Achieving High Strength and Tensile Ductility in Pure Nickel by Cryorolling with Subsequent Low-Temperature Short-Time Annealing

Ultra fine-grained pure metals and their alloys have high strength and low ductility.In this study,cryorolling under different strains followed by low-temperature short-time annealing was used to fabricate pure nickel sheets combining high strength with good ductility.The results show that,for different cryorolling strains,the uniform elongation was greatly increased without sacrificing the strength after annealing.A yield strength of 607 MPa and a uniform elongation of 11.7%were obtained after annealing at a small cryorolling strain(ε=0.22),while annealing at a large cryorolling strain(ε=1.6)resulted in a yield strength of 990 MPa and a uniform elongation of 6.4%.X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),and electron backscattered diffraction(EBSD)were used to characterize the microstructure of the specimens and showed that the high strength could be attributed to strain hardening during cryorolling,with an additional contribution from grain refinement and the formation of dislocation walls.The high ductility could be attributed to annealing twins and micro-shear bands during stretching,which improved the strain hardening capacity.The results show that the synergistic effect of strength and ductility can be regulated through low-temperature short-time annealing with different cryorolling strains,which provides a new reference for the design of future thermo-mechanical processes.

Achieving high ductility and low in-plane anisotropy in magnesium alloy through a novel texture design strategy

Texture regulation is a prominent method to modify the mechanical properties and anisotropy of magnesium alloy.In this work,the Mg-1Al-0.3Ca-0.5Mn-0.2Gd(wt.%)alloy sheet with TD-tilted and circular texture was fabricated by unidirectional rolling(UR)and multidirectional rolling(MR)method,respectively.Unlike generating a strong in-plane mechanical anisotropy in conventional TD-tilted texture,the novel circular texture sample possessed a weak in-plane yield anisotropy.This can be rationalized by the similar proportion of soft grains with favorable orientation for basalslip and{10.12}tensile twinning during the uniaxial tension of circular-texture sample along different directions.Moreover,compared with the TD-tilted texture,the circular texture improved the elongation to failure both along the rolling direction(RD)and transverse direction(TD).By quasi-in-situ EBSD-assisted slip trace analysis,higher activation of basal slip was observed in the circular-texture sample during RD tension,contributing to its excellent ductility.When loading along the TD,the TD-tilted texture promoted the activation of{10.12}tensile twins significantly,thus providing nucleation sites for cracks and deteriorating the ductility.This research may shed new insights into the development of formable and ductile Mg alloy sheets by texture modification.

Exploring a balance between strength and ductility of hexagonal BN nanoplatelet reinforced ZK61 magnesium composite

The practical applications of magnesium(Mg)alloys are usually beset by their relatively low strength and limited ductility.Herein we attempt to fabricate hexagonal BN nanoplatelet(BNNP)reinforced ZK61 magnesium composites using a combination of spark plasma sintering and friction stir processing.The resulting composites exhibit microstructural characteristics of homogeneous dispersion of BNNP in Mg matrix with refined equiaxed grains and(0002)basal texture roughly surrounding the pin column surface.Transmission electron microscopy observation illustrates that trace amounts of Mg_(3)N_(2)and MgB_(2)form at BNNP-Mg interface,in which Mg_(3)N_(2)locates at the basal plane of a BNNP and MgB_(2)grows at its open edge.The spatial distribution of Mg_(3)N_(2)and MgB_(2)facilitates interfacial wetting and stronger BNNP-Mg interface in such a way that interfacial products act as anchors bonding between them.In comparison with monolithic ZK61 alloy,the BNNP/ZK61 composites display simultaneous improvements in yield strength,hardness and ductility,achieving good strength-ductility balance.This research is expected to shed some light on BNNP potentials for designing and producing magnesium composites with high strength and good ductility.

