Zhenjun Zhang

Chinese Academy of Sciences | CAS · Materials Fatigue and Fracture Division

The effect of anisotropy on high‐cycle fatigue (HCF) property along the rolling direction (RD) and the transverse direction (TD) of a 7××× aluminum alloy super thick plate is mainly investigated in this study. The results show a similar microstructure at different thicknesses, and the HCF properties are close as well. The fatigue fracture morpholog...

Surface mechanical strengthening is an effective way to improve the fatigue performance, among which surface rolling has been vastly utilized for its significant enhancement in fatigue strength. However, traditional rolling process is only suitable for components with rotational symmetry, limiting its application. Herein, a newly developed technolo...

The advantage of 3D printing—that is, additive manufacturing (AM) of structural materials—has been severely compromised by their disappointing fatigue properties1,2. Commonly, poor fatigue properties appear to result from the presence of microvoids induced by current printing process procedures3,4. Accordingly, the question that we pose is whether...

The trade‐off relation between strength and plasticity is the bottleneck that limits the development of high‐strength and high‐plasticity Al–Cu alloys. Inspired from the influence of precipitate shape on the work‐hardening behavior of Al–Cu alloys, an Al–Cu–Zr–Sc alloy containing a mixed microstructure of spherical‐shaped Al3(Zr, Sc) phases and dis...

To investigate the fatigue crack propagation (FCP) behaviors of high‐strength 7075 and 2024 Al alloys, FCP experiments are conducted for the two alloys at different aging states (underaged [UA], peak aging, and overaged). It is found that strength and plasticity are the main factors influencing the FCP. For 7075 Al alloy, the FCP curves almost coin...

Herein, the effect of the aging state on the impact toughness of three typical wrought Al alloys (7075, 2024, and 6A01) is investigated. At room temperature, the fracture mode of the three aluminum alloys at different aging states is a ductile transgranular fracture. At low temperatures, high‐strength aluminum alloys exhibit a mixture fracture of t...

It remains an intricate problem how to enhance low-cycle fatigue (LCF) performance, in the premise of guaranteeing a relatively high strength (or cyclic stress) which is vital to long-time service, for engineering components. The underlying cause of this puzzle is the lack of practical theory on cracking evolution/life prediction for LCF. In this s...

In order to reveal the effects of cryogenic temperature on the relationship between mechanical properties and recrystallization percentage, the tensile mechanical behaviors of partial recrystallized copper have been investigated by tensile test at 293 K and 77 K, respectively. It is found the yield strength of copper maintains approximate linearity...

The development of multi-principal element alloys (MPEAs, also called as high- or medium-entropy alloys, HEAs/MEAs) provides tremendous possibilities for materials innovation. However, designing MPEAs with desirable mechanical properties confronts great challenges due to their vast composition space. In this work, we provide an essential criterion...

During the selective laser melting (SLM) process of Ti6Al4V, a special structure can be formed with columnar prior β grains along the building direction and fully martensitic α′ within the β grain. To investigate the influence of such special structure on the fatigue crack growth (FCG) rate, Ti6Al4V specimens fabricated by SLM were heat‐treated at...

The Al–Mg–Si alloy wire for overhead transmission line is in thermal service due to the interaction between electric current and microstructure during power transmission, which could affect its microstructure and properties. At present, researchers generally use the traditional annealed-heated (A-H) treatment to simulate the thermal service state o...

The mechanical properties and tensile deformation mechanism of Ti-6.5Al-3.5Mo-1.5Zr-0.25Si alloy (TC11) with different percentages of primary α phase (αp) were studied by conventional and interrupted tensile tests, respectively. The results show that the strength of TC11 alloy increases with the increase of the percentage of αp. During tensile defo...

The high‐cycle fatigue (HCF) experiments were carried out for different aging states to study the effects of the aging state and yield strength on the fatigue properties of a 6A01 Al alloy. The results show that the 6A01 Al alloy with the highest yield strength at a peak‐aging (PA) state can exhibit the highest fatigue strength in comparison with t...

The corrosion fatigue performance of Al alloy components is crucial for their engineering applications. This study focuses on the corrosion fatigue properties of 7075 Al alloys in three different aging states, i.e. over-aging (OA), peak-aging (PA) and under-aging (UA) states. The results show that the fatigue damage mechanism of the Al alloy is gre...

Prior β grain evolution and phase transformation of selective laser melted (SLM) Ti6Al4V alloy after subtransus and supertransus solution heat treatments are investigated. A method based on the special angle grain boundaries (in the range of 15-55° and 70-85°) is proposed for a clear and straightforward description of the prior β mesostructure. Pos...

