Simultaneous Enhancement Of Strength Research Articles

Effect of Microalloying Rare-Earth Nd on Microstructure Evolution and Mechanical Property of Cu Alloy

Cu alloys have been widely used in the manufacture of liners because of their high density, good plasticity, and excellent thermal conductivity. In order to achieve excellent jet stability and penetration performance, it is necessary to further improve the mechanical properties of Cu-based liners. Nevertheless, the simultaneous enhancement of strength and ductility of the Cu alloys remains a huge challenge due to the strength–ductility trade-off phenomenon of metals/alloys. In this study, the microstructure evolution of rare earth Nd-modified Cu alloy and its effect on mechanical properties were investigated using OM, SEM, EBSD, and TEM techniques. The results show that the ultimate tensile strength (218 MPa) and elongation (50.7%) of sample 1 without Nd are the lowest. With increasing Nd content; the tensile strength and elongation of the samples increase; and the mechanical properties of sample 4 are the best, with a tensile strength of 278.6 MPa and elongation of 65.2%. In addition, with the increase in Nd content, not only is the grain size of the Cu-Nd alloy refined, but also the strength and plasticity are improved so that the strength–ductility trade-off phenomenon is improved. The strength improvement is mainly attributed to grain refinement strengthening, dispersion strengthening, and strain hardening. The increase in ductility is mainly related to the improvement of the microstructure heterogeneity by the Nd element.

Simultaneous enhancement of strength and ductility of Al matrix composites enabled by submicron-sized high-entropy alloy phases

Our study investigated the reinforcing effect of submicron-sized (100–500 nm) Al0.5CoCrCuFeNi high-entropy alloy particles (HEAps) on the tensile properties of Al matrix composites. The HEAps were refined to the submicron-sized level via a thermal plasma process to maximize reinforcing efficiency by increasing specific surface (i.e., interface) area. The Al/HEA composites were produced by hot rolling of mechanically milled Al/HEA composite powder. The microstructural analysis demonstrated that the HEAps were uniformly dispersed within the Al matrix by forming a sound interface without interdiffusion brittle intermetallic layers or any noticeable voids. Moreover, the addition of 2 vol% HEAps resulted in a simultaneous increase in both yield strength from 355 to 403 MPa and tensile elongation from 1.3 to 3.3%. As a result, the composite experienced a synergistic effect due to the combination of intrinsic strengthening to promote uniform plastic deformation and extrinsic strengthening to mitigate plastic instability and crack propagation.

Enhanced strength–ductility synergy of SiC particles reinforced aluminum matrix composite via dual configuration design of reinforcement and matrix

To overcome the strength-ductility conflict in particle reinforced aluminum matrix composites (PRAMCs), a novel dual configuration strategy of microstructure was proposed in this work. The dual configuration including both heterogeneous grain structure and hybrid reinforcements was obtained by powder metallurgy, which was designed as submicron-sized SiC particles (SiCsm)/Al and micron-sized SiC particles (SiCm)/2024Al components. Representative alternating coarse grain (CG) bands containing SiCm and ultra fine grain (UFG) bands with dispersed SiCsm were revealed in microstructural characterizations. Compared to corresponding homogeneous composites with the same fraction particles, the dual configuration composite achieved simultaneous enhancement in strength and ductility and remained a comparable Young’s modulus of 98GPa, which represented 442 MPa in yield strength, 590 MPa in ultimate strength and 8.7 % in fracture elongation. The extra strength provided by hetero-deformation induced (HDI) strengthening is a potential dominant strengthening mechanism. The intrinsic toughening mechanisms primarily contribute to HDI strain hardening and enhanced dislocation accumulation capacity, while the extrinsic toughening mechanisms presumably attribute to more uniform microcrack distribution and blunting effect of CG zones on cracks. Our work provides a feasible route including ball milling and powder assembly to preparate high-modulus aluminum matrix composites for strength-ductility balance design.