Designing new low alloyed Mg-RE alloys with high strength and ductility via high-speed extrusion

Two new low-alloyed Mg-2RE-0.8Mn-0.6Ca-0.5Zn(wt%,RE=Sm or Y)alloys are developed,which can be produced on an in-dustrial scale via relatively high-speed extrusion.These two alloys are not only comparable to commercial AZ31 alloy in extrudability,but also have superior mechanical properties,especially in terms of yield strength(YS).The excellent extrudability is related to less coarse second-phase particles and high initial melting point of the two as-cast alloys.The high strength-ductility mainly comes from the formation of fine grains,nano-spaced submicron/nano precipitates,and weak texture.Moreover,it is worth noting that the YS of the two alloys can maintain above 160 MPa at elevated temperature of 250°C,significantly higher than that of AZ31 alloy(YS:45 MPa).The Zn/Ca solute segregation at grain boundaries,the improved heat resistance of matrix due to addition of RE,and the high melting points of strengthening particles(Mn,MgZn_(2),and Mg-Zn-RE/Mg-Zn-RE-Ca)are mainly responsible for the excellent high-temperature strength.

A new perspective to develop regiorandom polymer acceptors with high active layer ductility,excellent device stability,and high efficiency approaching 17%

The recently reported efficient polymerized small-molecule acceptors(PSMAs)usually adopt a regioregular backbone by polymerizing small-molecule acceptors precursors with a low-reactivity 5-brominated 3-(dicyanomethylidene)indan-1-one(IC)end group or its derivatives,leading to low molecular weight,and thus reduce active layer mechanical properties.Herein,a series of newly designed chlorinated PSMAs originating from isomeric IC end groups are developed by adjusting chlorinated positions and copolymerized sites on end groups to achieve high molecular weight,favorable intermolecular interaction,and improved physicochemical properties.Compared with regioregular PY2Se-Cl-o and PY2Se-Cl-m,regiorandom PY2Se-Cl-ran has a similar absorption profile,moderate lowest unoccupied molecular orbital level,and favorable intermolecular packing and crystallization properties.Moreover,the binary PM6:PY2Se-Cl-ran blend achieves better ductility with a crack-onset strain of 17.5% and improved power conversion efficiency(PCE)of 16.23% in all-polymer solar cells(all-PSCs)due to the higher molecular weight of PY2Se-Cl-ran and optimized blend morphology,while the ternary PM6:J71:PY2Se-Cl-ran blend offers an impressive PCE approaching 17% and excellent device stability,which are all crucial for potential practical applications of all-PSCs in wearable electronics.To date,the efficiency of 16.86% is the highest value reported for the regiorandom PSMAs-based all-PSCs and is also one of the best values reported for the all-PSCs.Our work provides a new perspective to develop efficient all-PSCs,with all high active layer ductility,impressive PCE,and excellent device stability,towards practical applications.

High-ductility fine-grained Mg-1.92Zn-0.34Y alloy fabricated by semisolid and then hot extrusion

The combination of semisolid and hot extrusion processing was applied to refine the icosahedral quasicrystalline phase(I-phase) in an extruded Mg-1.92Zn-0.34Y(wt.%) alloy for the first time. The semisolid isothermal heat treatment transformed the micron-sized I-phase particles into nano lamellar eutectic(α-Mg + I-phase) with a lamellar spacing of ?86 nm. After subsequent hot extrusion at 250 ℃, the nano lamellar eutectic phases were broken into uniformly dispersed nanoscale I-phase particles. What’s more, the matrix microstructure was significantly refined with an equiaxed average grain size of 2.59 ± 0.81 μm, and an unusual texture component(most of the grains’ c-axis is parallel to the extrusion direction) was observed. The processed alloy exhibited a high tensile elongation to failure(EL) of 44 ± 2.6%with an ultimate tensile strength(UTS) of 258 ± 2.0 MPa and a tensile yield strength(TYS) of 176 ± 1.6 MPa at room temperature.The high ductility from the combined effects of the grain refinement, dispersion of nanoscale I-phase particles, and the unusual texture.The uniform dispersion of nanoscale I-phase particles could promote grain refinement by particle stimulated nucleation mechanism, and thus bring the unusual texture(where the c-axis is aligned parallel to the extrusion direction during dynamic recrystallization, which contributed to ductility).

