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Despite being strong with many outstanding physical properties, tungsten is inherently brittle at room temperature, restricting its structural and functional applications at small scales. Here, a facile strategy has been adopted, to introduce high-density dislocations while reducing grain boundaries, through electron backscatter diffraction (EBSD)-guided microfabrication of cold-drawn bulk tungsten wires. The designed tungsten microwire attains an ultralarge uniform tensile elongation of ~10.6%, while retains a high yield strength of ~2.4 GPa. in situ TEM tensile testing reveals that the large uniform elongation of tungsten microwires originates from the motion of pre-existing high-density dislocations, while the subsequent ductile fracture is attributed to crack-tip plasticity and the inhibition of grain boundary cracking. This work demonstrates the application potential of tungsten microcomponents with superior ductility and workability for micro/nanoscale mechanical, electronic, and energy systems.

A series of sandwich hybrid metal (steel, aluminum) + carbon, glass fiber reinforcement plastic composite (CFRP, GFRP) + metal composite sheet was developed to achieve the lightweight design purpose. It was found that the CFPR and GFRP played an important role in reducing the density of the composite sheet up to 30%, as well as maximum 30% improvement of the specific strength. The bridging mechanism found in development of hybrid sheet attributed from CF and GF delayed the composite sheet fracture, which shall improve the safety for automotive components. This result offers new insights on design and processing of metal + fiber reinforcement plastic composite sheet for lightweight design. The developed sandwich hybrid sheet with metallic sheet surface and plastic/composite sheet mid-layer to provide lightweight application.

Flexible transparent conductive films are indispensable for nowadays wearable electronic devices with various applications. However, existing solutions such as ITO and metal mesh were limited by their poor intrinsic stretching ability. In this work, we designed and fabricated silver nanowires (AgNWs) on graphene hybrid films for enhanced mechanical and electrical performance. In situ TEM characterizations show that, beside conductive paths, silver nanowire network, can also contribute to the toughening mechanisms of the hybrid films. Furthermore, bending and electrical tests were applied to examine the corresponding flexible electronics’ performance. Finally, we showed that the fabrication of our AgNW/graphene hybrid films could be scaled up for large film applications and extended to other 1D/2D hybrid systems.

In this study, the work-hardening behavior of Ag microwires with different grain sizes has been investigated, and the results show that the work-hardening rate of Ag microwires does not decrease with the increase of grain size, suggesting that the work-hardening capacity of Ag microwires is insensitive to grain size. Moreover, the microstructure evolution of the samples before and after tensile tests has been characterized using scanning electron microscope-backscattered electron (SEM-BSE), electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). As a typical low stacking faults energy (SFE) material, stacking faults and twins are particularly easy to form in Ag microwires. Abundant stacking faults and twins, as well as minor lattice orientation adjustment in Ag microwires were observed and confirmed to play key roles on their grain-size insensitive work-hardening capacity. The current study provides insights for manufacturing Ag microwires for bonding process and other microelectronics applications.

Because of their high strength and oxidation resistance as well as low cost, Cu micro bonding wires have received increased interests in microelectronic packaging industry. The present work revealed that the coating boundary provided additional strength improvement by blocking dislocation gliding. Furthermore, the greater strain concentration along slip bands introduced larger cracks within the Pd coating layer with coarser grains. The present study provides insights for reliable Pd-coated Cu micro bonding wire processing and bonding applications.

Hall-Petch relation was widely applied to evaluate the grain size effect on mechanical properties of metallic material. However, the sample size effect on the Hall-Petch relation was always ignored. In the present study, the mechanical test and microstructure observation were performed to investigate the combined effects of grain and sample sizes on the deformation behaviors of gold microwires. The polycrystalline gold microwires with diameter of 16 μm were annealed at temperatures from 100 °C to 600 °C, leading to different ratios (t/d) of wire diameter (t) to grain size (d) from 0.9 to 16.7. When the t/d was lower than 10, the yield stress dropped fast and deviated from the Hall-Petch relation. The free-surface grains played key role in the yield stress softening, and the volume fraction of free-surface grains increased with the t/d decreasing. Furthermore, the effects of t/d on work-hardening behaviors and fracture modes were also studied. With t/d value decreasing from 17 to 3.4, the samples exhibited necking fracture and the dislocation pile-ups induced work-hardening stage was gradually activated. With the t/d value further decreasing (t/d 3.4), the fracture mode turned into shear failure, and the work-hardening capability lost. As the gold microwire for wire bonding is commonly applied in the packaging of integrated circuit chips, and the fabrication of microwire suffers multi-pass cold-drawing and annealing treatments to control the grain size. The present study could provide instructive suggestion for gold microwire fabrication and bonding processes.