An exponential strain-hardening (ESH) model for single phase metals was established and well verified by systematic experiments on Cu-Al alloys in an earlier study. In this report, several additional significant revelations will be documented for the tensile behaviors of several typical metals. Firstly, a unified interpretation of the well-known fi...

A simple exponential strain hardening model (ESH) has been developed in the framework of the Kocks-Mecking-Estrin formalism with a new microstructure based parameter that accounts for the effect of yield strength. The relevant parameters reflecting the effect of the composition (or dislocation annihilation distance) and the microstructure type (or...

The presence of a gradient layer with an increased maximum microhardness and extended thickness is extremely attractive because it can enhance the service performances for surface-strengthened metallic materials. In this research, Cu-Al alloys with different Al contents and microstructures were processed by surface spinning strengthening (3S) and s...

The gradient layer induced by surface mechanical strengthening attracts plenty of attention as it can effectively improve the service performance of metallic materials, but how to design a suitable gradient layer and evaluate gradient layer properties need to be investigated further. In this work, the 316 stainless steel and TC4 alloy processed by...

The evolution of the core structure and the cross-slip behavior of a screw [1 1 1] superdislocation are investigated by molecular dynamics simulations at external pressures and shear stresses in FeAl with the B2 structure. The result reveals that the transformation between different core configurations generally determines the cross-slip behavior o...

The effects of pressure on the generalized stacking fault energies (GSFE), core structure of dissociated dislocation, twinning propensity and phase stability are comprehensively investigated by molecular statics simulations and first principles calculations in three typical face-centered cubic (FCC) metals, Cu, Ag and the equiatomic CoCrFeMnNi high...

Mechanical properties of Cu-5at.%Al alloy with different recrystallization fractions ranging from 0% to 100% are studied by tensile tests at 77 K and 293 K, respectively. The relationship between uniform elongation and recrystallization fraction had been unveiled. The uniform elongation and recrystallization fraction have a transition from single-s...

A <110 > /2 screw dislocation is commonly dissociated into two <112 > /6 Shockley partial dislocations on {111} planes in face-centered cubic metals. As the two partials are not purely screw, different mechanisms of cross-slip could take place, depending on the stacking fault energy, applied stress and temperature. It is crucial to classify the mec...

The variation of stacking fault energy (SFE) in a number of binary Cu alloys is predicted through considering the Suzuki segregation by the full potential linearly augmented plane wave (FPLAPW) method. The calculated results show that some solute atoms (Mg, Al, Si, Zn, Ga, Ge, Cd, Sn, and Pb), which prefer to form the Suzuki segregation, may decrea...

Dislocation-dislocation interaction plays important roles in the strain hardening of crystalline materials. In this work, Molecular statics (MS) and dynamics (MD) simulations have been carried out to investigate the interaction of a screw-screw model which contains two non-parallel, non-coplanar 1/2<111> screw dislocations in niobium single crystal...

The {110} hexagonal dislocation networks (HDNs) act as important carriers of the low-temperature plastic deformation in the body-centered-cubic (BCC) metals. Erenow, only a handful of studies have been performed on the yield behaviors of this planar networks, resulting in it being perplexing. In this letter, by three types of loading modes, the gen...

The core structure and the mobility of [111] screw superdislocations are investigated under hydrostatic pressures by comprehensive atomic simulations in B2–FeAl. The pressure dependence of elastic constants and lattice parameter of FeAl is also revealed. The result indicates that the [111] screw superdislocation dissociates on the (1-10) plane unde...

Although coherency dislocation has been proposed for several decades, it is not yet accepted or even well known in the previous studies about grain boundaries. Here direct atomistic simulations are specially designed to prove the existence of coherency dislocations in grain boundaries. Our data show that coherency dislocations possess their own dis...

Excellent strength and electrical conductivity are of great significance for Al wires applied to overhead transmission lines, since the strength and the electrical conductivity are mutually exclusive. In this paper, the strength-electrical conductivity relation of an Al-1.13 wt% Fe wire fabricated by cold drawing process was investigated by means o...

The core structures, planar faults, and mobility associated with [111] screw superdislocations are systematically investigated by atomistic simulations using six different EAM potentials in FeAl. The results demonstrate that the core structures of [111] screw superdislocations transfer from twofold into triple configurations, and the planar faults...

In this work, the tensile and bending yield strengths of 304 stainless steel and H62 brass are effectively enhanced by surface spinning strengthening (3S) that can introduce a strengthening layer with gradient microstructure on the samples. The results show that the two metals exhibit distinct grain refinement in the top layer as well as severe gra...