Effect of ground motion duration on inelastic displacement ratio of SDOF systems

In this paper,the influence of ground motion duration on the inelastic displacement ratio,C_(1),of highly damped SDOF systems is studied.For this purpose,two sets of spectrally equivalent long and short duration ground motion records were used in an analysis to isolate the effects of ground motion duration on.The effect of duration was evaluated for observed values of C_(1) by considering six ductility levels,and different damping and post-yield stiffness ratios.A new predictive equation of C_(1) also was developed for long and short duration records.Results of non-linear regression analysis of the current study provide an expression with which to quantify the duration effect.Based on the average values of estimated C_(1) ratios for long duration records divided by C_(1) for a short duration set,it is concluded that the maximum difference between long and short duration records occurs when the damping ratio is 0.3 and the post-yield stiffness ratio is equal to zero.

Effect of structural characteristics distribution on strength demand and ductility reduction factor of MDOF systems considering soil-structure interaction

It is known that structural stiffness and strength distributions have an important role in the seismic response of buildings. The effect of using different code-specified lateral load patterns on the seismic performance of fixed-base buildings has been investigated by researchers during the past two decades. However, no investigation has yet been carried out for the case of soil-structure systems. In the present study, through intensive parametric analyses of 21,600 linear and nonlinear MDOF systems and considering five different shear strength and stiffness distribution patterns, including three code-specified patterns as well as uniform and concentric patterns subjected to a group of earthquakes recorded on alluvium and soft soils, the effect of structural characteristics distribution on the strength demand and ductility reduction factor of MDOF fixed-base and soil-structure systems are parametrically investigated. The results of this study show that depending on the level of inelasticity, soil flexibility and number of degrees-of-freedoms (DOFs), structural characteristics distribution can significantly affect the strength demand and ductility reduction factor of MDOF systems. It is also found that at high levels of inelasticity, the ductility reduction factor of low-rise MDOF soil-structure systems could be significantly less than that of fixed-base structures and the reduction is less pronounced as the number of stories increases.

Relations of Microstructural Attributes and Strength-Ductility of Zirconium Alloys with Hydrides

As the first safety barrier of nuclear reactors,zirconium alloy cladding tubes have attracted extensive attention because of its good mechanical properties.The strength and ductility of zirconium alloy are of great significance to the service process of cladding tubes,while brittle hydrides precipitate and thus deteriorate the overall performance.Based on the cohesive finite element method,the effects of cohesive strength,interfacial characteristics,and hydrides geometric characteristics on the strength and ductility of two-phase material(zirconium alloy with hydrides)are numerically simulated.The results show that the fracture behavior is significantly affected by the cohesive strength and that the overall strength and ductility are sensitive to the cohesive strength of the zirconium alloy.Furthermore,the interface is revealed to have prominent effects on the overall fracture behavior.When the cohesive strength and fracture energy of the interface are higher than those of the hydride phase,fracture initiates in the hydrides,which is consistent with the experimental phenomena.In addition,it is found that the number density and arrangement of hydrides play important roles in the overall strength and ductility.Our simulation provides theoretical support for the performance analysis of hydrogenated zirconium alloys during nuclear reactor operation.

