Compressive Yield Strength Research Articles

Mimicking the mechanical properties of cortical bone with an additively manufactured biodegradable Zn-3Mg alloy

Additively manufactured (AM) biodegradable zinc (Zn) alloys have recently emerged as promising porous bone-substituting materials, due to their moderate degradation rates, good biocompatibility, geometrically ordered microarchitectures, and bone-mimicking mechanical properties. While AM Zn alloy porous scaffolds mimicking the mechanical properties of trabecular bone have been previously reported, mimicking the mechanical properties of cortical bone remains a formidable challenge. To overcome this challenge, we developed the AM Zn-3Mg alloy. We used laser powder bed fusion to process Zn-3Mg and compared it with pure Zn. The AM Zn-3Mg alloy exhibited significantly refined grains and a unique microstructure with interlaced α-Zn/Mg2Zn11 phases. The compressive properties of the solid Zn-3Mg specimens greatly exceeded their tensile properties, with a compressive yield strength of up to 601 MPa and an ultimate strain of >60 %. We then designed and fabricated functionally graded porous structures with a solid core and achieved cortical bone-mimicking mechanical properties, including a compressive yield strength of >120 MPa and an elastic modulus of ≈20 GPa. The biodegradation rates of the Zn-3Mg specimens were lower than those of pure Zn and could be adjusted by tuning the AM process parameters. The Zn-3Mg specimens also exhibited improved biocompatibility as compared to pure Zn, including higher metabolic activity and enhanced osteogenic behavior of MC3T3 cells cultured with the extracts from the Zn-3Mg alloy specimens. Altogether, these results marked major progress in developing AM porous biodegradable metallic bone substitutes, which paved the way toward clinical adoption of Zn-based scaffolds for the treatment of load-bearing bony defects. Statement of significanceOur study presents a significant advancement in the realm of biodegradable metallic bone substitutes through the development of an additively manufactured Zn-3Mg alloy. This novel alloy showcases refined grains and a distinctive microstructure, enabling the fabrication of functionally graded porous structures with mechanical properties resembling cortical bone. The achieved compressive yield strength and elastic modulus signify a critical leap toward mimicking the mechanical behavior of load-bearing bone. Moreover, our findings reveal tunable biodegradation rates and enhanced biocompatibility compared to pure Zn, emphasizing the potential clinical utility of Zn-based scaffolds for treating load-bearing bony defects. This breakthrough opens doors for the wider adoption of zinc-based materials in regenerative orthopedics.

Optimisation of printing parameters of fused filament fabrication and uniaxial compression failure analysis for four-point star-shaped structures

PurposeThe purpose of this paper is to present an optimisation of four-point star-shaped structures produced through additive manufacturing (AM) polylactic acid (PLA). The study also aims to investigate the compression failure mechanism of the structure.Design/methodology/approachA Taguchi L9 orthogonal array design of the experiment is adopted in which the input parameters are resolution (0.06, 0.15 and 0.30 mm), print speed (60, 70 and 80 mm/s) and bed temperature (55°C, 60°C, 65°C). The response parameters considered were printing time, material usage, compression yield strength, compression modulus and dimensional stability. Empirical observations during compression tests were used to evaluate the load–response mechanism of the structures.FindingsThe printing resolution is the most significant input parameter. Material length is not influenced by the printing speed and bed temperature. The compression stress–strain curve exhibits elastic, plateau and densification regions. All the samples exhibit negative Poisson’s ratio values within the elastic and plateau regions. At the beginning of densification, the Poisson’s ratios change to positive values. The metamaterial printed at a resolution of 0.3 mm, 80 mm/s and 60°C exhibits the best mechanical properties (yield strength and modulus of 2.02 and 58.87 MPa, respectively). The failure of the structure occurs through bending and torsion of the unit cells.Practical implicationsThe optimisation study is significant for decision-making during the 3D printing and the empirical failure model shall complement the existing techniques for the mechanical analysis of the metamaterials.Originality/valueTo the best of the authors’ knowledge, for the first time, a new empirical model, based on the uniaxial load response and “static truss concept”, for failure mechanisms of the unit cell is presented.

