Simultaneous Improvement Of Strength Research Articles

Comparison of the effects of Mg and Zn on the interface mismatch and compression properties of 50 vol% TiB2/Al composites

Low ductility limits the extensive application of high volume fraction (>30 vol%) ceramic particle-reinforced metal matrix composites, and the simultaneous improvement of strength and ductility is still a challenge owing to the smaller amount of matrix contained in such composites. In this paper, the effects of various contents of Mg or Zn (0, 6, 10 and 14 wt%) on the interface mismatch and compression properties of 50 vol% TiB2/Al composite fabricated in situ are comparatively studied. The results indicate that Mg has a better refinement effect than Zn on the TiB2 ceramic particles. Mg can reduce the crystallographic mismatch degree of the Al/TiB2 interface. 6 wt% Mg simultaneously increases the σ0.2, σUCS and εf of the composite into 780 MPa, 1162 MPa and 10.68%, compared with the composite without the addition of Mg, increasing 8.5%, 2.8% and 30.6%, respectively. However, the addition of Zn leads to serious distortion of the Al lattice and deteriorates the interface matching degree of Al/TiB2, so the addition of Zn generally improves the σ0.2 and σUCS while sacrifices the plasticity simultaneously. Furthermore, the contributions of various strengthening mechanisms of the matrix in the high volume fraction TiB2/Al composites are analyzed through a comparative study.

Unique crystallographic texture formation in Inconel 718 by laser powder bed fusion and its effect on mechanical anisotropy

Additive manufacturing offers an exclusive way of anisotropic microstructure control with a high degree of freedom regarding variation in process parameters. This study demonstrates a unique texture formation in Inconel 718 (IN718) using a bidirectional laser scan in a laser powder bed fusion (LPBF) process for tailoring the mechanical properties. We developed three distinctive textures in IN718 using LPBF: a single-crystal-like microstructure (SCM) with a <110> orientation in the build direction (BD), crystallographic lamellar microstructure (CLM) with a <110>-oriented main layer and <100>-oriented sub-layer in the BD, and polycrystalline with a weak orientation. The microstructure observations and finite element simulations showed that the texture evolution of the SCM and CLM was dominated by the melt-pool shape and related heat-flow direction. The specimen with CLM exhibited a simultaneous improvement in strength and ductility owing to the stress-transfer coefficient between the <110>-oriented main and <100>-oriented sub-grains, showing superior mechanical properties compared to cast-IN718. This behavior is largely attributed to the presence of the boundary between the main and sub-layers (crystallographic grain boundary) lying parallel to the BD uniquely formed under the LPBF process. Furthermore, the strength–ductility balance of the part with the CLM can be controlled by changing the stress-transfer coefficient and the Schmidt factor through an alteration of the loading axis. Control of the crystallographic texture, including the CLM formation, is beneficial for tailoring and improving the mechanical performance of the structural materials, which can be a promising methodology.

The roles of oxygen content on microstructural transformation, mechanical properties and corrosion resistance of Ti-Nb-based biomedical alloys with different β stabilities

The effects of oxygen content on phase transformation, mechanical properties and corrosion resistance of TiNb based alloys with different Nb contents (15, 32 and 38 wt%), i.e. different β stabilities were investigated. The results show that the oxygen does not change the phase constitution of α’-type Ti15Nb based alloy with low β phase stability, while the oxygen can suppress the α” martensite and ω phase, acting as β-stabilizer in the higher β phase stability of Ti32Nb and Ti38Nb based alloys. The addition of oxygen increases strength through solid solution strengthening and/or modification of deformation behavior. It has been found that simultaneous improvement in strength and ductility can be achieved in each base alloy by doping a certain content of oxygen. Young's modulus of Ti-Nb-O alloys exhibits different trends with oxygen increasing, which is related to the different effects of oxygen on phase stability. A desirable balance between low Young's modulus and high strength can be obtained through controlling oxygen and Nb content. The Ti-Nb-O alloys exhibit a high degree of corrosion resistance within simulated body fluid (SBF) at 310 K. Particularly, the Ti-38Nb-0.5O alloy exhibits low Young's modulus (52 GPa), high yield strength (1141 MPa) and good elongation (22%), which has potential in biomedical applications.

