Improvement In Yield Strength Research Articles

Formation mechanism of Al-Zn-Mg-Cu alloy fabricated by laser-arc hybrid additive manufacturing: Microstructure evaluation and mechanical properties

A novel additive manufacturing followed by a hybrid process involving pulsed laser and tungsten inert gas (TIG) arc was proposed to balance the element vaporization, microstructure uniformity, and mechanical properties of the Al-Zn-Mg-Cu alloy. The amount of vaporized Zn in the laser-arc hybrid additive manufacturing (LAHAM) reduced by merely 2.5%, whereas the Zn vaporization loss of the WAAM specimens reached up to 8.3%. Compared with the grain sizes of specimen obtained via WAAM, those obtained via LAHAM decreased by approximately two times. The < 100 > texture in the LAHAM specimen was decreased significantly, due to the appearance of equiaxed grains and grain refinement. Furthermore, in contrast to WAAM specimen, the eutectics contained Al, Zn, Mg and Cu were evenly distributed in the LAHAM specimen, resulting in uniform element distribution. Nano-precipitates were dispersedly distributed within the grains in the LAHAM specimen, whereas they merely appeared around the grain boundaries in the WAAM specimen. Owing to microstructure changes, LAHAM improved the ultimate tensile strength and yield strength by up to 11.4% and 29.9%, as compared with WAAM. The substantial improvement in yield strength was primarily attributed to precipitation strengthening, instead of grain boundary strengthening or solid solution strengthening.

Effects of Al or Mo Addition on Microstructure and Mechanical Properties of Fe-Rich Nonequiatomic FeCrCoMnNi High-Entropy Alloy

In this work, a Fe-rich nonequiatomic Fe40Cr15Co15Mn10Ni20 high-entropy alloy was successfully prepared based on phase analysis and cost reduction. Fe40Cr15Co15Mn10Ni20 high-entropy alloy with a single-phase face-centered cubic (FCC) structure was strengthened by the addition of 11 at.% Al or 10 at.% Mo, and the variations of phase and mechanical properties of the strengthened alloys were subsequently investigated. It has been found that the addition of 11 at.% Al led to the formation of FCC and body-centered cubic (BCC) dual-phase structure in the Fe40Cr15Co10Mn4Ni20Al11 alloy, while its yield strength (σ0.2) and tensile strength increased from 158 ± 4 MPa and 420 ± 20 MPa to 218 ± 7 MPa and 507 ± 16 MPa, respectively, as compared to the single-phase FCC structure Fe40Cr15Co15Mn10Ni20 alloy. The addition of 10 at.% Mo introduced intermetallic compounds of μ and σ phases, which resulted in improved yield strength of 246 ± 15 MPa for the Fe40Cr15Co10Mn5Ni20Mo10 alloy. However, the alloy exhibited premature brittle fracture due to the existence of a large number of intermetallic compounds, which led to deteriorated tensile strength of 346 ± 15 MPa. The findings of this work suggest that the introduced secondary phases by the addition of Al and Mo can effectively strengthen the high-entropy alloy; however, the number of intermetallic compounds should be controlled to achieve a combination of high strength and good ductility, which provides a reference for the follow-up study of nonequiatomic high-entropy alloys.

Development of TiB and nanocrystalline Ti-reinforced novel hybrid Ti nanocomposite produced by powder metallurgy

Titanium monoboride (TiB) whisker-reinforced titanium (Ti) matrix composites were produced by powder metallurgy, through vacuum sintering. TiB is formed by thermal decomposition of TiB2 precursor. In addition, a new hybrid composite was developed by admixing nanograined and nanocrystalline (more important) Ti to enhance the transformation mechanism of TiB2 to TiB phase. The morphology and particle size of the initial powders, mixtures and the microstructure of the composites have been studied by scanning electron microscopy (SEM). The phase analysis and transformation monitoring were performed by X-ray diffraction (XRD). The sintered composites were also subjected to compressive strength and hardness measurements. According to XRD results, through the addition of nanocrystalline Ti, a probable enhancement of the TiB2 → TiB transformation occurred producing more TiB whiskers in the hybrid composites. All samples of the hybrid composites exhibited improved yield strength (1365 MPa) and hardness (358 HV) compared to the non-hybrid ones 927 MPa and 254 HV, respectively.Graphical abstract

