EFFECT OF THE CONTROLLED ROLLING CONTROLLED COOLING ON STRENGTH AND DUCTILITY OF THE BAINITE MICRO ALLOYED ENGINEERING STEEL

The continuous cooling transformation of hot deformation austenite austenite of test steel and the effect of different processing schedules of controlled rolling and controlled cooling on the strength and ductility have been studied. The theory and the experiment base are presented for controlled rolling and controlled cooling of the SBL micro alloyed engineering steel.

Strain rate and cold rolling dependence of tensile strength and ductility in high nitrogen nickel-free austenitic stainless steel

The tensile strength and ductility of a high nitrogen nickel-free austenitic stainless steel with solution and cold rolling treatment were investigated by performing tensile tests at different strain rates and at room temperature. The tensile tests demonstrated that this steel exhibits a significant strain rate and cold rolling dependence of the tensile strength and ductility.With the increase of the strain rate from 10^-4s^-1to 1 s^-1, the yield strength and ultimate tensile strength increase and the uniform elongation and total elongation decrease. The analysis of the double logarithmic stress–strain curves showed that this steel exhibits a two-stage strain hardening behavior, which can be well examined and analyzed by using the Ludwigson equation. The strain hardening exponents at low and high strain regions（n2and n1） and the transition strain（εL） decrease with increasing strain rate and the increase of cold rolling RA. Based on the analysis results of the stress–strain curves, the transmission electron microscopy characterization of the microstructure and the scanning electron microscopy observation of the deformation surfaces, the significant strain rate and cold rolling dependence of the strength and ductility of this steel were discussed and connected with the variation in the work hardening and dislocation activity with strain rate and cold rolling.

Constructing the coherent transition interface structure for enhancing strength and ductility of hexagonal boron nitride nanosheets/Al composites

The deformation incompatibility of components is a bottleneck restricting the exaltation of the strength and ductility of composites.Herein,the coherent transition interface was designed and produced in hexagonal boron nitride nanosheets(BNNSs)/Al composites by reaction sintering route,expecting to re-lieve the deformation incompatibility between BNNSs and Al.It is demonstrated that with the sintering temperature for composites raising from 600℃ to 650℃,700℃ and 750℃,different interface bonding characteristics,which involve nucleation and growth of AlN continuous nanolayer,were confirmed.Fur-thermore,first-principles calculations show that the generation of the coherent transition interface im-proved the interfacial bonding strength of BNNSs/Al composites through covalent bonds.The composites with coherent transition interface exhibit excellent strength-toughness combination in tensile and impact tests.The finite element simulation and in-situ approach under tensile tests were applied to investigate the influence of transition interface structure on deformation behavior of BNNSs/Al composite.It is found that the generation of the transition interface can not only weaken the stress partitioning behavior in the elastic stage,but also constrain the crack initiation and propagation behavior in the elastic-plastic stage and plastic stage,thereby improving the deformation compatibility between BNNSs and Al.The present work provides a novel view into the breakthrough for the trade-offrelationship of strength and ductility by coherent transition interface design in nanocomposites.

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.

First-principles study of the effects of selected interstitial atoms on the generalized stacking fault energies, strength, and ductility of Ni

We analyze the influences of interstitial atoms on the generalized stacking fault energy （GSFE）, strength, and ductility of Ni by first-principles calculations. Surface energies and GSFE curves are calculated for the （112） （111） and / 101） （ 1 1 1） systems. Because of the anisotropy of the single crystal, the addition of interstitials tends to promote the strength of Ni by slipping along the （10T） direction while facilitating plastic deformation by slipping along the （115） direction. There is a different impact on the mechanical behavior of Ni when the interstitials are located in the slip plane. The evaluation of the Rice criterion reveals that the addition of the interstitials H and O increases the brittleness in Ni and promotes the probability of cleavage fracture, while the addition of S and N tends to increase the ductility. Besides, P, H, and S have a negligible effect on the deformation tendency in Ni, while the tendency of partial dislocation is more prominent with the addition of N and O. The addition of interstitial atoms tends to increase the high-energy barrier γmax, thereby the second partial resulting from the dislocation tends to reside and move on to the next layer.