Surface decarburization directly influences the service performance of spring steel, which is an important scientific issue. The bending fatigue behavior of 50CrMnMoVNb spring steel with surface decarburization as well as treated by surface spinning strengthening (3S) was systematically investigated in this study. The results show that the decarbur...

The strengthening mechanisms and the strength degradation behaviors of the high-strength Al–Fe wire were investigated in this study. The dispersed nano-scale precipitates, the <111> texture and the fine grains in the radial section of the Al–Fe wire are the three main strengthening factors, i.e., precipitation strengthening, texture strengthening a...

The trade-off relation between the strength and the electrical conductivity has been a long-standing dilemma in metallic materials. In the study, three key principles, i.e. elongated grains, sharp texture and nano-scale precipitates, were presented for preparing Al wire with high strength and high electrical conductivity based on the specially desi...

Two Fleischer cross slip modes of a dissociated screw dislocation 〈1 1 0〉/2 are quantitatively investigated in silver by molecular dynamics simulations. It is shown that contrary to previous studies where the acute angle mode is always preferred, the obtuse angle mode is also obtained. Our theoretical analysis demonstrates that the transition of th...

The trade-off relation between the strength and electrical conductivity in the Al conductor is a significant scientific issue. Breaking such trade-off relation is an interesting challenge for preparing the Al conductor with high strength and good electrical conductivity. In this study, an abnormal strength-electrical conductivity relation was achie...

Surface strengthening is an important method which can effectively improve the fatigue property of metallic materials. In order to improve the fatigue property, for the first time, a new developed surface spinning strengthening-II (3S-II) method and the traditional shot peening (SP) treatment were applied to modify the microstructure and fatigue pe...

The surface strengthening behaviors of cold-rolled (CR) Cu, fully recrystallized (FR) Cu and partially recrystallized (PR) Cu with heterogeneous microstructures were investigated by using the surface spinning strengthening (3S) method. It was found that the heterogeneous microstructure significantly affects surface strengthening behaviors as the fi...

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 it...

Enhancing strength-ductility synergy of materials has always been a hot but difficult topic in material science, for most structural materials, steels in particular, it is inevitable to sacrifice ductility when increasing strength, and vice versa. In this study, by introducing a linear gradient in grain size into Fe-Mn-C twinning-induced plasticity...

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,...

As a significant scientific problem directly impacting on the long-term safety of engineering materials and facilities, the improvement of fatigue strength under fully-reversed cycling was comprehensively explored in this study. Advantageous material characteristics for the improvement of fatigue strength were summarized from the achievements of th...

The tensile, high-cycle fatigue (HCF) and fatigue crack growth (FCG) rate tests of Fe-30Mn-0.9C and Fe-30Mn-0.3C twinning-induced plasticity (TWIP) steels were performed. Meanwhile, the corresponding surface damages, fatigue fracture morphologies and microstructure evolutions were also investigated. It is detected that both the fatigue strength and...

It is a great challenge to improve the strength of disc superalloys without great loss of plasticity together since the microstructures benefiting the strength always do not avail the plasticity. Interestingly, this study shows that the trade-off relationship between strength and plasticity can be broken through decreasing stacking fault energy (SF...

A high efficient magnetic levitation melting technique was reported for fabricating bulk equiatomic CoCrFeMnNi high-entropy alloy (HEA) ingot with a diameter of 110 mm. The bulk ingot can be either forged or rolled. In particular, fully recrystallized ultrafine-grained (UFG) HEA with a minimum grain size of 503 ± 181 nm was successfully obtained th...

We report that materials with similar tensile properties can also exhibit quite different low-cycle fatigue (LCF) performances. Experimental results demonstrate that the LCF properties of twinning induced plasticity (TWIP) steels are naturally dominated by microscopic deformation mechanisms (mainly dislocation slip mode), which slightly influences...

Strength degradation during the electron transmission process is always a hidden danger to the overhead transmission lines. In this study, the microstructure evolutions and the strength degradation behaviors of a cold-drawn commercially pure Al conductor (CPAC) were investigated systematically by a series of annealing experiments. The results show...

It is confirmed that the fatigue strength of high-strength metals would not continuously increase as the tensile strength enhances. In order to find out the optimal fatigue strength of maraging steel, the tensile and cyclic pull-push (R = − 1) loading tests of 18Ni maraging steel (250 grade) aged under different conditions were carried out in the p...

Fatigue damage localization is a critical problem which greatly impacts on the fatigue strength improvement. As a main cause of fatigue damage concentration, the microstructure inhomogeneity of cold-rolled and annealed Cu-5at.%Al alloy has been paid much attention in this study. A notable plateau with constant fatigue strength is discovered in the...