Reinforcement with intragranular dispersion of carbon nanotubes in aluminum matrix composites

Carbon nanotubes (CNTs) reinforced Al composites with a unique intragranular dispersion were obtained by using ultra-short CNTs. Nano-scaled CNTs were uniformly distributed inside the ultrafine Al grains. In comparison with typical CNT/Al composites with intergranular CNTs dispersion, this intragranular CNT/Al composites enable stronger dislocation pinning and retention, thereby exhibits simultaneous improvement in strength and ductility. The present intragranular dispersion strategy will provide inspirations for fabricating strong and ductile nanocarbon reinforced metal matrix composites.

Keyhole mode induced simultaneous improvement in strength and ductility of Sc modified Al–Mn alloy manufactured by selective laser melting

The effect of melting modes on microstructure evolution and tensile properties of selective laser melted (SLM-ed) Sc modified Al–Mn alloy (Al–5Mn-0.6Sc) is investigated in this work. With the transition of melting mode from conduction to keyhole by coinstantaneous increasing the laser power from 200 W to 380 W and the scanning speed from 800 mm/s to 1400 mm/s, the columnar grain width significantly decreases by 88% from 34.9 μm to 4.2 μm. Consequently, the yield strength and the elongation increase simultaneously from 266 MPa and 10% to 308 MPa and 17%, which increase by 16% and 70%, respectively. The refinement and orientation diversification of the grains caused by keyhole mode simultaneously improve the strength and elongation by inducing the Hall-Petch effect and enhancing the crack path tortuosity. This work reveals the feasibility and the mechanism of changing melting mode acts as a method to regulate the SLM-ed microstructure and mechanical properties.

Simultaneous improvement in strength and ductility in low carbon steel via intercritical annealing and quenching treatments

Abstract Hot-rolled low carbon steel sheets offer huge potential to be used in automotive body structures. Hot rolled steel sheets were subjected to intercritical annealing and quenching treatment to obtain high strength and ductility. Optical, scanning electron microscopy and X-ray diffraction were carried out to understand the underlying mechanisms. Microstructure and mechanical property correlation were established. High strength was achieved by increasing hard martensitic phase volume fraction in the soft ferrite matrix. Ductility was imparted by the ferrite matrix and martensite plasticity. Simultaneous improvements in strength and ductility were obtained by optimizing the ferrite-martensite microstructure during intercritical annealing and quenching.

Simultaneous improvements in strength and formability of modified Mg–2Zn alloys by alloying addition and twin-roll casting process

The limited applicability of magnesium alloy sheets is attributed to the absence of strength and poor formability at room temperature. Strength is generally correlated to formability. It is crucial to achieve simultaneous improvements in both strength and formability. In this study, a novel Mg–2Zn based-alloy sheet was designed with modifications by adding particular alloying elements and processing via twin-roll casting (TRC) process. Microstructure evolutions during fabrication process in three experimental alloys were compared. The effects of alloying addition and TRC process on microstructure and mechanical properties were analyzed. The results showed that simultaneous improvements in strength and formability of Mg–2Zn were achieved, accompanied with excellent trade-off relationship between strength and formability in magnesium composition systems. Refined grain size, weakened basal texture and altered second phase type were obtained by alloying addition. Formation of high-density nanoscale particles with uniform distribution was the main benefit of using the TRC process. Under the promoted activation of prismatic <a> slip due to massive second phase particles, modified Mg–2Zn alloys exhibited weaker basal texture during the rolling process. The main strengthening mechanisms of modified Mg–2Zn alloys included grain refinement strengthening, grain boundary strengthening, and precipitation strengthening. Improvement of formability was attributed to weakened basal texture.

The synergistic effects of ultrafine grains and nano-size Cu-rich precipitates on the mechanical properties of DP steels

