Yield Strength Research Articles

Cracks-free yet ultrafine-grained 7050 aluminium alloys by selective laser melting

Eliminating hot cracking and achieving a good strength-ductility synergy in selective laser melted (SLMed) high-strength aluminium alloys remain challenging. We here inoculated 7050 high-strength aluminium alloy with 2 wt% Ti nanoparticles to eliminate hot cracking during SLM. Furthermore, ultrafine equiaxed grains with random textures were achieved in SLMed 7050 – 2 wt% Ti alloy, in contrast to the textured columnar grains observed in SLMed 7050 alloy. A high tensile yield strength of 393 MPa and an elongation of 11.6 % were achieved in SLMed 7050 – 2 wt% Ti alloy.

Cr content dependent lattice distortion and solid solution strengthening in additively manufactured CoFeNiCrx complex concentrated alloys – a first principles approach

In the previous study, the authors reported that multicomponent CoFeNiCrx (x = 0, 12, 18, 24 at%) complex concentrated alloys fabricated through laser directed energy deposition experienced a substantial reduction in the saturation magnetization (Ms) and the Curie transition temperature (Tc) with the increase in Cr content. The present investigation additionally explores the effect of Cr concentration on the structural and strengthening behavior in laser directed energy deposition processed CoFeNiCrx alloy system. The novel approach adopted in the present work included the integration of experimental and computational efforts involving laser direct energy deposition (L-DED) based synthesis/fabrication of a series of new CoFeNiCrx alloys through in-situ compositional tuning which is often difficult using conventional techniques and prediction of mechanical properties of these compositionally tuned alloys using a computational methodology based on the density functional theory (DFT). X-ray diffraction and nanoindentation studies revealed that while there was a slight reduction in lattice parameters, the elastic modulus increased by approximately 30 % and the yield strength increased by 25 % with increasing Cr content. The density functional theory framework was employed to interpret the influence of Cr atoms on local lattice distortions and observed yield strength. The calculated local lattice distortion, in terms of first nearest neighbors, significantly increased with Cr concentration, which is attributed to the enlargement of Cr atomic radius in the alloyed multielement environment in comparison to its radius in the elemental form. This distortion at the local level caused solid solution strengthening. The theoretically predicted solid solution strengthening values using the Varvenne model are consistent with experimental results.

Effects of post-processing and loading orientation on high-cycle fatigue of selective laser melted Ti-6Al-4V

Recent research on selective laser melted (SLM) Ti-6Al-4V showed that fatigue fracture differs depending on the post-processing and loading orientation. To better understand their influences, tensile and fatigue tests on samples with three post-processing conditions, namely, stress relief (SR), Sub-transus and hot-isostatic-pressing (HIP), were conducted in both the vertical and horizontal loading orientations. The elongation-to-failure of horizontal specimens are consistently higher than the vertical ones for the SR and Sub-transus state, but the opposite trend is observed for the HIP state. This discrepancy is owing to the reduced defect in combination with the {112¯0}α preferred orientation. Comparison of the SR and Sub-transus states suggests that coarser α-lath contributes to a longer initiation phase of microcrack from the defect, which improves overall fatigue performance. Fatigue strength of the HIP state is significantly higher than the other two states, exhibiting little anisotropy, and the fatigue-cracking source shifts from the defect to the microstructural facet. Subsequently, a model is proposed to evaluate the high-cycle fatigue of SLM-built Ti-6Al-4V, by incorporating yield strength and elongation-to-failure as additional variables, achieving the life prediction error band within two to five times with respect to the experimental data.