Au–Al intermetallic compounds (IMCs) were conventionally regarded as damage sources within wire bonding interfaces. Among the Au–Al IMCs system, Au2Al and AuAl2 IMCs were commonly observed after long-term service. Here, the intrinsic mechanical properties of Au2Al and AuAl2 IMCs were investigated by in-situ bending tests. The results clearly revealed that the transition from brittle to ductile facture behavior was determined by the atomic ratio of Au and Al elements, while Al-rich Au–Al IMC exhibits higher bending strength than that of Au-rich Au–Al IMC. The Al-rich Au–Al IMC such as AuAl2 indeed showed brittle fracture behavior, in which cracks propagated through the grain boundaries. In contrast, the Au-rich Au–Al IMC such as Au2Al appeared to be quite ductile and crack resistant, and its plastic deformation was undertaken by slip bands. This work suggested that not all Au–Al IMCs cause brittleness and lead to damages, only Al-rich IMCs should be avoided at wire bonding interfaces.

Three kinds of Fe–22Mn–0.6C–(x)Al (wt%) Twinning-Induced Plasticity (TWIP) steels were designed by changing the Al content. Uniaxial, unloading-reloading and stress-relaxation tensile tests were carried out to evaluate the mechanical properties. Meanwhile, electron channeling contrast imaging (ECCI), transmission electron microscopy (TEM) and X-ray tomography (XRT) techniques were used to investigate the microstructure evolutions. Firstly, it was found that the Al addition reduced the back stress level, suppressed twinning capability, and increased the stacking fault energy (SFE), leading to concession of work-hardening rates. Secondary, the Al addition improved the friction stress level and promoted the short-rang order (SRO) effect, which brought the transformation of dislocation slip from wavy to planar mode. Last but not least, the dynamic strain aging (DSA) effect brought the pinning of dislocations, forming high dislocation activation volume (> 100 b3). With increasing plastic strain, the deformation twins and SRO effect restricted dislocations gliding, resulting in low dislocation activation volume (

Tensile tests and microstructure observations were conducted for two types of twinning-induced plasticity steels, Fe-22Mn-0.6C and Fe-30Mn-3Si-3Al (wt pct), from 293 K to 443 K. With increasing temperature, Fe-22Mn-0.6C steel exhibited enhanced mechanical properties and stable twinning capability, but Fe-30Mn-3Si-3Al steel displayed a decline on its mechanical properties and twinning capability. Mechanisms for the different mechanical responses were analyzed by assessing the dynamic strain aging effect.

The effect of nitrogen addition on the mechanical properties of Fe–22Mn–0.6C (wt%) twinning-induced plasticity steel was studied. It was found that the stacking fault energies of the two steels were comparable, and the twinned grain fractions of FeMnC and FeMnC-N steels were similar before the true strain of 0.5. With increasing the strain to 0.7, the fraction of secondary twinned grain rose to support the further strong work-hardening rate of FeMnC-N steel. Moreover, the nitrogen addition suppressed the dynamic strain aging, which can trigger early shear fracture in FeMnC steel. Therefore, the work-hardening rate was kept increasing and the frequency of plastic instability was suppressed by nitrogen addition. As a result, the ultimate tensile strength and uniform elongation simultaneously increased in FeMnC-N steel.

Tensile tests were carried out to investigate the differences in fracture mechanisms between Fe-22Mn-0.6C and Fe-30Mn-3Si-3Al (wt pct) twinning-induced plasticity steels. Although both steels possess a strong twinning capability during tensile deformation, they display different tensile fracture modes of shear and necking. The Portevin–le Chatelier band is proposed as the key factor influencing the different fracture mechanisms.

In this study, it is found that the high-manganese austenitic FeMnC twinning-induced plasticity (TWIP) steel exhibits negative strain rate sensitivity (SRS), which is contrary to other face-centered cubic (fcc) metals or alloys. The negative SRS phenomenon of Fe-22Mn-0.6C (wt%) TWIP steel is considered to be suppressed or even convert to be positive through adding Al element. Meanwhile, the relation between tensile strength and uniform elongation of the FeMnC(Al) TWIP steels displays a transition from trade-off to synchronously improvement with decreasing the strain rate and Al content. It is suggested that the negative SRS phenomenon of FeMnC TWIP steel can be mainly attributed to the twinning mechanism assisted by dynamic strain aging (DSA). This mechanism can also explain well the negative to positive transition of SRS in FeMnC(Al) TWIP steel with the addition of Al element.

A fully recrystallized ultrafine-grained (UFG) Fe 22wt.%Mn 0.6wt.%C twinning-induced plasticity (TWIP) steel with mean grain size of 576 nm was fabricated by cold rolling and annealing process. Tensile test showed that this UFG steel possessed high yield strength of 785 MPa, and unprecedented uniform elongation of 48%. The Hall-Petch relationship was verified from the coarse-grained (CG) regime to the ultrafine-grained (UFG) regime. The microstructures at specified tensile strains were characterized by electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The microstructures and strain hardening behavior of the UFG TWIP steel were compared with the CG counterpart. The strong strain hardening capability of the UFG steel is supposed to be responsible for the high strength and good ductility.