Simultaneous improvement in strength and ductility has always been a major concern for ferrite/martensite dual-phase (DP) steels. To this end, the synergistic effects of ultrafine grains and nano-size Cu-rich precipitates on the mechanical properties of DP steels were studied using an experimental method combined with first-principles calculations and crystal plasticity (CP) simulations. Ultrafine-grained DP steels consisting of soft ferrite, with an approximately 10% volume fraction of martensite and dispersed nano-sized Cu-rich precipitates, were obtained through warm rolling and subsequent aging heat treatment. Compared to warm deformation with a 50% reduction, that with a 75% reduction leads to finer grains and a higher tensile strength of 976 ± 15 MPa, accompanied by a small loss in elongation due to the aligned connection of the martensite phase, preferred grain orientation distribution, and relatively higher dislocation density. The optimal mechanical properties are a yield strength of 876 ± 13 MPa, tensile strength of 976 ± 15 MPa and total elongation of 15.2%. The CP simulation results indicate that the heterogeneous distribution of martensite leads to strong strain and stress partitioning, thus facilitating early damage nucleation. Additionally, the strengthening effect of precipitation was evaluated based on shearing mechanisms, and the results suggest that the precipitation of nano Cu-rich precipitates contributes to a strengthening of approximately 300 MPa in the steels.

Effect of rotationally accelerated shot peening on the microstructure and mechanical behavior of a metastable β titanium alloy

Microstructural evolution and deformation mechanism of a metastable β alloy (Ti-10V-2Fe-3Al) processed by rotationally accelerated shot peening (RASP) were systematically investigated with optical microscopy, X-ray diffraction, electron backscatter diffraction and transmission electron microscopy. Different gradient hierarchical microstructures (gradients in α″ martensite and β phase, and hierarchical twins range from the nanoscale to microscale) can be fabricated by RASP via changing the shot peening time. The hardening behavior and tensile mechanical properties of gradient hierarchical microstructure were systematically explored. Novel deformation twinning systems of {112}α″ and {130}<310>α″ in the kinked α″ martensite were revealed during the tensile deformation. It was found that stress-induced martensitic transformation, twinned α″ martensite and the related dynamic grain refinement contribute to hardness and work hardening ability. Simultaneous improvement of strength and ductility of the metastable β titanium alloy can be achieved by introducing a gradient hierarchical microstructure.

Simultaneous improvement in strength and ductility of severely deformed niobium alloy

The present study is on the improved monotonic response of a severely deformed niobium-based alloy. Nb-1Zr alloy was processed at room temperature using equal channel angular extrusion and cold rolling. After 16 passes, a more than 2.5 times increase in yield strength is accompanied by a ductility level exceeding the as-received state. Cold rolling of the processed billets resulted in tensile strengths exceeding 1 GPa. The enhancement in both strength and ductility is explained by the microstructural evolution and the low homologous processing temperature.

Enhanced mechanical properties and corrosion resistance of a fine-grained Mg-9Al-1Zn alloy: the role of bimodal grain structure and β-Mg17Al12 precipitates

ABSTRACT A good combination of mechanical properties and corrosion performance is desired when employing Mg alloys in engineering applications. Therefore, it is essential to investigate both the mechanical properties and corrosion resistance of processed Mg alloys to determine the optimum combinations of materials properties. This study investigates the microstructure, mechanical properties, and corrosion resistance of AZ91 (Mg–9Al–1Zn, wt.%) alloys in chloride-containing environments under different processing conditions. The findings revealed that the AZ91 alloy exhibits good mechanical properties combined with high corrosion resistance after microstructure modification through equal channel angular pressing (ECAP). This microstructure was characterized by a bimodal grain structure with the formation of a high volume fraction of well dispersed β-Mg17Al12 precipitates. The superior mechanical properties of the AZ91 alloy after ECAP process were mainly attributed to the combined effect of significant grain refinement and high volume fraction of fine β-Mg17Al12 precipitates that provided grain boundary and precipitation strengthening and promoted a more uniform plastic deformation. The enhanced corrosion resistance of the fine-grained AZ91 alloy was related to the presence of a highly protective oxide layer, the formation of a highly adherent and compact layer of corrosion products, and the development of uniform corrosion with shallow corrosion pits. This simultaneous improvement in strength, ductility, and corrosion resistance of fine-grained AZ91 alloys can serve as a guide for future alloy design and represents a promising alternative for industrial applications.

The simultaneous improvement of strength and plasticity of a novel alloying steel by precipitation recovery annealing

The aim of the present study was to combine the beneficial influence of recovery annealing on plasticity and carbide precipitation on strength to simultaneously improve the plasticity and strength of the cold-rolled steel. A novel multi-alloying twinning induced plasticity (TWIP) steel bearing tungsten was designed. The microstructure and strength properties of the steel were investigated. It was observed that annealing at 400 °C with thermal stability of twins, annihilation of dislocations in addition to Fe21W2C6 precipitates, resulted in synchronous improvement of yield and tensile strengths and elongation of the cold deformed steel.