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.©2024 Chongqing University.Publishing services provided by Elsevier B.V.on behalf of KeAi Communications Co.Ltd.

Simultaneously Enhancing Strength, Ductility and Corrosion Resistance of a Martensitic Stainless Steel via Substituting Carbon by Nitrogen

Two martensitic stainless steels of 2Cr12Ni6 type hardened and tempered at 773 K have been studied:the first with 0.2%carbon content and the second with partial replacement of carbon by nitrogen(C0.1N0.1)in the first steel.It is found that the partial substitution of carbon with nitrogen contributed to an increase in ductility and strength of the steel,presumably due to the formation of more dispersive carbonitrides.Meanwhile,the addition of nitrogen suppressed the precipitation of carbonitrides,so that the solid solution strengthening effect of C0.1N0.1 did not decrease significantly after tempering treatment.In addition,the partial replacement of carbon by nitrogen contributed to improved ability against pitting corrosion(PC)in chloride-containing medium(3.5%NaCl at 303 K).The higher resistance to PC of tempered nitrogen-containing steel is apparently due to the lower content of massive carbonitrides,especially the reduced aggregation at grain boundaries.This leads to a lower acidity and aggressiveness of the test solution near the sample surface due to the accumulation of NH4^(+) ammonium ions in it.As a result of nitrogen addition,exception for Cr_(23)C_(6) and VC,Cr_(2)N and(Cr,V)N type precipitates have also been found in C0.1N0.1 steel and this is consistent with the thermodynamic calculation results.In conclusion,substituting carbon by nitrogen in traditional martensitic stainless steel could realize the simultaneous improvement of multiple properties of martensitic stainless steels.This result provides a promising composition optimization route to develop novel martensitic stainless steels.

Effect of Deformation on Microstructure and Mechanical Properties of Medium Carbon Steel During Heat Treatment Process

The current research of the Q-P and Q-P-T process has been focused on controlling the heating temperature and holding time,or adding alloy elements into the steel to induce precipitation strengthening and improve the strength and plasticity of the steel.In this article,based on a quenching-partitioning-tempering(Q-P-T)process combined with a hot deformation technology,a deforming-quenching-partitioning-tempering(D-Q-P-T)process was applied to medium carbon steel.The effect of the heat treatment parameters on the microstructure and mechanical properties of experimental steel under deformation was studied.Through use of a scanning electron microscope(SEM),transmission electron microscopy(TEM)and tensile tests,the optimal heat treatment conditions for realizing high strength and plasticity that meet the safety requirements were obtained.The mechanism for the D-Q-P-T process to improve the strength and plasticity of experimental steel was discussed.A multiphase composite structure of lath martensite and retained austenite was obtained.Compared with the Q-P-T process,use of the D-Q-P-T process can increase the strength of steel by 57.77 MPa and the elongation by 5%.This study proposes a method to improve the strength and plasticity of steel.

Strengthening and toughening bulk Ni_(2)CoFeV_(0.5) medium-entropy alloy via thermo-mechanical treatment

Single-phase face-centered cubic(fcc)medium-and high-entropy alloys(MEAs/HEAs)have high ductility but low yield strength.In this work,the microstructures of single-phase fcc Ni_(2)CoFeV_(0.5) MEAs were tailored by cold-rolling and subsequent annealing and typical heterogeneous lamella(HL)structures composed of recrystallized micro-grain lamellae(with an averaged grain size of∼4μm)and nonrecrystallized nano-/ultrafine-grain lamellae were obtained.Tensile tests revealed that most HL samples exhibited excellent strength and ductility synergy.The HL sample with∼23 vol%recrystallized grains annealed at 590℃ for 1 h had a high yield strength of 1120 MPa and a good fracture elongation of 12.3%,which increased by 5%and 46%,respectively compared with those of as-rolled sample.Annealing-induced yield strength increase is attributed to high-density annealing twin boundaries(TBs)in the recrystallized grains,the annihilation of mobile dislocations inside the non-recrystallized grains,and extra heterodeformation-induced strengthening produced by the HL structure.Hall-Petch relationship of Ni_(2)CoFeV_(0.5) MEA can be reasonably described by counting both TBs and grain boundaries,with lattice friction stress of 87.3 MPa and coefficient of 722.8 MPaμm1/2.Our work provides optional and controllable solutions for preparing MEAs/HEAs with excellent mechanical properties by low-cost and high-efficiency thermomechanical treatments.

