Increase In Yield Strength Research Articles

Effect of high-pressure heat treatment on the recrystallization and recrystallization texture of CC 5005 aluminum alloy

The CC 5005 aluminum alloy was cold-rolled to different reductions and then annealed at 537 °C for 1 h under different pressures. The changes in microstructure, mechanical property and texture were investigated. The results showed that high-pressure heat treatment significantly refines the recrystallized grain, and the refinement effect is enhanced with increasing rolling reduction. The grain refinement leads to an increase in yield strength, ultimate tensile strength and hardness of the CC 5005 annealed sheet, but a decrease in elongation. The high-pressure heat treatment also has a significant effect on the recrystallization texture. High-pressure heat treatment improves the intensities of the cube and the R textures in the fully recrystallized sheets with the same reduction. The intensity of the cube texture gradually decreases, while that of the R texture gradually increases with increasing rolling reduction.

Extraordinary strength and ductility of cold-rolled 304L stainless steel at cryogenic temperature

In present work, tensile behaviors of cold-rolled 304L stainless steel were investigated at both room temperature (RT) and liquid nitrogen temperature (LNT). After cold-rolling with a thickness reduction of ∼92%, the 304L stainless steel exhibits an ultrahigh yield strength of 1787 MPa at the expense of ductility (1.06% of uniform elongation) at RT. At LNT, the yield strength (upper yield point of σyu = 2308.4 MPa and lower yield point of σyl = 1894.2 MPa) and uniform elongation (23%) increase greatly. Detailed microstructural investigation reveals that the cold-rolled 304L stainless steel comprises mainly of deformation induced martensite and high density of dislocations (9.06 ×1014m−2), leading to a lack of dislocation storage capacity and thus brittle fracture at RT. While interrupt tests at LNT reveal a first increase and then decline in dislocation density with tensile strain, accompanied with phase transformation from austenite to martensite. The delamination events also occur, characterized by the multiple separated laminated ligaments observed at fracture surface. Therefore, the high dense dislocations and transformation-induced plasticity (TRIP) effect as well as delamination toughening mechanism contributes to the excellent combination of strength and ductility at LNT. Our work provides experimental and microstructural insights into the deformation mechanisms of the ∼92%-cold-rolled 304L stainless steel during tensile deformation at RT and LNT.

Exploring the potential of Mg-Zn-Mn-Ca/ZnO composites as a biodegradable alternative for fracture fixation: microstructural, mechanical, and in-vitro biocompatibility analysis

The current research investigates the microstructural, mechanical, in vitro degradation, biocompatibility, and in silico biomechanical behaviour of highly alloyed Mg-Zn-Mn-Ca quaternary system reinforced with ZnO nanopowder as candidate material for resorbable fixation devices. The as-cast composite materials showed dendritic microstructure comprising of α-Mg as major constituent and Mg7Zn3 and Ca2Mg6Zn3 phases distributed in interdendritic zones, as revealed by X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy. The addition of ZnO led to a 17% and 22% increase in ultimate and yield strengths in tension and a 24% and 27% enhancement in ultimate compressive and compressive yield strengths, respectively. The mechanical strengthening and observed tension–compression reversed yield asymmetry strongly correlated with the lattice distortion (c/a ratio) resulting from the macroalloying. The amplitude-dependent internal friction confirmed the presence of immobile obstacles to dislocations and their role through their hysteretic-type anelastic response. The in vitro degradation results revealed corrosion barrier effect of secondary phases. The cell adhesion, viability, and cytoskeleton observations favoured their biocompatibility except for hemolysis rate. The finite element results showed reduced stress-shielded zone for developed materials indicating the favourable mechanical environment for peri-implant tissues at fracture interface required for faster fracture healing.