A method for predicting the yield strength of AZ31 magnesium alloy bars processed by ambient extrusion

Magnesium alloys have strong mechanical properties anisotropy due to their universal basal texture. This study develops a novel method for predicting the yield strength of AZ31 extruded bars with basal fiber texture. From series tensile and compressive tests on ambient extruded bars with different loading direction, the relationship between yield strength, loading direction and extrusion strain was summarized. With varying loading direction, tensile and compressive yield strength can be fitted by linear and nonlinear equations in a strength coordinate system where yield strength can be calculated on different loading direction. Furthermore, parameters of yield strength equations can also be fitted by different equations. Then, from the parameter equations to yield strength equations, tensile and compressive yield strength can be predicted on different loading direction for extruded bars with different extrusion strain.

Numerical and experimental studies on bending behavior of circular aluminium-concrete-steel double skin tubular cross-sections and bending capacity design approach

Considering the excellent corrosion resistance of aluminium alloy, a new-type aluminium-concrete-steel double skin tubular (ACSDST) member is proposed by replacing the outer steel tube of concrete-filled double skin steel tubular members with an aluminium alloy tube to improve structures' corrosion resistance and durability. Until now, no literature has been available on ACSDST cross-section in bending. This paper presents experimental and numerical investigations on the flexural behaviour of circular ACSDST cross-sections in bending. Broad parameters are examined in this research, including varying diameter-to-thickness ratios of the outer tube (20–120), hollow ratio (0.2–0.75), concrete compressive strength (30–70 MPa) and steel yield strength (235–355 MPa). The experimental results show that the final failure is controlled by the tensile rupture of aluminium alloy tubes, but it generally happens after the maximum moment, and the composite section behaves in good curvature ductility. The parametric analysis based on the developed finite element (FE) model discloses the different influences of diameter-to-thickness ratios of the outer tube, hollow ratio, and concrete and steel strengths on the bending moment capacity. Among them, the diameter-to-thickness ratio of the outer tube and hollow ratio significantly affect the bending moment capacity. The design equations for bending moment capacity are induced based on the plastic stress distribution method. Those equations are safe and accurate for the maximum moment (a widely used definition of bending moment capacity) within a certain range of parameters. However, a reduction factor 0.9 is proposed for the equations to predict the moment at a longitudinal flexural tensile strain of 1% (another widely used definition of bending moment capacity). Moreover, the cross-section slenderness limit for the compact ACSDST section is recommended based on the analysis of the experimental and FE results.

Effect of different strut thickness on the mechanical behaviour of 3D printed auxetic structures

In the recent era, the demand for structure design and materials that have mechanical properties to absorb high energy absorption and fracture resistance is growing exponentially. In order to meet the demand for intently designed structures, various structures have been designed and made. Among different design structures, auxetic design structures emerged as a flexible design that fulfilled the needs available in different application fields such as aerospace, defence, biomedical, structural, sponge mops, and many more. The main advantage of auxetic design structure is to show the property of negative Poisson’s ratios (NPR). The materials with NPRexhibit unusual and counterintuitive mechanical behaviour. It means the materials become flatter when stretched. This property allows them to exhibit exceptional mechanical characteristics that make them ideal for a wide range of applications. Further, fabrication techniques were also impacted by the mechanical performance of the auxetic structure. In the context of different fabrication techniques, 3D printing was found to be the most effective method to induce significant mechanical strength in the fabricated parts.Therefore, the present work focuses on the fabrication of auxetic structures using fused deposition modelling (FDM), and FDM is a kind of 3D (Three Dimensional) printing technique. Furthermore, experiments were performed with variations in strut wall thickness ranging from 0.4 to 1.2mm. In order to evaluate the mechanical performance of fabricated structures, compressive testing was performed on the Universal Testing Machine (UTM). In addition, the effect of different strut wall thicknesses on compressive mechanical behaviour was evaluated. The results showed that the maximum compressive strength, compressive Young’s modulus, compressive yield strength, energy absorption capacity, and plateau stress were found to increase with the increase in strut wall thickness.