Comprehensive study of cellulose nanocrystals acetylation effects on poly (butylene adipate-co-terephthalate) nanocomposite films obtained by solvent casting and heat pressing

Interest in biodegradable polymers has been increasing exponentially due to the global environmental concerns about inappropriate disposal of plastic materials. Considering this issue, poly (butylene adipate-co-terephthalate) (PBAT) is a good candidate to be applied to films, since it presents desirable, promising processability and thermal-mechanical properties and lower water solubility compared with other biopolymers. However, PBAT exhibits inferior mechanical properties compared with polyolefins. To overcome this, acetylated cellulose nanocrystals (CNCs-Ac) were systematically investigated by incorporating different weight ratios to PBAT-based films produced via a solvent casting/heat pressing approach. This process combines a well dispersed hydrophobic filler with additional temperature and pressing, ensuring improvement in yield strength (30%) and Young’s modulus (90%), as well as an outstanding benefit in flexibility (> 650%), compared with neat PBAT film. This work provided a novel route to prepare PBAT bionanocomposites, showing greater potential for biodegradable packaging, which can be an alternative to conventional polymers.

Beneficial effects of Sc/Zr addition on hypereutectic Al–Ce alloys: Modification of primary phases and precipitation hardening

Al–Ce alloys possess desirable elevated-temperature performance due to the high stability of Al11Ce3 phases. The morphology and size of the Al11Ce3 phases play a significant role in determining the strengthening effect in Al–Ce alloys. In this paper, the effect of Sc/Zr addition on the microstructure, mechanical properties, and thermal stability of a hypereutectic cast Al–Ce alloy was investigated. The results demonstrated that Sc and Zr atoms could adsorb on the Al11Ce3 phase surfaces and control the growth process in the 0.13 wt % Sc-0.06 wt % Zr addition alloy, along with the size of primary Al11Ce3 phases was refined from ∼79 μm to ∼56 μm. As the total Sc/Zr content increased, the formation of primary Al3(Sc, Zr) phases could significantly refine the primary Al11Ce3 phases by acting as heterogeneous nucleation sites. Therefore, in 0.23 wt % Sc-0.16 wt % Zr and 0.49 wt % Sc-0.23 wt % Zr alloys, the modification effect on primary Al11Ce3 phases was based upon the interaction of adsorption effect and heterogeneous nucleation. The sizes of primary Al11Ce3 phases were refined to ∼37 μm and ∼32 μm, leading to a significant improvement in ultimate tensile strength (from ∼117 MPa to ∼182 MPa), yield strength (from ∼75 MPa to ∼145 MPa) and elongation (from ∼1.4% to ∼3.4%) in the 0.49 wt % Sc-0.23 wt % Zr alloy compared to the unmodified alloy. The Sc and Zr atoms that were dissolved in the matrix as a decomposed solid solution precipitated the L12-Al3(Sc, Zr) phases after thermal exposure, which maintained full coherency with the Al matrix, leading to a hardness increase, rather than a decrease, after 300 °C and 400 °C thermal exposure. Therefore, Al–15Ce-(Sc–Zr) alloys open a new alloy system for engineering materials useable in high-temperature applications.