Hydrogen-induced microstructure optimization and mechanical properties enhancement of forged (TiB + TiC)/Ti6Al4V

This study investigates the impact of hydrogen on the mechanical properties and microstructure of forged titanium matrix composites (TMCs) reinforced with 2.5 vol% TiB and 2.5 vol% TiC. Melt hydrogenation technology was used to fabricate the TMCs with different hydrogen contents, which were then forged at 880 °C. Microstructural analysis revealed that hydrogen accelerated atomic diffusion, resulting in an approximate network microstructure. Hydrogen also promoted dynamic recrystallization during forging, leading to grain refinement and reduced dislocation density. Room temperature tensile tests showed that hydrogen significantly improved the strength and ductility of the forged TMCs within a certain range of hydrogen content. The greatest improvement was observed in the forged TMCs with a hydrogen content of 7.87 × 10−2 wt%, which exhibited a 10.48% increase in yield strength and a 31.36% increase in ductility relative to those without hydrogen. The effects of hydrogenation on crack propagation mechanisms are also discussed in detail. Overall, these findings provide valuable insights into the strengthening and toughening of forged titanium matrix composites through hydrogenation.

Regulating microstructure of novel Al-Mg-Zn alloy for enhancing comprehensive performance through retrogression and thermo-mechanical treatment

A new generation aluminum alloy strengthened by T-Mg32(AlZn)49 phase has been created in the last decade based on 5xxx series AlMg alloy modified with the idea of precipitation strengthening in 7xxx series alloys, promising to overcome the trade-off between corrosion performance and mechanical properties. Herein, a novel retrogression and thermo-mechanical treatment (RTMT) was designed to further enhance comprehensive properties of the T-phase strengthened alloy through combining strain-hardening and precipitation-hardening. By comparing with traditional peak-aging treatment, retrogression and re-aging treatment, and final thermo-mechanical treatment, RTMT achieves an increase in tensile and yield strength of the alloy to 587.9 MPa and 537.5 MPa, respectively, and a significant reduction in the maximum intergranular corrosion depth to 37.5 μm simultaneously. Microstructure observation indicates that the enhanced interaction between the regulated precipitates and dislocations introduced during deformation is the key to synergistic improvement of corrosion and mechanical properties. The processing technology can be extendable to other age-hardening alloy systems for further development and application.

Microstructure and mechanical properties of Al–Zn–Mg–Cu (7075) alloy tubes prepared via power stagger spinning

The tubes of 7075 aluminum alloy were fabricated by power stagger spinning at 400 °C (HS) and room temperature (RTS), and then the microstructure evolution and mechanical properties were investigated. Results show that the grains after spinning are refined prominently, and the tubes after 60% and 70% thickness reduction (HS-60% and HS-70%) are dominated by the deformed structure, while the recrystallized structure is dominant in the tube after 85% thickness reduction at 400 °C (HS-85%). Furthermore, a bimodal grain structure with a weak Cube texture is obtained in the HS-85% sample due to the emergence of the dynamic recrystallization (DRX) and abnormal grain growth. As the thickness reduction increases from 0% to 85% during spinning at 400 °C, the yield strength (YS) and ultimate tensile strength (UTS) increase first and then decrease, while the elongation decreases first and then increases. Compared with that of the HS-85% sample, the UTS and YS of RTS-85% sample are 613.5 and 567.9 MPa, respectively, which are improved by 33.7% and 57.4%, while the elongation is only 7.3%.

Grain boundary segregation strengthening behavior caused by carbon chain network formation in nanocrystalline NiCoAl alloy

Grain boundary movement is closely related to plastic deformation of materials. In our contribution, C atoms are introduced into the grain boundary and a highly stable C chain network is formed through structural optimization. The results show that the formation of C chains greatly enhances the stability of the grain boundaries and exhibits strong dislocation pinning capability. With the increase of C content, the generation of phase transformation and the nucleation of dislocations are inhibited. The yield strength and tensile strength first increase and then decrease, showing three different deformation mechanisms during tensile deformation. High-density dislocations and unstable grain boundaries jointly control the mechanical properties in the first stage. When the C content comes to 1%, the formation of C chain network greatly enhances the stability of the grain boundaries and effectively hinder and pin the dislocations, inducing a strengthening effect. In the third stage, the further increase of C content severely inhibits the nucleation of dislocations, and leads to a decline in the mechanical properties of alloy. This new strategy of modifying grain boundaries by introducing non-metallic atoms provides an interesting and positive idea for grain boundary engineering.