Simultaneous enhancement of strength and ductility in Al-Zn-Cu casting alloy with trace Mg addition designed by first principle calculation

The Al alloy containing 17 wt% Zn exhibits enhanced strength through Zn precipitation after casting without the need for further aging treatment. DFT (Density Functional Theory) calculations revealed that the addition of Cu and Mg elements to Al-Zn alloy has the potential to stabilize the Zn phase in the Al matrix and reduce the interface energy between the Zn precipitate and Al matrix. Based on these findings, 0.5 wt% Cu and 0.1 wt% Mg were added to the Al-17 wt% Zn alloy. The trace element level of 0.1 wt% Mg addition led to a significant increase in both yield and tensile strength, from 132 to 278 and from 248 to 310 MPa, respectively, compared to the Al-17 wt% Zn alloy with 0.5 wt% Cu. Furthermore, their ductility surpassed 11 %. The trace amount of Mg greatly increased yield and tensile strength, while Cu enhanced the ductility in the Al-Zn alloy after casting without any aging treatment.

Simultaneous enhancements in strength and ductility of hexagonal BN nanosheet reinforced AlSi10Mg composites

We herein report fabrication of hexagonal boron nitride nanosheet (BNNS) reinforced AlSi10Mg composites using a combination of spark plasma sintering (SPS) and hot rolling, the microstructure and mechanical properties of the resulting composites were investigated. The obtained composites present dense microstructure with BNNS uniform distribution. Trace amounts of in-situ interfacial-reaction products such as AlN, AlB2 are observed to endow BNNS-Al interface with good adhesive strength, the interfacial reactions are greatly governed by atom competitive diffusion. In comparison with monolithic AlSi10Mg alloy, the BNNS/AlSi10Mg composites display simultaneous improvements in tensile strength and ductility. In particular, the AlSi10Mg composite with 0.5 wt% BNNS addition exhibits a yield strength of ∼221 MPa and an elongation of ∼8.3 %, representing enhancements of ∼12.7 % and ∼29.7 %, respectively. The possible synergetic strengthening and toughening mechanisms of the resulting composites are discussed based on the test results.

Simultaneous Enhancement of Strength and Sulfide Stress Cracking Resistance of Hot-Rolled Pressure Vessel Steel Q345 via a Quenching and Tempering Treatment.

Sulfide stress cracking (SSC) failure is a main concern for the pressure vessel steel Q345 used in harsh sour oil and gas environments containing hydrogen sulfide (H2S). Methods used to improve the strength of steel usually decrease their SSC resistance. In this work, a quenching and tempering (Q&T) processing method is proposed to provide higher strength combined with better SSC resistance for hot-rolled Q345 pressure vessel steel. Compared to the initial hot-rolled plates having a yield strength (YS) of ~372 MPa, the Q&T counterparts had a YS of ~463 MPa, achieving a remarkable improvement in the strength level. Meanwhile, there was a resulting SSC failure in the initial hot-rolled plates, which was not present in the Q&T counterparts. The SSC failure was not only determined by the strength. The carbon-rich zone, residual stress, and sensitive hardness in the banded structure largely determined the susceptibility to SSC failure. The mechanism of the property amelioration might be ascribed to microstructural modification by the Q&T processing. This work provides an approach to develop improved strength grades of SSC-resistant pressure vessel steels.