Effect of ball milling and solid solution treatment on microstructure and mechanical properties of ZrMgMo3O12p/2024Al composites

The 10 vol% ZrMgMo3O12/2024Al composites were fabricated using the powder metallurgy process and consolidation via vacuum hot pressing. The effects of the ball milling process and solution treatment time on the composites’ microstructure, Vickers hardness, and compressive properties were studied. Increasing the ball milling speed and extending the ball milling duration reduce the size of ZrMgMo3O12 particles, resulting in a more uniform dispersion within the aluminum matrix. Extending the solution treatment duration facilitates the dissolution of more primary Al2Cu phase into the aluminum matrix reducing the presence of coarse primary Al2Cu phase and increasing the number of fine Al2Cu precipitates formed during the aging process. The results indicated that an appropriate increase in ball milling speed, extension of ball milling duration, and solution treatment time can enhance the Vickers hardness and room temperature compressive strength of the composites. Specifically, the composites processed with a ball milling speed of 350 rpm for 6 h, a solid solution treatment at 495 °C for 24 h, and an aging treatment at 190 °C for 8 h exhibited a Vickers hardness of 277 HV and a compressive yield strength of 687 MPa, along with a compressive strain of 7.8 %.

Surface modification of biodegradable Mg/HA composite by electrospinning of PCL/HA fibers coating: Mechanical properties, corrosion, and biocompatibility

Mg/HA composite was fabricated using the stir-casting and extrusion processes and coated by electrospun PCL/HA fibers (2.5 and 5 wt.% HA) to enhance the corrosion resistance. The mechanical tests demonstrated an increment of 107% for the compressive yield strength of the composite (151 vs 73 MPa for pure magnesium). SEM, EDS, and XRD analysis illustrated that HA particles distribute in porous coatings. According to the polarization tests, all coated specimens show higher corrosion resistance compared to the uncoated ones. PCL coating reduces the corrosion current density of the sample by two orders of magnitude. The effectiveness of incorporating HA in the coatings was proved by polarization and in vitro corrosion tests. Employment of coatings and subsequent Ca–P layer formation prevents the penetration of simulated body fluid (SBF) and contact with the substrate, thus protecting the surface. PCL/2.5%HA coated sample has the lowest corrosion rate with an average value of 0.98 mm/a by a reduction of 81% compared to the uncoated composite in 14 d. Cell viability enhancement from 43% to 121% was achieved using PCL/2.5%HA coating according to 3 d 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) results. In conclusion, Mg/HA composites coated with PCL/2.5%HA fibers appear promising for bioabsorbable implant applications.

From 2D to 3D electrochemical microfabrication of nickel architectures at room temperature: Synthesis and characterization of microstructure and mechanical properties

Recent development in direct electrochemical 3D microprinting allows the fabrication of 3D metallic micro-components of predominantly noble metals with the positive standard reduction potentials (e.g., Cu, Au, or Pt). These pure metals (e.g., Cu, Au, or Pt) have a small shear modulus up to 60 GPa, which limits one of the important strengthening mechanisms, Taylor hardening. Hence, their mechanical strength is relatively low and limits the application in a structural component. 3D printing of mechanically high-strength metals (e.g., Ni), specifically, printing of microscale parts by direct electrodeposition using a voxel-by-voxel printing technique, is so far very challenging due to the negative standard reduction potential, which leads to hydrogen evolution and unstable printing. In this paper, we demonstrate the stable and successful room temperature (RT) electrochemical printing of Ni micro-architectures by using a newly formulated Ni ink and supporting electrolyte, which were developed through 2D voltammetry and deposition analysis. The micro manufacturing of Ni succeeds at a high deposition speed up to ∼61 nm/s, which is the fastest speed reported so far for microprinting of Ni. 3D printed micropillars feature a heterogeneous nanostructure from ∼13 nm at the center to ∼27 nm at the perimeter. By performing micropillar compression tests, the printed pillars exhibit a high compressive yield-strength of 2.3 ± 0.1 GPa, only ∼15 % lower than 2D processed samples (2.7 ± 0.1 GPa) featuring a homogeneous nanostructure of 27 ± 16 nm. Thus, by deposition of stronger, but less noble metals we show a new pathway to enhance the mechanical robustness of 3D-printed structures, opening up new applications where mechanical rigidity is essential.

Development and Characterization of a Remanufactured Motorcycle Clutch Hub from End-of-Life Aluminium Alloy