Experimental and Numerical Study on RC Beams Strengthened by NSM Using CFRP Reinforcements

Near Surface Mounted (NSM) Carbon Fiber-Reinforced Polymer (CFRP) reinforcement technique to improve the flexural strength of reinforced concrete members has become increasingly attractive in recent years. In this study, the practical problem of concrete cover depth cutting limitation was investigated. Twelve specimens were tested by four-point bending until failure. Experimental parameters include concrete cover depth, CFRP reinforcement type, CFRP positioning, and stirrups status. Furthermore, a nonlinear FEA model was developed to simulate the tested beams and was able to predict the experimental behavior satisfactorily. A series of parametric studies were then performed using this model to understand the effect of various reinforcement parameters on the flexural performance of the beam. The results showed that Strengthening with CFRP resulted in a significant increase in yield and ultimate strengths, but a significant ductility loss was recorded due to CFRP strip debonding in the strengthened beams, this problem was addressed by using more efficient strengthening techniques utilizing the effective bond length and a proper groove depth and positioning for the NSM bars.

Design and Performance of Layered Heterostructure Composite Material System for Protective Armors.

A new layered heterostructure composite material system (TC4 as front layer and 2024Al alloy as back layer) was developed and analyzed for its design and performance in terms of an enhanced absorption capability and anti-penetration behavior. The Florence model for energy absorption was modified, so that it can be utilized for the layered heterostructure composite material system with more efficacy. Numerical simulation through Ls-Dyna validated the analytical model findings regarding the energy absorption of the system and both were in good agreement. Results showed that two ductile materials with diverse properties, the hardness gradient and varied layer thickness joined together, specifically behaved like a unified structure and exhibited elastic collision after slight bending, which is possibly due to the decreased yield strength of the front layer and increased yield strength of the second layer. To validate the analytical and numerical findings, the samples of the layered heterostructure composite material system were subjected to a SHPB (Split Hopkinson pressure bar) compression test. The deformation behavior was analyzed in the context of the strain energy density and stain rate sensitivity parameter at different strain rates. The encouraging results proposed that two ductile materials with a hardness gradient can be used as an alternate structure instead of a brittle-ductile combination in a layered structure.

Dendrite structure-induced tunable plastic deformation behavior in (Ti-V-Cr)100-xWx refractory high entropy alloys

Inducing multiple deformation mechanisms to improve the plasticity of refractory high entropy alloys (RHEAs) is crucial for their engineering applications. In this work, the dendrite structure-induced deformation behavior in a series of novel (TiVCr)100-xWx (x = 5, 7.5, 12.5, 15 at.%) RHEAs was investigated. The formation of dendrite structures was confirmed by both theoretical (CALPHAD) and experimental methods, and the relationship between dendrite structure and mechanical properties was established. The findings indicated that the volume of interdendrite was conducive to enhance the fracture strain while the finer dendrite benefited the increase of yield strength. With the change of dendrite structure, the plastic deformation mode of the RHEAs also changed accordingly. The slip bands tended to concentrate in the interdendrite, and propagate along the softer interdendrite regions while being hindered by the harder dendrite. The dendrite refinement strengthening, as well as the solid solution strengthening contributed to the strength enhancement. Overall, the present (TiVCr)100-xWx RHEAs demonstrated high specific yield strength and good plasticity when compared with the similar W-containing HEAs. The present findings not only give more insight into the deformation behavior in RHEAs, but also provide a potential strategy to tune the mechanical properties of RHEAs with dendrite structures.

Abnormal mechanochemical effect in ultraprecision machining of an additively manufactured precipitation-strengthened high-entropy alloy