Experimental Investigation on the Strength and Ductility Performance of Steel-Timber-Steel Joints with Screw and Steel-Tube Fasteners

This article presents experimental results of steel-timber-steel(STS)joints loaded parallel to grain.Eight groups of specimens were designed,and tensile tests were performed.The fastener types and fastener numbers were considered to evaluate the tensile strengths and ductility performances of the STS joints.The screws with 6 mm diameter and the innovative steel-tubes with 18 mm diameter were adopted as connecting fasteners.The experimental results were discussed in terms of yielding and ultimate strengths,slip stiffness,and ductility factors.The ductility classification and failure mechanisms of each group of specimens were analyzed.It was demonstrated that the STS joint with large diameter steel-tubes showed acceptable ductility,which was close to the ductility of the STS joint with small diameter screws,thanks to the hollow structure of the steel-tube.The theoretical strengths of various failure modes for the joints with small diameter screws or large diameter steel-tubes were calculated and compared with the experimental results.The ductile performance of the STS joint was discussed by comparing the theoretical strengths of various failure modes.The effective number of the STS joint with multifasteners was also analyzed by considering the failure mechanisms in aspects of tensile strength and slip stiffness.

Influence of technical parameters on strength and ductility of AlSi9Cu3 alloys in squeeze casting

An orthogonal test was conducted to investigate the influence of technical parameters of squeeze casting on the strength and ductility of AISigCu3 alloys. The experimental results showed that when the forming pressure was higher than 65 MPa, the strength （ab） of A1Si9Cu3 alloys decreased with the forming pressure and pouring temperature increasing, whereas ab increased with the increase of filling velocity and mould preheating temperature. The ductility （6） by alloy was improved by increasing the forming pressure and filling velocity, but decreased with pouring temperature increasing. When the mould preheating temperature increased, the ductility increased first, and then decreased. Under the optimized parameters of pouring temperature 730 ℃, forming pressure 75 MPa, filling velocity 0.50 m/s, and mould preheating temperature 220 ℃, the tensile strength, elongation, and hardness of A1Si9Cu3 alloys obtained in squeeze casting were improved by 16.7%, 9.1%, and 10.1%, respectively, as compared with those of sand castings.

Enhancement of ductility in high strength Mg-Gd-Y-Zr alloy

A high strength GW94 alloy with fully recrystallized microstructure and equiaxed ultrafine grains of submicron size was produced by multiaxial forging and ageing. The alloy exhibits an ultimate tensile strength of 377 MPa, proof stress of 295 MPa and elongation to failure of 21.7%. The ductility is improved in comparison with that of the conventional extrusion processing. Superplastic ductility is achieved in tensile testing at 573 K with a maximum elongation of 450%. These high ductility and high strength are attributed to the coexistence of fully recrystallized grains and nanoscale Mg 5 （Gd, Y） particles dynamically precipitated at grain boundaries.

The Influence of the Closure of the East Paleo-Tethys Ocean on Southern South China:Evidences from Kinematics and^(40)Ar/^(39)Ar Geochronology of the Rongxian Ductile Shear Zone in Southeastern Guangxi

The Triassic was a crucial period in the tectonic evolution of the South China Block.Research on tectonic deformation during this period provides information on intracontinental orogenic mechanisms in South China.In this study,alongside thermochronological analyses,we examine the macroscopic and microscopic structural features of the Rongxian ductile shear zone,located south of the Darongshan granite in the southeastern part of Guangxi Province,on the southern margin of South China.Sinistral shear is indicated by the characteristics of rotatedσ-type feldspar porphyroclasts,stretching lineations defined by elongated quartz grains and the orientations of quartz c-axes.LA-ICP-MS U-Pb dating of zircons from two samples of granitic mylonite and one of granite yielded ages of ca.256 Ma.Furthermore,two samples of granitic mylonite yield muscovite^(40)Ar/^(39)Ar plateau ages of 249-246 Ma.These results indicate that the Rongxian ductile shear zone resulted from Early Triassic deformation of the late Permian Darongshan granite.This deformation was likely related to the closure of the eastern Paleo-Tethys Ocean and the subsequent collision of the South China and Indochina blocks,during the early stage of the Indosinian orogeny.