This study aims to employ reverse engineering in the development of the Yamaha CY 80 motorcycle clutch hub using end-of-life (EOL) aluminium alloy obtained from automotive vehicle scraps. The remanufactured motorcycle clutch hub underwent characterization and transient thermal analysis by integrating the geometric and structural features of the clutch hub. The EOL aluminium was thoroughly washed with a sodium hydroxide (NaOH) solution, cleaned with running water, and dried under sunlight to remove impurities trapped on the metal surfaces. The EOL aluminium alloy was melted in a gas furnace, and the molten metal was cast into the clutch hub using a permanent mold designed with the geometric features and characteristics of the Yamaha CY 80 motorcycle clutch hub. The EOL aluminium alloy was characterized using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The remanufactured CAD model of the Yamaha CY 80 motorcycle clutch hub was subjected to transient thermal analysis using ANSYS Workbench to predict the thermal behavior of the clutch hub during operation. The FTIR spectra exhibited the following distinctive bands: Al-O stretching modes in octahedral and tetrahedral structures, as well as symmetric bending of Al-O-H, with wavenumbers between 340 and 3131 cm-1 for -OH bonds and between 2109 and 1688 cm-1 for H-O-H bonds. The SEM-EDS micrographs indicated that the two main elements were bromine and silicon. Results from the transient thermal analysis indicated that the minimum and maximum temperatures were 40.109 °C and 250.09 °C within a time frame of 240 seconds. The maximum total heat flux was 30,271,000 W/m2. The compressive yield strength and tensile yield strength obtained in this study were 280 MPa, while the ultimate tensile strength was measured at 310 MPa. The alternating stress levels ranged from 62.05 MPa to 275.8 MPa. This study established that the material is susceptible to fatigue failure, as the alternating stress levels were below the material’s yield strength of 280 MPa.

Effect of Initial Microstructure on the Temperature Dependence of the Flow Stress and Deformation Microstructure under Uniaxial Compression of Ti-407

In this study, the influence of initial microstructure and deformation temperature on the flow stress behavior and microstructural evolution of TIMETAL®407 (Ti-407) alloy are investigated. For this purpose, compression cylinders were β-annealed at 940 °C and then cooled to room temperature using furnace cooling, static air, and water quenching to promote three initial microstructures with different α lath thicknesses. The annealed cylinders were compressed isothermally in the range of 750 °C to 910 °C at a constant crosshead speed of 0.05 mm/s up to an engineering strain of −0.8. The resulting stress–strain curves are discussed in terms of the morphology and distribution of the α and β phases. It was found that flow stress is inversely proportional to deformation temperature for all initial microstructures. At the lowest temperatures, compressive yield strength was higher in water-quenched and air-cooled samples than in furnace-cooled specimens, suggesting that the acicular α-phase morphology obtained by rapid cooling could enhance mechanical strength by hindering dislocation motion. Two high-temperature flow regimes were determined based on the shape of the flow stress curves, indicating microstructural changes occurring during deformation. At higher temperatures, the effect of the initial microstructure is negligible as the primary α phase is transformed to the β phase at around 850 °C irrespective of the initial α-lath thickness.

A novel cast Co68Al18.2Fe6.5V4.75Cr2.55 dual-phase medium entropy alloy with superior high-temperature performance

A newly-designed Co68Al18.2Fe6.5V4.75Cr2.55 medium entropy alloy (MEA) with FCC + B2 structure exhibits not only an excellent strength-ductility combination at room temperature, but also an outstanding high-temperature mechanical properties in particular. The phase formation, microstructure and deformation mechanism of this designed dual-phase MEA at room and high temperatures were investigated and discussed in detail. Based on experimental results (XRD, SEM and TEM) and theoretical analysis (calculated diagram and empirical thermodynamic parameters), it is demonstrated that this newly-designed MEA consists of a dual-phase structure of a face-centered-cubic (FCC) phase (70.3 vol %) plus chemically ordered body-centered cubic phase (B2) (29.7 vol %). Meanwhile, the FCC phase is enriched with Co, Fe and Cr elements, while the B2 phase is enriched with Al and Co elements. Furthermore, compared with some HEAs/MEAs and commercial alloys, this newly-designed dual-phase MEA exhibits excellent strength-ductility combination with a high compressive yield strength of ∼1254 MPa, a fracture strength of ∼2657 MPa and a large compressive plasticity of ∼34.6 % at room temperature. In particular, the studied MEA also shows an outstanding high-temperature performance with an ultrahigh yield strength of ∼1213 MPa at 600 °C and ∼626 MPa at 800 °C, respectively. The excellent comprehensive mechanical properties of this designed dual-phase MEA at both room and temperatures mainly originate from synergy effect of alternate FCC + B2 structure and strengthening contributions of B2 phase. These important findings not only reveal the deformation and strengthening mechanisms of the newly-designed dual-phase MEA, but also provides an effective alloy design strategy for developing advanced structural materials serving as a wide range of temperature.