Recently, researchers have explored the use of precipitation strengthening and finer microstructures with high-density dislocations in additive manufacturing to produce high-entropy alloys (HEAs) with adjustable properties. However, the inherent surface roughness and lack of machinability research in AMed HEAs limit their engineering applications. In this study, we systematically investigated the microstructural characteristics, mechanical properties, and machinability of Fe29.3Co28.7Ni28.6Al6.8Ti6.6 (at.%) HEAs with three different structures: single FCC phase cellular (SPC), dual precipitation-strengthened (DPS), and single precipitation-strengthened (SPS). These structures were fabricated by selective laser melting and isothermally annealing at 780 and 940 °C. Compared to SPC HEA, DPS HEA exhibits a significant increase in yield strength and ultimate tensile strength but with a dramatic sacrifice in ductility. SPS HEA exhibits similar mechanical properties to SPC HEA due to the pronounced coarsening of L21 precipitates. The ultraprecision machining micro-cutting test showed that SPC HEA had a significant mechanochemical effect, as evidenced by a sharp drop in cutting force for inked workpieces, but not DPS HEA. An abnormal finding was that the negligible reflection of cutting force for SPS HEAs suggested a negative mechanochemical effect, even though SPS HEA had equally excellent plasticity like SPC HEA. It was found that nanocrystallization-induced strength enhancement and ductility reduction of SPS HEA lead to chips’ deformation dominated by shear avalanche rather than chip folding of SPC HEA, which involves the reduction of surface energy and friction of chips’ interfaces. Overall, these results and our research findings may guide the machining of AMed precipitation-strengthened HEAs and accelerate their engineering application.

Revealing the Role of Cerium on Precipitation Behavior of In Situ TiC Particles and Wear Resistance of High‐Titanium Wear‐Resistant Steels

Compared to conventional martensitic wear‐resistant steels of the same hardness, high‐titanium wear‐resistant steels with in situ TiC particles can significantly improve wear resistance. However, micron‐sized TiC particles will decrease the toughness of high‐titanium wear‐resistant steels. Here, in order to improve wear resistance without reducing impact toughness, we incorporate 0.0025% cerium elements into high‐titanium wear‐resistant steels. Compared with no cerium steel, the steel containing cerium is demonstrating comparable mechanical properties, with the yield strength of 1283 MPa and impact toughness of 35.6 J, and the wear performance of the steel containing cerium is 1.78 times that of the steel with no cerium. The results show that with the addition of cerium the effective grain size of the steel decreases, and yield strength and toughness increase. The addition of cerium can form intermetallic compounds of Ce2O2S, which are used as heterogeneous nuclear particles in TiC to form rare earth composite particles calculated by the 2D mismatch theoretical model of Bramfitt. As the average spacing of the reinforcing phase particles in the steel decreases, the effective grain size of the steel decreases, and the number of reinforcing phase particles increases, the wear resistance of the steel with the addition of cerium is optimized.

Enhanced age-hardening of an Al–5Mg–2Zn–1Cu alloy by pre-aging combined with pre-straining

In this work, the synergistic effect of pre-aging and pre-straining on the enhanced age-hardening response of an Al–5Mg–2Zn–1Cu alloy has been systematically investigated using high-resolution transmission electron microscopy (HRTEM) and atom probe tomography (APT). After pre-aging, only Guinier Preston (GP) zones uniformly distribute in the α-Al matrix. Moreover, dislocations induced by pre-straining can promote the nucleation and growth of T″ and T′ precipitates. With the synergy of pre-aging (80 °C/5 h) and pre-straining (∼4%) treatments, the alloy after second-aging at 130 °C for 12 h exhibits a giant increase of yield strength (∼182 MPa) in comparison to the as-solutionized alloy, reaching ∼348 MPa. The above results show that pre-aging and pre-straining are effective in accelerating the hardening response of Al–Mg–Zn–Cu alloys. Especially, this extraordinary age-hardening response depends strongly on the high number density and uniform distribution of the GP zones induced by pre-straining, acting as preferential nucleation sites for T″ phase and T′ phases during subsequent aging treatment. In addition, it proves that pre-aging and pre-straining can effectively control the precipitation free zones (PFZs) size, relieving the strain concentration in PFZs and improving the comprehensive mechanical properties.

Influence of scandium addition on microstructure and mechanical properties in nickel-based superalloys: An integrated multiscale modeling and experimental approach