Substitutional and interstitial atoms co-doping overcomes the strength–ductility trade-off in lightweight refractory medium-entropy alloys

Interstitial or substitutional solid solution strengthening is a common method for enhancing material mechanical properties, however, it is unclear whether their synergy can lead to better mechanical properties in materials. Here, we have demonstrated that the synergy of interstitial and substitutional elements can overcome the strength-ductility trade-off, which was substantiated in an O and Al co-doping (TiZrNb)94.5O0.5Al5 (O0.5Al5) lightweight refractory medium-entropy alloy (LRMEA) with a density ∼6.0 g/cm3. The co-doping LRMEA exhibits a simultaneous enhancement in strength and ductility with a yield strength of ∼1025 MPa and a fracture elongation of ∼35%, compared with the O or Al single doped alloys, i.e. (TiZrNb)99.5O0.5 (O0.5) and (TiZrNb)95Al5 (Al5). This combined increase in strength and ductility was attributed to synergistic interstitial and substitutional solid solution strengthening and the modification of dislocation motion mode from planar slip delocalization to a relatively diffuse, three-dimensional dislocation pattern, effectively alleviating stress concentration. This work provides valuable insight into the development of high-performance lightweight alloys.

Simultaneously enhancing strength and ductility of coarse grain Cu–Al alloy via a macro dual-cable structure

The trade-off relationship of strength and ductility of metals leads to a strength increase accompanied by a ductility decrease. In the past two decades, despite significant efforts to increase strength while minimizing the ductility loss by tailoring microstructures, it has been rare to achieve simultaneous enhancement in strength and ductility, i.e., to disrupt the trade-off relationship. Here via rotary swaging and subsequent annealing, we prepared a macro dual-cable structured Cu–Al alloy rod with an inner micro-grain (MG) core (2.2 mm in diameter, 54% volume fraction) wrapped in an outer ultrafine-grain (UFG) shell (a thickness of 0.4 mm). Tensile tests revealed that the inner core has a yield strength of 472 MPa and a ductility of 29.1%, while the wrapping of the outer shell simultaneously enhances the yield strength to 552 MPa and ductility to 31.9%, respectively. The analysis of strain during the stretching process shows that the shell has a strong restraining effect on the core. Microstructure characterization indicates that the core blocks the propagation of the shear bands of shell and maximizes its density. At the same time, the restriction of the shell increases the lattice defect accumulation and work hardening ability as well as ductility of the core. Our research not only provides a method for preparing macro dual-cable structured materials with industrial scale and clean interface, but also explores a new strategy for simultaneously enhancing strength and ductility of metals, which designs macro millimeter-scale structures instead of adjusting microstructure from the micrometer scale.

Simultaneous enhancement of strength and conductivity via self-assembled lamellar architecture

Simultaneous improvement of strength and conductivity is urgently demanded but challenging for bimetallic materials. Here we show by creating a self-assembled lamellar (SAL) architecture in W-Cu system, enhancement in strength and electrical conductivity is able to be achieved at the same time. The SAL architecture features alternately stacked Cu layers and W lamellae containing high-density dislocations. This unique layout not only enables predominant stress partitioning in the W phase, but also promotes hetero-deformation induced strengthening. In addition, the SAL architecture possesses strong crack-buffering effect and damage tolerance. Meanwhile, it provides continuous conducting channels for electrons and reduces interface scattering. As a result, a yield strength that doubles the value of the counterpart, an increased electrical conductivity, and a large plasticity were achieved simultaneously in the SAL W-Cu composite. This study proposes a flexible strategy of architecture design and an effective method for manufacturing bimetallic composites with excellent integrated properties.

Simultaneous Enhancement of Strength and Ductility in AM60 Tubes Using a Novel Approach of Modified Tube Cyclic Expansion Extrusion

Simultaneous Enhancement of Strength and Ductility in AM60 Tubes Using a Novel Approach of Modified Tube Cyclic Expansion Extrusion

Making ultra-high strengthening and toughening efficiency in hybrid reinforcing of aluminum laminated composites via dispersion engineering