Sugar‐template method to construct a boron nitride filler network to enhance the thermal conductivity of epoxy composites

AbstractIn this work, a technique for constructing a three‐dimensional (3D) skeleton of hexagonal boron nitride (h‐BN) using sugar as the fulcrum and preparing composites by embedding in the epoxy (EP) in a vacuum environment is proposed. The study of thermal conductivity (TC) in polymer composites is conducted through a blend of techniques: laser flashing, theoretical modeling, and finite element simulation. The h‐BN skeleton exhibits a honeycomb structure through the scanning electron microscopy findings. Further investigation using finite element simulation demonstrates that conductive networks are formed by the h‐BN skeleton within the composites, leading to a notable enhancement in TC. Specifically, the composite for h‐BN/EP reaches a TC of 2.25 W/m K when composed of 52 vol% h‐BN. A dielectric loss of 0.008 for the composite with the same h‐BN loading shows a considerable improvement. The compressive yield strength of the 3D h‐BN/EP composites reached 312 MPa at 5 vol% h‐BN loading.

Optimizing Al content to eliminate the brittle phase in lightweight TiZrNbTa0.1Alx refractory high-entropy alloys

Body-centered cubic (BCC) lightweight refractory high-entropy alloys (LWRHEAs) with Al contents have attracted much attention due to their low density and excellent mechanical properties. However, these typical lightweight alloys often suffer from poor room temperature plasticity. In this study, we prepared TiZrNbTa0.1Alx LWRHEAs by using a high-vacuum arc-melting technique and investigated the influence of Al content on the phase structures and mechanical properties. It was found that the TiZrNbTa0.1Al1 alloy showed a BCC solid solution matrix with some micrometer-sized Al3Zr5 precipitates and exhibited a density of 6.110 ± 0.003 g/cm3. The TiZrNbTa0.1Al1 alloy had a low mixed enthalpy of −20.831 kJ/mol, a compressive yield strength of 1037 ± 178 MPa, and a fracture plasticity of ∼6%. As a result of reducing the Al content, the TiZrNbTa0.1Al0.2 alloy showed a simple BCC phase structure without any precipitates and maintained a low density of 6.743 ± 0.008 g/cm3. The TiZrNbTa0.1Al0.2 alloy had a relatively high mixed enthalpy of −4.5577 kJ/mol, a high yield strength of 1022 ± 51 MPa, and a plasticity of >70%. The TEM analysis results demonstrated that the excellent mechanical properties of this LWRHEA were mainly attributed to the reducing Al content, which could elevate the mixed enthalpy of the alloy to eliminate the brittle Al3Zr5 phase and induce the formation of dense network dislocations at the grain boundaries.

The role of the preparation route on microstructure and mechanical properties of AlCoCrFeNi high entropy alloy

Nearly equiatomic AlCoCrFeNi alloy samples were prepared by induction melting and mechanical alloying (MA) combined with spark plasma sintering (SPS). The cast sample showed a dendritic microstructure composed of spinodally decomposed nanometric constituents of the B2 and BCC phases. The spark plasma sintered sample exhibited an ultrafine-grained microstructure of B2 phase and FCC solid solution and Cr23C6 carbides. The MA + SPS sample was strengthened by compressive stress-strain test up to a yield strength of 2029 ± 5 MPa, resulting significantly higher compared to 1366 ± 32 MPa of the cast sample. In addition to the higher compressive yield strength, the sintered sample exhibited a hardness of more than 130 HV higher compared to the cast alloy. On the other hand, the cast alloy showed high plastic deformation (29%) and significantly high ultimate compressive strength of 3072 ± 122 MPa. Together with these mechanical characteristics, the MA + SPS sample showed good thermal stability while preserving the mechanical properties even after annealing at 800 °C. This was not the case with the cast sample, in which ductility and ultimate strength significantly decreased upon annealing at 800 °C. A substantial yield strength reduction of both MA + SPS and cast samples was recorded when tested at 800 °C. Nevertheless, stress-strain curve trends were observed to be quite different between the two samples, thus suggesting dissimilar deformation mechanisms under high-temperature compression.