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...

In this study, the performance of hot compressive deformation was investigated in two newly developed Ni-Co based superalloys having different stacking fault energy (SFE). It is interesting to discover that nanograins (NGs) can be produced in superalloy deformed at high temperature and relatively low strain rate. With the decrease of SFE and strain...

The evolution of microstructure in the drawing process of commercially pure aluminum wire (CPAW) does not only depend on the nature of materials, but also on the stress profile. In this study, the effect of stress profile on the texture evolution of the CPAW was systematically investigated by combining the numerical simulation and the microstructur...

Outstanding mechanical and conductive properties are vital to Al alloys used as overhead conductors. However, high strength and high electrical conductivity are usually mutually exclusive in metallic materials. In this study, we present a novel method to achieve high strength and high conductivity in an Al-Mg-Si conductor. Numerous dispersive nano-...

Compared to stress controlled high-cycle fatigue, enhancing strain controlled low-cycle fatigue (LCF) properties of material is much more difficult and less reported. In this study, we introduced two strategies and technologies to improve the LCF performance of Fe-Mn-C twinning induced plasticity (TWIP) steel. One is grain refining without introduc...

Based on the models of series and parallel connections of the two phases in a composite, analytic approximations are derived for the elastic constants (Young's modulus, shear modulus, and Poisson's ratio) of elastically isotropic two-phase composites containing second phases of various volume fractions, shapes, and regular distributions. Comparison...

Twin boundaries (TBs) are key factors influencing the mechanical properties of crystalline materials. We have investigated the intrinsic fatigue cracking mechanisms of TBs during the past decade. The effects of TB orientations on the fatigue cracking mechanisms were revealed via cyclic deformation of a series of grown Cu bicrystals with a sole TB....

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-0.6 C (wt.%) TWIP steel is considered to be suppressed or even convert to be posit...

Low-cycle fatigue tests were carried out on ultra-fine grained (UFG) Cu and Cu-Zn alloys to reveal the mechanisms of cyclic softening and the effects of dislocation slip mode. Based on careful examinations of the grain coarsening (GC), shear band (SB) evolutions and surface hardness change during cyclic deformation, the microscopic mechanisms of th...

Cu bicrystals of different sizes with a sole twin boundary (TB) inclined at 45° with respect to the loading direction were deformed under unidirectional and cyclic loading, respectively. It is found that the slip bands (SBs) parallel to the TB can be activated near the TB at all scales without obeying the Schmid’s law. It is concerned with the loca...

Three groups of Cu bicrystals with their component grains sharing one common {111} slip plane were cyclically deformed. By careful design on the loading direction, coplanar slip systems operated in the two component grains. Three kinds of grain boundaries (GBs): a low angle grain boundary (LAGB), a high angle grain boundary (HAGB) and an incoherent...

In this study, a synchronous improvement of the strength and plasticity (SISP) of Ni and Ni-Si alloys was found through introducing supersaturated vacancies into the microstructure. Detailed observations show that these vacancies tended to aggregate to form Frank loops, which impede dislocation annihilation and increase the strain-hardening capabil...

The low-cycle fatigue (including extremely-low-cycle fatigue) behaviors of the Fe[single bond]Mn[single bond]C TWIP steels are comprehensively investigated focusing on the effects of the imposed strain amplitude and Mn content on the deformation and damage characteristics. It is found that fatigue performance varies obviously with increasing Mn con...

It is commonly proposed that the fatigue strength can be enhanced by increasing the tensile strength, but this conclusion needs to be reconsidered according to our study. Here a recrystallized α-Cu-15at.%Al alloy with moderate grain size of 0.62 μm was fabricated by cold rolling and annealing, and this alloy achieved exceptional high fatigue streng...

The microstructure evolution behaviors and corresponding quantitative rules of polycrystalline pure Cu and Cu-Al alloys under cyclic push-pull loading with rather large strain amplitudes (Δε/2=±2%~±9.5%) were systematically investigated. Besides common dislocation structures, deformation twins (DTs), shear bands (SBs) and ultra-fine grains (UFGs) w...

During grain refinement, fatigue strength usually does not increase always simultaneously with tensile strength for a certain material. To optimize the fatigue strength of ultrafine-grained (UFG) materials, systematic studies were carried out on the high-cycle fatigue behaviors of UFG Cu and Cu-Zn alloys. It is found that as the grain size decrease...

Fully recrystallized Cu-4 at.%Al alloy and Cu-11 at.%Al alloy with grain sizes ranging from 0.5 μm to 80 μm were fabricated by cold rolling and annealing. Tensile tests showed that yield strength, ultimate tensile strength and uniform elongation of the two Cu–Al alloys had linear relationships with the inverse square root of the grain size, and bot...

