition zones. Typical β fibre texture is observed in the specimens suffered from annealing while S is predominant in both micro flexibly rolled and annealed specimens. Highlights • Inhomogeneous behaviour of aluminium alloy after micro flexible rolling and annealing • Microstructure and texture evolution along the varying thickness zones of micro flexibly rolled strips • The mechanics based on the special deformation features was proposed. • Isothermal and isochronal annealing on the recrystallised characteristics of thin varying thickness strips [ABSTRACT FROM AUTHOR]

In this study, the micro deep drawing (MDD) experiments of an austenitic stainless steel with 40 μm in thickness were conducted using the lubricants containing different mass fractions of graphene nanosheets (GNS) in ethanol. Prior to the MDD tests, the lubricants with GNS concentrations of 5, 10, and 15 mg/ml were synthesised by mixing different amounts of GNS with pure ethanol, and then sprayed uniformly on the blank surface. The friction-reduction mechanisms of the GNS in the MDD were discussed by analysing the profile and surface roughness of the microcups. The results indicated that the GNS could reduce the friction and improve the surface quality of the micro products during the MDD process. In particular, the lubricant with 10 mg/ml GNS enabled the lowest drawing force, wrinkling, and surface roughness of the drawn microcup. These findings contribute to a better understanding of the friction-reduction mechanisms of using GNS in the MDD of materials. • The coating behaviour of the graphene lubricants are compared. • The role of graphene lubricant in micro deep drawing is shown to be important in reducing the friction. • The effect of utilising graphene lubricants for improving the quality of the micro cups is demonstrated. [ABSTRACT FROM AUTHOR]

Manufacturing metallic micro channels is a critical issue in micro-electromechanical systems (MEMS), such as micro reactors, micro heat exchangers, micro heat sinks, and fuel cell bipolar plates. An ultra-thin metal foil rolling for the fabrication of micro composite channels was proposed in this study, which is able to improve product functions and reduce operational costs. Copper/SS304L composite foils after annealing at 900 °C were used to form micro channels under different rolling reductions (29.1%, 43.8% and 50.0%), in which the thickness of copper and SS304L are 0.3 mm and 0.1 mm, respectively. Accordingly, the microstructure evolution, material deformation behaviours and mechanical properties of the samples after micro rolling were investigated. From the characterisation of the micro channel region on the copper side, a double fibre texture is produced parallel to the rolling reduction, including a relatively strong <111> fibre and a weak <100> fibre. Moreover, a relatively strong <111> fibre and three weak <100>, <110> and α fibres along the rolling direction can be identified on the SS304L side. The hardness of copper and SS304L increases with the increase of rolling reduction, due to the strain-hardening effect for copper, and accumulated dislocation and formation of strain-induced α' martensite for SS304L during micro rolling, respectively. It is noted that in the ridge region for all the samples, the left fillet is harder compared to the right fillet, indicating the asymmetry of material flow. • Cu/SS304L composite micro channels were fabricated with various rolling reductions. • Stretched Cu grain and refined Fe grain are obtained as rolling reduction increases. • Strong <111> fibre is identified on Cu and SS304L of micro channels along RD. • The strain-induced α′ martensite was formed in SS304L after micro rolling. • Hardness of copper and SS304L increases with the increase of rolling reduction. [ABSTRACT FROM AUTHOR]

Al-10.0 vol% (TiC and GNPs) composites were fabricated with different volume ratios of TiC and GNPs from 10.0:0.0–8.0:2.0 by powder metallurgy. The results show particle free zones (PFZs) in as-sintered composites decrease and distributions of reinforcements become more uniform, and the hardness and wear resistance of hybrid composite increase as TiC-to-GNPs ratio decreases. Al-8.5 vol% TiC-1.5 vol% GNPs has the highest hardness at 200.5 HV and the best wear resistance with a wear rate of 4.99 × 10−4 mm3/Nm based on the collaborative effects of TiC and GNPs, respectively. However, as the GNPs fraction increases to 2.0 vol%, the hardness and wear resistance of the composite drop drastically because of GNPs agglomeration. [ABSTRACT FROM AUTHOR]

Different annealing treatments at 400-900 °C for 1 h were applied on copper/SS304L composite sheets, and the evolutions of microstructure and mechanical properties were investigated in this study. It is found that the diffusion distance of the elements at the interface is slightly increased with the increasing temperature. In addition, the grain coarsening in copper, the phase transformation from BCC to FCC in SS304L, and the decreased dislocation density after annealing soften the composite sheets, leading to decreased hardness and strength, as well as significantly improved ductility, especially when the temperature exceeds 500 °C. • Different heat treatments at 400–900 °C were applied on Cu/SS304L composite sheets. • Diffusion at the interfaces is promoted with the increase of annealing temperature. • Microstructure transforms from BCC to FCC in the SS304L sides after annealing. • Microhardness of the composites decreases as annealing temperature increases. • The strength decreases and the ductility increases as temperature exceeds 500 °C. [ABSTRACT FROM AUTHOR]