To overcome the strength-ductility trade-off dilemma, herein we propose a hybrid in-situ/ex-situ reinforced aluminum matrix composite to achieve a uniform dispersion of reinforcements and strong reinforcement-matrix interfacial bonding. To exploit the pros of inter/intra granular dispersion of reinforcements, nano- Al3BC particles have been in-situ synthesized into ultrafine-grained (UFG) Al grain interior reinforced by carbon nanotubes (CNTs) via an elemental powder mixture, mechanical activation and subsequent annealing process. The in-situ nano-scaled Al3BC were uniformly distributed inside the elongated ultrafine Al grains, enabling stronger dislocation pinning and retention, providing stronger effective stress which consequently helps to enhance strength and strain hardening. The as-fabricated (Al3BC, CNT)/UFG Al exhibits simultaneous enhancement in strength (394 MPa) and total elongation (19.7 %) compared with its counterpart without the nano-Al3BC, suggesting the promising strengthening effects of in-situ/ex-situ reinforcing benefitting from the uniform dispersion and the strong semi-coherent interface with the matrix.

Defect-healing of a laser-powder bed fusion Ti6Al4V alloy via electro-assisted micro-forging

In recent years, the concept of hybrid manufacturing has been proposed to heal the defects in additive manufactured (AM) materials, taking advantage of both the AM technique and additional secondary processes such as hot forging. However, the healing mechanism of defects, as well as the relationship between defects elimination and microstructure evolution need to be further studied. In this work, we designed laser-powder bed fusion (L-PBF) Ti6Al4V samples with high initial porosity, making it easier to trace the pores during the quasi in-situ X-ray tomography (XRT) observation. The samples were conducted hot forging by Gleeble-3800 system, which is named as electro-assisted micro-forging (EAMF) treatment, considering the characteristic of this process is to directly electrify the specimen to generate Joule heat. The results show that the porosity was effectively reduced by combining effects of electric current, heat energy and compressive stress during EAMF. Simultaneous enhancement of strength and ductility was realized. The defect-healing mechanism that comprising various stages was comprehensively disclosed. The competitive relationship between defect-healing and microstructure coarsening was revealed, which has a guiding effect on the subsequent optimization of process parameters.

Simultaneous enhancement of strength and ductility by combining heterogeneous microstructure and nanoprecipitates

Developing advanced metallic materials with high strength and ductility is an eternal theme, however, the strength and ductility are generally considered to be conflicted to each other. Here, a simultaneous enhancement of strength and ductility is achieved in a commercial Al6061 alloy by combining the heterogeneous microstructure (composed of recovered zones and partially recrystallized zones) and nanoprecipitates. This unique microstructure is produced by the cold-drawing (∼61%) and pre-torsion (∼360°) followed by low-temperature ageing treatments. When the ageing temperature decreases from ∼300 °C to ∼150 °C, the nanoprecipitates changes from the coexistence of the needle-like β′ and rod-shaped β′′ to exclusive granular β′′ with refined size and increased volume fraction, which leads to the remarkable improvement of yield strength from σy∼176.0 MPa to σy∼340.2 MPa. Concurrently, the evading of precipitate-free zones (PFZs), the suppression of the grain-boundary precipitates and the formation of extremely fine nanoprecipitates (<5 nm) contribute to the unexpected enhanced uniform elongation (from εu∼5.3–5.6%). Furthermore, the hetero-deformation induced (HDI) strengthening and work hardening by the heterogeneous microstructure are also beneficial for the synergistic enhancement of the strength and ductility.

FCC-BCC phase transformation induced simultaneous enhancement of tensile strength and ductility at high strain rate in high-entropy alloy