Constructing Coated Grain Nanocomposites and Intracrystalline Precipitates to Simultaneously Improve the Thermoelectric and Mechanical Properties of SnTe by MgB2 and Sb Co‐Doping

AbstractThermoelectric materials should be highly efficient and mechanically robust to satisfy the requirements of engineering applications. Herein, an integrated optimization strategy to improve both the thermoelectric performance and mechanical strength of SnTe is proposed. First, grain boundary engineering is applied to SnTe via MgB2 doping. The decomposition of MgB2 results in the Mg‐substituted SnTe solid solution and a special “core–shell” structure of Mg‐B compounds coated SnTe grain remarkably reducing the lattice thermal conductivity. Subsequently, trivalent Sb atoms are introduced to tune the carrier concentration and optimize the electrical performance of the MgB2‐doped sample. Sb‐rich Sn‐Te precipitates inside the grains further diminish the lattice's thermal conductivity. Consequently, a prominent improvement in average ZT of ≈117% is achieved for Sn0.78Sb0.16Te(MgB2)0.09 compared to pristine Sn1.03Te. Moreover, the compressive yield strength and Vickers hardness of Sn0.78Sb0.16Te(MgB2)0.09 are significantly increased by ≈168% and 176% relative to pristine Sn1.03Te, respectively. The quantitative strengthening models including grain boundary, dislocation, solid solution, intergranular, and precipitation strengthening in MgB2‐ and MgB2‐Sb‐doped Sn1.03Te samples are proposed, showing that the dominant strengthening mechanism is precipitation strengthening. This work provides an avenue for designing efficient and robust thermoelectric materials toward commercial application.

Ultrahigh-strengthened intragranular κ-Al2O3 nanoparticles dispersed Mo composite prepared via SPS sintering of core-shell Mo nanocomposite powder

Oxide dispersion strengthening (ODS) is an effective method to improve the mechanical properties of Mo-based materials. However, the mechanical properties of traditional ODS-Mo composites are always limited by the coarsening and intergranular distribution of second-phase particles. In this work, an effective nano-reinforcement dispersion strategy was developed to fabricate an ODS-Mo composite with ultrafine grain and intragranular distribution of second-phase particles. Core-shell structural Mo nanocomposite powders, with internally distributed sub-10 nm Al2O3 dispersoids, were prepared by nano atomization doping (AD) followed by a chemical vapor transport growth strategy. Then, ODS-Mo composites with ultra-fine Mo grain (below 700 nm) and high-density intragranular κ-Al2O3 (below 20 nm) nanoparticles were prepared via spark plasma sintering (SPS), in which a coherent interface between κ-Al2O3 and Mo matrix was formed. The composites present remarkably improved hardness (above 500 HV), bend strength, and compressive yield strength (above 1664 MPa) at room temperature, with a suitable strain to fracture of 27.1 %. The calculation of strengthening mechanisms indicates that the enhancement was mainly attributed to the intragranular κ-Al2O3 nanoparticles. This nano-sized reinforcement distributed within the grain can more effectively pin dislocations and achieve dispersion strengthening in ODS-Mo composites. Therefore, this strategy can efficiently construct intragranular second-phase nanoparticles and open up new avenues to fabricate high-performance ODS-Mo composites.

A viscoplastic self-consistent analysis of tensile anisotropy and tension-compression asymmetry in rare-earth magnesium alloy

The anisotropy and tension-compression asymmetry of rare-earth magnesium (Mg-RE) alloys have attracted significant attention. In this study, the room-temperature tensile anisotropy and tension-compression asymmetry of the extruded Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr alloy were investigated utilizing techniques such as optical microscopy (OM), electron backscatter diffraction (EBSD), and viscoplastic self-consistent (VPSC) modeling. Among the tensile samples, the T0 sample (with axis parallel to extrusion direction) exhibits the greatest tensile yield strength (TYS) of 270 MPa and ultimate tensile strength (UTS) of 336 MPa, the T45 sample (with axis inclined at a 45° angle to extrusion direction) and T90 sample (with axis perpendicular to extrusion direction) exhibit lower TYS and UTS. The C0 sample shows a slightly greater compressive yield strength (CYS) of 290 MPa. The ratio of TYS/CYS is approximately 1.07. This study significantly adjusts the VPSC hardening parameters through the Schmid factor of deformation mechanisms in Mg-RE alloy, particularly increasing the τ0 (critical resolved shear stress, CRSS) and τ1 values for basal <a> slip and {10-12} twinning. The ratios of CRSS for other deformation mechanisms to basal <a> slip are approximately as follows: CRSSTwin/CRSSBas = 2, CRSSPri/CRSSBas ≈ 2.7 and CRSSPyr/CRSSBas ≈ 3.3, while these ratios in traditional alloys are generally higher. The stress-strain curves and pole figures obtained from the modified VPSC model demonstrate excellent agreement with experimental results. According to the VPSC simulation results, the primary factor contributing to tensile anisotropy is the disparity in the activation levels of slip systems. The inclusion of rare-earth elements mitigates the tension-compression asymmetry by reducing the difference of CRSS between different deformation mechanisms.