Excellent strength-ductility combination of Cr_(26)Mn_(20)Fe_(20)Co20Ni_(14) high-entropy alloy at cryogenic temperatures

In the present study,a face-centered cubic non-equiatomic Cr_(26)Mn_(20)Fe_(20)Co20Ni_(14) high-entropy alloy(HEA)with a low stacking fault energy of 17.6 mJ m^(−2) was prepared by vacuum induction melting,forging and annealing processes.The recrystallized sample is revealed to exhibit an excellent combination of strength and ductility over a wide temperature range of 4.2–293 K.With decreasing temperature from 293 to 77 K,the ductility and ultimate tensile strength(UTS)gradually increase by 30% to 95% and 137% to 1020 MPa,respectively.At the lowest temperature of 4.2 K,the ductility keeps 65% and the UTS increases by 200% to 1300 MPa,which exceed those published in the literature,including conventional 300 series stainless steels.Detailed microstructural analyses of this alloy reveal a change of deformation mechanisms from dislocation slip and nano-twinning at 293 K to nano-phase transformation at 4.2 K.The cooperation and competition of multiple nano-twinning and nano-phase transformation are responsible for the superior tensile properties at cryogenic temperatures.Our study provides experimental evidence for potential cryogenic applications of HEAs.

Bimodal microstructure – A feasible strategy for high-strength and ductile metallic materials

Introducing a bimodal grain-size distribution has been demonstrated an efficient strategy for fabricating high-strength and ductile metallic materials, where fine grains provide strength, while coarse grains enable strain hardening and hence decent ductility. Over the last decades, research activities in this area have grown enormously, including interesting results onfcc Cu, Ni and Al-Mg alloys as well as steel and Fe alloys via various thermo-mechanical processing approaches. However, investigations on bimodal Mg and other hcp metals are relatively few. A brief overview of the available approaches based on thermo- mechanical processing technology in producing bimodal microstructure for various metallic materials is given, along with a summary of unusual mechanical properties achievable by bimodality, where focus is placed on the microstructure-mechanical properties and relevant mechanisms. In addition, key factors that influencing bimodal strategies, such as compositions of starting materials and processing parameters, together with the challenges this research area facing, are identified and discussed briefly.

Improved Mechanical Properties in Carbon Martensitic Steel Achieved by Continuous Carbon Gradient and Multilayered Structure

Increasing carbon content in martensite enhances the strength of carbon steel but reduces ductility and toughness.In this study,a multilayered carbon gradient steel was developed to overcome this trade-off by stacking high-carbon(1 wt%)and low-carbon(0.2 wt%)steel plates through preliminary diffusion and multi-pass hot rolling.The resulting microstructure showed a continuous gradient from high-carbon martensite to low-carbon martensite.After low-temperature tempering,the tempered samples exhibited hardness fluctuations along the normal direction,with a maximum value of approximately 700 HV or more in high-carbon regions and a lower value of 500 HV or less in low-carbon regions.Compared to low-carbon steel,the sample tempered at 200℃showed significant improvements in both strength and ductility,with 1880 MPa ultimate tensile strength and 4.7%uniform elongation.This larger uniform elongation than that of the plain low-carbon steel can be attributed to the greater strain hardening rate in high-carbon regions with a high carbon solid solution strengthening.Simultaneously,it is believed that more slip systems in high-carbon regions could be activated under the multiaxial stress around the layer interface,then showing a better ductility than that of the plain high-carbon steel.Additionally,the gradient structure between different regions effectively helped to avoid abrupt stress and deliver multiaxial stress at any location along the normal direction.The stepped path of the cracks under uniaxial tensile stress suggested a higher fracture toughness.