FCC-BCC phase transformation-induced plasticity (TRIP) has been extensively studied in high-entropy alloys (HEAs) to customize their mechanical properties through compression/tension loading or thermal fabrication processes. In this study, we employed a combination of molecular dynamics (MD) and Monte-Carlo (MC) simulations to investigate the effects of TRIP on the uniaxial strain tensile deformation of Co25Ni25Fe25Al7.5Cu17.5 HEA. Our results demonstrate that a complete FCC-BCC phase transformation occurs, in accordance with the N-W relationship, resulting in a simultaneous enhancement of strength and ductility. This is attributed to the HEA's significantly low stacking fault energy and pronounced lattice distortion (LD). However, short-range order (SRO) acts as an obstacle on atomic sliding, which further reduces the degree of phase transformation, leading to an increase in Young's modulus but a decrease in ductility. Furthermore, an increase in strain rate can promote the occurrence of the phase transformation to a certain extent but also leads to an increase in the degree of disorder defects. We also found that the HEA maintains excellent thermal stability up to 900 K, but the amount of phase transformation decreases with increasing initial temperature. Our systematic study of FCC-BCC transformation, considering the effects of SRO, LD, strain rate, and temperature, provides insights into tailoring the mechanical properties of HEAs for practical design purposes.

Simultaneous enhancement of strength and hydrogen embrittlement resistance of laser-powder bed fusion maraging steel via long-term low-temperature aging

This study reported an effective strategy for simultaneously enhancing the strength and hydrogen embrittlement resistance of laser-powder bed fusion(L-PBF) 18Ni300 maraging steel through a long-term low-temperature aging treatment (LTA). The beneficial roles of LTA are: (i) LTA produced a multi-scale and multi-dimensional hydrogen trap network composed of dispersed ω nanoprecipitates and dense cellular structures, which strongly hindered hydrogen enrichment at grain boundaries, thereby inhibiting hydrogen-enhanced decohesion. (ii) High-density ω precipitates not only enhanced the strength, but also affected H-dislocation interactions, thereby hindering hydrogen-enhanced localized plasticity. (iii) LTA eliminated the formation of austenite aggregation zone, reducing the additional risk of cracking.

Controllable selection of martensitic variant enables concurrent enhancement of strength and ductility in a low-carbon steel

A novel strategy through controlling the selection of martensitic variant in metallic materials is proposed to break through the trade-off between strength and ductility. Here we prepared a high-strength low-carbon steel by applying the two-stage mechanical processing combined with high-temperature large-reduction compression and the subsequent compression above the low critical point of austenitization. The steel has the lowest degree of static recrystallization and dynamic recrystallization after the two-stage mechanical processing, leading to the smallest prior austenite grains with an average diameter of 16.4 μm and the highest dislocation density of 10.21 × 1014 m−2. With the refinement of the prior austenite grains caused by the adjustment of the two-stage deformation process, the driving force required for martensitic transformation increases and variants selectivity becomes stronger, leading to a large number of fine martensitic laths and nanoscale twins after martensitic transformation. Consequently, the best combination of strength and ductility is obtained, with the yield strength of 871 MPa, tensile strength of 1054 MPa and the total elongation of 25%. The use of variant selection exploits the strengthening of both grain boundaries and dislocations, resulting in simultaneous enhancement of strength and ductility. These findings demonstrate how multiple deformation mechanisms can be deliberately activated via the controllable selection of martensitic variants.

Effect of Sc microalloying on fabrication, microstructure and mechanical properties of SiCp/Al–Cu–Mg-Sc composites via powder metallurgy

Overcoming the strength and ductility trade-off is a long-lasting research theme in aluminum matrix composites. Here, we present a strategy to promote strength-ductility synergy in aluminum matrix composites by utilizing the microalloying effect of Sc. 15 wt% SiCp/Al–Cu–Mg-Sc composites with varying Sc content were fabricated by high energy ball milling, hot pressure sintering and hot extrusion. With 0.2 wt% Sc addition, the SiCp/Al–Cu–Mg-Sc composite exhibits a yield strength of 600.6 MPa, an ultimate tensile strength of 681 MPa and a fracture elongation of 4.3%, achieving simultaneous enhancement in strength and ductility compared with the Sc-free counterpart. Particularly, the fracture elongation remarkably increased by 126% which originates from the reduction of stress concentration caused by the refinement of intergranular θ phase and the improvement of dislocation accumulation capability caused by the formation of intragranular θ' phase. Our work provides an accessible pathway consistent of high energy ball milling and microalloying of Sc to exploit aluminum matrix composites with advanced strength-ductility balance.