Evolution of microstructure homogeneity and mechanical properties in nano-/ultrafine eutectic CoCrFeNiNbx (0.45 ≤ x ≤ 0.65) high entropy alloy ingots and cast rods

We report the evolution of microstructure and hardness homogeneity in arc melted ingots (AMIs) and suction cast rods (SCRs) of CoCrFeNiNbx (0.45 ≤ x ≤ 0.65) eutectic high entropy alloys (EHEAs) solidified at cooling rates of ~10–103 K/s. The effect of cooling rate on the evolution of phase and microstructure, has been investigated thoroughly by using scanning electron microscopy, x-ray diffraction. Whereas the mechanical properties have been investigated by compression test and Vickers microhardness. The microstructure of the EHEAs comprised of FCC and Fe2Nb type Laves phase, which remained the same under different processing conditions. The AMIs exhibited a high yield strength of 1.4–2.0 GPa with high compressive fracture strain up to 17.4% at room temperature. The SCRs showed improved yield strength of 1.5–2.3 GPa, due to the higher cooling rate and nano-/ultrafine lamellae thickness (λw). The λw values and hardness vary between 130 and 220 nm and 581–620 HV, respectively, in fully eutectic x = 0.5 AMI pointing to the evolution of a homogeneous microstructure and homogeneous distribution of the alloying elements in the phases. The hardness in 3 mmØ SCRs is 10% higher than that of AMI due to similar microstructure homogeneity and refinement of λw. The proeutectic FCC shows low Nb solubility with a partitioning coefficient of kNb <<1, and Laves phase with kNb>>1 shows higher Nb solubility and preferential dissolution due to the high melting temperature, large atomic radii and large negative enthalpy with other constituent elements.

Achieving Exceptional Improvement of Yield Strength in Mg-Zn-Ca Alloy Wire by Nanoparticles

Achieving Exceptional Improvement of Yield Strength in Mg-Zn-Ca Alloy Wire by Nanoparticles

Simultaneous Improvement of Yield Strength and Ductility in Medium Mn Steel by Combining Gradient Structure and Trip Effect

Simultaneous Improvement of Yield Strength and Ductility in Medium Mn Steel by Combining Gradient Structure and Trip Effect

Varied enhancements in mechanical properties and sodium compatibility of Grade 92 by thermomechanical treatments

As a candidate material for advanced nuclear reactors, a ferritic-martensitic (FM) steel Grade 92 in the standard normalized and tempered (NT) condition was subjected to two types of thermomechanical treatments (TMTs) with one having a lower level of deformation (T5A) and the other having a higher level of deformation (T5B). The testing results of the three conditions indicated that the TMTs significantly improved yield strength, creep resistance, fracture toughness, and sodium corrosion resistance compared with the NT condition. T5A excelled at creep resistance while T5B at sodium corrosion resistance. Microstructural characterization of the three conditions supports the varied enhancements in the properties. This study suggests that an appropriate TMT can be developed and applied to FM steels to better meet specific application requirements.

Effects of wet shot peening on microstructures and mechanical properties of a 2060-T8 aluminum-lithium alloy

In this work, wet shot peening (WSP) was investigated to modify the microstructures and mechanical properties of a 2060-T8 aluminum-lithium (Al–Li) alloy through numerical and experimental methods. Gradient distributions of plastic strain and strain rate induced by WSP were obtained from simulation via coupled Eulerian-Lagrangian method and fitted by exponential functions. They were the primary extrinsic factors determining microstructural evolution and deformation mechanisms. In parallel, the hardening behaviors and heterogeneous microstructures in the modified layer with a thickness of about 200 μm were characterized by experiments. Experimental results showed that WSP improved yield strength, tensile strength and the microhardness at surface respectively by 16.15%, 11.83% and 10%, but the total elongation was reduced by 30.18%. The significant improvement of strength was associated with the combined influences of nanocrystalline, severe lattice distortion, precipitates variation, dense dislocations and stacking faults. Moreover, the gradient hierarchical microstructures fabricated by the non-uniform deformation of WSP can promote the accumulation of geometrically necessary dislocations (GNDs). The corresponding back stress caused by GNDs would produce extra hardening effects. Consequently, a modified composite model considering various microstructures, the volume fractions of modified layers as well as material continuity was proposed to predict the mechanical properties of materials processed by surface treatments. The estimated yield strength was found to agree well with experimental results.