A method is proposed to determine the accurate constitutive model of individual phase in multiphase steel with small phase size. The nanoindentation tests with continuous stiffness method (CSM) were implemented to obtain the hardness-displacement curves of the advanced high strength steel DP1180. The validity of the nanoindentation results was evaluated based on the EBSD results and classic indentation size effect (ISE) model. The extra loading of loading-displacement curves due to geometrically necessary dislocations (GNDs) was excluded based on the simple established model. The constitutive model of each phase was determined based on the corrected loading-displacement curves using the inversion method. The results of microstructure based simulation agree well with those of tensile tests, which proves the reliability and accuracy of the constitutive model of individual phase obtained from the method proposed in this study. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel designed austenitising bending process was realised on a thermomechanical simulator. • Integrated effects of SNL, martensite packet, PA grain, DRV and DRX were responsible for the strength gradient. • Parent grain reconstruction and martensite variants can be achieved a more effective technique. • The high consistency between simulation and experiments means valuable reference of the current study to simulate rail clip forming process. A systematic study was carried out on a novel designed austenitising bending process to explore the effects of quenching temperatures on the evolution of microstructure and mechanical properties of high-strength micro-alloyed steel. Results reveal that the qualified parts could be bent into a satisfactory shape without spring-back and cracks in bending temperatures of 850–1000 °C. The simulation was applied to predict the equivalent stress, stress neutral layer (SNL) and plate thickness. Strength presents a decreasing trend with the increase of bending temperature owing to integrated influences of high-temperature dynamic recovery (DRV) and dynamic recrystallisation (DRX). Beyond that, SNL nearby the geometrical centre line throughout the plate thickness and dislocation pile-ups on the tension/compression zones are responsible for the smaller hardness on middle regions while higher hardness on the surface areas. Through austenite reconstruction, a smaller martensite packet size would directly improve the strength of the plates bent at a lower temperature. The prior austenite size may be related to the appearance of martensite variants but not necessary. Furthermore, the high accuracy by comparing the experimental results with simulation would provide a high-value reference for the practical manufacturing process of railway spring clips. [ABSTRACT FROM AUTHOR]

[Display omitted] • An austenitising bending process was conducted on the thermomechanical simulator. • Work hardening was enhanced on thickness edge positions due to dislocation. • Finer prior austenite grains at edge position led to the improvement of hardness. • The numerical simulation was verified in good agreement with experimental results. The austenitising bending process was conducted on a medium-carbon micro-alloyed steel by Gleeble 3500 thermomechanical simulator to comparatively investigate the microstructural and mechanical evolution through thickness of the bent plate. A combination of bainite ferrite, lath martensite and acicular ferrite with a presence of partial dynamic recrystallisation was the main microstructural features. The increased work hardening in the compressive and tension zones after austenitising bending operation can be ascribed to synergistic effects of dislocation pile-up/cells, and finer prior austenite grains. Also, the reliability of this study was verified from the consistency between the results of simulation and experiment, which would provide a valuable reference for the practical manufacturing technology of railway spring clips. [ABSTRACT FROM AUTHOR]

Micro-hydromechanical deep drawing (MHDD) is a promising micro-manufacturing technology to fabricate micro-metallic products in batch scale. Size effects significantly affect MHDD regarding both material properties and friction. Hydraulic pressure on the blank and its development differ from that in conventional hydromechanical deep drawing. Combined influence of fluid pressure, surface roughness and material inhomogeneity of the blank was investigated in this study via MHDD experiments and advanced FE simulation considering strong fluid-solid interaction (FSI) and size effects. The MHDD experiments under different hydraulic pressures were conducted using the annealed foil followed by the advanced FE simulation. The foil can be successfully drawn into micro-cups, however, wrinkles occurred under high hydraulic pressures. Wrinkle height and number are affected by hydraulic pressure and size effects. Average hydraulic pressure on the blank is lower than the inlet pressure, and pressure development on the blank depends on location and is complex, due to transition of sealing between the blank and die. The maximum drawing force increases, while the contact forces and pressures on the blank holder and die decrease with an increase of hydraulic pressure. Optimal hydraulic pressure for MHDD should be determined with consideration of size effects and MHDD tool geometry. • Micro-hydromechanical deep drawing experiments and advanced simulation with consideration of FSI, material surface morphology and inhomogeneity were conducted. • Change of the sealing between the blank and die significantly affects mean and local hydraulic pressure development on the blank, which further impacts MHDD. • Hydraulic pressure reduces contact forces and maximum contact pressures on both blank holder and die, which benefits wear behaviour of MHDD tools. • Integrated effect of hydraulic pressure and size effects influences wrinkling. • Optimal hydraulic pressure should be determined with consideration of foil's properties and MHDD tool geometry. [ABSTRACT FROM AUTHOR]

To comprehend the role of water-based nanolubricant in micro flexible rolling, corresponding characterisation with respect to different concentrations of nanolubricants, surface roughness variation subjected to each micro flexible rolling phase and dispersion of nanoparticles (NPs) were studied systematically. The results reveal that increasing NPs get trapped into the surfaces from the thicker zone to the thinner zone. Downward transition zone with favourable deformation features leads to the smoother surface roughness. Nanolubricants can effectively decrease rolling traces due to the beneficial nanolubrication mechanisms. Notably, the maximum reduction for rolling force is around 18% for the case under 2.0 wt% nanolubricant rolling condition. The current study provides great potential insights in how nanolubrication takes effect in microforming areas. • Water-based nanolubricants distinctly reduce the rolling forces during micro flexible rolling. • Increasing NPs get trapped into the surfaces from the thicker zone to the thinner zone. • Downward transition zone with favourable deformation features leads to the smoother surface roughness. • More remained NPs are detected near the middle area along the transverse direction of the specimen. • Water-based nanolubricants can effectively decrease rolling traces due to the beneficial nanolubrication mechanisms. [ABSTRACT FROM AUTHOR]