Research progress of heterogeneous structure magnesium alloys:A review

In recent years,a new class of metallic materials featuring heterogeneous structures has emerged.These materials consist of distinct soft and hard domains with significant differences in mechanical properties,allowing them to maintain high strength while offering superior ductility.Magnesium(Mg)alloys,renowned for their low density,high specific strength,exceptional vibration damping,and electromagnetic shielding properties,exhibit tremendous potential as lightweight and functional materials.Despite their advantageous properties,high-strength Mg alloys often suffer from limited ductility.However,the emergence of heterogeneous materials provides a fresh perspective for the development of Mg alloys with both high strength and ductility.This article provided a fundamental overview of heterostructured materials and systematically reviewed the recent research progress in the design of Mg alloys with strength-ductility balance based on heterostructure principles.The review encompassed various aspects,including preparation methods,formation mechanisms of diverse heterostructures,and mechanical properties,both within domestic and international contexts.On this basis,the article discussed the challenges encountered in the design and fabrication of heterostructured Mg alloys,as well as the urgent issues that require attention and resolution in the future.

Activation of dislocations in Mg with solute Y

Mg-Y cast alloy shows excellent ductility(elongation to failure>15%)compared with pure Mg and commercial Mg cast alloys.By monitoring the microstructure evolution during an in situ tensile test of a Mg-2.5 wt%Y alloy,we identify the activation of prismatic<c>slip,which is rare in Mg.Synchrotron X-ray micro-beam Laue diffraction(μ-Laue)and transmission electron microscopy revealed the morphology of prismatic<c>slip bands and individual<c>dislocations.Density functional theory and molecular dynamics calculations indicate that solute Y can significantly reduce the stacking fault energy(SFE)along<c>direction on prismatic plane in Mg lattice and thus facilitate the nucleation of<c>dislocations during deformation.The presence of free<c>dislocations in the Mg lattice can also lead to nucleation of{10–12}twins even under unfavorable geometric conditions.

Phase-field modeling for anisotropic ductile damage of magnesium alloys at finite deformations

The damage anisotropy of an extruded ZK60 Mg alloy is characterized using tensile tests and scanning electronic microscopy.The accumulation of anisotropic deformations leads to the great differences of the dimple evolution and strains at fracture along different loading directions.To introduce the anisotropic deformation information into the damage constitutive relationship,a thermodynamically consistent phase-field model of ductile damage fully coupled with elastoplastic finite deformations is developed in this study.Using the user-defined constitutive relationship and displacement-temperature coupling element,the finite element simulations are conducted.The results show that:(1)ZK60 Mg alloys presents clear R-value difference in 0°,45°,and 90°tests of intact specimens.The 45°test possesses the greatest R-value(1.50)and the greatest strain at fracture,however,the R-value for 0°is less than 1,indicating the thinning is preferential.(2)The higher ultimate stress leads to a larger average dimension of the dimples,whereas the higher density correlates with a larger elongation ratio at the fracture.The disappearance of the stress-bearing area indicates that the phase-field assumption on stress degradation is completely compatible with the dimple analysis on fractography.(3)The simulation results of the stress-strain relationships and damage paths correlate well with the experimental ductile damage of magnesium alloys at 200◦C.Slight errors are basically attributed to the modeling parameters and finite element iteration algorithm.The proposed model presents fine applicability and reliability for the predictions of plastic deformations,ductile damage,and fracture of anisotropic Mg alloys.