Microstructure and Tensile Properties of Ni-Base Superalloy IN738LC according to Solidification Rate and Heat Treatment

The strength of Ni-base superalloys mainly depends on the γ' precipitates that improve the strength of the materials at high temperatures. The presence of γ' particles within the matrix restricts dislocation movement, and optimized heat treatments can tailor the size, shape, and volume fraction of γ'. In this study the effects of solidification rate and solution temperature on the tensile properties of IN738LC superalloy were investigated. The secondary dendritic arm spacing of casting materials with different diameters was measured and the solidification rate of the casting materials was derived by comparing the results of the solidification microstructure obtained from a directional solidification experiment. The D17 material, which had a faster solidification rate, showed higher values of tensile strength and yield strength than the D60 material, which had a slower solidification rate. The study also concluded that the monomodal γ' precipitates in the S80 material have higher tensile strength and yield strength at room temperature and 760℃ than the bimodal γ' precipitates in the S20 material. As for the deformation behavior at 760℃, an isolated stacking fault was observed in the S20 material only within the large γ’ precipitates. In the S80 material, the high dislocation density increased the yield strength due to the strong interaction between dislocations and fine γ’ precipitates.

Research on grain refinement and tensile properties strengthening of screw rolled MgO/Mg-Zn-Ca composites

Herein, a gradient microstructure with an average grain size of 1.27 μm was obtained for 0.5MgO/Mg-3Zn-0.2Ca (wt.%) composites through screw rolling. Results show that screw rolling improved the comprehensive tensile properties of the composites, with the yield strength, ultimate tensile strength and elongation increasing from 167.3 MPa, 247.7 MPa and 27.4% to 256.6 MPa, 284.1 MPa and 40.6%, respectively, after eight deformation passes. The strength increments are primarily attributed to fine-grain strengthening. Further, the plasticity of the composites increased with increasing number of deformation passes because of the texture weakening and strain hardening decrement resulting from continuous dynamic recrystallisation. Overall, this study lays a foundation for research on magnesium matrix composites and their application in the field of biomedical materials.

Data-driven machine learning approach for predicting dwell fatigue life in two classes of Titanium alloys

Predicting dwell fatigue life accurately in Titanium (Ti) alloys is vital for designing reliable components such as aero-engine discs and blades. This study proposes a data-driven machine learning (ML) approach for precisely predicting dwell fatigue life in two classes of Ti alloys: near α and α + β alloys. To build a robust model, the data-driven approach tackles this multi-dimensional problem by training a comprehensive dataset of various input features, including alloy composition, monotonic properties, and fatigue testing parameters. Advanced ensemble-based algorithms, Gradient Boosting (GBOOST) and Extreme Gradient Boosting (XGBOOST) are employed. The split-insensitive best-performing XGBOOST model achieved a high accuracy (R2) score of 89.9 %, indicating impressive prediction capability. The model’s robustness is further assessed using an unseen validation dataset to draw qualitative and quantitative conclusions. ML model’s validation further involved comparing its predictions with actual experimental trends across relationships, such as dwell life versus dwell time and dwell-debit versus dwell time. Dwell-debit is also predicted as a function of varying stresses normalized to 0.2 % yield strength, highlighting the susceptibility of investigated Ti alloys to dwell fatigue. Additionally, the SHapley Additive exPlanations (SHAP) analysis was conducted to gain deeper insights into various input features affecting dwell fatigue life.

Sc/Zr microalloying on strength-corrosion performance synergy of wire-arc directed energy deposited Al-Mg

ABSTRACT WADED Al-Mg and Al-Mg-Sc-Zr aluminium alloy thin-wall components were produced. Heat treatment (350°C aging for 4 h) was further conducted. The effects of Sc/Zr addition on porosity, microstructure, mechanical properties and corrosion behaviour were investigated. With Sc/Zr adding, pore area fraction decreased from 0.208 to 0.005% and grain size decreased from 84.34 to 19.54 μm. In WADED Al-Mg-Sc-Zr component, microstructure showed refined equiaxed grains. Mechanical properties were improved with 360 MPa ultimate tensile strength (UTS), 185 MPa yield strength, and 23.31% elongation. After heat treatment, UTS increased to 388 MPa with good ductility (22.53%) maintained. The grain refinement and Al3(Sc, Zr) particles were the key factors for mechanical property improvement. The corrosion behaviour was improved with introduced Sc/Zr and further optimised after heat treatment. The corrosion exhibited layered characteristics due to the distribution of primary Al3(Sc, Zr) while minor-size secondary Al3(Sc, Zr) along grain boundaries improved the corrosion behaviour.