Microstructure Characteristics and Strengthening Behavior of Cu-Bearing Non-Oriented Silicon Steel: Conventional Process versus Strip Casting

Based on conventional hot rolling processes and strip casting processes, Cu precipitation strengthening is used to improve the strength of non-oriented silicon steel in order to meet the requirements of high-speed driving motors of electric vehicles. Microstructure evolution was studied, and the effects of Cu precipitates on magnetic and mechanical properties are discussed. Compared with conventional processes, non-oriented silicon steel prepared by strip casting exhibited advantages with regard to microstructure optimization with coarse grain and {100} texture. Two-stage rolling processes were more beneficial for uniform microstructure, coarse grains and improved texture. The high magnetic induction B50 of 1.762 T and low core losses with P1.5/50, P1.0/400 and P1.0/1000 of 1.93, 11.63 and 44.87 W/kg, respectively, were obtained in 0.20 mm sheets in strip casting. Cu precipitates significantly improved yield strength over ~120 MPa without deteriorating magnetic properties both in conventional process and strip casting. In the peak stage aged at 550 °C for 120 min, Cu precipitates retained bcc structure and were coherent with the matrix, and the yield strength of the 0.20 mm sheet was as high as 501 MPa in strip casting. The main mechanism of precipitation strengthening was attributed to coherency strengthening and modulus strengthening. The results indicated that balanced magnetic and mechanical properties can be achieved in thin-gauge non-oriented silicon steel with Cu addition in strip casting.

Microstructure and Mechanical Property Correlation Between Rotary Friction Welded Nitinol–Nitinol Joints

In the present study, a rotary friction process was used to join nitinol in a similar welding combination. Macro- and microstructure characteristics of the weld zone were compared with adjacent zones and the base metal. The hardness and tensile properties of the joints were evaluated, and the results were discussed in relation to the weld microstructure. The weld macrostructure revealed a uniform flash around the circumference of the weld. The optical microstructure of the welded sample revealed fine recrystallized grains at the weld interface due to heavy deformation followed by dynamic recrystallization. The phase transformation behavior of the base metal and welded samples was studied by using a differential scanning calorimeter (DSC). The drift in phase transformation temperatures after rotary friction welding may be attributed to fine grain formation at the weld interface. Friction welded samples exhibited improved yield strength and hardness values compared to the base metal due to grain refinement at the weld interface.

Nanomechanical, Tribological, and Scratch Properties of Electroless Ni-B-W Alloy and Ni-B-W-SiC Composite Coatings

Abstract Electroless deposition process can develop composite coatings superior in mechanical and tribological characteristics. The deposited alloy matrix with the reinforcement of a hard ceramic phase can produce a stronger composite coating, favorable for industrial applications. Fabrication process of Ni-B-W-SiC electroless composite coating on steel substrate by reinforcing silicon carbide (SiC) in ternary Ni-B-W matrix is presented in this report. Characteristics of the developed composite coating are studied in reference to electroless ternary Ni-B-W alloy coating. These ternary alloy and composite coatings are also subjected to heat treatment (450oC, 1 hr) to observe the changes. All coated samples are characterized with FESEM, XRD, ICP-AES, and HRTEM analyses to draw conclusions in comparative studies concerning morphological features, compositions, and phase structures. Cross-sectional and Raman spectroscopic examinations are performed to authenticate the presence of SiC phases in alloy matrix. To get a further insight on the nature, various nanomechanical and tribological properties of these coatings are evaluated and subsequently co-related. Coatings developed with silicon carbide particles present in matrices show remarkable improvements in nano-hardness (H), reduced modulus (Er), yield strength, and fraction of plastic work done. Heat treatment imparts propitious effects on these mechanical properties due to the formation of harder nickel boride (Ni3B, and Ni2B) phases. Heat-treated Ni-B-W-SiC composite subjected to tribological and micro-scratch testing reveals a significant improvement in sliding wear and scratch resistance as compared to those in other coatings.