Microalloying has long been recognized as an effective method for improving the mechanical properties of metallic materials and developing new ones. In this study, we comprehensively investigate the effects of Sc addition on the microstructural evolution and mechanical performance of nickel-based superalloys using a combination approach of the experiment, first-principles calculation, and multiscale modeling. The results show that Sc addition simultaneously improves the yield strength increasing from 1068 MPa to 1172 MPa (9.7%) and elongation increasing from 13.4% to 19.7% (47%). The microstructural characterizations reveal that Sc addition refines the grain size, increases the volume fraction of primary precipitate, induces the coarsening of secondary precipitates, and produces a new type of Sc-rich particle. First-principles calculations from the atom probe tomography experiment show that the anti-phase boundary energy of secondary precipitate is significantly increased in Sc-containing superalloys. A modified alloying-dependent yield strength model is developed by considering the multimodal precipitate size distribution and microstructure evolution obtained from experiments and atomic simulations. The increased yield strength originates from not only the Sc addition induced increased volume fraction of primary precipitate at grain boundary to enhance grain boundary strengthening, but also Sc addition induced increased anti-phase boundary energy of secondary precipitate to improve the precipitate strengthening. The increased elongation depends on the fact that the Sc element has a good affinity to deleterious elements and forms Sc-rich particle and oxygen-rich precipitate to enhance grain boundary strength. This work integrating multiscale modeling and experiment can be denoted as a universal framework to study the influence of alloy element on the microstructure and properties, which gives guiding significance to screen and design high-performance superalloys.

Effect of low-temperature hot rolling on the microstructure and mechanical properties of air-cooling medium manganese martensitic wear-resistant steel

In this paper, the low-temperature hot rolling was conducted on air-cooled medium manganese martensitic steel, utilizing a finishing rolling temperature (FRT) that was significantly lower than the conventional used temperature. The effect of FRT on the microstructure, mechanical properties and wear resistance was systematically investigated. The results revealed that the pancaked austenite grain formed after low-temperature hot rolling could still be completely transformed into martensite structure under air-cooled condition. The lower FRT significantly refined the martensite multi-level microstructures, increased the grain boundaries density and dislocations density, and promoted the nano-scaled V(C, N) precipitation. These resulted in enhanced refinement strengthening, dislocation strengthening and precipitation strengthening. Compared to the FRT-900 sample, the FRT-700 sample exhibited increased yield strength, tensile strength, and Brinell hardness, with values rising from 973 MPa, 1526 MPa, and 454 HB to 1174 MPa, 1701 MPa, and 482 HB, respectively. In addition, the refined microstructure effectively increased the dimple region in the fractography of impact samples, preventing the propagation of crack and thereby enhancing the impact absorbing energy. Consequently, the impact absorbed energy at −40 °C of experimental steel was increased from 28 J to 38 J, while also increasing strength. Moreover, the low-temperature hot rolling effectively increased the surface hardness of the experimental steel, inhibited abrasive embedding and improved impact wear resistance. The mass loss rates of low-temperature hot rolling samples were 0.052 mg/s and 0.063 mg/s under the impact energy of 1 J and 2.5 J, respectively.

Effect of solution treatment of AZ91 alloy on microstructure, mechanical properties and corrosion behavior of friction stir back extruded AZ91/bioactive glass composite

In the present study, we investigated the effects of solution treatment and friction stir back extrusion on the microstructure, mechanical properties, and in-vitro corrosion behavior of the AZ91/64SiO2–31CaO–5P2O5 composite. The findings demonstrate that the reinforcing phase of bioactive glass in the AZ91 matrix exhibits a gradient distribution, resulting in grain refinement in the zone near the surface of the composite wire. The fabrication of the AZ91-3 vol% bioactive glass composite through friction stir back extrusion, utilizing a rotational speed of 1200 rpm and an extrusion speed of 20 mm/min, leads to a significant improvement in corrosion resistance compared to the solid solutionized AZ91 alloy, as demonstrated by a ∼93% increase in simulated body fluid (SBF). During the friction stir back extrusion of the solid solutionized AZ91 alloy, heat and plastic deformation result in the re-precipitation of the ß-Mg17Al12 phase in the α-Mg matrix. The presence of bioactive glass particles facilitates this re-precipitation process during friction stir back extrusion. In comparison to the solid solutionized AZ91 alloy, the AZ91-3 vol% bioactive glass composite exhibits a 23% increase in ultimate tensile strength (UTS), a 28% increase in yield strength (YS), and a 30% decrease in elongation.