The Early Mesozoic NE-SW Extensional Model and Exhumation Processes at the Southeastern Margin of the Central Asian Orogenic Belt:Insights from the Strain and Kinematic Vorticity Analysis of the Sonid Zuoqi Ductile Detachment Zone

The Sonid Zuoqi ductile detachment zone is located at the southeastern margin of the Central Asian orogenic belt(CAOB),striking EW and dipping to the S.The major rock type of the Sonid Zuoqi ductile detachment zone is mylonite derived from granite.The sequence of mylonite features is:(1)S and C foliations of mylonite,and(2)extensional crenulation cleavage(ecc)or C′and the kinematic vorticity(Wk)value changed from 0.70 to 0.95 and from 0.37 to 0.69,respectively;the strain type of the mylonites within the Sonid Zuoqi ductile detachment zone is compressional to planar strain.The strong deformation mylonite and Halatu plutons yielded a zircon U-Pb age of 244 Ma and a zircon(U-Th)/He age of 214 Ma,respectively.Based on the strain and kinematic vorticity analysis,together with the zircon U-Pb and zircon(U-Th)/He ages and the regional tectonic background,the study area experienced three stage evolution:tangential simpleshear(244 Ma),simple-shear-dominated general shear represented by upper crustal extension(224 Ma)and pure-shear-dominated general shear represented by the Halatu pluton doming(214 Ma),which constrained the early Mesozoic NE-SW crustal extension at the southeastern margin of the CAOB.This NE-SW extension probably originated from the postorogenic extensional collapse of the CAOB,subsequent exhumation being controlled by the far afield effects of the closure of the Mongol-Okhotsk belt.

Modeling the Interaction between Vacancies and Grain Boundaries during Ductile Fracture

The experimental results in previous studies have indicated that during the ductile fracture of pure metals,vacancies aggregate and form voids at grain boundaries.However,the physical mechanism underlying this phenomenon remains not fully understood.This study derives the equilibrium distribution of vacancies analytically by following thermodynamics and the micromechanics of crystal defects.This derivation suggests that vacancies cluster in regions under hydrostatic compression to minimize the elastic strain energy.Subsequently,a finite element model is developed for examining more general scenarios of interaction between vacancies and grain boundaries.This model is first verified and validated through comparison with some available analytical solutions,demonstrating consistency between finite element simulation results and analytical solutions within a specified numerical accuracy.A systematic numerical study is then conducted to investigate the mechanism that might govern the micromechanical interaction between grain boundaries and the profuse vacancies typically generated during plastic deformation.The simulation results indicate that the reduction in total elastic strain energy can indeed drive vacancies toward grain boundaries,potentially facilitating void nucleation in ductile fracture.

Nickel-based superalloy architectures with surface mechanical attrition treatment: Compressive properties and collapse behaviour

Surface modifications can introduce natural gradients or structural hierarchy into human-made microlattices,making them simultaneously strong and tough.Herein,we describe our investigations of the mechanical properties and the underlying mechanisms of additively manufactured nickel–chromium superalloy(IN625)microlattices after surface mechanical attrition treatment(SMAT).Our results demonstrated that SMAT increased the yielding strength of these microlattices by more than 64.71%and also triggered a transition in their mechanical behaviour.Two primary failure modes were distinguished:weak global deformation,and layer-by-layer collapse,with the latter enhanced by SMAT.The significantly improved mechanical performance was attributable to the ultrafine and hard graded-nanograin layer induced by SMAT,which effectively leveraged the material and structural effects.These results were further validated by finite element analysis.This work provides insight into collapse behaviour and should facilitate the design of ultralight yet buckling-resistant cellular materials.

An Elastoplastic Fracture Model Based on Bond-Based Peridynamics

Fracture in ductile materials often occurs in conjunction with plastic deformation.However,in the bond-based peridynamic(BB-PD)theory,the classic mechanical stress is not defined inherently.This makes it difficult to describe plasticity directly using the classical plastic theory.To address the above issue,a unified bond-based peridynamics model was proposed as an effective tool to solve elastoplastic fracture problems.Compared to the existing models,the proposed model directly describes the elastoplastic theory at the bond level without the need for additional calculation means.The results obtained in the context of this model are shown to be consistent with FEM results in regard to force-displacement curves,displacement fields,stress fields,and plastic deformation regions.The model exhibits good capability of capturing crack propagation in ductile material failure problems.