The strain rate sensitivity (SRS) of Fe–22Mn–0.6C and Fe–30Mn–3Si–3Al twinning-induced plasticity (TWIP) steel was studied in the strain rate range from 10 −4 to 10 °s −1 . The Fe–22Mn–0.6C steel exhibited negative SRS, while the Fe–30Mn–3Si–3Al steel showed positive SRS. Dynamic strain aging (DSA) was detected in Fe–22Mn–0.6C steel but not in Fe–30Mn–3Si–3Al steel. Accordingly, the two typical TWIP steels can be classified as DSA-facilitated and DSA-free TWIP steels. Meanwhile, the density of twin boundary obviously decreased in Fe–22Mn–0.6C steel but had little change in Fe–30Mn–3Si–3Al steel with increasing the strain rate. The different SRS phenomena were discussed based on the twinning mechanism and DSA effect.

For Fe–22Mn–0.6C (wt%) twinning-induced plasticity (TWIP) steel with grain sizes of 35 and 170 μm, both the ultimate tensile strength and uniform elongation decrease with increasing the tensile strain rates (from 10 −4 to 10 0 s −1 ). The density of twin boundary (DTB) is presumed to be the major factor influencing mechanical properties. Accordingly, a parameter 2/( t + s ) ( t and s represent the thickness and spacing of deformation twins), also the inverse of the mean free path for dislocation slip, is proposed to characterize the planar-oriented twinned structure in infinite grain size ( D » t ≈ s ). It also evaluates the effect of DTB on the work hardening ability and ductility of the TWIP steel.

In this study, the effect of strain rate on the tensile deformation behavior of Fe–22Mn–0.6C–(1.5Al) (wt%) twinning-induced plasticity (TWIP) steel was investigated. The experimental results indicated that the work hardening exponent (n), ultimate tensile strength (σu) and the uniform elongation (δu) decreased with increasing strain rates (from 10−4 to 100 s−1). This phenomenon exhibited negative strain rate sensitivity (NSRS), and the strain rate sensitivity value (m) was observed to be higher in the aluminum added FeMnC TWIP steel. In order to gain an in-depth understanding of this sensitivity and the subsequent effect of aluminum, the present research focused on the deformation twins and conducted comparative studies on their influence in terms of fractions (F), thickness (t) and spacing (s). Additionally, a twin boundary affected zone (TBAZ) model was proposed, where the relation between higher strain rates were directly applicable to the reduction of interfaces between the matrix and deformation twins. These result indicated that fewer sessile dislocations could be accommodated at high strain rates, thus weakening the work hardening ability. Finally, model calculations were performed to validate the findings, where TBAZ region fractions in FeMnC–Al were observed to be higher than that in FeMnC, corresponding to the increased strain rate sensitivity.

The Au–Al intermetallic compounds (IMCs) were commonly regarded as brittle within wire bonding interfaces. Here the in-situ micro-pillar compression tests of Au4Al IMCs were carried out to verify their intrinsic mechanical property. The result clearly shows that, surprisingly, the Au4Al IMC is ductile, while the yield stress appeared to be about 1 GPa. Furthermore, upon the compression tests of Au4Al IMC micro-pillars with initial crack, no brittle fracture was observed; instead, the plastic deformation of Au4Al was shown via shear band. This work suggests that pristine Au4Al IMC is ductile and crack-resistant, which provides new insights for wire bonding process and technology.

International audience; Fatigue crack growth tests with R=0 and 0.4 were carried out on Fe-22Mn-0.6C and Fe-22Mn-0.6C-3Al (wt. %) Twinning-Induced Plasticity (TWIP) steels with stacking fault energies around 21.5 and 37 mJ/m2, respectively. The former exhibits more crack closure effects, partly due to stronger asperity-induced closure. Strain-controlled push-pull tests followed by scanning electron microscope observations show that both steels are prone to mechanical twinning under low-cycle fatigue, associated with an increasing kinematic hardening. Twinning is however more profuse in Fe-22Mn-0.6C steel. Elastic-plastic finite elements simulations of crack growth, using specific constitutive equations able to capture the increasing kinematic hardening suggest that plasticity-induced crack closure is lower in Fe-22Mn-0.6C steel. Even after closure corrections, the Al-free steel, exhibits a lower resistance to fatigue crack growth, which is attributed to a pronounced strain localisation at the crack tip, and maybe also to environment effects.

International audience; In-situ tensile tests were carried out on Fe22Mn0.6C and Fe22Mn0.6C3Al (wt. %) twinning-induced plasticity (TWIP) steels specimens covered with gold micro-grids. High resolution atomic force microscopy (AFM) and scanning electron microscope (SEM) images were periodically captured. The latter were used for measurements of the plastic strain field, using digital image correlation (DIC). Although no meso-scale localization bands appeared, some areas were deformed three times more than average. Plastic deformation inside the grains was more heterogeneous in Fe22Mn0.6C, but at meso-scale, the degree of strain heterogeneity was not higher, at least up to 12% strain. Plastic deformation started from grain boundaries or annealing twin boundaries in both materials, due to a high elastic anisotropy of the grains. An original method based on DIC was developed to estimate the twin fraction in grains that exhibit a single set of slip/twin bands. Deformation twinning accommodated 60 to 80% of the plastic strain in some favourably oriented grains, from the onset of plastic flow in Fe22Mn0.6C, but was not observed in the Al-bearing steel until 12% strain. The back stress was important in both materials, but significantly higher in Fe22Mn0.6C.