Toward ultra-high strength high entropy alloys via feature engineering

Machine learning assisted design of materials is so far based on features selected by considering the accuracy of model predictions, and those features do not necessarily ensure a high efficiency in searching for new materials. Here we estimate the efficiency of active learning loop by resampling method using available data as an alternative criterion for selection. The selected features allow an optimization of targeted property with as few new experiments as possible. Input those features into machine learning, we synthesized new high entropy alloys (HEAs) with strengths 2.8–3.0 GPa within five experimental iterations. The alloy AlVCrCoNiMo is found to possess compressive specific yield strengths of 397, 144 and 105 (MPa cm3)/g at 25, 800 and 900 °C, respectively. The specific yield strength of AlVCrCoNiMo alloy at 800 °C is about twice that of the commercial Inconel 718 and the typical refractory HEA of VNbMoTaW. A unique microstructure consisting of multi-scale hierarchical B2 precipitates with coherent interfaces to the BCC matrix strengthens the alloy. Our strategy of maximizing active learning efficiency provides a recipe for selecting features that accelerate the optimization of targeted property.

Comparative Analysis of Piston Rings Made with Aluminum Titanium Carbide (AlTiC-75-2) and Carbon Cast Steel (AISI 1540) Materials Using Numerical Method

Aim: The main purpose of this study is to perform a comparative analysis of piston rings made with aluminum titanium carbide (AlTiC-75-2) and carbon cast steel (AISI 1540) materials using numerical method. Study Design: Numerical methods. Materials and Methods: The 3D piston rings were modelled with SOLIDWORDS version 2019 and imported to ANSYS 2020 RI environment for simulation and analysis. Results: The study revealed that AISI 1540 and AlTiC-75-2 had maximum deformations of 1.0356 mm and 1.0773 mm, respectively. Also, when the equivalent elastic strains of the piston rings were compared, it was revealed that, the maximum and minimum elastic strain of the AlTiC-75-2 piston was 4.8826e-3 and 2.2581e-5, respectively, whiles the maximum and minimum elastic strain of AISI 1540 was 2.1878e-5 and 2.1878e-5 respectively. Numerical results further showed that AISI 1540 piston suffered the least elastic strain while the AlTiC piston ring endured more elastic strain. Furthermore, results showed that the maximum Von Mises stresses induced in AlTiC-75-2 and AISI 1540 piston rings were 915.2 MPa and 911.27 MPa, respectively, which implies that stresses induced in both rings were beneath the compressive yield strengths of the individual materials, therefore both rings could withstand the load imposed. Conclusion: Result shows that the AISI 1540 ring has high minimum value than AlTiC which makes it more suitable material in terms of failure as against AlTiC-75-2 with a low minimum safety factor of 0.094187 as against 0.10182 for carbon cast steel. The study therefore recommends that AlTiC-75-2 should be considered as one of the most suitable materials for piston ring design.

Porous Mg–Zn–Ca scaffolds for bone repair: a study on microstructure, mechanical properties and in vitro degradation behavior

Biodegradable porous Mg scaffolds are a promising approach to bone repair. In this work, 3D-spherical porous Mg–1.5Zn–0.2Ca (wt.%) scaffolds were prepared by vacuum infiltration casting technology, and MgF2 and fluorapatite coatings were designed to control the degradation behavior of Mg-based scaffolds. The results showed that the pores in Mg-based scaffolds were composed of the main spherical pores (450–600 μm) and interconnected pores (150–200 μm), and the porosity was up to 74.97%. Mg-based porous scaffolds exhibited sufficient mechanical properties with a compressive yield strength of about 4.04 MPa and elastic modulus of appropriately 0.23 GPa. Besides, both MgF2 coating and fluorapatite coating could effectively improve the corrosion resistance of porous Mg-based scaffolds. In conclusion, this research would provide data support and theoretical guidance for the application of biodegradable porous Mg-based scaffolds in bone tissue engineering.Graphical