Influence of Deformation on the Structural–Phase State of Structural Steel and on the Formation of Its Yield Strength and Degree of Hardening

Influence of Deformation on the Structural–Phase State of Structural Steel and on the Formation of Its Yield Strength and Degree of Hardening

The B4C inclusion in Fe-Cu-Ni-Sn-WC for a composites creation applied in ornamental rock cutting tool: a mechanical characterization

In the present work, the experiments carried out aimed at the study and development of a composite based on Fe-Cu-Ni-Sn-WC, with different additions of Boron Carbide. The obtaining of this metallic matrix is intended for the production of pearls, for application in diamond wires used in cutting ornamental rocks. Five compositions were used for the investigation: samples with 2% B4C, 4% B4C, 5% B4C, 8% B4C, and 10% B4C. Initially, rectangular geometry composites were obtained via hot pressing, they were sintered under the same temperature conditions (800°C) and pressure (34MPa). The obtained segments reached approximately 18.00 mm in length, width between 12.80 mm and 15.20 mm, and 3.00 mm in height. The samples were characterized by the mechanical bending test, which allowed the investigation of properties at room temperature, such as yield strength, ultimate tensile strength, longitudinal elasticity modulus, toughness modulus, and resilience modulus. The results showed that the mixture containing 2% B4C presented better overall results. The studies conducted here serve as a basis for the development of new research aimed at producing diamond matrices for use in cutting tools. The inclusion of B4C in Fe-Cu-Ni-Sn-WC composites for creating ornamental rock cutting tools not only enhances efficiency and sustainability in the industry but also promotes significant advances in scientific research and the training of new specialists.

Simultaneously improving mechanical properties and electrical conductivity of Al-1.9Mn alloys with different Mg and Si addition

A simultaneous achievement of high strength and toughness, as well as high conductivity in traditional Al-1.9Mn cast aluminum alloy used in the manufacture of water-cooled radiator shells has proven to be challenging. The addition of Mg and Si elements was implemented in the cast aluminum alloy for a modified treatment to solve the problem. The results showed that the inclusion of Si facilitated the transformation of the plate-like Mn-rich phase (Al6Mn) in the initial Al-1.9Mn alloy into a Chinese-script phase (Al15Mn3Si2) in the new Al-1.9Mn alloy. A higher Si content resulted in an increased volume fraction of Al15Mn3Si2 and a decreased solid solution of Mn in the matrix. Furthermore, a high content of Mg (0.9 wt%) in the Si modified Al-1.9Mn alloy resulted in a notable property reduction, not only in its elongation, but also in its electrical conductivity. It can be attributed to the formation of Mg2Si and the increased solid solution of Mg in the matrix. Through the optimization of the Mg and Si contents, new Al-1.9Mn alloys with superior mechanical properties and excellent electrical conductivity were successfully developed. With the addition of 0.45 wt% magnesium and 0.75 wt% silicon, the new Al-1.9Mn alloy increased its tensile strength to 170 MPa and yield strength to 88 MPa while maintaining 10 % elongation. At the same time, its electrical conductivity increased by 10.7 % compared to the original Al-1.9Mn alloy. The addition of magnesium and silicon elements can achieve a simultaneous enhancement of both the strength and electrical conductivity of the Al-1.9Mn alloy. This holds the potential to meet the usage requirements for cast aluminum alloys used in water-cooled radiator shells.

Local relaxation of residual stress in high-strength steel welded joints treated by HFMI

AbstractThis research studies the influence of high-peak loads on local relaxation of residual stress and fatigue damage in high-strength steel welded joints treated by high-frequency mechanical impact (HFMI) treatment. The joint behavior is simulated with elastic–plastic finite element analyses that account for the combined effect of geometry, residual stress, and material properties. This simulation uses two treated geometry models: with or without surface roughness on HFMI groove, and two material properties: S690QL and AH36 structural steels. The results show that surface roughness and load history, including high-peak loads, significantly influence fatigue response. It is revealed that the model neglecting the surface roughness cannot represent the amount of residual stress change and fatigue damage at less than 100 µm depth from the surface. In addition, the local yield strength in the HFMI-treated zone affects the plasticity behavior near the surface imperfection under the high-peak loads, which provides comparatively different fatigue damage between S690QL and AH36 in some cases. As a result, this study provides the further understanding needed to develop a robust modeling approach to the fatigue life estimation of HFMI-treated welds subjected to high-peak loads.