Nanocrystalline Materials: Synthesis, Characterization, Properties, and Applications

Nanostructuring is a commonly employed method of obtaining superior mechanical properties in metals and alloys. Compared to conventional polycrystalline counterparts, nanostructuring can provide remarkable improvements in yield strength, toughness, fatigue life, corrosion resistance, and hardness, which is attributed to the nano grain size. In this review paper, the current state-of-the-art of synthesis methods of nanocrystalline (NC) materials such as rapid solidification, chemical precipitation, chemical vapor deposition, and mechanical alloying, including high-energy ball milling (HEBM) and cryomilling was elucidated. More specifically, the effect of various process parameters on mechanical properties and microstructural features were explained for a broad range of engineering materials. This study also explains the mechanism of grain strengthening using the Hall-Petch relation and illustrates the effects of post-processing on the grain size and subsequently their properties. This review also reports the applications, challenges, and future scope for the NC materials.

Influence of Nb on the Structure and High Temperature Performance of Billet for High-Rise Structural Steel

Reasonable control of the niobium (Nb) content in steel slabs is of great significance for improving the surface quality of the slabs. In this study, a Gleeble-3500 thermal simulation testing machine was used to test the high-temperature mechanical properties of steel slabs with four different Nb contents (A: 0.006%, B: 0.031%, C: 0.050%, D: 0.065%) and to analyze the effect of Nb on the high-temperature performance of the steel slabs. Optical microscopy and transmission electron microscopy (TEM) were used to study the microstructure of the casting slabs with different Nb contents and the precipitation in the samples after heat treatment at different temperatures. The results of the study show that the microstructure of the cast slab is mainly composed of ferrite and pearlite. The distribution of each of the two structures was found to become more uniform and a significant improvement in yield strength was observed with increasing Nb content. After heat treatment, the precipitates in the high-rise structural steel were mainly square and star shaped Nb(C,N) precipitates. Increasing the Nb content was found to increase the amount of precipitates in steel. Beyond a threshold, increasing the Nb content did not increase the amount of precipitates. However, the size of the precipitates increased.

Nano-scale heterogeneity-driven metastability engineering in ferrous medium-entropy alloy induced by additive manufacturing

Selective laser melting (SLM) offers unprecedented advantages in fabrication of metals and alloys with complex geometry and unique microstructural features with hierarchical heterogeneity. The SLM process also induces a unique cell structure with high dislocation density and solute segregation at cell boundaries. Here, we propose an innovative utilization of unique dislocation network to achieve superior mechanical properties through metastability engineering of ferrous-medium entropy alloy (FeMEA). While the high dislocation density at cell boundaries contributes to the improvement of yield strength as additional barriers of dislocation movement, the solute segregation at cell boundaries can beneficially control the phase instability of matrix in materials produced by SLM. Our results demonstrate that solute segregation at cell boundaries decreases the face-centered cubic phase stability in the matrix and activates transition of the deformation mechanism from slip to metastable plasticity (i.e., transformation-induced plasticity). Furthermore, the high density of dislocation at cell boundaries also has an effect on not only yield strength enhancement but also controlling kinetics of metastable plasticity, and it beneficially contributes the high ductility of the SLM-processed FeMEA. This work presents a new microstructural design strategy for beneficially customizing the material performance of high-quality products based on SLM-driven metastability engineering of metallic materials.

Experimental and Finite Element Analysis of the Tensile Behavior of Architectured Cu-Al Composite Wires.

The present study investigates, experimentally and numerically, the tensile behavior of copper-clad aluminum composite wires. Two fiber-matrix configurations, the conventional Al-core/Cu-case and a so-called architectured wire with a continuous copper network across the cross-section, were considered. Two different fiber arrangements with 61 or 22 aluminum fibers were employed for the architectured samples. Experimentally, tensile tests on the two types of composites show that the flow stress of architectured configurations is markedly higher than that of the linear rule of mixtures’ prediction. Transverse stress components and processing-induced residual stresses are then studied via numerical simulations to assess their potential effect on this enhanced strength. A set of elastic-domain and elastoplastic simulations were performed to account for the influence of Young’s modulus and volume fraction of each phase on the magnitude of transverse stresses and how theses stresses contribute to the axial stress-strain behavior. Besides, residual stress fields of different magnitude with literature-based distributions expected for cold-drawn wires were defined. The findings suggest that the improved yield strength of architectured Cu-Al wires cannot be attributed to the weak transverse stresses developed during tensile testing, while there are compelling implications regarding the strengthening effect originating from the residual stress profile. Finally, the results are discussed and concluded with a focus on the role of architecture and residual stresses.