A simultaneous improvement of both strength and ductility by Sn addition in as-extruded Mg-6Al-4Zn alloy

Commercial wrought Mg alloys normally contain low alloying contents to ensure good formability. In the present work, high-alloyed Mg-6Al-4Zn-xSn (x = 1, 2 and 3 wt.%, respectively) alloys were fabricated by extrusion. Hereinto, Sn was proven to play an effective contribution to simultaneous improvement in strength and ductility that are traditional trade-off features of synthetic materials. It was found that the average grain size of those alloys decreases significantly from ∼11 to ∼4 μm as a function of Sn contents increasing from 0 to 3 wt.%, while the amounts of Mg2Sn and Mg17Al12 particles continuously increase. More importantly, the addition of Sn leads to the transformation of dominated deformation modes from {101¯2} extension twinning (1 wt.%) to pyramidal <c+a> slip (3 wt.%) during tensile tests along the extrusion direction at room temperature. The advantageous combination of ultimate tensile strength (∼366 MPa) and elongation (∼19 %) in Mg-6Al-4Zn-3Sn alloy is mainly attributed to the strong strain hardening ability induced by the enhanced activity of non-basal <c+a> slip. This work could provide new opportunities for the development of high-alloyed wrought Mg alloys with promising mechanical properties.

Damage tolerance of lamellar bone

Lamellar bone is known to be the most typical structure of cortical bone in large mammals including humans. This type of tissue provides a good combination of strength and fracture toughness. As has been shown by John D Currey and other researchers, large deformations are associated with the appearance of microdamage that optically whitens the tissue, a process that has been identified as a contribution to bone toughness. Using finite-element modelling, we study crack propagation in a material with periodic variation of mechanical parameters, such as elastic modulus and strength, chosen to represent lamellar bone. We show that a multitude of microcracks appears in the region ahead of the initial crack tip, thus dissipating energy even without a progression of the initial crack tip. Strength and toughness are shown to be both larger for the (notched) lamellar material than for a homogeneous material with the same average properties and the same initial notch. The length of the microcracks typically corresponds to the width of a lamella, that is, to several microns. This simultaneous improvement of strength and toughness may explain the ubiquity of lamellar plywood structures not just in bone but also in plants and in chitin-based cuticles of insects and arthropods.

Sandwich Method: Strategy to Fabricate Al/SiC Composites by FSP

The present study aimed to address the effect of multi-pass friction stir processing on the microstructure and mechanical features of AA3105/SiC composites fabricated using the sandwich method. To this end, 11–18-µm SiC particles were deposited as a layer between AA3105 aluminum sheets using the spraying method, and then, the sheets were sandwiched. The results indicated that an effective shear zone was generated on the advancing side of the stir zone after the second pass, where the reinforcement particles existed and were distributed by the matrix and no particle agglomeration was observed. In addition, the bulk composite fabricated with four passes exhibited that particle distribution became even more homogeneous and showed excellent bonding between the SiC particles and the AA3105 matrix. The results also revealed that after each FSP pass, toughness and ultimate tensile strength showed progressive improvement. Further, the microstructure homogeneity promoted by increasing FSP passes resulted in simultaneous improvement in strength and toughness in the FSPed samples.

Simultaneously enhancing strength and ductility of a high-entropy alloy via gradient hierarchical microstructures

Although many high-entropy alloys (HEAs) possess excellent mechanical properties, they are not exempt from the common dilemma of strength–ductility trade-off in most cases, which limits their potential applications. Herein, rotationally accelerated shot peening was used to introduce different gradient hierarchical microstructures, including gradients in twin and dislocation densities, and hierarchical nanotwin, into a CoCrFeNiMn HEA by adjusting the processing parameters. The resulting gradient structures and their effect on hardening behaviour and mechanical properties were systematically explored. Quantitative analysis indicates that deformation twinning, including hierarchical nanotwinning could be more important than dislocation slip in terms of their contribution to hardness and strain hardening capability, depending on the gradient structure profile. It was found that simultaneous improvement of strength and ductility can be achieved in a gradient structure with a thin deformed layer and an undeformed core. Based on our experimental results, we propose that a gradient structure with a largest possible strength difference between the surface layer and the undeformed core would maximize the strength–ductility synergy.