Behavior of Circular Hollow Steel-Reinforced Concrete Columns under Axial Compression

The circular hollow steel-reinforced concrete (HSRC) column consists of an inner circular hollow steel tube and outer circular hollow reinforced concrete (RC). This design provides several advantages, including being lightweight, having a wide sectional profile, and having a high flexural stiffness. This paper aims to investigate the behavior of the circular HSRC columns under axial compression through testing and finite element (FE) modeling. An FE model was established to simulate the circular HSRC columns under axial compression, which was validated against the test data. Additionally, the load distribution and the interface stress between the outer hollow RC and inner steel tube were analyzed. Subsequently, a systematic parametric analysis was conducted on the diameter (d) and thickness (t) of the steel tube; slenderness ratio (λ); strength of concrete (fcu); yield strength of steel tube (fsy), longitudinal rebar (fly), and stirrup (fgy); as well as the stirrup spacing (s). The critical influencing factors of the circular HSRC columns under axial compression were identified. fcu, λ, d, fly, and fsy dramatically influence the bearing capacity, and the stiffness is notably affected by λ and fcu. Finally, three simplified design methods were summarized and evaluated for calculating the bearing capacity of the circular HSRC columns under axial compression.

A Study of Microstructural Tensile and Fatigue Properties Coupled with Digital Image Correlation of Hybrid Manufactured Inconel 718 Parts by Extrusion and Powder Bed Fusion

To overcome challenges associated with additive manufacturing (AM), a combination of AM and conventional manufacturing (CM) can be explored, enabling the production of hybrid structures. Nonetheless, realizing aerospace hybrid structures requires investigation into the process–structure–properties relationships of the AM and CM material and the interface zone between them. Herein, Inconel 718 is deposited onto extruded bars of the same material by powder bed fusion (PBF). The interface zone from the CM zone to the PBF zone is investigated using destructive and nondestructive testing. It is found that fractures during tensile tests occur in the CM zone. The PBF zone proves to be stronger than the CM zone (average yield strength of 1295 and 1167 MPa, respectively). A higher strength of PBF parts is related to the finer microstructure of δ‐phase precipitates and dendrite cell structure. The fatigue limit of the hybrid samples is high (Sa = 305 MPa, R = 0.1). Coupled fatigue and digital image correlation at the highest stress amplitude show distinctive plastic flow dominating the CM zone. In reverse, fracture of hybrid parts at lower stress amplitudes forms preferentially in the PBF zone because of process‐related defects (gas pores and lack of fusion).

Microstructures and mechanical properties of additively manufactured Fe–21Mn-0.6C TWIP steel using laser powder bed fusion

Twinning induced plasticity (TWIP) high manganese steel exhibits high ultimate tensile strength (UTS) and ductility, but its low yield strength restricts its applications. This research presents a Fe–21Mn-0.6C TWIP steel with enhanced mechanical properties additively manufactured using laser powder bed fusion (LPBF). The average grain size of the LPBF-fabricated Fe–21Mn-0.6C was 17.1 μm in the vertical direction, which was a quarter of that of a wrought one. The tensile yield strength was 657 MPa and the UTS was 1089 MPa with an elongation of 47.9% for the vertical direction. Compared to the wrought Fe–21Mn-0.6C, the yield strength increased by 110%. The high strength of LPBF-fabricated Fe–21Mn-0.6C is primarily attributed to solution, grain boundary and dislocation strengthening. Serrations were observed in the stress-strain curves at the initial stage of deformation, showing large stress drops. In the annealed sample, serrations appeared at a later stage of deformation with little stress drops. This difference in serration phenomenon is attributed to the varying dislocation density in the two samples.