Mechanical and thermal performance of additively manufactured copper, silver and copper–silver alloys

On-demand additive manufacturing (three-dimensional printing) offers great potential for the development of functional materials for the next generation of energy-efficient devices. In particular, novel materials suitable for efficient dissipation of localised heat fluxes and non-uniform thermal loads with superior mechanical performance are critical for the accelerated development of future automotive, aerospace and renewable energy technologies. In this regard, this study reports the laser powder bed fusion processing of high purity (&gt;99%) copper (Cu), silver (Ag) and novel copper–silver (CuAg) alloys ready for on-demand additive manufacturing. The processed materials were experimentally analysed for their relative density, mechanical and thermal performance using X-ray computed tomography, destructive tensile testing and laser flash apparatus, respectively. It was found that while Ag featured higher failure strains, Cu in comparison showed a 109%, 17% and 59% improvement in yield strength ([Formula: see text]), Young’s modulus ( E) and ultimate tensile strength, respectively. As such the [Formula: see text], E and ultimate tensile strength for laser powder bed fusion Cu is comparable to commercially available laser powder bed fusion Cu materials. CuAg alloys, however, significantly outperformed Ag, Cu and all commercial Cu materials when it came to mechanical performance offering significantly superior performance. The [Formula: see text], E and ultimate tensile strength for the novel CuAg composition were 105%, 33% and 94% higher in comparison to Cu. Although slightly different, the trend continued with a 106% and 91% rise for [Formula: see text] and ultimate tensile strength, respectively, for CuAg in comparison to industry-standard Cu. Unfortunately, E values for industry-standard Cu alloys were not available. When it came to thermal performance, laser powder bed fusion Ag was found to offer a 70% higher thermal diffusivity in comparison to Cu despite the variation in density and porosity. CuAg alloys however only showed a 0.8% variation in thermal performance despite a 10–30% increase in Ag. Overall, the study presents a new understanding regarding the three-dimensional printing and performance of Cu, Ag and CuAg alloys.

Superior Strength and Ductility of 304 Austenitic Stainless Steel with Gradient Dislocations.

Materials with designed gradient nanograins exhibit unprecedented mechanical properties, such as superior strength and ductility. In this study, a heterostructured 304 stainless steel with solely gradient dislocation structure (GDS) in micron-sized grains produced by cyclic-torsion processing was demonstrated to exhibit a substantially improved yield strength with slightly reduced uniform elongation, compared with its coarse grained counterparts. Microstructural observations reveal that multiple deformation mechanisms, associated with the formation of dense dislocation patterns, deformation twins and martensitic phase, are activated upon straining and contribute to the delocalized plastic deformation and the superior mechanical performance of the GDS 304 stainless steel.

Microstructural evolution in pure copper during accumulative skin pass rolling: experimental and crystal plasticity numerical investigations

Surface mechanical treatments are known to introduce deformation heterogeneity, thus entailing a combination of excellent strength and ductility in metallic metals. Accumulative skin pass rolling (ASPR) was employed to introduce heterogeneous structure in pure copper, which significantly improved yield strength and maintained high ductility. The experimental observations of the ASPR processed copper showed that surface grains possessed a much larger magnitude of misorientations and geometrically necessary dislocations (GNDs) than the centre grains. Crystal plasticity finite element modelling was utilised to provide an in-depth understanding of microstructure evolution during ASPR. It was found that the surface grains accommodated higher shear strain and had higher slip resistance than the centre grains. The multiple active slip systems in the surface grains induce the lattice rotations and then the formation of intragranular misorientations accompanied by a high density of GNDs, while the single active slip system in the centre grains can accommodate the applied material rotation without the lattice rotation.