Enhanced yield symmetry and strength-ductility balance of caliber-rolled Mg–6Zn-0.5Zr with ultrafine-grained structure and bulk dimension

This study investigated a caliber-rolled Mg–6Zn-0.5Zr (ZK60) alloy as part of an effort to achieve enhanced mechanical properties and bulk dimension out of lab scale. The caliber-rolled ZK60 alloy presented a high fraction of dynamically recrystallized (DRXed) grains with submicron sizes. The alloy also exhibited simultaneous improvements in strength and ductility in comparison to commercially extruded ZK60 alloys. The ultrafine-grained (UFG) structure and enhanced mechanical properties were attained while maintaining bulk dimension, which was difficult with severe plastic deformation processes. Furthermore, caliber rolling gave rise to nearly symmetric behavior in terms of yielding. These mechanical improvements in the caliber-rolled ZK60 alloy were interpreted in light of its microstructural characteristics, such as UFG structure, DRX, precipitates, basal texture with tilting of c-axes, and activation of mechanical twinning.

Preparation of hyperbranched polymeric ionic liquids for epoxy resin with simultaneous improvement of strength and toughness

The present work is based on a study of methylhexahydrophthalic anhydride (MHHPA) cured diglycidyl ether of bisphenol A (DGEBA) in the presence of a hyperbranched ionic liquid (HBP-Mim). Differential scanning calorimetry studies confirmed that the curing reaction was accelerated by HBP-Mim. The impact strength of DGEBA (17.1 kJ/m2) increased to 39.5 kJ/m2 after the addition of 9 phr HBP-Mim-2. Tensile and flexural properties also showed a significant improvement as the incorporation of 9 phr HBP-Mim-2 resulted in 63.1% and 135.2% increase in the tensile and flexural strengths of epoxy thermosets, respectively, compared with neat DGEBA. Thermal stability and thermomechanical properties of the HBP-Mim modified epoxy thermosets also showed a significant improvement. The simultaneous improvements in the mechanical and thermal properties could be attributed to increased free volume and cross-link density.

Simultaneous improvement of strength and ductility in hypoeutectic Al-Si-Mg and Al-Mg alloys with high contents of Mg

Changes of strength and ductility in a hypoeutectic Al-7mass%Si-Mg with increasing Mg content and Al-7.5mass%Mg alloys with increasing Ca content were investigated. The elongation of Al-7.5mass%Mg alloy was improved with increasing Ca content up to 0.1mass% without trade-off with the strength. With increasing Mg and Ca contents simultaneously, the Al-7mass%Si alloys showed the modification of eutectic Si particles. After aging, the alloys had the distribution of residual Mg2Si in their grain boundaries with increasing Mg content over the Mg solubility. Al-7mass%Si-0.8mass%Mg alloy including a small amount of residual Mg2Si showed a significant improvement of strength after the aging

Carbon nanotube/carbon composite fiber with improved strength and electrical conductivity via interface engineering

Carbon nanotube/carbon (CNT/C) composites show potential for lightweight structural materials and non-metal electrical conductors for aerospace, military, and other industries where the combination of lightweight, high strength and excellent conductivity are required. Most research attempts have been reported to fabricate CNT/C composite focusing on the high CNT alignment and dense carbon matrix. However, simultaneous improvement of strength and electrical conductivity in materials still presents a great challenge. In this study, pyrolyzed polydopamine (py-PDA) with selected surface treatments is introduced as an interface enhancer between CNTs and the carbon matrix. Due to the presence of py-PDA, the effective physical interlocking and conductive pathways are rebuilt at the interface area between CNTs and carbon matrix, resulting in better load transfer and electron transport. The CNT/py-PDA/C composite fibers demonstrated remarkable improvements in electrical conductivity (2.1 × 103 S cm−1 or 228 S m2 kg−1) and tensile strength (up to 727 MPa or 790 MPa/(g·cm−3)), which should prove to be vastly advantageous as compared to the previously reported CNT/C composites. The outstanding thermal stability of fully carbonized materials is also an attractive feature. Coupled with scalable manufacturing methods, these integrated characteristics of CNT/py-PDA/C composite fiber can potentially have broad applications for lightweight structural materials and non-metal conductors.