3D printed CoCrMo personalised load-bearing meta-scaffold for critical size tibial reconstruction

Porous scaffolds have evolved, allowing personalised 3D-printed structures that can improve tissue reconstruction. By using scaffolds with specific porosity, Poisson's ratio and stiffness, load-bearing tissues such as tibial reconstruction can be improved. Recent studies suggest the potential for negative Poisson's ratio (−υ) meta-scaffolds in mimicking the behaviour of natural tissue, leading to improved healing and tissue reintegration. This study reveals a porous meta-scaffold that offers high −υ and can be personalised to match desired stiffness. By using laser powder bed fusion (L-PBF) of CoCrMo, a porous structure was created, characterised by its ability to achieve heightened −υ. Prototype testing and numerical modelling unveiled a proxy-model capable of predicting and personalising the porosity, yield strength, elastic modulus, and −υ of the tibial meta-scaffold representing a novel contribution to the field. The surrogate model also aids characterising the impact of design variables such as of the scaffold on the key performance requirements of the tibial scaffold. This approach enables the fabrication of porous biomaterials with personalised properties, specifically suited for load-bearing tibial reconstruction. The resulting meta-scaffold offers −υ ranging from -0.16 to -0.38, porosity between 73.46% and 85.36%, yield strength of 30–80 MPa, and elastic modulus ranging from 8.6 to 22.6 GPa. The optimised architecture feature −υ of 0.223 and a targeted elastic modulus of 17.53 GPa, while also showcasing yield strength and porosity of 57.2 MPa and 76.35%, respectively. By combining 3D printing with tailored scaffolds, this study opens doors to mass customisation of improved load-bearing porous biomaterials that of negative Poisson's ratio and stiffness matching.

Unveiling yield strength of metallic materials using physics-enhanced machine learning under diverse experimental conditions

In the materials science domain, the accurate prediction of the yield strength of metallic compositions has often resulted in extensive experimental endeavors, leading to inefficiencies in both time and resources. Here, we introduce an innovative approach to predict yield strength, which can be applied to a variety of metallic substances ranging from the simplest pure metals to the most intricate alloys under varying temperatures and strain rates. The fusion of grain boundary sliding mechanism and cutting-edge machine-learning algorithm forges an expansive framework, which can help realize the critical factors influencing yield strength. The validity and wide applicability of the proposed framework were rigorously confirmed through experimental evaluations conducted on selected Fe-based alloys, such as Fe60Ni25Cr15, Fe60Ni30Cr10, and Fe64Ni15Co8Mn8Cu5. This breakthrough study significantly streamlines experimental design processes, optimizes resource utilization, and marks a significant leap forward in creating a reliable predictive framework for realizing material properties.

Response Modification Factor of High-Strength Steel Frames with D-Eccentric Brace Using the IDA Method

The design innovation of high-strength steel frames paired with D-eccentric bracing exhibits remarkable resistance to plastic deformation during seismic events. This method strategically combines regular steel connections (with yield strengths below 345 MPa) and high-strength steel beams and columns (such as Q460 or Q690, with yield strengths over 460 MPa), effectively reducing cross-sectional sizes while preserving the elasticity of non-energy-dissipating members. This configuration results in substantial ductility and superior energy dissipation capabilities. The response modification factor (R) is vital for achieving both effective and economical seismic resilience, particularly in the development of efficient and cost-effective seismic designs. However, the 2016 edition of the Code for Seismic Design of Buildings (GB50011-2010) fails to incorporate the concept of R, opting instead to apply a uniform value to all structural systems. This oversight is fundamentally flawed, necessitating a comprehensive investigation into the R value specifically for the high-strength steel frame with a D-eccentric brace. This research primarily aims to improve structural performance design, provide guidance for future projects, and encourage the adoption of this advanced seismic performance structure in earthquake-prone areas. To achieve these objectives, a performance-based seismic design approach is employed. This method involves designing structures with varying numbers of stories (4, 8, and 12), different link lengths (900, 1000, and 1100 mm), and various steel strengths (Q460 and Q690). This study uses the Incremental Dynamic Analysis (IDA) method to determine the R values for each prototype. The derived performance coefficients act as crucial references for the development of future innovative structural designs. This research greatly enhances seismic design practices and facilitates the wider adoption of high-strength steel frames with D-eccentric braces due to their outstanding seismic performance.