Simultaneous enhancement of strength and ductility in friction stir welded AZ31 alloy via multi-pass hot-rolling and subsequent annealing

Friction stir welding (FSW) is a new solid-state joining process for joining light metals, such as magnesium (Mg) alloys. However, the texture-induced softening mechanism (in stir zone, SZ) tends to cause the worsening of mechanical properties in FSW Mg alloys. In this work, multi-pass hot-rolling and subsequent annealing is used to ameliorate the FSW AZ31 alloy plate. The results show that multi-pass hot-rolling leads to the c-axes of most grains in the SZ approximately perpendicular to the normal direction (ND) transforming into these almost parallel to the ND, accompanied with multiple twin types. After subsequent annealing, twins, as nucleation sites, promote the formation of new grains with off-basal texture, resulting in the weak basal texture. Compared with the FSW plate and the initial plate, the rolled-annealed FSW plate exhibits a relatively uniform hardness distribution and a “strength-ductility” synergy, which are mainly attributed to an appropriate texture feature and a homogeneous grain structure. This work provides a new idea for the development of new high-performance FSW Mg alloys.

Simultaneous enhancement of strength and ductility in a medium carbon low-alloy steel induced by secondary martensite and Cu-rich particles

This study aims to simultaneously improve the strength and ductility of a medium carbon low-alloy steel via Cu addition and the partitioning treatment. The obtained microstructure was heterogeneous that included temper martensite, retained austenite, M-A island/secondary martensite, bainitic ferrite, and nanosized Cu-rich particles. The partitioning temperature had significantly influence on the microstructure, leading to the distinct variations of mechanical properties. With the increase of partitioning temperature from 240 °C to 330 °C, yield strength decreased from 1470 MPa to 1110 MPa. However, it increased to 1210 MPa when the partitioning temperature further increased to 380 °C. In contrast, the ultimate tensile strength gradually decreased from 2300 MPa to 1440 MPa with the increase of partitioning temperature from 240 °C to 380 °C, while the ductility significantly increased from 9% to 26%. The concurrent increases of yield strength and ductility is attributed to the numerous nanosized Cu-rich particles formed in the temper martensite. In contrast, the increase of ultimate tensile strength was caused by the increasing secondary martensite which had high carbon concentration. By using the band contrast values obtained by EBSD mapping and Gaussian fitting, the distribution of temper martensite, secondary martensite, and bainitic ferrite were quantified. The results showed that the distribution of temper martensite and bainitic ferrite were correlated, which was apt to improve the coordinated deformation between the neighboring phases. In addition, the Cu-rich particles were found to preferentially nucleate at the edge of the strip carbide because the carbide edge acted as a channel for the rapid diffusion of Cu atoms. Surprisingly, the formation of numerous nanosized Cu-rich particles was always accompanied with the increasing ductility without the loss of strength, which provides a great potential for breaking through the trade-off between strength and ductility in steels.

Significantly improved strength and plasticity of a refractory high-entropy alloy at small length scale

Refractory high-entropy alloy (RHEA) VNbMoTaW exhibits remarkably high strength in a much wide temperature range, whereas the brittle fracture behavior limits the applications. Here we show a significant size effect on the strength, plasticity and fracture behaviour of the VNbMoTaW RHEA. As sample size goes from millimeter to sub-micrometer scale, the brittle cracking behavior of the RHEA is greatly suppressed, along with a simultaneous enhancement of strength and plasticity. The improved mechanical properties can be attributed to the disappearance of crack initiation sites, the size-dependent dislocation plasticity at small length scale and the size-dependent competition in thermodynamics driving-force for cleavage cracking and plastic yielding. The results imply a promising potential of the RHEA for making microscale devices with high temperature environment.