Effect of various non-isothermal aging on properties and microstructure of 7055 aluminum alloy

This study investigated the effect of various non-isothermal aging processes on the mechanical properties and corrosion resistance of 7055 aluminum alloy extruded bars. The investigation utilized electrical conductivity, mechanical properties, local corrosion resistance and slow strain rate tensile test combined with microstructure characterization techniques such as metallographic microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that the NIA-2 (120 °C→200 °C/30 min→120 °C, v = 30 °C/h) process significantly improves the strengths of the alloy compared to the T73 temper, the tensile strength and yield strength increase by 53.0 MPa–632.5 MPa and by 64.7 MPa–605.4 MPa respectively. Additionally, the maximum depths of intergranular corrosion (IGC) and exfoliation corrosion (EXCO) decrease from 80.6 μm to 97.7 μm–71.4 μm and 89.5 μm respectively. Therefore, the NIA-2 process can achieve both high strength and excellent corrosion resistance. Furthermore, the study shows that the sizes of grain boundary precipitates (GBPs) and matrix precipitates (MPs) increase with the sequence of NIA-1 (120 °C→200 °C→120 °C, v = 30 °C/h), NIA-2, and NIA-3 (120 °C→200 °C→120 °C, v = 20 °C/h) processes. The atomic percentages of Zn, Mg, and Cu in GBPs also vary with the different processes. The increases in the sizes of GBPs, MPs, and the widths of precipitation-free zones (PFZs), as well as the segregations of GBPs components, are primarily responsible for the improved mechanical properties and corrosion resistance of the alloy.

Molecular dynamics studies of the effect of intermediate Fe layer thickness on the enhanced strength and ductility of Cu/Fe/Ni multilayer

The synergistic strength-ductility is very important for composite materials. In this work, we studied the effect of intermediate layer thickness on the mechanical properties of Cu/Fe/Ni multilayer by introducing harder intermediate layer and non-coherent interface using molecular dynamics simulation, and revealed the relationship between the deformation mechanism and the strength-ductility from atomic scale. The results show that the yield strength and flow stress increase with increasing Fe layer thickness, but the tensile strain is opposite. Plastic deformation of all models are triggered by slipping of misfit partial dislocation originating from the decomposition of perfect dislocation on semi-coherent interface. However, the addition of Fe layer and non-coherent interface increases the resistance of dislocation crossing interface, and changes the dominant deformation mechanism from Shockley partial dislocation slipping to deformation twinning migration, thus improving the strength and ductility of multilayer. In addition, the evolution laws of the dislocation length and interface morphology as well as the shear strain distribution are discussed.

Rolling-induced enhancement of strength in Mg-3Al-3Nd-0.5Mn alloy

In this study, the microstructures and mechanical properties of a rolled Mg-3Al-3Nd-0.5Mn alloy were studied. The rolling process successfully produced a mixed crystal structure in the alloy. The Al2Nd, Al8Mn4Nd phases and the broken Al11Nd3 during the rolling process were found to refine the grains significantly, the theory of Particle Stimulated Nucleation (PSN) can explain the phenomenon. In addition, the formation of a mixed crystal structure was promoted by the precipitation of nano-sized Al8Mn4Nd in a dynamic manner. After comparing the rolled alloys to the as-cast alloys, there was an increase in Yield Strength (YS) and Ultimate Tensile Strength (UTS) of 107.4 MPa and 48.4 MPa, respectively.

Improvement of mechanical properties and thermal stability of Al–Cu–Mg–Ag alloy by warm rolling

In this paper, the microstructure, mechanical properties and thermal stability of Al–Cu–Mg–Ag alloys processed by warm rolling were compared with cold rolling with same strains using scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the strengthening mechanism has been quantitatively investigated. The mechanical properties of the Al–Cu–Mg–Ag alloy are significantly improved by warm rolling at 200 °C and subsequent artificial aging at 180 °C, both before and after heat exposure at 200 °C for 100 h. Microstructure investigations revealed that compared to cold-rolled samples, warm-rolled samples have a higher number density of Ω plates after artificial aging, and the increase in yield strength caused by precipitation strengthening is greater. After heat exposure at 200 °C for 100 h, although the Ω plates in the warm-rolled samples are coarser compared to the cold-rolled alloys, the number densities are higher. Therefore, warm-rolled samples exhibit better mechanical properties than cold-rolled samples.