Microstructural evolution and cryogenic and ambient temperature deformation behavior of the near-α titanium alloy TA15 fabricated by laser powder bed fusion

Titanium alloys produced by additive manufacturing show excellent mechanical properties at room temperature. However, their deformation behavior at low temperature is still not fully understood. In this study, the microstructural evolution and tensile behavior of the near-α titanium alloy Ti-6.5Al-2Zr-Mo-V (TA15), fabricated via laser powder bed fusion (LPBF), were determined at both 25 °C and −196 °C. The LPBFed TA15 alloy shows the microstructure of α laths and acicular α′ martensite due to the rapid cooling rate during LPBF processing. Pyramidal <c+a> slip and numerous twins, including nano-twins and triple twins, were activated at cryogenic temperature, leading to the high ultimate tensile strength (UTS) up to 1750±8 MPa and yield strength (YS) up to 1548±25 MPa, which is higher than the strength at room temperature (YS∼1103 MPa, UTS∼1281 MPa). The dominant deformation mechanism changes from dislocation slip to twinning with decreasing temperature, leading to uniform deformation with an elongation of 5.2±0.1 %. The results can guide the control of the microstructure of LPBFed near-α titanium alloys at cryogenic temperature.

Effect of Strontium Modification on Microstructure and Mechanical Property Al12SiCuMgNi Alloy in Squeeze Casting

Abstract The Al-Si series alloys, which have excellent fluidity and castability, are the most common aluminum material in the casting industry. However, the coarse eutectic Si phase with laminar morphology leads to the stress concentration of material and has a detrimental effect on the mechanical properties of aluminum alloy components. In this study, the Strontium (Sr) modifier was added to Al12SiCuMgNi alloy and the effect of Sr on microstructure and performance of Al12SiCuMgNi in squeeze casting was investigated. The experimental results show that the eutectic Si phase was well modified to fibrous morphology. Although the yield strength (YS) was leveled, the ultimate tensile strength (UTS) and elongation (EL) of the alloy were obviously enhanced after Sr addition. When the 0.012wt.% Sr was added to Al12SiCuMgNi alloy. The YS, UTS, and EL of alloys were up to 311 MPa, 401 MPa, and 3.4%, respectively. Moreover, the microstructure and performance of Al12SiCuMgNi alloy in the hot forging process were also compared to Al12SiCuMgNi alloy with and without Sr addition in squeeze casting. It is concluded that the Al12SiCuMgNi alloy in hot forging shows higher ductility (4.7%) and lower strength than Al12SiCuMgNi alloy in squeeze casting.

Enhanced strength-ductility-impact toughness synergy of CT20 titanium alloy by introducing a multi-level lamellar martensitic α structure

In this work, different morphologies and structures of lamellar α are obtained by controlling the cooling rates, i.e., water cooling (WC), air cooling (AC) and furnace cooling (FC), and their effects on tensile properties and impact toughness of a new near α CT20 alloy (Ti-3Al-2Zr-1Mo) are investigated. Results showed that a heterogeneous three-dimensional network lamellar martensite α structure was formed after WC, a mixed structure composed of fine lamellar α/β and a small amount of martensite was formed after AC, and a coarse lamellar α structure was formed after FC. The tensile strength gradually decreased with decreasing cooling rate, and AC had the superior strength-plasticity match (yield strength was 13% higher than FC while their plasticity is equivalent). However, the impact toughness of AC (comparable to that of WC) was about 16% lower than that of FC (90 J/cm2). During tensile deformation, the synergistic effect of the good plasticity of the α colony, the obstruction of dislocations by the colony interface and the plastic deformation of the martensite of the AC contribute to the best strength-plasticity matching. During impact, crack initiates and propagates rapidly at the V-notch root, and the finite element simulation results showed that the plastic deformation was concentrated in a tiny region near the crack tip, resulting in the coordination deformation among the microstructures in AC cannot be fully realized. By contrast, the coordinated deformation of multi-level martensite and the generation of nano twins in WC make its impact toughness comparable to that of AC. The highest impact toughness of FC was attributed to the superior plasticity of coarse lamellae, slip transfer between coarse α and β lamellae, the generation of twins and the formation of a small jagged and large wave-like composite crack propagation path.