Discovering a generalized criterion that can predict the mechanical failure of various different structural materials is one of ultimate goals for scientists in both material and mechanics communities. Since the first study on the failure criterion of materials by Galileo, about three centuries have passed. Now we eventually find the "generalized e...

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 1 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-3...

The cyclic deformation and damage behaviors of the Fe-Mn and Fe-Mn-C TRIP/TWIP steels are comprehensively studied in a wide range of strain amplitude (from 0.3% to 8.0%). It is found that with increasing C content, the dislocation structures change from wavy slip to planar slip after cyclic deformation. In order to evaluate the low-cycle and extrem...

Zn–22Al alloy was processed using a well-designed two-step equal channel angular extrusion/pressing (ECAE/P), and ultrafine-grained (UFG) microstructure with 200 nm grain size was achieved. UFG Zn-22Al was subjected to long-term (up to 60 days) aging at room temperature (RT) and it was seen that natural aging caused limited grain growth in the micr...

Vast experiments have demonstrated that the external specimen size makes a large difference in the deformation behavior of crystalline materials. However, as one important kind of internal planar defects, the role of grain boundary (GB) in small scales needs to be clarified in light of the scarce and inconsistent experimental results at present. Th...

In this study, the recovery of strain-hardening rate (RSHR) was discovered for the first time in polycrystalline materials (Ni-Si alloys) that have only dislocation activities during tensile test. Detailed microstructure characterizations show that the activation of dislocations in the secondary slip systems during tensile deformation is the major...

Quasi-single phase (dilute) Zn–0.3Al alloy was subjected to severe plastic deformation via equal-channel angular extrusion/pressing (ECAE/P), and the effects of ECAP on its room temperature (RT) and high strain rate (HSR) superplasticity and deformation mechanism were investigated. Multi-pass ECAP may refine the coarse-grained microstructure into t...

Despite the extensive investigation on the structure of natural biological materials, insufficient attention has been paid to the structural imperfections by which the mechanical properties of synthetic materials are dominated. In this study, the structure of bivalve Saxidomus purpuratus shell has been systematically characterized quantitatively on...

Hexagonal dislocation networks (HDNs) formed by the reaction of /2 screw dislocations are frequently observed in association with anomalous slip in body-centred cubic (bcc) metals. However, its role assigned in anomalous slip remains obscure due to the absence of quantitative description of its response to uniaxial loading. Here, systematic atomist...

Cu bicrystals with a twin boundary (TB) and a {1 1 1} grain boundary (GB) were cyclically deformed. It is shown that the slip bands in the two component grains of both bicrystals are parallel to the TB and GB, respectively. Despite no piling up of dislocations, fatigue cracks still nucleate preferentially along the TB and GB in a shearing mode. The...

In this study, the concept of "twinning induced plasticity (TWIP) alloys" is broadened, and the underlying intrinsic microscopic mechanisms of the general TWIP effect are intensively explored. For the first aspect, "TWIP copper alloys" was proposed following the concept of "TWIP steels", as they share essentially the same strengthening and tougheni...

The extremely-low-cycle fatigue (ELCF) behaviors of pure Cu and Cu–Al alloys are comprehensively studied following the cyclic push–pull loading tests with extremely high strain amplitudes (up to ±9.5%). Compared with the common low-cycle fatigue (LCF) region, several unique features in the ELCF regime can be noticed, including the deviations of fat...

Two Cu bicrystals with identical component grains involved in twinning relationship but different boundaries were cyclically deformed. The results reveal that the coherent twin boundary (CTB) strongly resists fatigue cracking while the incoherent twin boundary (ITB) is intrinsically prone to nucleate fatigue cracks. It is suggested that the same di...

For Fe-22Mn-0.6C (wt%) twinning-induced plasticity (TWIP) steel with grain sizes of 35 and 170 mu m, 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. Accord...

Dilute Zn-0.3Al, eutectic Zn-5Al and eutectoid Zn-22Al alloys were processed by multi-pass equal channel angular pressing (ECAP) in order to achieve fine grained (FG) or ultrafine-grained (UFG) microstructure and room temperature (RT) superplasticity. ECAP refined the microstructure of Zn-0.3Al and resulted in a FG Zn-rich η-matrix with an average...

A criterion is proposed to predict the transition from slip to twinning in the face-centered cubic (FCC) metals within the framework of the generalized stacking fault energy (GSFE) curves, which are calculated by using the full potential linearly augmented plane wave method incorporating local orbital based on density functional theory. The criteri...