Combining gradient structure and supersaturated solid solution to achieve superior mechanical properties in WE43 magnesium alloy

In this study,surface mechanical attrition treatment was employed to sucessfully produce a gradient nanostructured layer on WE43 magnesium alloy.X-ray diffraction,energy dispersive X-ray spectrometer,and high-resolution transmission electron microscope observations were mainly performed to uncover the microstructure evolution responsible for the refinement mechanisms.It reveals that the grain refinement process consists of three transition stages along the depth direction from the core matrix to the topmost surface layer,i.e.,dislocation cells and pile-ups,ultrafine subgrains,and randomly orientated nanograins with the grain size of~40 nm.Noticeably,the original Mg;RE second phase is also experienced refinement and then re-dissolved into the α-Mg matrix phase,forming a supersaturated solid solution nanostructuredα-Mg phase in the gradient refined layer.Due to the cooperative effects of grain refinement hardening,dislocation hardening,and supersaturated solid-solution hardening,the gradient nanostructured WE43 alloy contributes to the ultimate tensile strength of~435 MPa and ductility of~11.0%,showing an extraordinary strain hardening and mechanical properties among the reported severe plastic deformation-processed Mg alloys.This work provides a new strategy for the optimization of mechanical properties of Mg alloys via combining the gradient structure and supersaturated solid solution.

Improving the Mechanical and Tribological Properties of NiTi Alloys by Combining Cryo-Rolling and Post-Annealing

By combining cryo-rolling and post-annealing treatments,the nanostructured NiTi alloy is produced.A diff erential scanning calorimetry measurement was used to test the eff ect of the preparation process on phase transformation.The cryo-rolling changes the tensile fracture of NiTi alloy to a ductile manner.Interestingly,the recovered structure exhibits signifi cant strength improvement,while the tensile plasticity is still comparable to that of the coarse-grained structure.This optimized mechanical performance is due to the strengthening eff ect of refi ned microstructure and the high work hardening capability rendered by moderate dislocation density.Ball-on-plate reciprocating dry-sliding wear test reveals that the nanostructured NiTi alloy also has enhanced wear resistance,which is primarily ascribed to the high content of residue martensite formed during cryo-rolling.These results provide an eff ective route to optimize the mechanical and wear properties of NiTi alloys.

Towards ultrastrong and ductile medium-entropy alloy through dual-phase ultrafine-grained architecture

Advanced materials with superior comprehensive mechanical properties are strongly desired,but it has long been a challenge to achieve high ductility in high-strength materials.Here,we proposed a new V 0.5 Cr 0.5 CoNi medium-entropy alloy(MEA)with a face-centered cubic/hexagonal close-packed(FCC/HCP)dual-phase ultrafine-grained(UFG)architecture containing stacking faults(SFs)and local chemical order(LCO)in HCP solid solution,to obtain an ultrahigh yield strength of 1476 MPa and uniform elongation of 13.2%at ambient temperature.The ultrahigh yield strength originates mainly from fine grain strength-ening of the UFG FCC matrix and HCP second-phase strengthening assisted by the SFs and LCO inside,whereas the large ductility correlates to the superior ability of the UFG FCC matrix to storage disloca-tions and the function of deformation-induced SFs in the vicinity of the FCC/HCP boundary to eliminate the stress concentration.This work provides new guidance by engineering novel composition and stable UFG structure for upgrading the mechanical properties of metallic materials.

Development of Flake Powder Metallurgy in Fabricating Metal Matrix Composites:A Review

Powder metallurgy （PM） is one of the most applied processes in the fabrication of metal matrix composites （MMCs）. Recently, a novel PM strategy called flake PM was developed to fabricate MMCs with nano-laminated or hierarchical architectures. The name ＂flake PM＂ was derived from the use of flake metal powders, which could benefit the uniform dispersion of reinforcements in the metal matrices and thus result in balanced strength and ductility. Flake PM has been proved to be successful in the dispersion of nano aluminum oxides, carbon nanotubes, graphene nano-sheets, and microsized B4C particles in aluminum or copper matrix. This paper reviews the technique and mechanism developments of flake PM in previous studies, and foresees the future develop of this new fabricating method.